Webb @ STScI UpdateK. Pontoppidan (pontoppi[at]stsci.edu)
JWST Communication from STScI
JWSTObserver, the official STScI system for communication with the scientific community, continues to provide you with news and information about observing with Webb. For the most up-to-date JWST information for scientists, follow @JWSTObserver on Twitter and Facebook, or subscribe to the JWSTObserver newsletter. The JWST Observer website at jwst.stsci.edu was recently updated to a new design, but still contains the same information, news, and events as usual.
The first JWST Master Class, taking place at STScI in Baltimore November 18–22, 2019, has been announced. The Master Class is a 4.5-day "train-the-trainer"-style workshop for proposal planning, intended to seed our distributed observer community with local expertise. As the name suggests, train-the-trainer workshops train participants in the subject matter and empower them to educate others in that subject matter. Workshop participants are expected to organize training events in their local communities, in a three-month window before the JWST GO1 proposal deadline, nominally January to April 2020. The ultimate goal of this model is to reach a wide fraction of geographically dispersed Webb Observers. Travel support is available, as well as support for the participant-organized local events (for participants at US institutions).
ESA will organize a similar train-the-trainer workshop in Europe in January 2020. For more information on applying for the JWST Master Class, please see the call for applications.
Rehearsals at the Mission Operations Center
In the course of the deployment and initial checkout while Webb travels to L2, and during science operations, daily communications with the mission operations center at the institute will be essential. In September 2018, the JWST flight operations team successfully completed two critical communications rehearsals. Many more rehearsals of various aspects of JWST operations are planned in the coming months.
The first rehearsal demonstrated that—from the moment Webb launches through the first six hours of flight—complex exchanges could be accomplished among five service providers around the world, alternately conveying command and telemetry communications. The second rehearsal showed that our mission operations center could successfully command the telescope. The success of these exercises is a testament to the hard work of NASA, our industry partners, and the flight operations team, as well as teams across the country and around the world.
JWST User Committee
The JWST User Committee (JSTUC) met on January 30th, 2019 to be updated on the status of the JWST Science and Operations Center, and on the science planning and schedule for the Cycle 1 Call for Proposals.
Following the meeting, the JSTUC sent a recommendation letter to STScI Director, Ken Sembach, on the process and timing of soliciting large (100–1000 hours) observing programs for Webb. This letter, as well as previous correspondence from the JSTUC to the institute, is posted on the JWST Observer website.
The JSTUC welcomes feedback from the JWST Observer community; they may be contacted by email on firstname.lastname@example.org.
JWST at the AAS and DPS
The institute supported Webb at the winter AAS in Seattle, Washington and at the 50th Division for Planetary Sciences (DPS) meeting in Knoxville, Tennessee. At the AAS, JWST was represented at the STScI booth where the astronomical community could get their questions about the scientific capabilities of JWST and proposing answered, as well as explore Webb in the STScI Virtual Reality experience. A number of the investigators from the Directors' Discretionary Early Release Science (DD-ERS) program presented their science at the NASA Hyperwall. The DPS meeting featured a JWST Solar System Observers Town Hall, which updated the planetary science community on planned GTO and ERS observations of Solar System targets, and discussed how the Webb proposal tools can be used to plan Solar System observations.
HST @ STScI UpdateR. Osten (osten[at]stsci.edu)
HST @ AAS
The Hubble presence at the recent winter AAS meeting in Seattle consisted of the STScI booth with informational pamphlets, opportunity for interaction with instrument experts, and posters on calibration performance. In addition, a special session entitled "A Hubble Space Telescope for the 2020s: Capabilities and Opportunities" occurred on Thursday, January 10. This special session highlighted new results from the observatory in some of the forefront science areas in which Hubble excels. The session was forward-looking and intended as the start of a dialogue between Hubble’s science operations center and the scientific community about the role Hubble should play in the science of the 2020s. The format consisted of a few short talks to describe new results and motivate future observing strategies, followed by a panel discussion with input from the community.
Panel discussion afterward touched on lifetime-limiting aspects to observatory operations, plans and capabilities in reduced gyro mode, and interest in the ultra-flexible observing programs (described in the 2016 STScI Newsletter Article Volume 33, issue 2). The oral session was accompanied by a poster session with numerous submissions, ranging from updates on new observing modes and tools (some described in the 2018 STScI Newsletter Article in Volume 35, issue 3) to specific science topics that could be addressed with Hubble in the next decade. Collected talks are available at this link.
The winter AAS meeting also marked the second instance of an STScI Town Hall at the AAS meeting. This is a recognition by the society of the valuable role the institute plays in enabling science. The agenda for the Town Hall included general updates on the status of STScI, a description of public engagement opportunities for astronomers, as well as how the institute is leveraging work on Hubble and Webb for WFIRST science operations. A series of short talks highlighted: Hubble research and results in Solar System and exoplanet science; work on the exoplanet characterization toolkit (ExoCTK); laboratory work exploring planetary atmospheric conditions; and technology development for high-contrast imaging with segmented telescopes. A description of some of the processes implemented at STScI to build a safe and inclusive workplace in astronomy concluded the session. The charts presented at the meeting can be found at this link.
On January 8, 2019 the Wide Field Camera 3 on Hubble suspended operations due to an anomaly on the instrument's UVIS channel, and was restored roughly a week later, with a return to science observations a few days after that date. The anomaly occurred within the CCD Electronics Box (CEB) on the UVIS channel. Analysis indicated that it was safe to reset the electronics and recover the instrument to an operational state. Those steps were performed without incident. An investigation into the cause of the corrupted telemetry that triggered the suspension of operations concluded that it was likely caused by a single event upset within the analog to digital collection electronics for CEB telemetry. Since that recovery, WFC3 UVIS has been operating nominally. Figure 1 shows an image obtained shortly after recovery.
ACS experienced a temporary suspension of operations from February 29 to March 6. An error arose during a check of the ACS memory, which occurred while the instrument was transitioning between operational states. Several tests performed to troubleshoot the anomaly—involving different ways of writing to and reading from the ACS memory—executed successfully. Recovery of the instrument proceeded following a detailed review of schematics and anomaly signature characterization. The on-board memory check was expanded to include the affected chip area. Observations with the remaining instruments continued unimpeded during the ACS suspension. The search for the most likely cause continues; it does not appear to be due to a failure in a memory chip (for which ACS retains significant redundancy). The instrument experienced a second temporary suspension on the morning of April 3. The instrument was recovered that afternoon and troubleshooting is happening in parallel. In both events, ACS was in the process of returning to operations after its monthly anneal and reboot, with the suspension triggered by erroneous values in an unused portion of instrument memory. The repeat indicates that the problem is unlikely to be a random event. There is consensus that it is safe to operate the instrument. Changes to the monthly maintenance procedures will mitigate or prevent future problems. Since that recovery, ACS has been operating nominally; see Figure 2.
Recent Gyro Behavior
Last year saw the failure of two of Hubble's gyroscopes, used for pointing and control (STScI Newsletter Volume 35, issues 1 and 3). During the time before Gyro-2 failed, the observatory experienced an elevated level of jitter which resulted in an increase in the failure rate of acquisitions and re-acquisitions. Operations with Gyro-3, brought up after the failure of Gyro-2, indicate that while the jitter levels are stable at values consistent with those seen in prior years, this gyroscope does exhibit large rate bias shifts which impact acquisitions and re-acquisitions.
There continue to be short periods of time where there are an increased number of failures in acquisitions and re-acquisitions. There does not appear to be one single cause. The large rate bias shifts of Gyro-3 can result in the Fine Guidance Sensors requiring a larger search radius during acquisitions and re-acquisitions; this can extend the time to find the guide stars, and delay or lose the ability to take data for science. Performing an On-Board Attitude Determination before most re-acquisitions is minimizing the attitude error and limiting failures. Additionally, adding extra time (~60 seconds) for re-acquisitions ameliorates the situation in some instances, without significant loss of science. Changes to the magnitude limit used to select guide stars and the sampling rate for those stars are also expected to mitigate some of the acquisition issues. On-board bias updates are now done routinely and frequently, particularly for Solar System observations. This results in increased difficulty scheduling programs and crafting the weekly observation plan.
Sun Angle Constraints
The nominal Sun Angle limit for science observations with Hubble has historically been 50 degrees. As noted above, Gyro-3 experiences large rate bias shifts; having a large uncompensated bias while on gyro control can lead to large undetected attitude errors. This poses a number of risks to the spacecraft. Since the return to science using Gyro-3 on October 26, a more conservative Sun Angle limit has been in place to ensure observatory protection against thermal concerns in the event of unexpected Gyro-3 behavior. It is currently 54.3 degrees, which is likely the limit for the foreseeable future in three-gyro mode.
Longevity of Hubble, Reduced-gyro plans
This April marks the 29th anniversary of the start of Hubble’s on-orbit science operations, and plans are already underway for next year's 30th anniversary since launch. In addition, in May a full decade will have passed since the last servicing mission. With the exception of a few minor anomalies with instruments, the observatory health is generally very good. The instruments are aging gracefully, and scientists' and engineers' understanding of and compensation for instrument degradation generally outpaces the rate of actual declines. NASA's Engineering and Safety Center routinely re-examines assumptions driving the probability lifetimes of Hubble's subsystems. Current estimates give an 80% reliability or better for all subsystems in 2025, including having at least one gyro for pointing and control.
Gyroscopes have long been a limiting factor to Hubble's performance. A complement of three gyroscopes is normally used for regular science operations. The current gyroscope configuration uses Gyro-3 together with Gyro-4 and Gyro-6. All three have enhanced flex leads, with an anti-corrosive coating to overcome a vulnerability discovered on earlier generations of gyros. The gyros which have failed, Gyro-1 and Gyro-2 last year, and Gyro-5 earlier, were all non-enhanced and lasted as expected, for about 50,000 hours. Gyros 3, 4, and 6 are the remaining gyroscopes on the observatory. The current plans are to proceed using all three, until there is another failure, at which point Hubble will enter either one-gyro mode or two-gyro mode (depending on the particular condition of the remaining gyros at that time). On-orbit experience with reduced gyro mode occurred in Cycles 15 and 16, with two gyros for pointing and control, in addition to a one-week period when tests of one-gyro operations occurred. There is very little difference operationally between the two reduced-gyro modes, and the longevity is extended by keeping one gyro in reserve. The science capabilities of Hubble in reduced-gyro mode are also only modestly decreased from that in three-gyro mode operations, with expectations of science productivity at roughly 75% that obtainable previously, and most observing modes still realizable.
Instrument teams are proactively examining calibration plans for their sensitivity to reduced-gyro mode in monitoring of external targets, and modifying as appropriate to be robust against the impact of any changes to the number of gyroscopes on target availability. In addition, user documentation has been updated with reduced-gyro information to be prepared when this is needed.
The CubeSat Revolution: A New Platform for Space Science and Technology DevelopmentJ. Tumlinson (tumlinson[at]stsci.edu) and M. Postman (postman[at]stsci.edu)
Astronomers involved with space astrophysics missions are long familiar with the basic contours of NASA mission categories from Small Explorers (SMEX) to flagships like Hubble and Webb. Below this, quite literally, is the long-standing "suborbital program," which has used sounding rockets for flights of minutes, and balloon payloads for flights of weeks.
"CubeSats" are a kind of miniature spacecraft bus that began as a way to fly student-level engineering projects in space for short-duration flights. Since their invention in the late 1990s, the basic "1U" bus, a 10 x 10 x 10 cm3 platform, has grown to encompass larger satellites ("6U" meaning 30 x 20 x 10 cm) with a wide range of academic and commercial applications. By some counts, over 1000 CubeSats have been launched over the last decade.
