STScI Logo

Hubble's 25th Anniversary Symposium
Poster Presentations

Rachael Alexandroff: Johns Hopkins University

Indirect Evidence for Escaping Ionizing Photons in Local Lyman Break GalaxyAnalogs

A population of early star-forming galaxies is the leading candidate for the re-ionization of the universe. It is still unclear, however, what conditions and physical processes would enable a significant fraction of the ionizing photons to escape from these gas-rich galaxies. We have uncovered a sample of local analogs to high-redshift, star-forming Lyman Break Galaxies (LBGs) called Lyman Break Analogs (LBAs) by matching the Sloan Digital Sky Survey (SDSS) and Galaxy Evolution Explorer (GALEX) catalogs. We obtained HST COS far-UV spectroscopy plus ancillary multi-waveband data of a sample of 22 LBAs to look for indirect evidence of escaping ionizing radiation (leakiness). We measure three parameters: (1) the residual intensity in the cores of saturated interstellar low-ionization absorption-lines, which indicates incomplete covering by that gas in the galaxy. (2) The relative amount of blue-shifted Lyman alpha line emission, which can indicate the existence of holes in the neutral hydrogen on the front-side of the galaxy outflow, and (3) the relative weakness of the [SII] optical emission lines that trace matter-bounded HII regions. We find all three diagnostics agree well with one another. Finally, we find the strongest correlation between these leakiness indicators and both the compactness of the galactic star-forming region (size and star formation rate/area) and the speed of the galactic outflow. This suggests that extreme feedback- a high intensity of ionizing radiation and strong pressure from both radiation and a hot galactic wind- combines to create significant holes in the neutral gas. These results not only shed new light on the physical mechanisms that can allow ionizing radiation to escape from intensely star-forming galaxies, they also provide indirect observational indicators that can be used at high-redshift where direct measurements of escaping ionizing radiation is impossible.

Thomas Ayres: University of Colorado

The Advanced Spectral Library Project

Advanced Spectral Library (ASTRAL) is a Hubble Large Treasury Project, whose aim is to collect high-quality ultraviolet (115-310 nm) spectra of representative bright stars, utilizing powerful Space Telescope Imaging Spectrograph, with resolution and signal-to-noise rivaling the best that can be achieved at ground-based observatories in the visible. During Cycle 18 (2010-2011), ASTRAL was allocated 146 orbits to record eight late-type ("cool") stars, all well-known cosmic denizens including (vaguely unpronounceable) Procyon, Betelgeuse, and Beta Cassiopeia. In Cycle 21 (2013—2014), ASTRAL was awarded an additional 230 orbits to extend the project to the hot side of the H-R diagram: 21 targets including equally iconic Vega, Sirius, and Regulus. I will describe the scientific motivations for observing hot and cool stars in the UV, the unique instrumental characteristics of STIS that enable a broad survey like ASTRAL, progress in the program to date, and prospects for the future.

Daniel Batcheldor: Florida Institute of Technology

Roll Differential Imaging.

The most compelling questions in modern astrophysics now require the use of advanced data collection techniques that overcome the problems associated with extreme contrast ratios (ECRs). These questions include, but are not limited to, the nature of terrestrial exoplanets, circum-stellar debris disks, and quasar host galaxies. In addition, there are the binarity fraction of low mass companions, the low mass end of the initial mass function in general, and the properties of brown dwarfs. A major problem to overcome when performing ECR imaging is the effect of the point spread function (PSF). Much of this can be suppressed with nulling interferometry, or blocked with coronagraphy, but each of these techniques have complications that make them difficult and/or expensive to execute. However, roll differential imaging (RDI) - the combination of angular differential imaging and roll subtraction - allows for relatively easy and inexpensive PSF suppression. This presentation will provide the community with the residual noise levels, effective inner working angles, the impact of PSF stability and optimal data reduction techniques for recovering faint extended symmetric and asymmetric emission around bright objects using archived RDI data. This technique could provide a major step forward in our ability to address some of the most fundamental questions remaining in modern astrophysics.

Luciana Bianchi: Johns Hopkins UNiversity

Hot Massive Stars and Dust in the Local Universe: 25 Years of HST Imaging and Spectroscopy

The study of hot massive stars in nearby galaxies is the stepping stone for interpreting distant star-forming galaxies. Massive stars drive the dynamical and chemical evolution of the interstellar medium, yielding feedback on local and galactic scales; very luminous, they dominate the light of distant star-bursts and can be seen at large distances. HST enabled enormous progress in studies of stellar populations, thanks to its spatial resolution providing measurements of individual stars in nearby galaxies, and access to UV from space. UV is key to identifying the hottest stars, and to precisely measuring their physical parameters, critical for correct estimates of age, energy-balance, and stellar mass content of star-forming regions. Dust is also an essential component of galaxies, closely connected to the formation and evolution of massive stars. HST UV-to-IR measurements contribute to clarifying properties of dust in differing environments. UV spectroscopy (available for a very limited sample) yields details of selective extinction and grain properties and their variations related to hot-star radiation, metallicity, etc.; UV imaging characterizes dust properties and massive stars across entire portions of galaxies. Using multiband UV--nearIR photometry, we derived a detailed age- and spatial- tomography of selected star-forming regions in a variety of galaxy environments and quantified the hierarchical structure of star formation, as well as provided constraints to new stellar evolution and galaxy evolution models. We present new results from two recent large programs in particular, TrImS (Bianchi et al. 2012a, b, 2014) and PHAT, combined with some of our previous spectroscopic and imaging programs.

Luciana Bianchi: Johns Hopkins UNiversity

An Unprecedented View of Hot-Star Atmospheres from ASTRAL-II UV Spectra: The O-Type Sample.

The ASTRAL-II hot stars treasury program (P.I. T. Ayres) is constructing a library of UV spectra (1150-3100 Ang), with unprecedented high signal-to-noise and resolution, of prototypical hot stars representing major types, including some emission line ('e') and 'peculiar' types. Such high quality spectra will remain a benchmark reference for stellar atmosphere modeling for years to come. The overall program is described by Ayres et al. in this Symposium. We present a first look at the spectra of the five O-type stars in the sample. Results include variations in the wind of Zeta Puppis between two observations taken 6-days apart, and preliminary line comparison among the sample and with theoretical models.

