New Challenges for Astronomical Calibration (A Perspective from GAIA)
I will present the status of the Gaia mission, launched in December last year and just coming out of commissioning. Gaia is an ESA astrometric mission, aiming at microarcsecond positions, parallaxes, and proper motions for stars (down to V~20 mag). Gaia will obtain images in white light (G band) and dispersed images in two broad bands (the blue RP and red RP) for approximately 10^9 point-like sources. It will also have a radial velocity spectrometer to obtain spectra in the calcium triplet region for bright objects (V~16.5 mag). Its main goal is a census of the Milky Way but many diverse results are expected in almost all areas of astrophysics, from Solar system objects to Quasars, to fundamental physics. After a general introduction on the Gaia mission, I will review the commissioning results, including the few critical issues that have emerged. Finally I will show a gallery of images obtained during commissioning.
The Status of HST
Helmut Jenkner (STScI)
The Hubble Space Telescope remains at the peak of its capabilities and promises several more years of scientific exploration. The current status of its various components and the outlook for the future will be presented.
The Status of HST/FGS
Barbara McArthur (University of Texas at Austin)
The three Fine Guidance Sensors(FGS) on board the Hubble Space Telescope (HST) are white light interferometers in space that have been used to not only point the telescope for other instruments, but to make astrometric scientific measurements. Each FGS contains two interfering elements (Koester’s prisms), one for each axis (X and Y). There are two modes used, position and scanning, but the majority of the scientific results have come from position mode astrometry. We have used M35 to calibrate the instrument since 1992, and over this time period have continued to refine both the M35 catalog and the actual calibration of the instrument. Most recent results indicate that we are achieving parallaxes with errors in the tens of micro-arcseconds range.
The Status of HST/NICMOS
Rodger Thompson (The University of Arizona)
The overall status of NICMOS and the NICMOS Cryo-cooler System (NCS) will be reviewed as of the date of the workshop. The basic status is that the NCS system has not been restarted and NICMOS remains ready to become operational if the NCS is returned to operational status. The capabilities of NICMOS will be reviewed with an emphasis on those capabilities that are unique to NICMOS. These include very high resolution imaging, observations at wavelengths longer than 1.7 microns, polarimetry and observations of Pa Alpha atomic hydrogen emission and molecular hydrogen emission lines. The NICMOS database continues to supply relevant data with publications utilizing that data still being produced.
The Hubble Space Telescope Frontier Fields Overview
Anton Koekemoer (STScI)
The Frontier Fields program is a new Director's Discretionary program to probe deeper into the universe than ever before, by means of ultra-deep imaging of up to six strong lensing clusters and their parallel fields with HST using ACS and WFC3/IR, along with coordinated observations using Spitzer and Chandra. Over the course of three years, each cluster is being observed for 140 orbits, spread across two epochs, probing to 29th magnitude with ACS (F435W, F606W, F814W) and WFC3/IR (F105W, F125W, F140W, and F160W). This talk summarizes the results from the first year of the program, including the special pipelines that we have developed at STScI for the data processing and calibration, and the solutions that we have implemented for a number of calibration challenges, in order to produce full-depth mosaics in all filters. These high-level science products are released through the Mikulski Archive for Space Telescopes (MAST) to the community on a rapid timescale to enable the widest scientific use of these data, as well as ensuring a public legacy dataset of the highest possible quality that is of lasting value to the entire community.
The Status of HST/ACS
Norman Grogin (STScI)
The Advanced Camera for Surveys (ACS) has been a workhorse HST imager for over twelve years, subsequent to its Servicing Mission 3B installation. The once defunct ACS Wide Field Channel (WFC) has now been operating longer since its Servicing Mission 4 repair than it had originally operated prior to its 2007 failure. Despite the accumulating radiation damage to the WFC CCDs during their long stay in low Earth orbit, ACS continues to be heavily exploited by the HST community as both a prime and a parallel detector. I review recent advances in ACS calibration by the STScI ACS Team, with particular attention to the Wide Field Channel, that enable the continued high performance of this instrument. Highlights include: 1) the refined characterization of the WFC geometric distortion and its time dependency; 2) the mapping of scattered-light danger zones just outside the WFC CCDs; 3) the extension of pixel-based charge-transfer efficiency (CTE) correction to the WFC 2K subarray mode; and 4) the pros and cons of using LED post-flash to improve WFC CTE prior to read-out.