CubeSats currently fill an important niche in NASA's space science portfolio. Like the traditional suborbital rockets and balloons, they offer hardware-training opportunities for scientists and engineers while tolerating the higher degrees of mission risk need to develop new technologies for space instruments. NASA’s CubeSat Launch Initiative has already launched 85 such missions with a tremendous range of applications from solar system plasmas, to cosmic ray and gamma-ray monitoring, to solar sails and space-to-ground communications.
Perhaps highest on the gee-whiz scale were the two 6U CubeSats ("EVE" and "WALL-E") that accompanied NASA's InSight Mars lander and, in November 2018, relayed the lander's radio signals back to Earth during the critical entry, descent, and touch-down phase. This was a huge leap in capability and expectations: EVE and WALL-E showed that CubeSats can get to Mars, operate as a science platform there, provide communications back to Earth, and act as helpers to larger spacecraft. There are now plans brewing to use this low-cost platform for deeper interplanetary missions.
And lately, CubeSats have drawn attention as a low-cost, risk-tolerant platform for developing the advanced technologies needed by future flagship astrophysics missions. Their most appealing feature is the chance to test observatory components like gratings, mirrors' coatings, control systems, and electronics in a fully relevant space environment, yet on a mission that can go from design to orbit on timescales of a couple years. In this case, degraded performance or failure risks just a tiny fraction of the cost of an Explorer, Probe, or flagship mission.
The University of Colorado's SPRITE mission provides a great example of CubeSat-based technology development. SPRITE is the "Supernova Remnants/Proxies for Reionization/and Integrated Testbed Experiment." That slightly unwieldy name nevertheless captures the exciting potential of the platform to do cutting-edge scientific measurements, while also proving technologies for future missions. SPRITE will use a compact UV imaging spectrograph to map shocked gas in Magellanic Cloud supernova remnants and to observe 100 low-redshift starburst galaxies looking for escaping ionizing radiation, a key problem in understanding the early "reionization" of the cosmos.
At the same time, SPRITE will be testing advanced coatings and low-background photon-counting detectors that would be used by future UV-capable flagships like LUVOIR or HabEx. By monitoring the performance of its advanced UV coatings and detectors over a two-year mission, SPRITE will advance these new technologies to high readiness long before the next flagship needs them, and guide future efforts to make them even better. SPRITE is also the first CubeSat mission that will archive its data at STScI's Mikulski Archive for Space Telescopes, in what we hope sets a precedent for community access to data from this rapidly growing platform.
Delivering TESS Data to the WorldM. Fox (mfox[at]stsci.edu) and I. Momcheva (imomcheva[at]stsci.edu)
The first data release from the Transiting Exoplanet Survey Satellite (TESS) was one of the most anticipated events of 2018 across the exoplanet community. In the months leading up to the first release, engineers and scientists across the Data Management Division (DMD) and the Data Science Mission Office (DSMO) spent significant amounts of time and effort setting up and testing our infrastructure, developing tools and interfaces, and preparing documentation and tutorials such that users can have a smooth experience downloading the data and getting started on the analysis. In this article we highlight some of the innovative solutions and services we used for this release to give you a "behind-the-scenes" look at the first TESS data release.
Our primary concern was our ability to serve data to users immediately after the release. Based on our previous experience hosting the Kepler and K2 datasets, we expected that the first public release—of Sectors 1 and 2 scheduled for early December 2018—would drive the highest volume of downloads within the shortest amount of time. While we expected that most users would only download data for their targets of interest, we also anticipated that many would download all the data in the release. With a data volume of ~6.9 TB in the first release (~3.5 TB per sector), multiple concurrent requests could quickly saturate our capacity to deliver data and result in slow downloads and time-outs for many users. Our highest demand prediction required the Mikulski Archive for Space Telescopes (MAST) to be capable of delivering 400 TB of data per day, which is over six times the current MAST bandwidth capacity! Clearly, we would need to make use of additional infrastructure.
Evaluating third party infrastructure options required us to set up performance tests, which would simulate the expected global demand. Our team decided to use the Amazon Web Services (AWS) Lambda functionality to drive these performance tests. Lambda is a serverless compute service, where a user can write a function and execute it in different geographic regions around the world. We set up a simple Lambda function that simulated a user downloading TESS data products from MAST, checked for errors and recorded performance metrics such as connect time, transfer time, bytes downloaded, etc. The Lambda function was run in multiple global regions, where each region would have a pre-configured concurrency level. For example, for a concurrency of 1000, each region would be running 1000 concurrent instances of our Lambda function simulating 1000 users requesting data simultaneously.
In order to understand the performance edges of third-party services, we needed to analyze the data captured in the tests. We found an elegant solution was to push the metrics and error codes directly to AWS CloudWatch from our Lambda function. CloudWatch is an AWS service that provides a graphical interface allowing analysis of captured metrics. Tuning the performance test was mostly a matter of adjusting the Lambda concurrency and monitoring the CloudWatch graphs to note performance trends and any errors.
We evaluated two third-party infrastructure solutions: a cloud object storage provider and a content delivery network (CDN) service. Cloud object storage (e.g., AWS S3) provides high availability, but while it could potentially double our bandwidth, it fell short of our goal to get to six times our current bandwidth rates. Here is where the CDN service really shines, particularly given our expected large global concurrent demand. A CDN service caches files in data centers around the world. For example, when someone in Tokyo requests a file, the CDN caches a copy of that file at the CDN edge data center in Japan. All future requests from users in Japan would be delivered from the CDN edge data center there, thus taking pressure off MAST and using edge data centers around the globe to serve TESS data products. Our Lambda tests showed that CDN performance scaled linearly up to a point we felt would meet our expected demand.
On the release day—December 6th, 2018—we observed the CDN reducing bandwidth demands to MAST (the CDN origin) and pushing out data products at record rates. During the highest demand periods we saw TESS products moving out to the community at rates up to 1.2 GB/s, more than twice the MAST capacity. Figure 1 shows a fine-grained record of the bandwidth as a function of time (binned in five minute increments) within the first day after the release. Demand on the MAST servers (orange line) remained almost constant while the edge locations (blue line) experienced significant spikes. Within the first 24 hours of the release, users downloaded 24 TB of data and Figure 2 shows the global distribution of those users. The performance for the user community was even, regardless of their global location. We received no complaints from users and there was a significant amount of excitement across the community with many posting on social media about the seamless experience. Equally important, users requesting data from other MAST missions were unaffected by the spike in demand for TESS data.
All in all, the CDN allowed us to seamlessly serve a large volume of data within a short period of time to the global astronomical community. Even though the demand did not reach our worst-case estimates, we were satisfied with the technological solution we chose and the experience with the TESS delivery can be transferred to future data releases where we expect high volume of downloads.
A number of other innovative solutions were developed for the TESS data.
For users interested in exploring the full suite of MAST holdings of a given known exoplanet, TESS data were added to exo.MAST, an interface that caters specifically to the needs of the exoplanet community. Specifically, users can search on a TESS threshold-crossing event (TCE), find the TESS-derived metadata, view the TESS light-curves and download the TESS data products for their targets of interest directly in exo.MAST.
The full frame images (FFI) which are saved every 30 minutes by TESS (as opposed to the monthly cadence for Kepler) are expected to be a major source of new discoveries. As part of our mission to provide high-quality access to astronomical datasets, we built an image cutout service for TESS FFI images. Users can request image cutouts in the form of TESS pipeline-compatible TPFs without needing to download the entire set of images (>1400 images with a total volume of >750 GB). For users who wish to have more direct control or who want to cutout every single star in the sky, the cutout software (python package) is publicly available and installable for local use. The main barrier in writing performant TESS FFI cutout software was the number of files that must be opened and read from. To streamline the cutout process, we performed a certain amount of one-time work up front, which allowed individual cutouts to proceed much more efficiently. The one-time data manipulation work takes an entire sector of FFIs and builds one large (~45 GB) cube file for each camera chip, so that the cutout software need not access several thousand FFIs individually. Additionally, we transpose the image cube, putting time on the short axis, thus minimizing the number of seeks per cutout. By creating these data cubes up front, we achieved a significant increase in performance.
Helping users get from zero to science as fast as possible is also a major part of our work. In order to expedite this process for TESS, our archive scientists developed a series of tutorials in the form on Jupyter notebooks. These covered a wide range of topics including reading and displaying different types of files, searching the catalog around a target, retrieving data from a guest investigator program and creating FFI cutouts. All notebooks conformed with our internal style guide and were automatically tested to guarantee their functionality. Users were excited by the availability of "executable documentation" and at least one user announced on social media that the notebooks were helpful in the fast turn-around of a discovery. The notebook library is open to contributions! In the future, we hope to expand the notebook library to other missions supported by the institute.
A final notable development was the staging of all TESS data on Amazon Web Services (AWS). The goal here is to make the TESS data highly available next to the vast computational resources offered by AWS. Using these data from within the US-East (N. Virginia) AWS region does not incur any charges, but downloading data from this copy to other AWS regions or outside of AWS will. For any large-scale analysis which would require touching most or all of the data and/or needs a large amount of computational resources, we recommend that users consider using the AWS dataset. An example of accessing and working with the AWS dataset is available on the MASTLabs blog.
Hosting the TESS data at MAST has been an exciting experience across STScI data management. It allowed us to experiment with new technologies, prototype new services and be part of the worldwide wave of science delivered by this amazing mission. We look forward to the many discoveries to come.
ULLYSES—A DD Spectroscopic Legacy ProjectN. Reid (inr[at]stsci.edu)
As the Allocating Official for Hubble, STScI Directors have the authority to allocate up to 10% of the observing time at their discretion. This Director’s Discretionary (DD) time is used for a number of purposes. The most frequent use is for small-scale, community-requested, peer-reviewed programs that are designed to follow up on transient events that occur during a given cycle. However, DD time is also used for monitoring programs (e.g., the Outer Planet Atmosphere Legacy program), for public outreach (e.g., anniversary images); to subsidize GO programs (e.g., the Multi-Cycle Treasury programs and the recent Fundamental Physics initiative), and for larger-scale programs that tackle questions that are difficult, or even impossible, to address through the standard TAC process (e.g., the original Hubble Deep Fields, the Hubble Ultra-Deep Field, and the Frontier Fields). The ULLYSES program is the latest addition to the last category, but with a focus on spectroscopy of (relatively) nearby stars rather than deep imaging for galaxy evolution.
ULLYSES was developed over the past year. Following discussions with the Space Telescope Users Committee (STUC), the current STScI Director, Ken Sembach, constituted a Working Group (WG), chaired by Professor Sally Oey (U. Michigan), to advise him on how best Hubble could use its unique UV capabilities to probe star formation and the associated stellar physics. As a first step, the WG polled the general community for their input on outstanding "must do" science questions in these science areas that remain outstanding for Hubble, which programs fell beyond the purview of the standard GO Call, and how those programs could be conducted most effectively. The WG also invited the submission of short white papers to expand on particular themes. Some 196 survey responses were received by the deadline of December 7, together with 34 white papers.
Two science themes emerged as predominant favorites in the survey feedback: UV spectroscopy of young OB stars, particularly at low metallicities, as an aid to stellar population modelling; and UV spectroscopy of young low-mass stars to probe accretion processes. The WG recruited additional members to supplement its expertise and developed a comprehensive science case through a series of discussions. The final report was submitted to the STScI Director on February 5. Once received, the report was distributed for high-level review by four experienced researchers who were asked to assess the likely scientific impact, the potential for complementary and supplementary observations, and the potential for related theoretical investigations. The reviews were overwhelming positive, and the Director has informed the STUC that he intends to proceed with the program.