William Blair: Johns Hopkins University, Dept. of Physics & Astronomy

Stellar Birth and Death in M83: Leveraging HST through Multiwavelength Observations

The sensitivity and spatial resolution of HST is ideal for observing the stellar life cycle in nearby spiral galaxies. For the face-on grand design spiral galaxy M83 (d=4.6 Mpc), we are combining HST-WFC3 multiband imaging (7 fields in 9 continuum and emission-line filters) with deep Chandra observations (729 ks) to study star formation, stellar death, and the global impacts of these processes on the host galaxy. M83 is an actively star-forming galaxy, with spiral arms filled with giant H II regions and an intense nuclear starburst. The galaxy itself is a veritable supernova factory, having generated six observed SNe in under 100 years, so numerous young SN remnants are expected. Chandra reveals over 450 point X-ray sources (~350 intrinsic to M83) plus extensive diffuse X-ray emission. Several optical/X-ray sources of particular interest have been identified, including a new ULX, a new microquasar, a new very young SN remnant, and the X-ray counterpart to SN 1957D. More generally, with HST and ground-based data, nearly 300 SN remnants are now known in M83, with: 100 X-ray-optical coincidences, the largest number known in any galaxy to date. Interestingly, there is very little correlation between the Halpha luminosities of SNRs and their X-ray luminosities, which points to the need for multi-wavelength campaigns such as this to obtain the most complete picture. The HST data have allowed the characterization 63 SN remnants with diameters below 10 pc (hence the youngest remnants). Only a few of these objects show the high velocities and enhanced ejecta abundances similar to the youngest core-collapse SNRs we know of locally (e.g. Cas A in our Galaxy, E0102-7219 in the SMC, etc.) Instead, most of the young SNRs appear to have evolved rapidly into the radiative phase. This fact, together with the presence of bright diffuse X-ray emission in M83 is pointing to a relatively high density/high pressure ISM in M83 compared with other nearby galaxies. We are using photometry of the WFC3 data near many of the X-ray sources and SN remnants to constrain the ages of the precursor populations. For instance, both SN 1957D and the new young SNR mentioned above arise from stellar groupings less than 10 Myr in age, and thus must have had massive (>17 Msol) progenitors, confirming that they were both core-collapse SNe even though the types were not observed directly. This work is supported in part by STScI grant HST-GO-12513.01-A and Chandra grant SAO-GO1-12115C to Johns Hopkins University

Peter Blanchard: Harvard University

Searching for Progenitor Clues in the Local Environments of Long GRB Hosts

While it is now established that long-duration gamma-ray bursts (LGRBs) are a rare outcome of the death of some massive stars, it remains unclear what special conditions are required for the production of an LGRB. Studies of the preferred locations of LGRBs within their host galaxies can shed light on this open question. Hubble Space Telescope observations of: 20 pre-Swift LGRBs from over a decade ago showed that their locations are correlated with bright star-forming regions, but the sample was small, heterogeneous, and only spanned to z~1. With HST observations of Swift LGRBs it is now possible to overcome all of these shortcomings. In this talk I will present the results of an extensive HST imaging study of: 100 Swift LGRBs using relative astrometry from ground-based afterglow observations. Using these data, I measure the distribution of LGRB offsets, as well as their relation to the underlying host rest-frame UV light distribution. The study also aims to use LGRBs as probes of the metallicity gradients in distant galaxies, by combining their host locations with afterglow ISM absorption line measurements. This presentation is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE1144152.

Rongmon Bordoloi: STScI

The COS-Dwarfs Survey: Mapping the CGM Around Dwarf Galaxies

I will present the first results mapping the 2-D distribution of circumgalactic gas around nearby dwarf galaxies from the COS-Dwarfs survey. COS-Dwarfs survey uses HST/COS spectroscopy to probe the halos of low redshift galaxies with luminosities L = 0.02 - 0.3L*, stellar masses (M*) = 10^(8-10) M⦿, up to impact parameters of 150 kpc. Using sensitive UV absorption-line measurements of the multiphase gas diagnostics such as Lyα, CII/IV, Si II/III/IV I will present the radial and azimuthal distribution of such gas around these galaxies. I will also show how the absorption strengths vary with host galaxy color, mass, star formation rate, orientation, and how they compare with that of the L* galaxies probed by our related COS-Halos survey. In particular, I will present how CIV absorption depends on the specific star-formation rate (sSFR) of the host galaxies and show that the CGM of these galaxies host a significant fraction of metals the the galaxies have produced.

Annalisa Calamida: Space Telescope Science Institute

The Galactic Bulge Initial Mass Function

Accurate and deep photometry of the low-reddening Sagittarius window in the Galactic bulge, collected at different epochs, with the Advanced Camera for Surveys on the Hubble Space Telescope, allowed us to separate disk and bulge stars down to very faint magnitudes, V: 28 mag, with a proper-motion accuracy better than 0.1 mas/yr. We then derived the bulge initial mass function in the mass range 0.15 < M/Mo < 1, by using theoretical mass-luminosity relations and by correcting for the presence of undetected binaries. Photometric errors, the distance modulus and reddening estimate uncertainties, the metallicity dispersion and the adoption of different theoretical relations were taken into account. We find that the initial mass function of the bulge has a power-law break at M: 0.5 Mo, with a steeper slope - alpha = -2.0+/-0.6 - for M >= 0.5Mo, and a shallower slope - alpha = -1.0 +/- 0.3 - at lower masses, 0.15 < M/Mo < 0.5. This mass function agrees quite well, within current uncertainties, with the mass function derived for other regions of the bulge and for the Galactic field in similar mass ranges. In the near future, with the advent of the James Webb Space Telescope, we will be able to constrain the bulge initial mass function down to the hydrogen-burning limit and, by observing in the near-infrared regime, where interstellar extinction is at least an order of magnitude lower, we will be able to probe more obscured regions and the far side of the Galactic bulge.

Kenneth Carpenter: NASA's GSFC

Exploring the ASTRAL High-Definition UV Spectrum of the Ap Star HR 465

The "Advanced Spectral Library (ASTRAL) Project: Hot Stars" is a Hubble Space Telescope (HST) Cycle 21 Treasury Program (GO-13346: Ayres PI). This program is producing a set of 21 high-resolution (R~30,000-100,000), high signal/noise (S/N>100), full UV coverage (~1200 - 3100 Ċ) spectra of early-type stars, utilizing the high-performance Space Telescope Imaging Spectrograph (STIS). The targets span the range of spectral types between early-O and early-A, including main sequence and evolved stars, fast and slow rotators, as well as chemically peculiar and magnetic objects. These extremely high-quality STIS echelle spectra will be available from the HST archive and, in post-processed and merged form, at http://casa.colorado.edu/~ayres/ASTRAL/. T. Ayres presents further details on the ASTRAL programs (Hot and Cool Stars) within this Symposium. In this paper, we analyze the ASTRAL high definition UV spectrum of the prototypical A-type magnetic chemically-peculiar (Ap) star HR 465, which has a global magnetic field of: 2200 Gauss. This spectrum, composed of 21 co-added and merged individual spectra and taken in REE (Rare Earth Element) minimum state, is of superb quality and shows an absolute forest of absorption lines, completely blanketing the spectrum from 1200 - 3100 A, to the extent that the true continuum is not discernible. Earlier analyses of IUE spectra of this star show strong iron-peak element lines, along with heavy elements such as gallium and platinum, while being deficient in the abundance of some ions of low atomic number, such as carbon. We demonstrate the high quality of the ASTRAL data relative to these earlier data and present a guide to the contents of this spectrum. By comparison of the observed spectra with calculated spectra, we also provide estimates of select element abundances, and place these measurements in the context of earlier results for this and other Ap stars.