ACS/WFC CTE Correction for Point Source Photometry
Marco Chiaberge (STScI)
I will show the latest results on the CTE photometric correction formula, based on the observations of 47 Tuc taken as part of our routine external CTE monitor calibration program. We are now able to characterize CTE losses down to the lowest background levels (~0.2e-) without significant loss of accuracy with respect to higher sky levels. Using post-SM4 data I was able to derive a new model that is significantly more accurate that those previously published. The new formula may be used to correct stellar photometry for CTE losses on drizzled images taken after SM4. I will show a comparison of the results obtained with this new CTE correction with previous versions of the correction formula for ACS/WFC, and with the pixel-based CTE correction that is currently available as part of CALACS. I will show that the formula currently provides the most accurate CTE correction for point source photometry.
Self-Calibration Strategies for the Frontier Fields
Jay Anderson (STScI)
When the Frontier-Field team was meeting to construct an observing and data-reduction plan, we brainstormed about how best to collect the calibration data for it. We considered taking a set of post-flashed darks that would match the science exposures in terms of background, since such an approach would minimize errors in de-trailing the hot pixels. But, unfortunately, this would would require a prohibitive number of internal orbits, and with the uneven post-flash of ACS, would not even be an optimal calibration. We decided, instead, to pursue a limited self-calibration strategy, wherein we use the data itself to correct systematic errors caused by errors in the dark subtraction (and other imperfect calibrations). This strategy ends up improving the S/N of each pixel by about 20%. I will describe the FF reduction strategy and will discuss other data sets that might benefit from this approach.
Precision Imaging Polarimetry with ACS/WFC
Dean C. Hines (STScI)
Polarization can provide vital and otherwise unobtainable constraints on the origin of light from astronomical sources, the nature of particles involved in emission and scattering processes that result in polarized light, and the geometry of the regions producing polarized light. HST has had many instruments with polarimetry capabilities (e.g., FOC, FOS, WFPC2, NICMOS & ACS/HRC, ACS/WFC), but the ACS/WFC is currently the only asset available to astronomers. I briefly discuss renewed efforts to enhance the capability of the ACS/WFC visible polarizers, by improving the calibration of these polarizers in combination with two broad-band filters (F606W and F775W). This has enabled extremely precise and accurate measurements of the polarization of sungrazing Comet ISON in 2013, and the system will be used to observe Comet 67P/Churyumov-Gerasimenko in support of the Rosetta comet rendezvous mission. The ACS/WFC is currently the only instrument, either in space or on the ground, capable of delivering high precision (~0.003) and high accuracy (~0.003) fractional polarization measurements at visible wavelengths with high spatial resolution (~0.1").
Concepts of Measurement Astrophysics
John T. McGraw, Peter C. Zimmer, Daniel C. Zirzow (Department of Physics and Astronomy, University of New Mexico)
Measurement Astrophysics (MAP) describes high precision astronomical measurements calibrated to obtain high accuracy descriptions of the measured universe. Calibration converts astronomical measurement into astrophysical information. In this overview we’ll specifically discuss radiation from thermal sources transported to optical detectors, and spectral measurements will be assumed.
The majority of information about the observable universe is obtained by measurement of electromagnetic radiation propagating from a source to a detector. Thus, any radiometric measurement represents a scientific problem in radiative transfer, almost always involving significantly different regimes of index of refraction of the media through which the light travels. In particular, an astrophysical radiometric distance is always an optical path length. Astrophysical models are the repository of the physical descriptions of the different domains of refractive index. As an example, measurement of a standard star involves emission by the source (the photosphere of the star), transport through the stellar atmosphere, the intervening interstellar medium, Earth’s atmosphere and the telescope to the detector. Each physical domain physically imprints the source spectrum, e.g. scattering and absorption, yielding the data from which we derive physical information on and model the structure and composition of the stellar atmosphere, interstellar medium, Earth’s atmosphere, and the throughput of the telescope/instrument.