The primary recommendation of the report is "…that the HST UV Initiative be devoted to obtaining a Hubble UV Legacy Library of Young Stars as Essential Standards (ULLYSES) to serve as a UV spectroscopic reference sample of high- and low-mass young stars. The recommended library will provide observations that uniformly sample the fundamental astrophysical parameter space for each class of stars, i.e., spectral type, luminosity class, and metallicity for massive stars; and spectral type, age, and disk accretion rate in low-mass stars…" The program envisages obtaining UV spectroscopy of 70 LMC and 70 SMC OB stars, as well as a sprinkling of lower-metallicity high-mass stars, together with UV spectra of 40 K- and M-type T Tauri stars and brown dwarfs in Galactic star-forming regions. The full WG report will be released to the community in mid-April.
ULLYSES will be implemented following the model of the successful Frontier Fields. All of the data obtained will be non-proprietary. STScI is currently constituting an in-house implementation team to construct the detailed observing program and produce an appropriate set of high-level data products. The in-house team will continue to work with the community to ensure that the program is implemented in an effective manner. The final target list will not be constructed until after the Cycle 27 TAC results have been finalized and will be adjusted to avoid pre-empting any GO programs selected through that process. The Cycle 27 TAC will be instructed to focus on the science inherent in each GO program without speculation on ULLYSES.
Exploiting the Power of Metallicity Studies in the UV: Dissecting the Nearby Spiral Galaxy M83S. Hernandez (sveash[at]stsci.edu)
Metallicities of galaxies at all redshifts are critical for deciphering a plethora of physical and evolutionary processes that take place among and inside galaxies, including star formation, stellar feedback, and interstellar/intergalactic chemical enrichment. In the last decades it has become evident that a large fraction of the stellar mass in the universe was assembled in intense episodes of star formation (SF) at high (z > 1) redshift. Studies of local starbursts and star-forming galaxies can be performed at exquisite signal-to-noise, spatial and spectral resolution, which are not achievable at higher redshift. Such studies provide an invaluable tool for creating a baseline in understanding how gas and stellar properties evolve through cosmic time.
In this Newsletter I present a brief summary of our latest findings in the nearby spiral galaxy M83 (Hernandez et al. 2019). Using young star clusters, we performed a detailed metallicity gradient analysis. Our measurements provide us with hints to the chemical history, as well as physical properties of this face-on, star-forming galaxy. We identify two possible breaks in the metallicity gradient of M83 at galactocentric distances of R ∼ 0.5 and 1.0 R25.The metallicity gradient of this galaxy follows a steep-shallow-steep trend, a scenario predicted by three-dimensional (3D) numerical simulations of disk galaxies. We propose a scenario where the first steep gradient originated by recent star-formation episodes and a relatively young bar (<1 Gyr). The shallow gradient, on the other hand, is created by the effects of dilution of outflowing enriched gas mixing with low-metallicity material present at larger radial distances. And finally, the second break and last steep gradient mark the farthest galactocentric distances where the outward flow has penetrated.
Metallicity of Galaxies
With the purpose of understanding how galaxies are formed and evolve with time, astronomers continuously search for new tools that can provide clues to their past. One of these tools that can lead to strong constraints on the history of cosmic chemical enrichment of galaxies is the measurement of their chemical composition. It is through such studies that we can learn about the evolution of the Universe from a primordial metal-free system to the present-day chemically diversified environment.
The metallicity of a galaxy, [Z], is mainly controlled by two components: 1) chemically processed material in stars, and 2) exchanges between the galaxy and the intergalactic medium (IGM). Given the dependence of metallicity on these two factors, studies focused on metallicity relations and metallicity gradients in galaxies hold a wealth of information on their formation and evolution.
Back in 1979, Lequeux discovered that the masses and metallicities of several star-forming, irregular, and blue compact dwarf galaxies, correlated with each other in the sense that more massive galaxies appeared to have higher metallicities. This same correlation was later confirmed by several other independent studies making this mass-metallicity relation (MZR) widely used for studying star-formation episodes, galactic winds, and chemical enrichment in general. Similarly important, the metallicity gradients in individual galaxies track some of the complex dynamics taking place within them, such as outflows and infall of material. Given the importance of accurate metallicities, it is crucial to obtain reliable metallicity indicators in order to correctly interpret the processes influencing these relations.
In the last decade, new techniques have been developed to study the chemical content of nearby galaxies using blue supergiant stars (BSGs) and red supergiant stars (RSGs), as well as the integrated light of star clusters. These are in addition to the more classical techniques where nebular emission lines at optical and infrared wavelengths are used to infer the metallicity of H Ⅱ regions or absorption-line spectra arising from heavy elements against bright background UV sources are analyzed to make a census of the metals in the interstellar medium (ISM) of galaxies. With current telescopes, star clusters well outside of the Local Group and at distances of several megaparsecs (Mpc), appear not to be resolved into individual stars. This facilitates measurement of their chemical composition through the analysis of their integrated light (IL) spectra. This kind of spectroscopy has shown ample potential; however, until recently most efforts have focused on the optical and infrared regimes. Young stellar populations, for instance, when observed in the near-infrared are strongly dominated by RSGs, which facilitates their analysis through modeling of the whole population as a single RSG star. When studying globular clusters (GCs), on the other hand, one needs to make the assumption that all stars in the cluster are coeval and implement full population synthesis techniques to perform a similarly detailed abundance analysis. By way of contrast, the UV spectral coverage for IL metallicity analyses of clusters is rather unexplored.
Piecing together the History of M83
In our latest publication, Hernandez et al. (2019), we performed a metallicity study of the nearby (4.9 Mpc) face-on star-forming galaxy M83. This was accomplished by merging ground-based optical observations from the X-Shooter spectrograph on the Very Large Telescope (VLT) in Chile with space-based far-ultraviolet observations with the Cosmic Origin Spectrograph (COS) onboard the Hubble Space Telescope (HST). Our sample of young star clusters was comprised of 23 targets covering the inner disk of the galaxy (Figure 1). Our metallicity measurements confirm a relatively steep gradient in the inner disk of the galaxy.
To obtain a more complete picture of the metallicity trends in M83, we combined our measurements with those from Bresolin et al. 2007 and 2009 covering the outer disk of M83 as shown in Figure 2. Based on the trends in this figure, we proposed that M83 exhibits a metallicity gradient with two possible breaks at R ∼ 0.5 R25 and R ∼ 1.0 R25. If the metallicity breaks are genuine, the metallicity gradient of this galaxy follows a steep-shallow-steep trend, a scenario predicted by three-dimensional (3D) numerical simulations of disk galaxies. The first break is located near the corotation radius. This first steep gradient may have originated by recent starformation episodes and a relatively young bar (<1 Gyr) possibly triggered by an interaction or merger. In the numerical simulations the shallow gradient is created by the effects of dilution of chemically enriched material outflowing and mixing with lower metallicity gas present at larger galactic distances. The second break and last steep gradient mark instead the farthest galactocentric distances where the outward enriched gas flow has penetrated the disk.
Our work has demonstrated that the integrated-light method can be used as an alternative metallicity tool to nebular and interstellar gas techniques, applicable not only in the optical and infrared, but also in the UV. By successfully expanding the metallicity analysis of stellar clusters to UV wavelengths we have made it possible to simultaneously study the multi-phase gas and stellar properties. Such analysis can bridge our understanding of galactic outflows, stellar evolution and stellar feedback not only locally, but also at higher redshifts (z ~ 2) where the rest-frame UV light is shifted into the optical/IR wavelengths.
Bresolin, F., 2007, ApJ, 656, 186
Bresolin, F., Ryan-Weber, E., Kennicutt, R. C., & Goddard, Q. 2009, ApJ, 695, 580
Hernandez, Svea, Larsen, Søren, Aloisi, Alessandra, Berg, Danielle A., Blair, William P., Fox, Andrew J., Heckman, Timothy M., James, Bethan L., Long, Knox S., Skillman, Evan D., & Whitmore, Bradley C., 2019 ApJ, 872, 116H
Poetry in (Proper) Motion: Internal Kinematics of Globular Clusters with HSTM. Libralato (libra[at]stsci.edu) and A. Bellini (bellini[at]stsci.edu)
Globular clusters (GCs) have revealed themselves to be far more complex than we originally thought: GCs rotate, present kinematic anisotropies, host multiple stellar populations (mPOPs), slowly interact with the surrounding Galaxy and break apart forming tidal tails. Most of the new findings in the field of GCs of the two last decades have been made possible thanks to exquisite photometry and spectroscopy, but now the contribution (and impact) of high-precision astrometry is exponentially growing.
The internal kinematics of GCs is one of the research fields that is benefiting the most from the new "Renaissance of astrometry" in the Gaia era. Nevertheless, stars in the very core of GCs and at the faint end of the color-magnitude diagrams (CMDs) are and will be out of Gaia's reach, leaving Hubble Space Telescope (HST) as the only tool to obtain high-precision astrometric measurements for these stars.
In this newsletter we describe the results obtained for the GC NGC 362 (Libralato et al. 2018). The results of this paper are part of a broader project focused on producing high-precision proper motion (PM) catalogs for over 60 GCs for the "Hubble Space Telescope UV Legacy Survey of Galactic GCs" (GO-13297) and ancillary programs, and are obtained within the HSTPROMO collaboration. NGC 362 is a post core-collapsed cluster, and as such its centermost regions are extremely crowded. This cluster therefore represents an ideal benchmark to test our reduction tools, which are optimized for crowding environments. We were able to measure internal PMs with a precision of a few tens of μas year-1 even for faint main-sequence stars in the cluster's core. For brighter Hubble stars at the faint limit of Gaia, our PM precision is >80 times better than Gaia's end-of-mission predictions.
Internal Proper Motions of Multiple Stellar Populations
In the recent years, the paradigm of GCs made up of simple stellar populations, i.e., stars born at the same time from the same proto-cluster cloud and with the same chemical composition, has been demolished. It is a fact now that formally all GCs host mPOPs characterized by stars with different chemical composition and age, forming well-distinct sequences on a CMD. So far, most of the theoretical effort has been focused on developing formation scenarios able to account for all the photometric and spectroscopic observational pieces of information, but all the proposed theories failed to account for all the available evidence (see the review of Renzini et al. 2015), and many questions are still unanswered.
Dynamical models (e.g., Vesperini et al. 2013) predict that second-generation (2G) stars, born at a later stage from the material processed by first-generation (1G) stars, formed initially more centrally concentrated than 1G stars, and then slowly diffused outward preferentially along radial orbits, due to two-body interactions. After many local two-body relaxation times, any difference in spatial distribution and kinematics of 1G and 2G stars is expected to be erased. This happens first in the cluster's core, where the local two-body relaxation time is short, and later also in the cluster's outskirts, where the local two-body relaxation is much longer, reaching a few Gyrs in some clusters. Massive clusters have longer relaxation times at any radial distance, so they are more likely to still retain some fossil signature of the initial spatial segregation between 1G and 2G stars. Since GC stars migrate outward preferentially along radial orbits, if this fossil signature is still present we would expect 2G stars to be more radially anisotropic (σrad > σtan) than 1G stars at least in the cluster outskirts. High-precision PMs represent one of the most-effective ways to measure these effects and constrain the formation and dynamical evolution of these ancient stellar systems (see the discussion in, e.g., Hénault-Brunet et al. 2015).
The internal kinematics of mPOPs in GCs might seem a niche research field at a first glance, but GCs are among the oldest objects in the Universe and understanding how their mPOPs formed and have evolved will shed light on the chain of events that occurred at the dawn of GCs, and hence of the Milky Way. To date, there exists only a handful of observational works on the internal kinematics of mPOPs.
For instance, Anderson & van der Marel (2010) investigated the core of the GC NGC 5139 (ω Cen), and found no significant kinematic differences between 1G and 2G stars. Similarly, Libralato et al. (2019) found no difference in the kinematics of the mPOPs in the core of NGC 6352. These results work in favor of theoretical predictions, since the relaxation time in the core of these GCs is too short and any initial difference between the kinematic properties of 1G and 2G stars have long been erased. It is in the clusters' outskirts where our attention should be focused. Richer et al. (2013; but also Milone et al. 2018 with Gaia) showed that 2G stars in the outskirt of 47 Tuc are more radially-anisotropic than 1G stars. Similar results have been found for stars in the outskirts of NGC 2808 (Bellini et al. 2015) and ω Cen (Bellini et al. 2018).