Stefano Casertano: STScI

The Distance to Galactic Cepheids - High Precision Parallax Measurements with the Perpendicular Spatial Scan Mode of WFC3

We will present the first several measurements of trigonometric parallaxes for Galactic Cepheids obtained with the Perpendicular Spatial Scan capability of WFC3. This mode allows much more accurate one-dimensional position measurements for sufficiently bright targets than possible with either imagers or the FGS on HST. We estimate a final parallax accuracy ranging from 20 to 30 micro-arcseconds, resulting in a distance accuracy of: 5% at 2 kpc. When complete in mid-2015, our program will obtain distance measurements for 18 long-period Galactic Cepheids, which will form the best available calibrator for the local value of the Hubble constant (expected error: 1.8-2.1%) until the final results from the GAIA mission are released in 2022. Achieving the desired accuracy required careful planning and a thorough understanding of the peculiarities of both WFC3 and of guiding with HST. We describe the key elements for successful observations and analysis, including choices of filter and scan rate, consideration of the number and density of reference stars, time- and filter-dependent changes in the geometric distortion, and correction for micro-rotations in the HST reference frame. As the required precision of: 0.001 pixels exceeds what can be achieved with direct observations, many of these elements require extensive analysis of available spatial scan calibration observations and/or self-calibration from the data themselves.

Michele Cignoni: STSCI

Dissecting 30 Doradus: Optical and Near Infrared Star Formation History of the Starburst Cluster NGC 2070 from the Hubble Tarantula Treasury Project

We present a study of the recent star formation (SF) of 30 Doradus in the Large Magellanic Cloud (LMC) using the panchromatic imaging survey Hubble Tarantula Treasury Project (HTTP). In this paper we focus on the stars within 20 pc of the center of the massive ionizing cluster of 30 Doradus, NGC 2070. Comparison of the F110W vs F110W−F160W and F555W vs F555W−F775W Color-Magnitude Diagrams (CMD) with synthetic CMDs generated with PARSEC isochrones suggests the following history for the recent SF of the region: i) about 20 Myr ago the region began to produce more stars than the average LMC rate; ii) 7 Myr ago the SF accelerated; iii) 1-3 Myr ago the SF reached a major peak.

John Clarke: Boston University / Center for Space Physics

HST Planetary Observations Coordinated with the Galileo, Cassini, Mars Express, Venus Express, and MAVEN Missions

An extended series of HST observing programs has been conducted over the years in coordination with various planetary missions of NASA and ESA. Planetary auroral observations were coordinated with Galileo (Jupiter) and Cassini (Jupiter and Saturn), and more recently airglow/coronal observations of Mars and Venus were coordinated with the MEX and VEX missions. Most recently observations of Mars are being coordinated with the first data from Mars from the MAVEN mission. This presentation (either a talk or a poster) will give an overview of the science goals and outcomes of these programs.

John Debes: STScI

Planetary Systems Around White Dwarfs as a Bridge Between HST and JWST

Major advances in most astronomical fields come from a combination of a statistical investigation of large populations with small amounts of detailed information and small populations of bright objects that can be investigated in detail. The WISE Infrared Excesses around Degenerates (WIRED) survey has aimed at both approaches by constructing a statistical sample of white dwarfs while at the same time discovering several new white dwarfs in local space. We present three gold-standard dusty white dwarfs initially discovered with the WIRED survey, confirmed through Keck/HIRES+Magellan echelle spectroscopy, and further examined by COS FUV spectroscopy. These white dwarfs along with a handful of other targets, will be prime targets for JWST, where dust mineralogy can be directly compared with the elemental abundance of the white dwarf photospheres. We also show how COS TIME-TAG spectroscopy can be leveraged into high quality lightcurves, which has a bearing on the prospects for characterizing the atmospheres of transiting planets around UV-bright objects.

Rosa Diaz: Space Telescope Science Institute

JWST Science Operations Design Reference Mission: One Year into JWST Observations

The James Webb Space Telescope (JWST) will enable scientific breakthroughs, much like HST. As we approach our scheduled 2018 launch, HST users should look closely to the scientific goals of JWST and identify science opportunities and those areas yet not explored by HST that will enhance JWST science and that will greatly impact many of the themes we research today. The Science Operations Reference Mission (SODRM) is a suite of realistic JWST science programs that cover the main scientific themes of the observatory. STScI is using the SODRM to uide development of the JWST ground system, but the contents of the SODRM also highlight science observations well suited to the capabilities of JWST. We summarize the contents of the SODRM, both scientifically and in terms of instrument capabilities.

Adriano Fontana: INAF-OAR

The ASTRODEEP high quality catalogs of the Frontier Fields: Abell2744 and MACS0416

ASTRODEEP is multi-year, EU-funded program that aims at improving the processes of catalog extraction in crowded extragalactic fields, delivering to the community, both revised procedures (including public software) as well as public catalog. The Frontier Fields are an obvious exciting test-bed for this project. We report here the results in the First two Frontier Fields that have been completed, Abell 2744 and MACS0416.. The goal of this effort is to obtain high quality photometric catalogs including all HST bands (from F435W to H160) as well as the ground-base K band, and to study the possibility of including a reliable photometry of the IRAC images. To this end, we have performed a careful subtraction of bright cluster members,including also an estimate of the ICL, that we describe in some detail here. This has allowed us to identify and properly measure faint galaxies in the core of the cluster. We then performed a properly optimized detection and an optimal photometry using a combination of public codes (SExtractor and TPHOT). We discuss here the basic steps of the process. The final catalogs include photometry in all available bands, photometric redshift, stellar masses and other rest frame parameters derived from the photometry. All catalogs will be made publicly avaialble very soon.

Ori Fox: University of California-Berkeley

UV Spectroscopic Signatures from Supernovae Interacting With Their Circumstellar Medium

Type IIn supernovae (SNe IIn) are defined by their relatively narrow spectral features associated with a dense circumstellar medium (CSM) formed by the progenitor star. The nature of the progenitors and mass loss remains relatively unknown. Shock interaction with the dense CSM offers an important probe of the CSM characteristics, progenitor mass-loss history, and ultimately the progenitor itself. While most supernovae tend to be faint in the UV at late times (>200 days), shock interaction and dust formation in the dense CSM often result in significant emission ranging from X-ray to radio for many years post-explosion. Here we present HST/STIS observations of 4 relatively bright, nearby SNe IIn that reflect the diversity and significance of the subclass: SNe 2005ip, 2006gy, 20009ip, and 2010jl. These new observations offer new insights regarding both the progenitor and explosion characteristics of the SN IIn subclass.

Karl Glazebrook: Swinburne University

HST Observations of Turbulent Disks at z=0.1

Almost the very first remarkable observations of HST was it's first views in to deep space and time (the HDF and Medium Deep Survey) which showed a remarkable evolution in high-redshift galaxy morphology, in particular the prevalence of irregular massive galaxies - now called 'clump cluster', 'tadpole' and 'chain galaxies'. The astrophysical community is still working to understand these early observations but we now have an excellent working model that explains the physical morphologies in terms of the evolution of gas rich Toomre-unstable disks. However the observations are still limited by spatial resolution and signal:noise. In our 'project DYNAMO' we have selected a sample of 'local analogues' - these are now confirmed as gas rich high-SFR galaxies at z~0.1 with clear rotation, high internal turbulence and clumpy morphology. Such nearby objects allow us to take a fresh look at high-redshift physics with much better signal:noise and resolution. Using HST we have had a GO program to image them, we obtain sub-200 pc resolution, which is 5x better than in direct high-z observations, and has allowed us to (1) determine true clump size and measure the effect of limited spatial resolution at high-z and (2) critically test the Toomre-stability model. This sheds new insight in to the physics of early galaxy morphology and new understanding of these 20-year old results.