The accurate, comprehensive description and analysis of the physics of the optical path of the detected radiation depends upon accurate calibration of radiometric measurements to a physical standard.
We discuss MAP measurement of the transmission of starlight through Earth’s scattering and absorbing atmosphere using simultaneous NIST calibrated atmospheric lidar measurements and stellar spectroradiometric observations. This transmission correction, of common utility for all ground-based astronomical observations, provides an example for the other domains of radiative transfer.
Special Calibration Needs: 1) Spectroscopy (Spectral Maps/High Precision Spectroscopy)
Susana Deustua (STScI)
Spectroscopy is simple in concept, and, which can be easy to implement with one optical element to disperse light. Or, spectrographs can be complex instruments with multiple elements. Regardless, to extract the best science they all need to be calibrated. Common calibration needs are dispersion and spectrophotometric characterization however, the details are different, and depend on both spectral instrument and the science objectives. I will discuss some of the issues surrounding high precision spectroscopy and spectral maps.
Special Calibration Needs: 2) Imaging (Extended Sources & Crowded Fields) - PHAT
Dustin Lang (Carnegie Mellon University)
In the Panchromatic Hubble Andromeda Treasury (PHAT) multi-cycle program, we tiled one quadrant of the Andromeda galaxy (M31) with 414 pointings covered by ACS and WFC3. We collected images from the ultraviolet to near-infrared (WFC3 UVIS/F275W and F336W, ACS F475W and F814W, and WFC3 IR/F110W and F160W). In total we collected roughly 7,500 exposures, and we photometered over 100 million stars in the images.
Due to overlaps in the tiling, we observe many stars multiple times in different exposures. This allows us to do precise astrometric alignment and mosaicing, and also allows us to find flat-field corrections. I will sketch the methods we use for these calibration steps, and present the results of this work.
Coronagraphic Imaging with HST
Glenn Schneider (Steward Observatory and the Department of Astronomy, The University of Arizona)
Since its inception, the Hubble Space Telescope has hosted five instruments optically augmented for coronagraphic imaging. While such capabilities were initially planned for WFPC/(PC8) and FOC(/f288), those were defeated in the 1st generation instruments by spherical aberration in the telescope's primary mirror. Staring with SM2, NICMOS and STIS then began a long era of HST coronagraphy, then joined by ACS/HRC. Each of these space-based coronagraphs provided their own observational "uniqueness spaces" with nearIR vs. optical, small inner working angle vs. wide-field of view, filter-band photometry vs. broadband deep sensitivity, and augmentation (or not) with polarimetry. For a time, HST was rich with coronagraphic options enabling a diversity of "high contrast" investigations making best use of each. Each instrument also posed its own set of unique challenges for efficacious starlight suppression via classical coronagraphy, but in common shared a performance-limiting reliance upon a not-fully stable telescope point spread function - independent of coronagraph design and implementation. Over the years, innovative observational and data reduction/processing methodologies lead to successive improvements in obtainable coronagraphic contrasts, image fidelity, and instrument-limited "effective" inner working angles. Today, 17 years after its deployment, only the STIS coronagraph is operating, and is still returning new, innovative, and remarkable science results. All three of these instruments are leaving behind a rich set of archival and legacy data exploitable anew by powerful reduction/processing methods unconceived when the instruments were built, and when the original now-archived data were taken. Herein we review the HST coronagraphic legacy, the rocky-road toward (and trials-and-tribulation of) HST imaging coroangraphy with an eye to "lessons learned" in the coming era of JWST, AFTA, and ground-based (narrow-field) EX/AO coronagraphs.