NGC 362 hosts at least four distinct stellar populations (one 1G and three subsequent 2Gs), which we isolated by means of the distinct location of theirs stars on CMDs and pseudo-two-color diagrams (e.g., see the top panels of Fig. 1 for red-giant-branch stars). We computed tangential and radial velocity-dispersion profiles for each population, and found no significant difference between the kinematics of the mPOPs. We did find a marginal (~2.2-σ level) signature of 2G stars with a smaller velocity dispersion than 1G stars (see bottom panels of Fig. 1). In addition, we found no evidence of radial anisotropy for both 1G and 2G stars.
Kinematics of GCs as a Whole
The exquisite PMs of Hubble allowed us to analyze the kinematics of NGC 362 as a whole. NGC 362 is a dynamically old GC that experienced a collapse of its core. To verify this, we measured the level of systemic rotation of the cluster in the plane of the sky, and found it consistent with being a non-rotating cluster. As GCs age, they loose angular momentum (e.g., Tiongco et al. 2017), and NGC 362 has likely lost most of its initial angular momentum, thus confirming its advanced dynamical state. We further confirmed this through the measurement of the cluster's state of energy equipartition.
GCs are expected to evolve over time toward a state of full energy equipartition. When this happens, the velocity dispersion of their stars, σμ, should scale with the stellar mass m as m-η where η, the level of energy equipartition, is equal to 0.5 (Spitzer 1969, 1987). Recent N-body simulations have instead shown that full energy equipartition is actually never reached, and GCs only achieve at best partial energy equipartition (e.g., Trenti & van der Marel 2013; Bianchini et al. 2016; Webb & Vesperini 2017). Furthermore, η is not constant over the entire cluster, but is expected to decrease as the distance from the cluster's center increases (the two-body relaxation time in the outskirts of GCs is longer than in the centermost regions).
Measuring how the velocity dispersion varies as a function of the stellar mass in GCs is a challenging task because it requires to measure very precise PMs for stars several magnitudes fainter than the main-sequence turn-off. Over the years, many efforts (and reduction tools) have been developed in exploiting very crowded environments with Hubble data, so that we can use Hubble PMs to study the actual state of energy equipartition in GCs for the first time.
We computed the velocity dispersion of stars in NGC 362 down to stellar masses of about ~0.45 (i.e., five magnitudes below the main-sequence turn-off) and estimated the global and the local (i.e., at different radial distances) values of the level of energy equipartition η (Fig. 2). We find that η decreases from ~0.4 at the center to ~0.1 at 2 half-light radii: a result also supported by numerical simulations. Bianchini et al. (2018) also proposed that the collapse of the core in a GC should leave peculiar kinematic signatures in the global and local levels of energy equipartition. Following Bianchini et al. prescriptions, we compared the local and global level of energy equipartition and were able, for the first time, to infer that NGC 362 is in a post-core-collapsed state using kinematic arguments.
The aforementioned examples are only a few proofs of the key role of high-precision astrometry in stellar astrophysics. Hubble has now paved the path. The upcoming James Webb Space Telescope (JWST) and Wide-Field InfraRed Space Telescope (WFIRST) will help us to explore fainter and further regions, and build a complete kinematic picture of GCs.
Anderson & van der Marel 2010, ApJ, 710, 1032
Bellini et al. 2015, ApJL, 810, L13
Bellini et al. 2018, ApJ, 853, 86
Bianchini et al. 2016, MNRAS, 458, 3644
Bianchini et al. 2018, MNRAS, 475, 96
Hénault-Brunet et al. 2015, MNRAS, 450, 1164
Libralato et al. 2018, ApJ, 861, 99
Libralato et al. 2019, ApJ, 873, 109
Milone et al. 2018, MNRAS, 479, 5005
Renzini et al. 2015, MNRAS, 454, 4197
Richer et al. 2013, ApJL, 771, L15
Spitzer 1969, ApJL, 158, L139
Spitzer 1987, Dynamical Evolution of Globular Clusters (Princeton, NJ: Princeton Univ. Press)
Tiongco, Vesperini & Varri 2017, MNRAS, 469, 683
Trenti & van der Marel 2013, MNRAS, 435, 3272
Vesperini et al. 2013, MNRAS, 429, 1913
Webb & Vesperini 2017, MNRAS, 464, 1977
Reclaiming WFC3 Pixels for ScienceB. Sunnquist (bsunnquist[at]stsci.edu), M. Bourque (bourque[at]stsci.edu), S. Baggett (sbaggett[at]stsci.edu), and E. Sabbi (sabbi[at]stsci.edu)
Installed in May 2009, the Wide Field Camera 3 (WFC3) has spent nearly 10 years on-orbit. The high-energy radiation in this harsh low-Earth orbit environment damages detectors and changes pixel behavior. By analyzing pixel levels as a function of time in both the UVIS and IR detectors, we were able to quantify these changes and generate time-dependent bad pixel tables and dark calibration files that represent them—a process that saves many thousands of typically discarded pixels for use in scientific analysis.
Each day, the WFC3/UVIS detector acquires roughly 1000 new hot pixels (WFC3 ISR 2016-08). By warming the detector during the monthly WFC3 anneal procedures, ~10–20% of these hot pixels are fixed and return to their normal level; however, the remaining hundreds of thousands of hot pixels are flagged as bad in the WFC3/UVIS dark calibration reference files and are typically discarded from any analysis. During evaluation of the WFC3/UVIS pixel levels as a function of time, we developed a stability criterion to identify any pixels that vary significantly above and beyond the expected uncertainty. Surprisingly, ~95% of the WFC3/UVIS hot pixels were found to be stable and thus can be successfully calibrated during dark calibration. These hot-but-stable pixels are now identified as such in updated WFC3/UVIS bad pixel tables—and users have the opportunity to reclaim them for use in scientific analyses. Also, the new bad pixel tables flag a newly identified population of tens of thousands of cold and unstable pixels that were previously treated as good but should now be discarded by users. For more information on the new UVIS bad pixel tables see WFC3 ISR 2018-15.
In the WFC3/IR detector, roughly 3.5% of pixels have changed their behavior since launch (WFC3 ISR 2019-03); such variations include normal pixels becoming hot, unstable pixels regaining their stability, some pixels transitioning between many stable dark current levels, other pixels alternating between two stable levels, and more. In general, the WFC3/IR detector experiences an increase of ~200 hot pixels per year while the unstable pixel population can vary by up to ~4000 pixels per year (~0.02% and 0.4% of the detector, respectively). Past WFC3/IR reference files combined all of the calibration data together and were insensitive to these changes, simply flagging as bad any pixels which spent the majority of their time in a hot and/or unstable state. In our new approach, we use subsets of the calibration data to better monitor any time-variable pixel behaviors and capture those changes in a collection of time-dependent superdarks and bad pixel tables. As a result, the new superdarks provide an improved calibration for the changing hot and unstable pixels. Furthermore, with the new data quality file (DQF) flagging methodology, users have the opportunity to include stable pixels—even when hot—in their analyses; doing so can reclaim about 0.5% of the detector. Likewise, the WFC3/IR bad pixel tables now track the time-variable bad pixel populations which ensures that new bad pixels are flagged in a timely fashion and that the thousands of pixels which convert to good are not flagged. For more information on these new IR bad pixel tables and superdarks, see WFC3 ISR 2019-03 and 2019-04.
Bourque, M., & Baggett, S. 2016, WFC3/UVIS Dark Calibration: Monitoring Results and Improvements to Dark Reference Files, WFC3 ISR 2016-08, STScI
Bourque, M., Borncamp, D., Baggett, S., Desjardins, T., & Grogin, N. 2018, Using Dark Images to Characterize Pixel Stability in the WFC3/UVIS Detector, WFC3 ISR 2018-15, STScI
Sunnquist, B., Brammer, G., & Baggett, S. 2019, Time-dependent WFC3/IR Bad Pixel Tables, WFC3 ISR 2019-03, STScI
Sunnquist, B., Mckay, M., & Baggett, S. 2019, Time-dependent WFC3/IR Superdarks, WFC3 ISR 2019-04, STScI
Hubble and LIGON. Reid (inr[at]stsci.edu) for the HST-LIGO Working Group
Sometimes the Universe surprises us. Observational gravitational-wave astronomy only became a reality recently with the commissioning of the advanced Laser Interferometric Gravitational-wave Observatory (LIGO) in 2015. The first event, a black hole/black hole merger, was detected soon after the first campaign started (September 14, 2015) with several similar events following over the next two years. Then, on August 17, 2017, LIGO not only detected a different type of event, a neutron star/neutron star merger, but an optical counterpart was quickly identified in the outskirts of the spiral galaxy NGC 4993. It would be fair to say that finding a bright optical counterpart so early in LIGO's career came as a surprise to the astronomical community. Plans for coordinated follow-up observations were not at a highly developed level. And to complicate matters, mid-August 2017 saw approximately 95% of US astronomers distributed across the country on a line stretching from Salem, Oregon through Columbia, South Carolina observing a total solar eclipse.
Follow-up observations were obtained of course, including photometry and low-resolution spectroscopy with Hubble. However, to better prepare for the future, the STScI Director convened a Working Group,* chaired by Professor Raffaella Margutti (Northwestern), to advise him on options for maximizing the scientific impact of future Hubble observations of optical counterparts to gravitational wave sources. The Working Group (WG) met through the late spring and summer of 2018 and their report was submitted to the Director and presented to the Space Telescope Users Committee in October 2018.
The recommendations from the WG fall under four broad categories: guidance for optimizing the observing strategy with Hubble; suggestions on associated policy, coordination among observatories; and maximizing the Hubble impact on time domain astronomy at large.
STScI is actively exploring options for implementing the recommendations.
Since the submission of the report, the Cycle 26 Telescope Allocation Committee met and a major ToO follow-up program has been accepted for execution (GO 15664: New insights from gravitational waves combined with electromagnetic light). This large non-proprietary program aims to obtain multi-epoch, multi-band imaging and spectra of gravitational-wave counterparts, including one ultra-rapid ToO for observations with the UV prism on Wide-Field Camera 3. LIGO's O3 observing campaign begins in April; we look forward to more surprises.
*The HST–LIGO Working Group members are Raffaella Margutti (Northwestern University – chair), Brad Cenko (GSFC), Ben Farr (University of Oregon), Ori Fox (STScI), Erik Kuulkers (ESA/ESTEC), Emily Levesque (University of Washington) and Danny Milisavljevic (Purdue). Further details, including the full report, are available here.
Science Planning and Scheduling in the Multi-Mission Era: Meet the Science Mission Scheduling BranchD. Adler (adler[at]stsci.edu)
You’ve seen Hubble's scientific results and the beautiful OPO images. But how does the whole process get started?
Once Hubble's (and soon, Webb's) annual Time Allocation Committee selects the science programs for a given observing cycle, the Observatory Planning Branch iterates with the Principal Investigators to fine-tune their programs utilizing the Astronomer's Proposal Tool (APT) to get them into a form where they can be scheduled. It's then up to the Science Mission Scheduling Branch (SMSB), with Bill Workman as Branch Lead, to create the Long Range Plan (LRP) at the beginning of the observing cycle. Once in place, SMSB also creates the weekly flight schedule and the instructions that get uplinked to the telescope.