Kathryn Grasha: University of Massachusetts

The Clustering of Young Stellar Clusters in Nearby Galaxies

We present measurements of clustering among star clusters for several galaxies drawn from the Legacy ExtraGalactic UV Survey (LEGUS), in order to establish whether the clustering strength depends on properties of the cluster population. We use the two point autocorrelation function to study clustering as a function of spatial scale, age, concentration index (CI), and mass. We separate the clusters into different classes, defined by their (a)symmetry and number of peaks, comparing the trends of the autocorrelation functions between all the cluster classes. We find that, in general, younger and less concentrated star clusters are more strongly clustered, which is what is expected if star clusters disperse with ageing. We also measure the power-law slope and amplitude of the autocorrelation functions and discuss the results.

Theodore Gull: NASA/GSFC

Eta Carinae: Constraining Changes in the Massive Winds

Over the past decade, Eta Carinae has undergone very significant changes in multiple wind-associated line-profiles and apparent brightness. An obvious explanation is that the interacting, massive winds that heavily obscure the massive binary are changing, but by how much? The primary star models of Hillier et al. (2001 ApJ 553, 827; 2006 ApJ 642, 1098) suggest that the change is small. Others claim that the primary wind mass loss rate has dropped by two- to four-fold. Yet the primary mass loss velocity does not appear to have changed, nor has the X-ray luminosity, modulated by the 5.54-year period, substantially changed. We have constrained the changes in winds by observations of forbidden line emissions that HST/STIS uniquely resolves both spatially and spectrally. In coordination with many ground-based visible and X-ray observatories, we have mapped these emissions at predicted critical phases of Eta Carinae over the most recent binary period. We measured a) expanding, slightly-accelerated, red-shifted [Fe II] shells of primary wind from the previous three cycles, b) related blue-shifted [Fe III] arcs of primary wind, directly photo-ionized by the hot secondary and watched their ionization change across the broad high-state as the secondary-star, FUV radiation scanned across the winds, analogous to a lighthouse beam moving across the night sky, c) observed the rapid drop in [Fe III] preceding the 2014.5 periastron passage as the hot secondary plunged deeply into the massive primary wind that ultimately engorges the FUV radiation and d) followed the slow recovery of [Fe III] from the periastron passage as the secondary winds carved a new low-density cavity out of the primary wind accompanied with secondary star re-ionization of expanding primary winds. Three-dimensional hydrodynamical models with radiative transfer were developed in parallel with the observations (Madura et al 2013 MNRAS 436, 3820; Clementel et al 2014 MNRAS 443, 2475 and others in press). These models detail the ionization structure of hydrogen and helium leading to models of [Fe III] and [Fe II] emissions for direct comparison to the observational spatial-velocity data cubes at critical phases of the binary orbit. We find that changes in the primary wind are significantly less than two-fold and that the observed changes are due more to our line-of-sight which passes through large amounts of the wind-wind interaction regions, thus amplifying perceived changes in the spectrum. Additional mappings with the HST/STIS will further establish limits of interacting wind properties. These observations were funded through STScI by the HST Project through programs 12508, 13054 and 13395. The supercomputer modeling was supported by the NASA high speed computing program and University of Leiden.

Sally Heap: NASA's Goddard Space Flight Center

Does the Extremely Metal-Poor Dwarf Galaxy, I Zw 18, Harbor Pristine Stars?

Cosmological simulations predict that massive galaxies in the early universe grew primarily by accretion of pristine or near-pristine streams (Dekel et al. 2009). As the local, extremely metal poor (XMP) dwarf galaxy, I Zw 18, has long been thought to be a template for primitive galaxies in the early universe, it provides an excellent test case for accretion of pristine streams. Recent studies suggest that it may harbor stream-fed metal-free gas (Lebouteiller et al. 2013, Skillman et al. 2013). We have therefore searched COS far-UV spectra of I Zw 18–NW for evidence of metal-free stars and gas. The spectrum shows nebular He II recombination emission at 1640 Ċ indicating the presence of extremely hot, potentially Pop III stars, but the stellar spectrum indicates XMP stars no hotter than: 40,000 K. We describe our investigation of the two most likely candidate sources of nebular He II ionization -- XMP early-WN stars, and young, massive, zero-metallicity stars – and find that the latter is favored by observation and models.

Alaina Henry: NASA GSFC

Lyman Alpha Emission from Green Peas: High Redshift Clues from Low Redshift Galaxies

I report new observations of the Lyman Alpha Emission line and ultraviolet interstellar absorption lines in a sample of ten actively star-forming galaxies at z~0.2. Selected on the basis of high equivalent width emission lines in their SDSS spectra, the sample, dubbed "Green Peas" make some of the best analogs for young galaxies in an early Universe. Using COS on HST, we detect Lyman alpha emission in the entire sample, with 9/10 galaxies showing double-peaked spectral profiles. We measure Lyman-Alpha/H-Alpha flux ratios of 0.5 to 5.6, implying that 5% to 60% of the Lyman alpha photons escape the galaxies to be observed by COS. We show that the velocities traced by HI Lyman series lines are well matched by the blue-shifted Lyman alpha emission kinematics, demonstrating that the Lyman Alpha Emission is arises from scattering in an envelope rather than a single-velocity shell of HI gas. Comparison of the Lyman series absorption with low ionization metal absorption challenges the traditional assumption that these lines trace the same gas. Rather, if the Green Peas are host to a multi-phase, clumpy circumgalactic medium, then the data imply a significant neutral H I fraction in the warm-ionized phase. Finally, we discuss whether scattered emission and aperture effects can be responsible for some of the trends in kinematics, equivalent widths, and Lyman alpha escape.

Brian Hicks: NASA GSFC

Next Generation Visible Nulling Coronagraph

We present efforts to advance an approach to broadband, high-order, starlight suppression for enabling direct detection and characterization of exoplanetary systems with arbitrary telescope apertures using a single nuller. The techniques being advanced include phase-occulting optics and a wavefront control strategy modified to incorporate achromatic phase shifters. Both polarization components are nulled simultaneously. Science yield with future large aperture telescopes is discussed.