The Status of HST/COS and HST/STIS
Cristina Oliveira and the COS/STIS team
Abstract: The Space Telescope Imaging Spectrograph (STIS), a 2nd generation HST instrument, has been in operation for ~17 years, and was repaired during the fourth HST servicing mission (SM4) in 2009. STIS provides spatially resolved spectroscopy from 1150 to 10,300 A at low to medium spectral resolution, high spectral resolution echelle spectroscopy in the ultraviolet, direct imaging in the UV and optical and broad-band optical coronographic imaging. The Cosmic Origins Spectrograph (COS) is complementary to STIS, and was installed on HST in 2009 during SM4. COS provides low and medium resolution spectroscopy of faint sources from the Lyman limit at ~900 A to ~3200 A as well as limited imaging capabilities in the near ultraviolet. Here we present updates on the performance of the two instruments and discuss ongoing calibration improvements.
Coronagraphic Spectroscopy with STIS
Jessica Donaldson (University of Maryland)
Coronagraphic spectroscopy is the method we use to obtain spatially resolved spectra of circumstellar disks with HST STIS long slit spectroscopy. This unsupported mode uses a 0.86 arcsec wide fiducial bar to block the central star so the spectrum of the much fainter disk can be measured. We obtained spectra from 2900 to 10500 Angstroms of three edge-on debris disks with the long slit oriented parallel to the position angle of the disk and the fiducial bar blocking the central star. The observations were repeated on a diskless star of similar spectral type for point spread function (PSF) subtraction. Short unocculted exposures without the fiducial bar were also taken of the target star and the PSF reference star so the differences in brightness and spectral type could be adjusted before the PSF subtraction. We will present our data reduction methods and share some preliminary results.
STIS Neutral Density Filters
Thomas Ayres (University of Colorado)
For UV-bright continuum sources, like early-type stars, the Global Count Rate (GCR) limit on STIS's MAMA cameras becomes an important consideration and limitation. A "safe" source must be counting below the 200 kcps (kilo-counts per second) limit, say 100 kcps. When divided among the typically 40 echelle orders of about 500 spectral resolution elements each, such a continuum source will deposit roughly 5 cps per resol. This is about two orders of magnitude less (efficient) than if just the other bright-limit, Local Count Rate, was the limiting factor. The maximum S/N for a GCR-safe observation is about 100 in one orbit (2.5 ks exposure), which sounds like a lot, but we are talking about UV-bright stars and a 2.4-m telescope; and state-of-the-art ground-based echelle spectrographs routinely achieve S/N>200. To match that with STIS implies four, or more, orbits per wavelength setting. With about seven mixed-resolution settings needed to cover the full 115-310 nm interval, that adds up to Medium-size project per target. Thus, the global limit already negatively impacts the possibility to carry out large spectroscopic surveys with STIS, if one wants to achieve full UV coverage at the highest practical S/N on a diverse sample of objects. But, it gets worse. If a target is predicted to be close to the CGR limit, or exceeds it, a neutral density (ND) filter must be used. Two such slits are supported for STIS echelle work: 0.2x0.05ND2 (0.01 transmission) and 0.3x0.05ND3 (0.001). If the target just exceeds the GCR limit, say at 300 kcps, you would have to use the ND2 slit. The 100x attenuated GCR will be safe, but very low: about 50x smaller than it would have been had the source been counting safely below the limit, say 150 kcps. To reach the same S/N as for the safe case now would require 50 orbits, instead of one; cruel reality of Poisson statistics. If just one wavelength setting, of the perhaps seven, is GCR-limited, the candidate target would be rendered unfeasible; a potentially crippling limitation on a broad survey that aspired to include representative interesting objects in an unbiased way. The limitations imposed by having only ND2 and ND3 in the STIS toolkit inspired a Cycle 19 pilot study (GO-12567) to validate three "available but unsupported" ND-filtered long slits (31x0.05): NDA (ND=0.6), NDB (1.0), and NDC (1.3). The program not only evaluated slit throughputs vs. wavelength utilizing observations of the hot white dwarf G191B2B; but also demonstrated -- by high-res (E140H) observations of UV-bright, sharp-lined Vega -- that there was no significant bleeding of light between orders, or negative impact on the spectral LSF, by the tall slits compared with the normal short echelle apertures (0.2 arcsec high). The attenuation factors of the newly validated long slits nicely bridge the gap between the default clear echelle apertures and ND2, and in fact have enabled surveys like current Cycle 21 Large Treasury Program "Advanced Spectral Library (ASTRAL): Hot Stars" (GO-13346).