The LRP (Long Range Planning) Group—Dave Adler, Brigette Hesman, and Ian Jordan—has two main tasks. First, they create an observing plan that enables Hubble to be scheduled as efficiently as possible. These observing plans typically span ~18 months, to give some flight-ready material for the transition to the next observing cycle, and include 2000–2500 individual science "visits," generally spanning from 1–5 orbits (1.5–7.5 hours) each. Time is money, as the saying goes, so the more time Hubble is observing, the better. With the four science instruments having varied observing characteristics, and targets spread throughout the sky requiring spacecraft slews, all factors are considered when creating the LRP. Most science observations don't require specific timing or telescope orientation, and can be scheduled throughout the observing cycle. But some observations have precise period/phase requirements (i.e., transiting exoplanets), or are coordinated to observe specific events (such as Juno orbital passes of Jupiter, or Europa's flaring plumes). With a lot of recent interest from the astronomical community in regards to specifically timed events, the percentage of highly constrained Hubble observing time has risen in recent years. The LRP group sorts these out to avoid scheduling conflicts, and consults the Hubble Mission Office for priorities as needed.
Second, the LRP group maintains the observing plan by making adjustments, as needed, on a daily basis. That's right, the LRP isn't static—it's a living, breathing entity! Target-of-Opportunity programs can interrupt an executing timeline; failed visits and new material (Director's Discretionary time, mid-cycle programs) get added back to the LRP as soon as possible. When there's a spacecraft anomaly, the LRP group determines the observing priorities and helps get the spacecraft back online as quickly as possible.
The LRP group also looks for ways to increase productivity. In 2009, right after Servicing Mission 4, they changed the planning process to better take advantage of Hubble science that could schedule through the South Atlantic Anomaly (SAA). That efficiency gain allowed 3–4 more science orbits to be completed each week, i.e., up to 200 orbits (300 hours) of extra Hubble science per year. Those gains have been maintained to this day.
Along with ongoing Hubble operations, the LRP group is creating and testing tools for the James Webb Space Telescope science observing plans. The concept is mostly the same, but specifics certainly differ. For instance, Webb orbiting L2 means there are no concerns from the SAA as with Hubble, but on the flip side, spacecraft momentum will have to be actively managed. The different field of view, due to sunshade placement and pointing constraints, also create a challenge of how often a specific target is visible throughout an observing cycle. Through it all, the goal for Webb will be the same as for Hubble—maintain the highest observing efficiency possible.
Each week, the Short-Term Schedulers (STS)—Gary Bower, Jim Caplinger, Bill Hathaway, RJ Lampenfield, Ryan Logue, and Kristen Wymer—query the Hubble LRP for the next week of observations, starting 11 days before the one-week flight products start executing. The exact order of the science and calibration visits isn't determined ahead of time; these "calendar builders" put things together to create the most efficient schedule as possible. In addition to the observations, they take into account things like spacecraft slews, guide star acquisitions, target acquisitions for positioning in the appropriate aperture, and communications with the TDRS satellites (for Hubble). STS is ably supported by software developers Don Chance and Danny Jones.
While Webb has yet to launch, there will be a similar process in place to proceed from querying the LRP for the mix of science, to building short-term schedules, to producing flight products that will be uplinked to the telescope using the Deep Space Network. In anticipation of Webb operations, both the LRP and STS groups have been involved in numerous Science Operations Rehearsals, and participated in the NASA operational exercises.
For the past ~30 years, SMSB has been planning and scheduling a single telescope. The dawn of a multi-mission environment—with more missions yet to come—will be a challenge, but SMSB is ready for this exciting time at the institute.
Wavefront Sensing and Control on JWST During CommissioningM. Meléndez (melendez[at]stsci.edu)
"It is difficult to say what is impossible, for the dream of yesterday is the hope of today and the reality of tomorrow." ― Robert H. Goddard
NASA's Webb will be the first space observatory with an actively controlled segmented primary mirror. The Wavefront Sensing and Control (WFS&C) working group, a collaboration between Ball Aerospace and Technologies Corp, STScI, and NASA Goddard scientists and engineers, will have the responsibility to perform the precise optical alignment of the telescope. In the WFS&C office at the institute, we have been actively rehearsing, practicing, writing, and developing the procedures, algorithms, and tools necessary to carry out the processes required to go from a misaligned telescope after deployment to a fully phased single 6.5-meter telescope. This article summarizes the wavefront activities and how we are preparing for OTE commissioning including the milestones successfully reached thus far and the upcoming activities before the launch of Webb in early 2021.
Wavefront Sensing and Control on JWST
Imagine having access to an instrument so advanced and sensitive that you could detect the heat signature of a bumblebee at the distance to the Moon (Dr. John Mather, https://jwst.nasa.gov/faq_tweetchat2.html). A golden time machine steadily floating in space 1.5 million kilometers away from Earth with a shiny sunshield, undisturbed in the cold temperatures of space. Certainly, this would have been an impossible dream for Galileo, but in a couple of years it will be our reality. NASA's James Webb Space Telescope will be our unobscured window into the history of our Universe—from detecting the signature of the first galaxies that illuminated the nascent Universe to the formation of solar systems capable of supporting life on planets like Earth. In this unimaginable cosmic puzzle, the Space Telescope Science Institute (STScI) in Baltimore, MD, will be home to the flight operations and science center, crucial for the success of one of NASA's most ambitious space missions.
Webb is an infrared telescope providing both imaging and spectroscopy in the wavelength range from 0.6 to 28.5 μm with a 6.5-meter primary mirror (PM) composed of 18 hexagonal-shaped segments (about 1.32 meter each). A convex secondary mirror (SM) steers light from the PM into a Cassegrain focus before the light is collected and focused by a fixed concave tertiary mirror and directed to the instruments by a flat Fine Steering Mirror. These mirrors and the supporting structure and subsystems comprise the Optical Telescope Element (OTE), gathering light from space and feeding it into the science instruments. At the heart of Webb is the Integrated Science Instrument Module (ISIM) which holds the main science payload containing four science instruments as well as the fine guidance sensor. The Near-Infrared Camera (NIRCam), Near-Infrared Spectrograph (NIRSpec), Mid-Infrared Instrument (MIRI) and the Fine Guidance Sensor/Near InfraRed Imager and Slitless Spectrograph (NIRISS). The specifications and science goals for Webb and each of the instruments are explained in great detail elsewhere, for example, check JWST Observatory and Instrumentation Documentation and JWST Observer website.
NASA's Webb will be the first space observatory with an actively controlled segmented primary mirror. To achieve this, the development, testing, and implementation of a complex set of technologies and algorithms were required. All this complexity, wrapped up with a great deal of ingenuity, will be crucial to ensure that we will see the image produced by a large 6.5-meter mirror and not 18 bumblebees randomly floating in space. The Wavefront Sensing and Control (WFS&C) working group, a collaboration between Ball Aerospace and Technologies Corp, STScI, and NASA Goddard scientists and engineers, will have the responsibility to perform the precise optical alignment of the telescope, so the wavefront from each of the 18 individual segments coherently add up in order to form a diffraction-limited image of a full 6.5-meter mirror telescope. In the WFS&C office at the institute, we have been actively rehearsing, practicing, writing, and developing the procedures, algorithms, and tools necessary to carry out the processes required to go from a misaligned telescope after deployment to a fully phased single 6.5-meter telescope ready to unveil some of the mysteries of the Universe.
Wavefront Activities During Commissioning
Roughly 36 days after launch, deployment, and with temperatures cool enough for the instruments to start taking the first images, the WFS&C commissioning activities begin. Detailed descriptions of the commissioning activities are described in various articles, e.g., Acton et al. 2004; Perrin et al. 2016. One way to think about commissioning is to split it into three different processes (Acton et al. 2012): PM segment location and positioning, segment-level wavefront control, and global phasing of all the controllable mirror segments.
The first process involves a tense game of hide and seek, trying to find each of the primary mirror segments as they are misaligned after initial deployment. In addition, this first process will yield a better determination of where the telescope is pointing (i.e., its boresight). For this, we need to be clever about systematically pointing the telescope until we find all the 18 segments in a series of mosaic images covering a large area surrounding a bright and isolated star. Once we find all the 18 bumblebees, we need to identify them, initiating a well-coordinated ballet as each of the mirrors are commanded, in turn, to perform a pirouette. At the end of this choreography, we arrange the segments into an array on a single NIRCam detector. This will allow us to better quantify the alignment of the telescope and the segment-level wavefront errors in the ensuing measurements.
During the segment-level wavefront control process, we try to improve the wavefront error for each segment by adjusting a total of 131 degrees of freedom among the primary mirror segments and the secondary mirror (113 unique degrees of adjustment). During this stage, we start with the first set of Global Alignment (GA) corrections. During GA, the SM is moved in piston to create defocused images. Using phase retrieval algorithms these images can be analyzed in order to reconstruct the phase for each individual segment. GA is an iterative process in which at each step the leading terms of wavefront error, e.g., power and astigmatism, are corrected locally by moving the PM segments and globally, by moving the SM. After GA, we stack the segments in preparation for the initial iteration of Coarse Phasing. To achieve sub-pixel stacking, caution must be taken when moving the mirrors in order to avoid large uncertainties associated with the coarse mechanism of the segment actuators. In Coarse Phasing, large piston errors are corrected by using the Dispersed Hartmann Sensors (DHS) in NIRCam, which enable measurement of the piston difference between 20 pairs of segments. In practical terms, piston errors translate into a fringe pattern in the DHS spectra; by analyzing these fringes, relative piston offsets can be determined accurately (for piston differences smaller than about 350 microns).
After global alignment and coarse phasing, the main cause of misalignment in the telescope would be an incorrect position of the secondary mirror. To address this issue, we need to determine the WF performance across the field of view (FOV). We begin this process using only the NIRCam FOV, with a program dubbed "Coarse MIMF." During Coarse MIMF we can determine the SM position error by measuring the relative centroid positions of an unstacked PM configuration (small array) moving around to different field locations on a single NIRCam detector. Following Coarse MIMF, another step of Global Alignment is executed to correct any residual wavefront errors without any further adjustment of the secondary mirror.
Finally, towards the end of commissioning, we start the global phasing steps in which we execute an iterative process, a loop of coarse and fine phasing corrections resulting in a wavefront error of less than 50 nanometers. During fine phasing, phase retrieval algorithms are applied to weak lens images from NIRCam (internal defocus images) permitting reconstruction of the phase of the PM and correction for small wavefront errors between PM segments. At the end of the WFS&C commissioning process there is the multi-instrument and multi-field component (MIMF) where corrections to ensure low wavefront error over the entire field of view are calculated and implemented. In order to determine these errors, phase retrieval algorithms are applied to a set of defocus images (about +/- 100 microns of SM piston) collected at five different field points in each of the science instruments. After MIMF, we expect to have reduced the wavefront error of a large 6.5-meter telescope into the range of tens of nanometers.
How are we preparing for OTE Commissioning?
For the past couple of years, we have been participating in various successful rehearsals and team practice exercises involving large collaborations between the different subsystems that comprise the SOC. To first order, the objectives of these rehearsals are to evaluate the ability of the SOC personnel to sustain operation over a period of time and to exercise the various channels of communication, team interactions, and coordination between the different subsystems and operators.
In March 2018, we participated in Wavefront Rehearsal #1 where we used accurate optical simulations to practice our procedures, tools and analyses for some of the OTE commissioning activities, namely, identifying the primary mirror segments (Segment ID), applying the first set of segment-level corrections to reduce the wavefront errors of the telescope (Global Alignment #1), and correcting for large piston errors after deployment (Coarse Phasing #1). In October 2018, we participated in Wavefront Rehearsal #2, where we incorporated lessons learned from the previous exercises and practiced the process with which we will determine the WF performance across the NIRCam field of view (multi-field corrections, Coarse MIMF).