Dean Hines: STScI

Polarimetry with the Hubble Space Telescope

Polarimetry capabilities have been an integral part of many instruments flown aboard the Hubble Space Telescope (HST). Analysis of polarized light can provide vital and otherwise unobtainable constraints on the origin of light from astronomical sources, the nature of particles involved in the emission, scattering processes that result in polarized light, and the geometry of the emitting regions. Polarimetry has been crucial in unraveling the emission mechanisms in radio loud active galaxies, proving conclusively that synchrotron emission dominates in jets such as M87, even at visual wavelengths. It played a key role in the development of the Orientation-Dependent Unified Scheme for Active Galactic Nuclei, which unifies Seyfert 1 & 2 galaxies, Type 1 & Type 2 Quasars and Hyperluminous Infrared Galaxies, and narrow- and broad-line radio galaxies. It has yielded unprecedented views into planet-forming circumstellar disks, and has been used successfully to determine the distances to astronomical objects geometrically. Polarimetry also has wide applicability as a generic tool for exploration within the Solar System, potentially allowing probes of aerosols, clouds, dust, surfaces, both icy and solid, high energy phenomena and even, through circular polarimetry, may be used as a biomarker. Among the initial instruments aboard HST, the Faint Object Camera (FOC), Wide Field & Planetary Camera (WFPC), Faint Object Spectrograph (FOS), and High Speed Photometer (HSP) enabled polarimetry. Wide Field Camera 2 provided imaging polarimetry after Service Mission (SM1), and the Near Infrared Camera & Multi-Object Spectrometer (NICMOS) enabled coronagraphic polarimetry for the first time after SM2. The Advanced Camera for Surveys (ACS) High Resolution Camera (HRC) enabled visible coronagraphic polarimetry after SM3B. Today, the ACS Wide-Field Camera is 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 arcsec). We will summarize some of the very exciting science that has been produced using the polarimetry modes on HST, including recent precision imaging polarimetry of comet ISON and comet 67P/Churyumov–Gerasimenko (in support of the ESA Rosetta Mission). These results are an outstanding legacy of HST, but also a lesson that future space missions should seriously consider polarimetry capabilities. Indeed, most designs for future space-based telescopes, and especially those with a goal of investigating exo-solar systems (e.g., WFIRST-AFTA, ATLAST), will benefit from inclusion of polarimetry capabilities.

Kandis Lea (Kandi) Jessup: Southwest Research Institute

Coordinated Hubble Space Telescope and Venus Express Observations of Venus’ Upper Cloud Deck

The European Space Agency's Venus Express (VEx) mission arrived at Venus on 11 April 2006, and began its 8 year long mission observing Venus. The goal of the mission was to investigate the structure, dynamics, and composition of Venus’ H2SO4 clouds with the hope of gaining insight regarding the radiative balance in the past, present and future evolution of the planet’s atmosphere. Chemical reactions in Venus’ atmosphere that involve the sulfur oxide gas species are closely linked to the global-scale H2SO4 cloud and H2SO4 aerosol haze layers located between 30-100 km, which in turn are closely linked to Venus’ overall climate change an atmospheric evolution. Thus, the acquisition of the density and distribution of the sulfur oxide species (SO, SO2, SO3, etc.) is highly prized, and can be done directly via observations obtained between 170-310 nm which probes the 65-80 km sulfur-oxide gas density; likewise, observation of Venus' 4.0 ?m SO2 gas absorption signature may be used to probe the 65-100 km region of the atmosphere. Additionally, repeated observation of Venus at these wavelengths expands the temporal extent of the 65-80 km sulfur-oxide observation database, and by thus contributes to our ability to assess the nature and frequency of sulfur-oxide volcanism on Venus. In order to study Venus’ sulfur-oxide chemistry and the H2SO4 formation cycle, the VEx mission has relied heavily on the SPICAV (Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus) instrument. Utilizing SPICAV’s three different observing modes : the Solar Occultation in the Infrared (SOIR) mode, the SPICAV-IR mode, and the SPICAV-UV mode, the VEx mission has obtained vertical profiles of Venus’ SO2, SO, H2O, HDO, CO2, temperature and aerosol species (presumed to be predominantly H2SO4) based on occultations of both the sun and stars (c.f. Belyaev et al. 2012, Wilquet et al. 2012, Mahieux et al. 2014), VEx has obtained detailed information on the spatial distribution of the SO2 gas based on nadir viewing SPICAV-UV observations. However, due to the 1.5 nm resolution of the SPICAV-UV instrument, VEx has only been able to define the SO vertical profiles at the terminator; it is completely unable to uniquely define the horizontal distribution of the SO gas species as a function of latitude or time of day. However these measurements are needed to the assess impact of photochemistry as a function of time of day (in the transition from day to night, or in the most general gas of day vs. night). Additionally, because of the observation geometry required to obtain the occultation measurements, VEx/SPICAV is unable to simultaneously measure Venus’ vertical and horizontal SO2 distribution—yet these measurements (in the absence of simultaneous SO and SO2 retrievals) are needed to assess the role of vertical mixing in the atmosphere. Fortunately, the repair of HST/STIS in 2009 returned to the astronomical community the ability to observe planetary atmospheres in the UV at a spectral resolution high enough to uniquely define the gas absorption signatures of SO2 and SO gas in the 210-230 nm range. Taking advantage of the newly repaired instrument, in December, 2010 and January 2011 170-310 nm, high spectral (0.3 nm) and spatial (40-60 km/pixel) resolution observations of Venus’ low latitude dayside atmosphere were obtained using Hubble’s Space Telescope Imaging Spectrograph (the HST/STIS), (Jessup et al. 2014a & b, Vandaele et al. 2014). The principal objectives of these observations were to probe Venus’ 65-80 km SO2 and SO (collectively SOx) gas absorption signature as at multiple latitudes and local times in order to support and enhance the science return of the Venus Express (VEx) mission. In order to obtain the highest science return, the 2010 and 2011 HST/STIS observations were coordinated with several VEx measurements of the H2SO4 and CO2 cloud properties, which we describe below: (a) the HST/STIS spectra were obtained in regions spatially coincident with the south pole to low latitude Venus Express Monitoring Camera (VMC) cloud top imaging—thus, the acquired HST observations provided the first direct spectral assessment of the SO2 and SO gas composition balance and distribution relative to the observed UV (365 nm) cloud contrast (which is expected to be related to the presence of an unknown UV absorber responsible for over 50% of Venus energy budget). (b) HST/STIS spectra of Venus’ low-latitude gas distribution extending from the morning terminator to local noon were obtained temporally coincident with 60-100 km aerosol and SO2 vertical profiles acquired from solar occultation spectroscopy obtained at Venus’ morning terminator in regions geographically coincident with the HST terminator observations using the SOIR mode of SPICAV. These observations provided for the first time simultaneous measurement of Venus’ vertical and horizontal SO2 distribution, in regions that were geographically coincident/relevant. (c) and lastly, the HST/STIS spectra were obtained contemporaneously with SPICAV-IR stellar occultation spectra used to obtain an accurate measure of the upper boundary of the CO2 clouds (as well as the large aerosol haze layer) in Venus atmosphere at the time of observation. Because only HST/STIS can uniquely define the both the SO2 and SO gas signatures in the UV, the coordination of the HST and VEx observations allowed for a unique definition of the aerosol properties, relative to the specific balance of SO and SO2 in the atmosphere at the time of observation. Because SO is formed via the photolysis of SO2, these types of measurements provide the data needed to assess how photochemistry influences the formation of the H2SO4 aerosol which is strongly linked to the SOx balance in the atmosphere. The SOx gas densities derived from the coincidentally obtained HST/STIS and Venus Express observations provide a detailed picture of the latitudinal, longitudinal, time of day, and wind-driven variation of several of the key species involved in the sulfur-oxidation cycle. The results derived from these observations are being used to inform and develop models designed to i) investigate outstanding questions regarding the formation of Venus global sulfuric acid (H2SO4) clouds and the abundance of oxygen in the atmosphere and ii) investigate the climatic evolution of Venus atmosphere. Additionally, the HST/STIS observations obtained in December 2010 and January 2011 serve as a complement to the high-spatial, low-spectral (1.5 nm) resolution nadir viewing SPICAV-UV spectra obtained (Macrq et al. 2013) throughout the lifetime of the Venus Express mission. We will present an overview of the coordinated 2010 and 2011 observations, the key results derived from the coordinated observations, and an overview of how the coordinate observation results relate to the long-term average SO2 gas density values obtained by Venus Express during the lifetime of the mission. We will also discuss our observation goals for the 2015-2019, and how the acquisition of new Hubble observations in this time period can further expand the science return of the ground-based and spaced-based data obtained during the Venus express mission, including the coordinated observations obtained in 2010 and 2011.