Moving COS/FUV to Lifetime Position 3
Julia Roman-Duval (STSc)
The COS/FUV detector is a micro-channel plate, whose response (gain) decreases with usage due to a process called gain-sag. To mitigate these gain-sag effects, the location of COS/FUV science spectra are moved to pristine areas of the detector, i.e. different lifetime positions, every 2-3 years. Science spectra were moved from the original lifetime position (LP1) to the second lifetime position (LP2), located at +3.5" from LP1, in July 2012 and a move to the third (LP3) lifetime position is planned in February 2015. LP3 is located at -2.5" from LP1 (or -6" below LP2). The -2.5" position was chosen to optimize the spectral resolution at LP3 and future lifetime positions, and to extend the lifetime of the COS/FUV detector to 2020. New extraction techniques are being implemented in order to minimize the effects of LP1 gain-sagged regions and ensure the spectral quality of observations acquired at LP3. Due to their wide cross-dispersion profiles, the G130M/1055 and G130M/1096 settings will remain at LP2. The impact of gain-sag on these modes can be effectively mitigated with spectral dithering.
Issues and Improvements with the COS FUV Wavelength Solution
Jason Tumlinson (STScI)
I will describe recent investigations into the COS wavelength solution for the FUV M gratings. The talk will highlight some quality issues and propose some solutions that will improve the overall calibration.
COS Blue Modes
Steve Penton (STScI)
Prelaunch component level testing of the Hubble Space Telescope’s (HST) Cosmic Origins Spectrograph (COS) suggested that there could be significant throughput at FUV wavelengths blueward of the approximately 1150 Å lower limit achieved by previous HST spectroscopic observations. This is made possible because the Far-Ultraviolet Spectroscopic Explorer (FUSE) heritage COS FUV detector is windowless, and the mirrors and gratings retain a small reflectivity even below the nominal short wavelength MgF2 cutoff near 1150Å. Soon after installation in 2009, low-resolution G140L HST/COS observations indicated that there was indeed usable throughputs down to about 900Å. In HST Cycle 19 (2011) two central wavelength settings (1055 and 1095) were offered for the medium-resolution G130M grating that extended HST's UV bandpass down to 900Å, however due to instrument safety concerns, these modes were not initially offered at optimum focus/resolution. By Cycle 20, these safety concerns had been addressed and the G130M/1055 and 1096 cenwaves were offered at full resolution. Unlike the standard G130M central wavelengths, the focus for these modes does not allow full resolution over both detector segments, but can only be optimized over an ~100Å window. The G130M/1055 cenwave is optimized for observations from ~900-1000Å, and the G130M/1096 cenwave is optimized from ~980-1080Å. To bridge the gap to the shortest wavelength observable with the standard G130M/1291 setting (1135Å), a third "blue mode" central wavelength setting of G130M/1222 was also added in Cycle 20 and optimized for observations from ~1060-1180Å. This talk will review the current calibration status of these "blue modes", discuss the calibration requirements at future lifetime positions, and discuss some of the scientific windows opened up with these HST/COS modes.
The Status of HST/WFC3
John W. MacKenty (STScI)
The Wide Field Camera 3 continues to provide the majority of HST science observations after 5+ years in operation. The instrument meets or exceeds its requirements and is operating nominally. Extensive characterization and calibration efforts, together with exceptional instrument stability, have combined to steadily increase the range of scientific applications. This talk will summarize the current status and performance of WFC3, provide highlights of several major initiatives undertaken since the last Calibration Workshop, discuss the aging of the instrument and its expected evolution over the remainder of this decade, and raise some calibration issues we are considering for future enhancement.