In 2019, we'll follow a WF rehearsal schedule that includes a third WF rehearsal in April followed by a fourth (and possibly last) rehearsal towards the end of the year, around October 2019. In our last rehearsal, we are planning to practice the final step on the commissioning, i.e., applying MIMF corrections. In addition to these rehearsals, the WFS&C group will also participate in the Launch Readiness Exercises sometime in 2020.
Beside these full-scale rehearsals, involving various SOC subsystems, the WF team has been busy organizing team practice activities, scheduled approximately every six months in between rehearsals. The last two team activities took place in June 2018 and January 2019 where, using simulated images, we exercised our procedures, analyses, and internal communications between the different team members operating inside the WFS&C office. In a couple of years, we won't need to imagine such an amazing and ambitious telescope, it will be our reality. Until then, we need to practice and prepare for the unexpected until we are ready to discover the Universe with the reality of tomorrow.
Acton, D. S., Atcheson, P. D., Cermak, M., et al. 2004, "James Webb Space Telescope Wavefront Sensing and Control Algorithms." In Mather, J. #C., editor. Optical, Infrared, and Millimeter Space Telescopes (Proc SPIE; Vol. 5487); Oct.; 2004. p. #887–896. Acton et al. 2004, SPIE 5487, 887.
Acton, D. S., Knight, J. S., Contos, A., et al. 2012, "Wavefront Sensing and Controls for the James Webb Space Telescope." In: Space Telescopes and Instrumentation 2012: Optical, Infrared, and Millimeter Wave (Proc SPIE; Vol. 8442); Sep.; 2012. p. #84422H. Acton et al. 2012, SPIE 8442, 84422H.
Perrin, M. D., Acton, D. S., Lajoie, C. P., et al. 2016, "Preparing for JWST Wavefront Sensing and Control Operations." In: Space Telescopes and Instrumentation 2016: Optical, Infrared, and Millimeter Wave (Proc SPIE; Vol. 9904); Jul.; 2016. p. #99040F. Perrin et al. 2016, SPIE 9904, 99040F.
A New Class of Fellows for the NASA Hubble Fellowship ProgramA. Fruchter (fruchter[at]stsci.edu)
Twenty-four early-career astrophysicists have been selected for the second class of the NASA Hubble Fellowship Program. As described in an earlier newsletter article (The New NASA Hubble Fellowship Program), NASA has combined the Einstein, Hubble, and Sagan fellowships into a single program, the NASA Hubble Fellowship Program (NHFP). The NHFP, like the fellowships that superseded it, supports outstanding postdoctoral scientists to pursue independent research in any area of NASA Astrophysics, using theory, observation, experimentation, or instrumental development.
The NHFP preserves the legacy of NASA's previous postdoctoral fellowship programs; once selected, fellows are named to one of three sub-categories corresponding to NASA's "big questions":
The NHFP received 385 applications from astophysicists who are completeing their PhD this year, or have completed their PhD in the last three years. In January, seven topical panels met to sort through the applications. Ten of the new fellows were chosen directly by the panels, and the remaining fourteen were chosen by a committee made up of the panel chairs and the Selection Chair from short lists created by the topical panels. About three-quarters of the Panel members and chairs came from the U.S. astrophysical community; the remainder hailed from Europe.
Fellows receive a salary and funds for their research and can take the fellowship to a U.S. host institution of their choice. However, no more than two new fellows are permitted to go to any one institution in a given year, and no more than five fellows may be resident at any host instituition—a limitation that will become important next year, the third year of the program. The list below provides the names of the 2019 awardees, their host institutions, and their proposed research topics:
TESS Data WorkshopS. Mullally (smullally[at]stsci.edu)
From February 11th to 14th of 2019, more than 70 astronomers gathered at the Space Telescope Science Institute to discuss NASA's latest planet-hunting mission. TESS (Transiting Exoplanet Survey Satellite) is designed to observe nearly the entire sky in 96 × 24 degree sections to find small variations in the brightness of stars. The mission is designed to find thousands of transiting exoplanets, many of which are ideal for further study with instruments like the Hubble Space Telescope and the James Webb Space Telescope. However, because TESS is an unprecedented survey of how the universe varies on time scales of a few minutes to several months, these data appeal to astronomers working in various astronomical fields. The goals of the TESS Data Workshop were to discuss features of the TESS data, software tools, and how to effectively combine it with data from other missions to maximize scientific output. This workshop brought together astronomers, whose research expertise ranged from small exoplanets to giant stellar pulsations and supernova explosions, who wanted to learn more about the effective use of TESS data.
The workshop was held only two months after the public release of the TESS data set and many of the participants were still building experience with the data and how to best use it for scientific studies. Scientists from the TESS Science Team graciously supported the meeting by sharing their knowledge and experiences from using the data to commission the telescope. That experience was combined with presentations about analysis techniques; and thus, the workshop successfully acted as a platform to teach the participants about efficient and innovative ways use the TESS data.
The workshop started with a talk from the PI of the TESS Mission, George Ricker. Dr. Ricker gave participants an overview of the mission, highlighting that the unique lunar orbit will be stable for more than 30 years and showing off some of the first exoplanets found in the data, e.g., Pi Mensae c and some of the first supernovas observed by TESS. Roland Vanderspek then took the audience through a tour of some of the data anomalies created by Earth-shine, asteroids, or the so-called "fireworks" that occur because of individual particle events. Jeff Smith from NASA Ames then discussed the TESS photometric pipeline and Scott Fleming, from STScI, gave a thorough overview of the many ways to retrieve the data from its home at the Mikulski Archive for Space Telescopes at STScI (MAST).
The workshop included talks by several groups that discussed different ways to create TESS light curves from the Full Frame Images. Mikkel Lund described the TESS Asteroseismic Consortium pipeline, T'DA , which is optimized for stellar variability. For measuring variability in clusters, Luke Bouma described how to perform difference imaging photometry. Several speakers discussed the advantages of combining TESS data with other data sets, such as those from CHEOPS, Kepler, Gaia, or Neid to obtain masses of exoplanets or better characterize the star of interest. All talks were webcast and recorded. Visit this page for direct links to the recordings.
The workshop devoted a full half-day to software tutorials on how to use six different public tools to obtain, reduce, and analyze TESS data. The software tools were presented using the TESS Science Platform, a JupyterHub-based computing environment running on Amazon Web Services. By having an environment that could run tutorials provided by the invited speakers, participants were able to participate in the tutorials regardless of their experience with installing code or managing a software environment. As a result, many attendees remarked on how they were able to easily participate in this part of the workshop where they otherwise would not have been able to. Many of the participants continued to use this platform for the hack day in order to hone their new skills with these software tools. Participants continue to use this science platform to pursue scientific inquiries with TESS data using the tools they learned at the workshop.
The TESS Data Workshop provided a platform for collaboration and understanding, spanning a vast range of astrophysical communities. e expect many collaborations and science results to come from this program. Ultimately, what was learned from this workshop will yield high-quality science results, some of which will likely be presented at the first TESS Science Conference in Boston in July 2019.
The 21st Century H-R Diagram: The Power of Precision PhotometryD. Soderblom (drs[at]stsci.edu)
STScI's 2018 Spring Symposium
The Hertzsprung-Russell Diagram (HRD) has become a precision research tool. Einar Hertzsprung's and Henry Norris Russell's first sketches from a century ago were based on photographic magnitude estimates, spectral types, and crude distances. The form of the HRD we know today was barely resolvable. In the post-WWⅡ years, the application of photoelectric photometric instruments allowed much more detail to show through: think Sandage and V versus (B–V) for open and globular clusters you're likely to have seen in introductory astronomy. The advent of the charge coupled device (CCD) made photometric measurements not just much more efficient by imaging many stars at once, but also improved data quality by enabling better background measurements, point spread function (PSF) fitting, and so on.
Going to space has also been a big breakthrough for improving the observations, and one of Hubble's greatest scientific achievements has to be the discovery and detailed study of multiple populations in globular clusters (notably ω Centauri). Only with diffraction-limited optics on a stable platform has it been possible to reach the faint magnitudes needed to achieve that.
Over 3½ days in April, about a hundred international astronomers met at STScI to discuss these topics and more. Fortuitously, Gaia Data Release 2 occurred during the meeting and two people connected to the project, Sofia Randich and Marcella Marconi, gave us an exciting synopsis of its contents.
But we started with David DeVorkin (National Air and Space Museum) showing us how the HRD came to be in the first place, guided in no small part by the obvious asterism that is the Pleiades, since having a well-populated cluster of stars at a single distance removed one source of ambiguity. Hertzsprung and Russell worked independently, and it was not really until the mid-20th century that their names were consistently attached to the construct.
Each day we started with a similar talk that provided the deep background one needs to be able to appreciate how far we've come. Peter Stetson (Dominion Astrophysical Observatory) related the development of DAOPHOT in the early days of imaging photometry, while Francesca D'Antona helped us understand the past half-century of modeling stars and the HRD. In both areas, technology has been fundamental by permitting more and faster computations, and with each advancement new physical insights were gained.
With increasing precision in measurement has come the need for further improvements in the models. When we think of HRDs, we are likely to think of clusters and the morphology of how their stars lie in the HRD. And yet even after all this time it remains difficult to assign ages to clusters that are both accurate and precise. In part that is because the cluster's age often relies heavily on just a few stars at the main sequence turn-off, and an unknown binary among them can confound. Recent models show how including the effects of rotation in intermediate-mass stars leads to much better consistency of ages for such canonical clusters as the Hyades, Praesepe, and Pleiades. The age scale, on the other hand, has changed in recent decades as the effects of core convective overshooting has been included, and there is now direct asteroseismological evidence from Kepler to back up that physics.
The self-evident power of high-precision space-based photometry has been reaffirmed by the commitment to build and launch WFIRST. Its long stares at the Galactic Bulge should be especially revelatory for the processes that have formed and altered that critical portion of our Milky Way.
The Spring Symposium is an annual event at the institute. I proposed the topic and chaired the Scientific Organizing Committee. The following contributed their broad knowledge by serving on the SOC:
- Andrea Bellini
- Martha Boyer
- Joleen Carlberg
- Roger Cohen
- Matteo Correnti
- William Fischer
- Mario Gennaro
- Paul Goudfrooij
- Jason Kalirai
- Margaret Meixner
- Greg Sloan
These functions at the institute work so well because of our administrative support, notably Martha Devaud and Sherita Hannah of the Science Mission Office.
.Astronomy X Baltimore: Mining the Past, Making Space for the FutureS. Kendrew (skendrew[at]stsci.edu)
From September 24th to 27th, the Space Telescope Science Institute hosted the 10th edition of the .Astronomy ("dot astronomy") conference. This annual event brings together a community of astronomy researchers, communicators, and educators to share their work and ideas for how technology, in particular software and the Web, can advance our research, collaboration, and communication. For the 10th anniversary, the organizing committee chose as theme "Mining the Past, Making Space for the Future"—exploring the duality of "past" and "future" that is an inherent theme in astronomy, as the science of the history and future of our Universe. For the conference itself, the anniversary marked the opportunity to examine the impact of our past events, and look towards the future.
.Astronomy was first organized in 2008, during the exciting early growth years for social media and blogging platforms, and the increasing standardization of web technology. Scientists were using the web in innovative ways for their research, as with the citizen-science project Galaxy Zoo; and for science-communication projects such as science blogs and podcasts. The International Year of Astronomy in 2009 played a significant role in mobilizing the community around such public engagement projects.
.Astronomy brought novel approaches in conference programming from the tech world, such as participant-led discussion sessions ("unconferences"), and hack days, to astronomy for the first time. Its focus is uniquely on how we do astronomy—on methods as well as outcomes—and on how the web can support more open, transparent, and equitable science. Over the past decade, this has increasingly included discussions on career development, diversity and equity in the astronomy community.
With its commitment to open, accessible science, the Space Telescope Science Institute shares the values of .Astronomy. The institute was therefore an excellent partner and host for this 10th edition of the conference.