Graziela Keller: IAG/Universidade de Sao Paulo

HST/STIS UV Spectroscopy of GALEX-Selected Hot White Dwarfs

We have obtained UV HST/STIS G140L+G230L (1150-3100 Ċ) spectroscopy (cycle 21, program 13397 - P.I. Bianchi) of a benchmark sample of 14 hot white dwarfs (WD), 11 of which in binary systems with a cooler companion. Targets were selected from an unbiased census of hot WDs from clean catalogs of GALEX UV sources (Bianchi et al. 2014 J.ASR 53, 900) cross-matched to SDSS optical data, among candidates in low extinction sightlines and having also SDSS optical spectra. The UV spectra constrain temperature and extinction concurrently and allow for the WD parameters to be derived accurately. In the binary systems, the analysis of UV and optical spectra enables derivation of parameters for both components, allowing a distance estimate for the pair and the accurate placement of the hot WDs on the post-AGB tracks.

Adam Kowalski: University of Maryland and NASA/GSFC

New HST/COS Observations of Flares on the M Dwarf GJ 1243

A large amount of the radiated energy during solar and stellar flares is emitted as white-light continuum emission, extending through the ultraviolet and optical wavelength regimes. Broadband photometry and optical spectral observations of M dwarf flares suggest that the white-light peak is located in the near-ultraviolet wavelength regime similar to a blackbody with T: 10,000 K, whereas radiative-hydrodynamic models using a solar-type flare heating mechanism (nonthermal electrons with a flux of 10^11 erg / s / cm^2 accelerated in the corona) predict that the peak lies at redder wavelengths at the head of the Balmer continuum. We have completed a successful flare monitoring campaign on the dM4e star GJ 1243, in order to constrain the time-evolution of the peak of the white-light continuum. The campaign took place over 12 hours on Aug 31/Sept 1, 2014, and included optical monitoring from nine ground-based telescopes as the Hubble Space Telescope recorded time-tagged spectra in the near-ultraviolet (2450-2840 Ċ) with the Cosmic Origins Spectrograph. Two flares occurred during the HST observations, and we show preliminary results relating the continuum and line (Fe II and Mg II) emission to the simultaneous ground-based optical spectra and photometry. This dataset provides new constraints for radiative-hydrodynamic modeling of the lower flaring atmosphere and can be compared to spectral observations of solar flares with the recently launched IRIS instrument. I will also discuss how NUV flare spectra can be used to better understand the effects of flares on biomarkers that will be observed with the James Webb Space Telescope.

Peter Kurczynski: Rutgers, The State University of New Jersey

Sizing Up Dwarf Galaxies at z > 1: UV Colors, Stellar Masses and Star Formation Rates

Deep HST imaging allows the detection and study of dwarf galaxies at z > 1. Our recent multiwavelength analyses of continuum and Ly-alpha selected galaxies in the Hubble UltraDeep Field (HUDF) and CANDELS fields reveals a diversity of physical properties. We show that these galaxies are on the whole bluer than comparable luminosity galaxies in the local universe, although they are as diverse in their UV colors as local dwarf galaxies (Kurczynski et al. 2014, ApJL 793 5). On the SFR-M* diagram, Ly-alpha selected galaxies fall above the main sequence, implying bursty star formation (Vargas et al 2014, ApJ 783 26). In this presentation, we illustrate that low luminosity continuum selected galaxies appear to lie on the main sequence, suggesting a more quiescent evolution. The systematic study of low luminosity galaxies spanning the epoch of peak cosmic star formation will elucidate the mechanisms of formation and evolution for the bulk of the present day galaxy population.

Laurent Lamy: LESIA, Observatoire de Paris

The Auroral Planetary Imaging and Spectroscopy (APIS) Service

The Auroral Planetary Imaging and Spectroscopy (APIS) service, accessible online, provides an open access to processed auroral observations of the outer planets and their satellites. Such observations are of interest for a wide community at the interface between planetology, magnetospheric and heliospheric physics. APIS consists of (i) a high level database, so far based on almost all planetary auroral observations acquired by the Hubble Space Telescope (HST) since 1997 with its mostly used Far-UltraViolet spectro-imagers, (ii) a dedicated search interface aimed at browsing efficiently the database through relevant conditional search criteria and (iii) the ability to interactively work with the data online through plotting tools developed by the Virtual Observatory (VO) community, such as Aladin and Specview. This service is VO compliant and can therefore also been queried by external search tools of the VO community. The diversity of available data and the capability to sort them out by relevant physical criteria shall in particular facilitate statistical studies, on long-term scales and/or multi-instrumental multi-spectral combined analysis.

John MacKenty: Space Telescope Science Institute

Design, Operation, and Evolution of Wide Field Camera 3

The Wide Field Camera 3 is built upon and extends the capabilities of HST's imaging instruments. We review the key scientific objectives that drove its design and discuss how these have played out in flight. Beyond the many expected applications, WFC3 has accomplished forefront science in directions not anticipated during its design. For example, spatial scans are enabling extremely high precision spectrophotometric measurements of exoplanet transits and astrometric measurements of parallax which significantly surpass the capabilities of the HST Fine Guidance Sensors. We discuss future expected performance, enhancements to its calibration and data processing tools, and lessons and implications for future missions including JWST and WFIRST. Of particular interest is the substantial use of the slitless spectroscopic modes and ongoing efforts to create improved software tools to best utilize these data.

Simona Mei: GEPI-L'Observatoire de Paris/Université Paris Diderot

Galaxy Cluster Science with HST in 2020

Galaxy clusters and proto-clusters are unique environments for galaxy formation and cosmological studies. The next generation of wide-field infrared space missions, such as WFIRST and Euclid, will permit us to detect and characterize thousands of these massive objects, through both imaging and grism spectroscopy, and to examine their galaxy properties with powerful integral field units. HST observations of clusters at z>1.5 permit us to prepare this promising science, with both HST/WFC3 grism spectroscopy detections and follow-up of high redshift cluster candidates detected with the Spitzer space telescope. We will present our new high redshift (z >1.5) cluster and protocluster detections in the HST CDF-S, CANDELS and SPT Spitzer Deep Field, using deep observations with Spitzer, the HST/WFC3 grism spectroscopy (Mei et al. 2014; Licitra et al., in preparation) and VLT/KMOS IFU spectroscopy (Mei et al., in preparation; Licitra et al., in preparation).