Ivelina Momcheva (STScI)
The grism spectroscopic capabilities of HST/WFC3 are one of the unique features of Hubble: they allow for spatially resolved spectra of high-redshift galaxies over the full 0.8 to 1.6um range. At redshifts 1<z<3, this range captures the rest frame optical specta and allows for studies of galaxy evolution impossible from the ground. However, the lack of slits and the low resolution of the spectra have presented us with new challenges in reducing and analyzing the data. In an effort to improve upon the existing WFC3 grism reductions, the 3D-HST team has developed a new pipeline and derived new calibration images. In this talk I will review our approaches to background and sky subtraction, co-adding dithered exposures, modeling and redshift-fitting of the grism spectra and discuss their effects on the final data products. Even thought these techniques have been developed for 3D-HST, they have proved applicable to many other WFC3 grism programs and have also been generalized to the ACS grism spectra.
Persistance in Near-IR Detector Arrays
Knox S. Long
Persistence is an afterglow of earlier exposures seen in all HgCdTe detectors. Persistence from saturated pixels in the HgCdTe IR array that is part of WFC3 can last for several HST orbits, and is an image anomaly that should be taken into account when analyzing WFC3/IR data. STScI has developed tools that estimate the amount of image persistence in an WFC3/IR image, based upon the degree of saturation in earlier images and the time since these images were obtained. Using these tools, we make estimates of persistence in all WFC3/IR images, and to aid observers, make these estimates available through MAST. While these estimates show that the amount of persistence in most IR images is small, observers should check their data and consider flagging as bad pixels with significant persistence and/or using persistence-subtracted images in their analysis of WFC3/IR data. Our existing tools provide a first approximation to the amount of persistence in an WFC3/IR image, but persistence actually depends, as one might expect, on the entire exposure history of each detector pixel. Experiments show, for example, that at the same saturation level, more persistence is seen from long exposures than short exposures, an effect which is not accounted for in the tools we use at present. Here, we describe ongoing efforts to better characterize persistence in the IR detector on WFC3, to incorporate the results into an improved persistence prediction algorithm, and to determine the accuracy with which persistence can be removed from WFC3/IR images.
Special Calibration Needs: 3) Exoplanets
Nikole Lewis (MIT)
Exoplanet observations present a unique set of challenges to observational calibrations. With the number of exoplanet discoveries increasing at an almost exponential rate, efforts to characterize the physical properties of these planets with ground- and space-based observatories have also increased rapidly in the last decade. Exoplanet transit, eclipse, and phase-variation signals are generally 100-1000 ppm relative to the flux of the host star and must be measured with high precision. Additionally, exoplanet observations often rely on long-duration stares on the order of a few hours to a few days. Here I will focus on systematic effects that have revealed themselves through exoplanet long-stare observations with the Spitzer and Hubble Space Telescopes and the exoplanet specific calibration efforts developed to help achieve photon-noise limited precision levels. I will also discuss how these lessons learned with Spitzer and Hubble can be applied to calibration efforts for exoplanet observations with the James Webb Space Telescope.
WFC3 Spatial Scanning (Exoplanets)
Peter R. McCullough (STScI)
We review a nominal analysis of times series of spatially scanned spectra of transiting exoplanets. We focus on the analysis procedures with only a brief introduction of the motivations and only a cursory summary of some current scientific results in the literature. Most of the procedures we will review are documented already in the following papers: Deming et al. 2013 (HD 209458 and XO-1, transits), McCullough et al. 2014 (HD 189733, transit), Crouzet et al. 2014 (HD 189733, eclipse), and Knutson et al. 2014 (HD 97658, transits).