Over four days, .Astronomy brought around 65 participants to Baltimore from all over the world—from North America, Europe, Southern Africa, and Australia. We were particularly excited to welcome our invited speakers, whose talks stimulated discussions and provided inspiration for the unconference session topics. Dr. Alcione Mora of the European Space Agency presented an overview of science, data, and challenges of the Gaia mission, whose new data releases are providing revolutionary new insights into the history and dynamics of our Galaxy and its nearest neighbors.
Prof. James Howison of the University of Texas at Austin talked about the role of software in scientific research in his talk entitled "Software Makes Science Better, but Is It Research? Arguments for a Research Agenda in Scientific Software Work." Prof. Sarah Hörst of the Johns Hopkins University presented her innovative laboratory experiments to simulate (exo-)planetary atmosphere chemistry, in which the pathway into her chosen research field was woven into the narrative of the research itself.
Looking towards the future, NASA's Dr. Jane Rigby gave an overview of future NASA space missions; and Prof. Andy Connolly of the University of Washington showed progress on the ground-breaking Large Synoptic Survey Mission (LSST), currently under construction in Chile. The demands on data processing and automated classification from the LSST data are a major driver of research into machine learning and artificial intelligence in astronomy—subjects of significant interest amongst the .Astronomy community.
Our final invited speaker was Prof. Jarita Holbrook of the University of the Western Cape, South Africa, discussing her anthropological research into the experiences of astronomers of different ethnicities and genders, at different career stages, in South Africa as well as the United States. Her work gives a unique perspective on the now-common debates on diversity and inclusion in the scientific community, and highlights the importance of a cross-disciplinary approach to sociological questions in academia and research: to understand the human aspects of research, we should seek out and collaborate with experts in this field.
A number of contributed talks from our participants spoke similarly of the connections between the technical and human aspects of our research. Dr. Brian Nord of Fermilab/University of Chicago spoke of the ethical questions in the development of artificial intelligence tools, and Dr. Dara Norman (NOAO) described how the NOAO Data Lab is designed to help make research fairer and more equitable. Improving access to data is an important part of building an inclusive community by removing the power from human gatekeepers, thus leveling the playing field for all. The need for interdisciplinarity in science, and teaching science and technology studies alongside science, was demonstrated by Lauren Chambers' (STScI) impressive work at the intersection of Astronomy and African American Studies.
During the first introductory day ("Day Zero") and the unconference sessions, a number of participants gave tutorials on technical tools, such as the interactive plotting library Bokeh; multi-dimensional data visualization with Glue; cloud computing; Github; Flask; astropy; astroquery; and others. There were career-focused discussions, including one led by one of our Google participants and founder of .Astronomy, Dr. Rob Simpson. Some of these skills were put on display during the hack day, where participants produced new proof-of-concept projects such as an interactive display of FITS images using Bokeh; astropy for exploration of Gaia DR2 data; custom data analysis tutorials in jupyter notebooks; and many more.
As with the previous nine editions of the conference, .Astronomy X provided a wide range of inspirational talks and discussions. The conference is frequently cited as "a place to talk about the topics other conferences don’t cover"; we feel that the culture in research is connected to research itself. The conference was supported by the American Astronomical Society, who provided generous travel grants for some of our junior participants, including dedicated dependent-care grants for participants with extra expenses related to caring responsibilities. As diversity is a high priority for .Astronomy, we were particularly pleased to offer this support.
.Astronomy X took place at the Space Telescope Science Institute from 24 to 27 September 2018. The organizing committee consisted of Sarah Kendrew (ESA, Chair), Arfon Smith (Co-chair), Erik Tollerud, Joshua Peek, Ivelina Momcheva, Tom Donaldson and Susan Kassin. The organizers are grateful to the STScI leadership and events team for supporting the conference; and to the AAS for providing generous financial support. The next edition of .Astronomy will be held in Toronto, in October 2019.
Deep Field: Symphonic and Cinematic AstronomyF. Summers (summers[at]stsci.edu), G. Bacon (bacon[at]stsci.edu), J. DePasquale (jdepasquale[at]stsci.edu), and D. Player (dplayer[at]stsci.edu)
The Hubble Deep Field, released in 1996, revolutionized our view of the distant universe. Within a single image, astronomers got a glimpse of the vast array of galaxies stretching more than 10 billion light-years into the universe. Later projects, including the Hubble Ultra-Deep Field, extended this view both farther into space and across infrared and ultraviolet wavelenths. The light from those remote galaxies takes billions of years to cross the intervening space, and thereby shows us what these galaxies looked like billions of years ago. Within these deep fields, we see not just the extent of our universe in space, but also its history across time.
That vision of cosmic wonder inspired the Grammy award-winning composer and conductor Eric Whitacre to write a symphony entitled "Deep Field." At the premiere in May 2015, a special app on the audience's cell phones spread Hubble visuals throughout the concert hall during the live performance. Suggestions naturally arose that the audio of the symphony be paired with video of Hubble imagery to maximize the scientific basis and artistic effect.
Such ideas came to fruition starting with Whitacre's visit to the institute in early 2016. The immense possibilities of soaring orchestrations combined with immersive visualizations were immediately apparent. The following year, the Office of Public Outreach (OPO) began a collaboration with Whitacre's management company, Music Productions, and a London-based multimedia house, 59 Productions, on crafting visual sequences to accompany the movements in the score.
The film, "Deep Field: The Impossible Magnitude of Our Universe," had its world premiere at the Kennedy Space Center in November 2018. The piece was simultaneously relased in full 4K resolution on YouTube, and can be accessed via the deepfieldfilm.com website. The film is being used in conjunction with symphony performances, as well as playing on its own in venues around the world.
As the symphony is 24 minutes in length, the visuals need to explore much more than just the galaxies of the distant universe. The main astronomy storyline became a classic one, moving from near to far and from the familiar to the unfamiliar. Separate sections are devoted to the solar system, to stars and nebulae, to galaxies, and to the deep field.
These astronomical sections comprise about two-thirds of the film. NASA solar system mission images provide the vibrant views of the Moon, Mars, Jupiter, Saturn and the Sun. Hubble visuals (described below) cover the rest of the cosmos. In contrast, the introductory and final segments are rooted in our planet, Earth. The first serves as a launching point for the journey, while the last brings us home again.
The opening soft, shimmering, and hanging notes of the symphony suggested the magical time at dusk when the stars slowly appear in the night sky. OPO image-processing specialist Zolt Levay, who is also an accomplished photographer, observed the stars and Milky Way for this sequence. While serving as artist-in-residence at Capitol Reef National Park, he captured a glorious time-lapse in those dark skies.
One production note is that, even though the park is somewhat remote, dozens of airplane flights crossed through the sequence. At 59 Productions, they assigned a dedicated artist to the task of removing these interlopers frame by frame.
The final movement of the symphony/film brings in a signature feature of Whitacre's works: a virtual choir. More than 8,000 singers from 120 countries submitted videos of their performances for this project. The multitude of choral voices were mixed into the soundtrack, and the video clips are presented in conjunction with International Space Station views of our planet, creating a visual and literal global choir. The film ends with our planet hanging in the blackness of space, as an homage to Carl Sagan's "Pale Blue Dot."
For the OPO Visualization Team, this project presented a wonderful opportunity to reinterpret old sequences and create new ones in an artistic style different from the usual press-release videos. Whitacre's music provides a lyrical and thoughtful setting that's appropriate for relaxed contemplation of the cosmos. In collaboration with 59 Productions, the pacing, camera moves, and transitions were adjusted and fashioned to match the ebb and flow of the symphony.
The Stars and Nebulae sequence featured several previously produced pieces combined into a continuous visual journey. After leaving our Sun, the camera traverses the local stars to explore the star-forming region Sharpless 2‑106, the Bubble Nebula, the Lagoon Nebula, and the star cluster Westerlund 2. Misty, veil-like segues between the pieces were created from semi-transparent layers of these and other Hubble images.
The Galaxies sequence required three new pieces, utilizing three separate techniques. The Stephan's Quintet visualization demanded careful extraction of overlapping galaxies into isolated layers that could express the 3-D nature of the galaxy group. In contrast, Hubble's high-resolution image of the Whirlpool Galaxy provided great detail for a point-cloud model containing five structural components and some 80 million points. Finally, the Galaxy Traverse sequence used a computer simulation from researchers at CalTech and UC Davis as the basis for an intricate point-cloud realization of a Milky Way proxy.
The climax of the film flies through the tens of thousands of galaxies in the CANDELS Ultra-Deep Survey as a lead-in to the triumphant reveal of the Hubble Ultra-Deep Field. These previously produced pieces transport the viewer to the farthest reaches of the observed universe. Astute observers may notice one small change, though. A high-redshift "red dot" galaxy was shifted to a central position in the camera path, so that one of these farthest and earliest objects would be the last astronomical image for the audience.
Symphonic and Cinematic Astronomy
The eighteen months of work on the film developed into a wondrous example of blending art and science. Every member of the team—musician, filmmaker, visualizer, or astronomer—shared their knowledge across disciplines and developed a deep appreciation for the skills and insights of their collaborators. A major goal of the producers was to promote the integration of STEM fields with "Art and Design," thereby creating the powerful force of STEAM education. Hopefully, this piece will serve as an inspiration to many in pursuing such multi-facted projects.
Gender Diversity in Scientific Committees and Their Activities at Space Telescope Science InstituteC. Oliveira (oliveira[at]stsci.edu) and G. de Rosa (gderosa[at]stsci.edu)
The Women in Astronomy Forum at Space Telescope Science Institute has a new initiative to increase gender diversity and inclusion in the institute's scientific committees and the activities they generate. This initiative offers new and uniform guidelines on binary gender representation goals for each committee and recommendations on how to achieve them in a homogenous way, as well as metrics and tools to track progress towards defined goals. While the new guidelines presented here focus on binary gender representation, they can be adapted and implemented to support all groups. By creating diverse committees and making them aware of and trained on implicit bias, we expect to create a diverse outcome in the activities they generate, which in turn will advance science further and faster.
Space Telescope Science Institute (STScI) has taken many steps through the years to increase diversity and inclusion. Both of these are key core values adopted by the institute. Past efforts have focused on a variety of actions, including creating internal diversity, inclusion and affinity groups, providing all-gender restroom, lactation, and health room facilities, extending medical coverage to pay for transgender transition and same sex/domestic partner medical and dental benefits, offering teleworking options, flexible work schedules, training, paid parental leave, and mentoring for career advancement. Not only have the efforts been focused internally, but the institute has established a double-anonymous selection process for Hubble proposals—a first-of-its-kind peer-review process for allocating time on NASA's facilities—that led in 2018 to higher success rate of women-led proposals for the first time in 18 years (https://physicstoday.scitation.org/do/10.1063/PT.6.3.20190301a/full/).
STScI has roughly 127 research staff members. A number of scientific committees carry out a variety of activities ranging from recruiting, evaluating, and promoting research staff; to organizing the yearly scientific symposium. Until now, ensuring a balanced gender representation in the institute's scientific committees was left to the goodwill of the committee's chair. To address this issue, the Women in Astronomy Forum, one of STScI's affinity groups, proposed new and uniform guidelines on binary gender representation goals for each committee, and recommendations on how to achieve them in a homogeneous way, as well as metrics and tools to track progress towards defined goals. By creating diverse committees and by making them aware of and trained on implicit bias, the related activities of those committees will create a diverse outcome (Casadevall & Handelsman 2014) that will advance science further and faster.
As part of the new guidelines, every committee will receive implicit bias training and all the members will be encouraged to take an implicit bias test.
The new binary gender representation guidelines include a target goal of 40% and a floor of 27% for representation of women on all the scientific committees at STScI. The floor of 27% corresponds to the current fraction of women research staff, including all career levels.