Takahiro Morishita: Tohoku University

From Diversity to Dichotomy, and Quenching: Milky-Way-Like and Massive-Galaxy Progenitors at 0.5 < z < 3.0

I will present our recent study on the stellar mass accumulation of the progenitors of the Milky Way (MWs) and massive galaxy (MGs). Using the HST/WFC3 and ACS multi-band imaging data taken in CANDELS and 3D-HST survey, we investigated the general properties and the diversity of MWs and MGs at 0.5

Erica Nelson: Yale University

Spatially resolved HST grism Halpha maps of 2000 galaxies at z~1: Evidence for the inside-out formation of disk galaxies

Imaging surveys with HST have demonstrated that many galaxies attained their current forms at z~1. Key to understanding this process is a direct measurement of the distribution of star formation within galaxies at this crucial epoch. This is now possible with the WFC3 grism capability on HST, as it provides Hα maps of all galaxies at 0.7

Paulo Penteado: Northern Arizona University

Deep Field TNO Colors with the HST Frontier Fields

The HST Frontier Fields observations, designed to obtain extremely deep multi-filter images of galaxy clusters and blank fields, also present a unique opportunity to probe the outer Solar System, by studying the faintest observable Trans Neptunian Objects (TNOs). Currently, only: 1000 such objects are known, and almost all our knowledge of this region is derived from the largest TNOs (100-300 km). Previous studies of the smallest and faintest TNOs have indicated different size distributions for high and low inclination objects ("hot" and "cold" populations), and a break in the size distribution at magnitude R>25, which has been interpreted as a result of their collisional evolution. Currently, none of the faintest objects have known colors, which would provide a crucial constraint to their origin and evolution. TNOs are likely to pass through Frontier Fields pointings - especially those close to the ecliptic plane - and we are harvesting those serendipitous observations to constrain the evolution of the outer Solar System. We are processing the HST Frontier Fields observations to find faint TNOs and measure their color distribution. We are probing dynamically hot objects smaller than the break in the TNO size distribution. By comparing the color distribution of objects larger and smaller than the break, we will test whether the break in the size distribution of hot objects is collisional, and if the bluer colors of this population are primordial. This is an ongoing project (HST-AR-13247; PI Fuentes), and we will present the first results from the first Frontier Fields we analyzed.

Andrea Prestwich: Harvard-Smithsonian Center for Astrophysics

Hubble and Luminous X-ray Binaries in Starburst Galaxies

High resolution X-ray images of star forming galaxies are spectacular, showing a multitude of luminous X-ray binaries (XRB). Hubble observations place crucial constraints on the formation and evolution of XRB, including potential Intermediate Mass Black Holes which may be the "seeds" from which AGN form. In nearby galaxies Hubble can resolve the stellar population in the vicinity of the ULX allowing the star formation history of the ULX local environment to be determined. This provides important constraints on the age of the ULX. It is sometimes possible determine the stellar type of the donor star - a crucial component of XRB models. Some ULX appear to be spatially co-incident with star clusters, while others are apparently associated with clusters but slightly offset from the cluster core. These studies suggest that some XRB are formed in clusters and are subsequently ejected. Finally, Hubble and Chandra observations show that some of the most luminous XRB in dwarf starbursts are coincident with massive star clusters and may be Intermediate Mass Black Holes and the "seed" black holes from which AGN form.

Marc Rafelski: Goddard NPP Fellow

Ultraviolet Through Near-infrared HST Imaging and Photometric Redshifts of Galaxies in the Hubble Ultra Deep Field

We present Hubble Space Telescope near-ultraviolet (NUV) observations of the Hubble Ultra Deep Field (UDF). Photometry and redshifts are derived from eleven HST bandpasses covering an observed wavelength range from the NUV to the near-infrared (NIR). Our NUV images use new dark calibrations to minimize background gradients and pattern noise. Our NIR images combine the UDF09, UDF12, and CANDELS data to provide coverage for the entire UDF field of view. We measure photometric redshifts sampling both the Lyman break and Balmer break of galaxies at z~0.8-3.4, and one of the breaks over the rest of the redshift range. Our comparison of these results with a compilation of robust spectroscopic redshifts shows an improvement in the galaxy photometric redshifts by a factor of two in scatter and a factor three in outlier fraction over previous UDF catalogs. The inclusion of the new NUV data is responsible for a factor of two decrease in the outlier fraction compared to redshifts determined from only the optical and NIR data, and improves the scatter at z<0.5 and at z>2. The panchromatic coverage of the UDF from the NUV through the NIR yields robust photometric redshifts of the UDF, with the lowest outlier fraction available.

Aki Roberge: NASA Goddard Space Flight Center

Hubble's View on Gas in Debris Disks

Debris disks are often described as gas-free. Compared to protoplanetary disks, they do in general have low gas abundances, as evidenced by the very few detections of sub-mm CO emission from bona fide debris disks to date. However, some debris disks do contain low levels of detectable gas, typically seen in absorption against the stellar spectrum at UV and optical wavelengths. UV spectroscopy in particular, mostly provided by HST, reveals valuable information on the gas composition and origin that is difficult to obtain any other way. Here we summarize that information for two of the best studied debris disks - Beta Pic and 49 Ceti - and describe prospects for future studies of debris gas in the ALMA era.

Kailash Sahu: STScI

Detecting Isolated, Stellar-Mass Black Holes through Astrometric Microlensing Using HST

All stars with initial masses of larger than 20 solar mass are expected to end their lives as black holes. Yet, not a single isolated black hole has been unambiguously detected in the Galaxy. Astrometric microlensing is the only available technique capable of detecting isolated black holes and measuring their masses. I will discuss the technique of astrometric microlensing, and two HST programs that we have undertaken, aimed at the first detections of isolated, stellar-mass black holes through this technique. I will present the first results from these two programs.

Claudia Scarlata: University of Minnesota

The WISP Survey: Overview and Recent Results

The WFC3 Infrared Spectroscopic Parallel Survey (WISP) is a large: 1000orbit program that uses WFC3 slitless spectroscopy to detect thousands of galaxies across a wide redshift range. WISP is unique in using both WFC3 grisms, probing the full 0.8-1.6mic wavelength range over hundreds of uncorrelated independent fields, and overcoming the cosmic variance that mostly impacts the studies of the most-massive and brightest galaxies. I will present the WISP survey and an overview of new and recent results, including: 1) evolution of the passive galaxy population to z~1.5, and implications for their size-growth with time; 2) evolution of the mass-metallicity relation in star forming galaxies down to stellar masses of a few 10^8 Msun, up to z~2.3; 3) limits on the number density of bright Lyman-alpha emitters, during the end of the reionization epoch (z~7).

Glenn Schneider: The University of Arizona

Space-Based Optical/Near-IR Coronagraphy with HST and Beyond

Over the past two decades, HST and its suite of optical/near-IR coronagraphic imagers have played a seminal and foundational role in the discovery and study of circumstellar (CS) starlight-scattering materials of all size scales, from sub-micron dust particles to giant planets. Prior to the advent of space-based coronagraphy as implemented with HST, with the sole exception of the exceptionally bright, close-proximity and angularly large debris disk about Beta Pictoris, the overwhelming glare of the host-star light proved an insurmountable challenge to the detection and characterization of light scattering materials in exoplanetray environments. Subsequently, the symbiotic high contrast imaging capabilities of HST's coronagraphs have provided a means to map out and characterize potentially planet-hosting CS environments across the posited epochs of exoplanetary system formation, evolution and maturity. In addition to direct detection of giant exoplanets this includes disk/planetesimal/planet studies of: (1) physical properties of icy (or dry) grains in proptoplanetary and transitional disks, (b) second-generation debris dust in older systems possibly replenished in disks through systemic lifetimes, (c) collisional and other dust-production events, (d) dynamical sculpting of CS material by perturbations (asymmetries) in dust distributions from unseen planets, (e) other forces acting upon the systems, (f) planet presence (or absence) through inferred disk/planet interactions, and (g) sub-structures that may inform on planet formation/migration and systemic architectures. Herein we review the key events, discoveries, and capabilities (including observational and data reduction/analysis methods) informing exoplanetary science via HST coronagraphy. We highlight the most recent successes and the HST uniqueness space to end-of-mission. Importantly, we draw from, and discuss lessons learned for future advancements beyond HST with coronagraphically-augmented space missions such as JWST and WFIRST/AFTA that will build upon the HST legacy and are symbiotic with the new and next generation of ground-based AO and other instrumental systems.