WFC3 Spatial Scanning (Astrometry)
Stefano Casertano & Adam Riess (STScI)
We will discuss a new technique, the use of WFC3-UVIS to measure high precision relative astrometry from spatial scans. This technique has the ability to reach 20-40 microarcsecond precision. We will discuss the parameters of such observations and the tools we have developed to analyze this unique data. Among other applications, this technique offers an order of magnitude improvement in the ability to measure trigonometric parallaxes with HST approaching the level expected from Gaia. We will also discuss the use of rapid spatial scans to measure photometry of very bright targets.
WFC3 UVIS Shutter Blade
Kailash Sahu (STScI)
WFC3 UVIS uses a shutter blade with two sides, A and B, consecutively in exposures. Stellar PSFs in short-exposures taken with shutter B show larger FWHM and lower sharpness compared to those taken with shutter A. The difference in the FWHMs is most pronounced in the shortest (0.5 sec) exposures. The difference decreases as the exposure time increases and is negligible for exposure times of 30 seconds or larger. There are about 1000 to 2000 short-exposure images taken per year, which constitute about 10% of the total number of exposures. For about half of them, a good and stable PSF is crucial for the science. To facilitate the science, an option has now been added to APT to select the shutter side A, which will be particularly useful for exposure times of < 30 seconds. However, choosing the shutter side involves some additional mechanism movements and thus should only be done when required to achieve the science goals. Various tests were performed to confirm that these movements do not cause any unforeseen or undesirable behavior in the science data.
Elevated Sky Backgrounds in WFC3 from He 10830
Gabe Brammer (STScI)
We investigate the cause of strong time-dependent variations of the background levels observed in a variety of filters of the infrared (IR) channel of the Wide-Field Camera 3. These variations appear within an exposure in the F105W and F110W filters and both IR grisms (G102 and G141), with background count rates reaching 5 e/s/pix in extreme cases (c.f. the zodiacal background is typically ~1 e/s/pix.). We use IR spectra from both grisms to identify the source of this excess background to be a strong, spatially-diffuse, emission line at 10,830 Å from metastable helium atoms in the solar-illuminated upper atmosphere. The He background contribution is negligible in Earth’s shadow but increases sharply when the telescope is outside of the shadow. The He background increases with decreasing limb angle but can also be significant even high above the Earth limb, affecting, to variable extent, a majority of observations that use the spectral elements sensitive to the feature.
WFC3 Time Variable Background Correction
Bryan Hilbert, Massimo Roberto & Ray Lucas (STScI)
Recent investigations have revealed telluric helium emission causing temporally variable background signal in WFC3 observations made through several filters. (Brammer et al. 2014) Using contaminated Frontier Fields observations as a testbed, we have developed a new data reduction strategy designed to isolate and remove this excess signal from raw WFC3 data. This strategy searches for excess background signal by comparing the signal up the ramp to that predicted by a model of signal accumulation within the detector. Differences are interpreted as temporally-variable signal, and are subtracted. While the excess signal from the emission line contamination is spatially uniform, this calibration strategy has the ability to identify and remove any excess temporally variable background signal, whether spatially uniform or not. By subtracting the excess background signal from the raw data, we are able to subsequently run the data through the calwf3 pipeline without having to reject any of the contaminated reads.
Brammer, G., Pirzkal, N., McCullough, P., and MacKenty, J. 2014. WFC3 ISR 2014-03. "Time-varying Excess Earth-glow Backgrounds in the WFC3/IR Channel".
Observing the Solar System with HST
Solar System observations present special challenges when calibrating Hubble data. In my talk, I will focus on the unique needs of solar system observations and observers, with detailed discussion of giant planet imaging. As extended objects, the giant planets require good knowledge of the photometry across the entire image, and in some cases, careful fringe correction. In addition, as Solar System objects are time variable, accurate cross calibration between instruments and over time is important. I will present examples of calibration mishaps and successes and conclude with lessons learned for future pipeline calibrated and archived data.