The chair of each scientific committee will be in charge of submitting a yearly report to the Science Mission Office documenting the committee's results towards the guidelines. The report will also include a summary of the gender demographics for each step of the activities of the particular committee. For example, for the committee responsible for organizing the yearly Spring Symposium, the summary would include information about gender for: invited speakers, submitted and accepted contributed talks, submitted and accepted poster contributions, and symposium participants. This information is used not only to assess the success of the committee in meeting diversity and inclusion goals and reward successful committees, but also to track consistency and progress over time by comparing it with data from previous years.
The guidelines are currently centered on binary gender representation (women/men), with gender being assigned based on name and/or apparent gender expression. While we recognize that gender is non-binary, this information is usually unavailable for privacy reasons.
The first phase of the implementation of these guidelines is ongoing. We are in the process of finalizing Python tools that will quickly and easily display all the statistical information needed to track progress in graphical form, and we hope to share these tools with the community in the future. STScI is actively working on expanding these guidelines to include all of the institute's committees, not just the ones related to the research staff.
Diversity: STScI's Introduction to SACNASJ. Medina (jmedina[at]stsci.edu)
The Society for Advancement of Chicanos/Hispanics and Native Americans in Science (SACNAS) hosts an annual conference for underrepresented members of the STEM community to meet, share their work, and provide a sense of support for one another. The conference hosts various professional development sessions and workshops on both technical and non-technical topics, with many of the non-technical topics bringing awareness to the benefits of diversity and intersectionality in STEM. SACNAS also provides networking opportunities to all attendees through social gatherings, workshops, and the exposition hall booths and poster presentations. In 2018, Space Telescope Science Institute held its first booth in the SACNAS exposition hall, where students and professionals were able to learn more about the institute and its career opportunities. SACNAS's mission of promoting diversity and inclusion parallels with the initiatives being taken at the institute, and attending the annual SACNAS conference is a great opportunity to reach out to a diverse pool of professionals from all areas of STEM with the skills to further enrich the STScI community.
STScI's first SACNAS
The Society for Advancement of Chicanos/Hispanics and Native Americans in Science (SACNAS) is an organization designed to help underrepresented groups in STEM further their education and advance in their careers. The annual SACNAS conference contributes to this mission by providing attendees in all career levels an opportunity to connect and share their research, and 2018 marked the first year that STScI was in attendance.
The 2018 SACNAS conference was held mid-October in San Antonio, Texas, and became their most-attended national conference to date—gathering over 4,200 professionals of all career levels to celebrate the organization’s 45th anniversary. The conference spanned three days, with the first day of the conference being kicked off by an opening keynote address from the first Hispanic woman in space and former Director of NASA Johnson Space Center, Dr. Ellen Ochoa (Figure 1, left).
Each day's itinerary was populated with networking receptions, professional development sessions, and scientific symposia sessions on a variety of topics ranging from machine learning to conservation biology. Many of the professional development sessions were on soft skill topics relevant to today's work climate, such as the benefits of intersectionality in the workplace.
In the conference's Expo Hall, attendees were able to share their research and connect with institutions from all over the nation. The hall was open most of the day for all three days, and was filled with over 1,000 research posters in every STEM discipline. On the other side of the hall was the Exhibitors' section, where the institute held a booth (Figure 1, right) alongside Google, the National Security Agency, and many other employers and universities looking to recruit new talent from a diverse pool of professionals.
The Luncheon Plenary Session was held on the second day of the conference with the three featured speakers—Dr. Lauren Esposito, Dr. Kat Milligan-Myhre, and Ed Yong—all sharing inspiring stories about their careers. Later in the evening, SACNAS held the annual Pow Wow, a Native American social gathering that involves music, dancing, and other live performances (Figure 2). Attendees were able to participate in several of the dances, which helped make this event a memorable experience.
The Influence of Culture in Our Work
What made this conference unique was its celebration of culture. Many of the professional development sessions highlighted the influence of culture in our work: how someone's background can provide them with a lens through which they can look at a problem, and offer a new perspective. One of the attendees, Lauren Chambers, noted this when saying "As a researcher interested in the culture of science, SACNAS showed me how rich the intersection is between our work and our identities. I love the sessions about how Native American scientists enrich and improve their science by integrating indigenous values and perspectives into how they ask questions and perform analysis."
Diversity and creativity in the workplace go hand-in-hand, as a more diverse community allows for different perspectives of the same problem, and different ways of approaching a solution. Diversity in the workplace also encourages open-mindedness, as people become more exposed to philosophies and ways of thinking that are far from their own. SACNAS spreads this message clearly throughout the conference: through its professional development sessions and workshops, it teaches individuals to embrace what makes them unique, and how these qualities can be an asset in the workforce. By attending SACNAS, the institute was able to reach this audience of students and professionals from every STEM field who might have otherwise gone unnoticed.
Cultivating a Community
One of the motivations behind these annual conferences is to cultivate a community among underrepresented groups in STEM where friendships and mentee/mentor relationships can develop. In between the professional development and science sessions, there were receptions for groups such as LGBTQ+ (Figure 3), Native Community, and Women in STEM, providing an opportunity for people in these communities to connect. These kinds of social gatherings have the potential to enrich one's experience at SACNAS, as expressed by SACNAS attendee and symposium moderator, Dr. Nicole Cabrera Salazar: "As a professional, I learned that connecting genuinely with junior scientists of color, even for just a few minutes, can have a significant positive impact."
Celebrating Our Differences
Overall, STScI's introduction to SACNAS was eye-opening. There were many aspects of this conference that parallel with the initiatives being taken at the institute. Sheryl Bruff summarized the experience nicely when explaining her major takeaways from attending the conference: "First, the attendees were talented and enthusiastic, able to tell their stories and promote their expertise with ease. Second, the content of the conference—the sessions, keynote speakers, etc.—was timely, intriguing, and useful. The overall atmosphere of the conference was one of the best I have experienced."
Through the multicultural celebrations and diverse set of speakers and presentations, this conference sent a powerful message which was to not only accept people's differences, but rather to celebrate them. Moving forward, I know there are things we can continue to learn from this organization, and others like it.
The Pan-STARRS1 Data ArchiveRichard L. White (rlw[at]stsci.edu)
The second data release from the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) survey was opened to the astronomical community on January 28th, 2019. The Pan-STARRS1 (PS1) survey data, hosted at STScI, is both the largest database and the largest image collection in the MAST archive. It is useful for a wide variety of scientific investigations, ranging from studies of rapidly moving near-Earth objects to the discovery of supernovae and high-redshift quasars. It can serve as faint photometric and astrometric reference data over a large fraction of the sky. And the PS1 data is also being used to develop new high-performance interfaces at MAST that can be applied across all of our mission and catalog holdings.
The PS1 project was carried out by a consortium of scientific institutions using a telescope and camera built and operated by the University of Hawaii. PS1 is the first part of Pan-STARRS to be completed and is the basis for both Data Release 1 (DR1; 2016 December 19) and Data Release 2 (DR2). Links to access the PS1 DR2 data as well as the PS1 documentation can be found at https://panstarrs.stsci.edu.
The PS1 DR2 archive includes images and catalogs from observations covering three quarters of the sky (the 3Pi Survey), carried out several times per filter and over a four-year time span. PS1 DR2 is the first release to include the time-dependent photometry, astrometry, and images collected by PS1. The total data volume of the release is approximately 1.6 petabytes, including a 150-terabyte database along with the single-epoch and stacked images. The catalog includes more than 2.5 billion objects having detections at two or more epochs. In total, there are more than 70 billion detections with an average of ~50 epochs for each object (~10 epochs per filter).
Astrometry and Photometry in PS1
The PS1 catalog astrometry and photometry are well calibrated. Median astrometric errors for brighter sources (18–19 mag) compared with Gaia are about 20 milliarcsec (the PS1 astrometric calibration is based on the Gaia DR1 reference frame). As a demonstration of the astrometric quality, we cross-matched the PS1 catalog with the ICRF2 astrometric reference catalog. The cross-match SQL query completed in less than four minutes using CasJobs. Note that the mean object positions in the PS1 catalog are biased toward the Gaia DR1 positions for stars with Gaia matches, so this comparison instead uses the unbiased mean positions computed directly from the PS1 Detection table. The results are shown in Figure 2 below. The PS1 positional accuracy is 16–18 milliarcsec for these moderately faint objects with median magnitudes around i = 19. The STScI Astrometry Working Group is currently exploring the possibility of recalibrating the PS1 positions using the Gaia DR2 catalog, which would both improve the absolute astrometry and also allow the calculation of proper motions from PS1 measurements.
The PS1 systematic photometric errors are about 7 millimag. Several different measurements are provided in the catalog, including PSF magnitudes, aperture magnitudes and Kron magnitudes. Great care was taken to correct for variations in atmospheric transparency, seeing, and camera sensitivity (see Magnier et al. 2016 for details). The noise in the photometry obviously depends on the brightness of the star, but for moderately bright stars the results are very consistent. The Figure 3 below shows a typical light curve for an RR Lyrae star.
Access to PS1 data
MAST provides a number of tools to help users explore the data products of the PS1 archive:
- A simple image search form for retrieving image cutouts and full images for both the stacked and single-epoch images.
- A powerful new catalog search form provides a simple tool to search the catalogs for objects near a sky position. The new interface features the ability to constrain searches on any catalog parameters along with an easy-to-use API for scripted access.
- A CasJobs SQL interface allows expert users to craft more sophisticated queries.
- A new VO TAP service allowing access to PS1 DR2 through a variety of VO-enabled tools.
See our 'How to retrieve and use PS1 data' page for more information and links to additional documentation. Note that there are also sample Python Jupyter notebooks that query the DR2 catalog using both the new MAST API and a Python interface to CasJobs, and that extract image cutouts. An additional notebook sample for DR2 TAP access is also in development.
The following image and catalog products are available in DR2:
- The source catalogs created from the stacks (also in DR1), which include point-source and extended-object photometry measured from the stack images is included.
- Deep, co-added stack images made from the multiple exposures taken over the survey (also in DR1).
- Single-epoch "warp" images (new in DR2), which are the result of resampling and realigning the camera images onto a common pixel grid.
- Mean values of the point-source and extended-object photometry from the single-epoch warp images (also in DR1).
- Photometry and astrometry at each epoch are included in the Detection table and the ForcedWarpMeasurement table (both new in DR2).
AAS AddendumC. Christian (carolc[@]stsci.edu)
STScI @ the 234th AAS Meeting June 9-14 2019
Institute staff representing the Hubble, Webb, and WFIRST missions will be available at the Institute booth to provide information on new developments and updated status of these missions, and also to describe our upcoming initiatives for user community support. Learn how to search for the newly added Webb planned proposals.
Our interactive area this year will feature daily sessions of augmented reality, virtual reality, and touchscreen demonstrations. Come visualize the three observatories with augmented reality, or use virtual reality to explore a protoplanetary disk or throw stars into a black hole. There will also be mission demonstrations of support tools for proposing and observing with Hubble and Webb.
Looking to get involved, share your science, and enable science learning? Come explore ways in which you can become involved in the "NASA's Universe of Learning" (UoL) and help us engage audiences of all ages from across the US.
STScI Town Hall
With the Decadal Survey under way, the summer 2019 AAS meeting provides key opportunity to engage astronomers in shaping the future of our profession. STScI will contribute to a wide range of workshops, science sessions, splinter meetings, and exhibits throughout the meeting. The STScI Town Hall will serve as the centerpiece for our presence at AAS 234. We will report on the status of our existing and upcoming missions and data archives, and report on new opportunities designed to advance astrophysics into the 2020s. The Town Hall will consist of a mix of presentations from STScI’s user-engagement leads from our missions and related cross-mission activities. We will include time for discussion to receive community input regarding new initiatives and to answer questions about our activities in the coming year.