The Hubble Source Catalog
Steve Lubow (STScI)
The Hubble Source Catalog (HSC) is designed to optimize science from the Hubble Space Telescope by combining tens of thousands of visit-based source lists in the Hubble Legacy Archive (HLA) into a single master catalog. It is based on observations from WFC2, ACS/WFC, WFC3/IR, and WFC3/UVIS. The catalog is available as a Beta0.3 release at archive.stsci.edu/hst/hsc/. It is based on algorithms described in Budavari & Lubow (2012). We have been investigating properties of that catalog that provide information about the astrometric and photometric accuracy of HST data.
Data Management Subsystem - Data Processing, Calibration and Archive Systems for JWST with Implications for HST
Gretchen Greene & Perry Greenfield (STScI)
We will describe the plans for the JWST data management system, and the upgrades to the HST data management system underway that will affect data from these telescopes and the way users access the data. Changes to the HST ground system will provide users much quicker access to calibrated data without removing the ability to obtain the most recent calibrations and processing. JWST will share these benefits as well as provide an easier way to run calibrations at their home institutions. Both will share a standard interface through the archive that allows users to use the same means of accessing data and also use the same account to sign on for all aspects of web interactions with STScI that require authentication.
Archival Legacy Investigations of Circumstellar Environments (ALICE)
Christine H. Chen, E. Choquet, R. Soummer, M. Perrin, L. Pueyo, B. Hagan (STScI)
We have been reprocessing all of the data obtained using the HST NICMOS coronagraph to conduct a comprehensive and consistent search for faint planetary companions and higher level science products. By applying advanced PSF subtraction techniques such as Karhunen-Loeve Image Projection (KLIP) and Locally Optimized Combination of Images (LOCI), we have reached the photon noise limit and discovered more than a dozen planetary companion candidates and imaged half a dozen new debris disks in scattered light for the first time (Soummer et al. 2014). Our pipeline produced not only PSF subtracted images but also noise maps and contrast curves. We are currently leveraging our experience to develop a high level science products pipeline for James Webb Space Telescope (JWST) coronagraphs. Together, the JWST Near Infrared Camera (NIRCam) and the Mid Infrared Instrument (MIRI) provide coronagraphic imaging at wavelengths 2.0 - 23 micron with inner working angles ~2-6 lambda/D and raw contrast performance 1.0e-2 to 1.0e-3 (Krist et al. 2007, Boccaletti et al. 2005). We anticipate that a high level science products pipeline for JWST will similarly produce PSF subtracted images at the photon noise limit.
AstroDrizzle Products for HST and JWST
Jennifer Mack (STScI)
In June 2012, AstroDrizzle replaced MultiDrizzle in the HST pipeline. An abbreviation for 'Astrometric Drizzle', this new software was designed from the ground up to improve the handling of astrometric data. AstroDrizzle corrects for geometric distortion and time-variable sky, flags cosmic-rays, and combines images with optional subsampling. For HST, archival drizzled products are generated for single visits only. They make use of a default set of parameters for general use and as such may not be optimal for scientific analysis. For multi-visit programs, TweakReg may be run offline to improve the alignment and update the header World Coordinate System before combining with AstroDrizzle. For JWST, observations will be associated by proposal rather than by visit, and TweakReg will run in the pipeline to refine the alignment of the full stack prior to drizzling. Development of this software for JWST is currently underway.
The Status of JWST
Jeff Valenti (STScI)
The James Webb Space Telescope is NASA’s flagship mission, and provides forefront observing capabilities in the near- and mid-infrared in order to address key questions about the early universe, the assembly of galaxies, the birth of stars and protoplanetary systems, and planetary systems and the origins of life. Launch is expected in 2018, and major milestones in the mission timeline are occurring now. I will provide an introduction to the science and instrument capabilities of the James Webb Space Telescope, with an update on recent activities occurring throughout the mission. The siting of the Science and Operations Center for JWST at the Space Telescope Science Institute affords a considerable amount of synergy between JWST and HST, and I will describe some of the ways in which the knowledge of HST is being applied to JWST.