Karl Stapelfeldt: NASA GSFC

HST Imaging of Young Circumstellar Disks

Several hundred young circumstellar disks have been targeted for HST scattered light imaging over the life of the mission. Most are undetected due to small radii, self-shadowing, or the limited contrast capabilities of HST instruments. Nevertheless several dozen have been imaged, most prominently in edge-on systems where the disk itself serves to occult bright starlight. In these systems disk vertical flaring is directly observed, dust properties have been derived and show clear evidence for grains larger than in the ISM, and variable illumination patterns tracing inner disk properties have been observed. I will review HST's existing legacy of young disk images and suggest what might still be accomplished in the years ahead.

David Thilker: Johns Hopkins University

The Controversial Nature of Diffuse UV Emission in Star-Forming Galaxies

It remains difficult to reliably measure star formation within galaxies using dust-corrected UV light, owing to the local variations in stellar population and dust properties. The UV should be a direct tracer of young stellar populations and recent star formation, yet UV colors in the 'diffuse' interarm regions of spiral galaxies are unusually red relative to those of spiral arms, even after accounting for estimated dust attenuation. This suggests a complex mix of moderately aged stars and dust, plus perhaps scattered light. We are conducting a Cycle 22 HST (PID 13743) investigation to unveil the origin of those UV colors with new ACS/SBC far-UV (FUV) and WFC3 near-UV (NUV) images and archival B, V, I data of the nearby, prototypical spiral NGC300. By exploiting the dust-insensitivity of the HST FUV-NUV color for resolved stars and subsequent SED-fitting, we will obtain a census of both O and B stars in order to: (1) uncover the nature of the UV-emitting interarm stellar populations, while estimating the true diffuse fraction; (2) constrain the extinction law in both interarm+arm regions; (3) place UV-based SFR indicators on a secure footing for use both at low and high redshift. By directly addressing the use and limitations of UV colors to trace young stellar populations and dust attenuation in galaxies, this project maximizes the return from the large investment of HST time devoted to high-z surveys. For this contribution, we will contrast our results for the inner disk of NGC300 with similar work on the sparsely populated, extended UV disk (XUV-disk) of M83.

Harley Thronson: NASA GSFC

Building On the HST Legacy with the Next Leap Forward in UVOIR Space Astronomy: The ATLAST Reference Design

Our joint NASA GSFC/MSFC/STScI/JPL study team used community-developed science goals to derive mission needs and reference mission architectures for a future large-aperture UVOIR space observatory: the Advanced Technology Large-Aperture Space Telescope (ATLAST). Conceptual designs have been developed for non-cryogenic, segmented telescopes capable of carrying out a variety of scientific programs in the 0.09 – 2.5 μm range operating in a Sun-Earth L2 orbit, which provides a stable thermal environment and excellent field of regard. Our most-detailed reference design is for a 36-segment 10 m-class telescope that stows within a five-meter diameter launch vehicle fairing. Our basic design is compatible with three different launch vehicles, which mitigates programmatic risk. The telescope and instruments are dynamically isolated from spacecraft disturbance sources and the secondary mirror is actively controlled. Our team is assessing larger apertures and long lifetimes that would be made possible by the availability of an SLS vehicle and/or on-orbit assembly, servicing, and upgrade. We describe the assessment we are conducting on the requirements of system thermal and dynamic stability that support: 10-10 starlight suppression necessary to achieve some of the most challenging scientific goals of the coming decades.

Monica Tosi: INAF - Bologna Observatory

The Star Formation History of the Very Metal-Poor Star-Forming Galaxy DDO 68

According to hierarchical formation, dwarf galaxies are the first systems to collapse and start forming stars. In this scenario, present-day dwarfs are expected to host the most ancient stellar populations. However, the most metal-poor dwarf star-forming galaxies, with their high gas content, blue colors, and low metallicities, have been repeatedly pointed out as good candidate "primeval" galaxies in the nearby Universe. Studies of their star formation histories (SFHs) based on deep color-magnitude diagrams (CMDs) with HST are fundamental to test the possibility of "truly" young galaxies in the present-day Universe. In this respect DDO 68, which holds the same record low metallicity (12 + log(O/H)=7.15) as the long-standing controversial case of I Zw 18, is an ideal target, being a factor of 2 closer in distance than I Zw 18. We present the SFH of DDO 68 obtained through the comparison of deep V and I-band HST/ACS photometry with synthetic CMDs. A statistical analysis was implemented for the identification of the best-fit SFH and relative uncertainties. We show that DDO 68 is not a truly young galaxy, having started forming stars at epochs possibly as old as a Hubble time. This kind of studies will greatly benefit from the advent of JWST and E-ELT, that will allow to resolve both young and old stellar populations in dwarfs out to the distance of the Virgo cluster (~ 15 Mpc).

Stephen Unwin: JPL/Caltech

Exoplanet Exploration Program – Support for Future Missions

The objective of Exoplanet Exploration Program (ExEP) is to implement the NASA space science goals of detecting and characterizing exoplanets and to search for signs of life. ExEP manages space missions, future studies, technology investments, and ground-­‐based science that completes mission science or enables future missions. In this paper, we highlight the technology investments. The Program engages the exoplanet science community through the ExoPAG, and STDTs for probe-­‐scale mission concepts. ExEP includes Kepler, K2, and WFIRST-­AFTA. WFIRST represents a major investment that includes dark energy science, a wide-­field infrared survey, a microlensing survey for outer-­exoplanet demographics, and a coronagraph for direct imaging of large around nearby stars. Program elements also include follow-­up observations using the Keck Observatory that contribute to the science yield of Kepler and K2, and mid-­IR observations of exo-­‐zodiacal dust by LBTI. These provide critical input to the design and predicted science yield of the next generation of direct imaging missions. ExEP includes NexScI, which provides archives, tools, and professional education for the exoplanet community. All of these elements contribute to the goal of detecting and characterizing exoplanets. The Program seeks to respond to rapid evolution in this discovery-­driven field and to ongoing programmatic challenges through engagement of the scientific and technical communities. This paper focuses on technologies supported by ExEP for future large exoplanet imaging missions. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Copyright 2015. California Institute of Technology. Government sponsorship acknowledged.

Nolan R. Walborn: STScI

Revealing the Structure and Dynamics of the Winds of Magnetized O-Type Stars Through UV Spectroscopy with the Hubble Space Telescope

UV resonance line profiles are key diagnostics of circumstellar material surrounding O-type stars. For non-magnetic stars, P Cygni profiles of UV resonance lines are the classic signature of their supersonic, radiation-driven winds. However, in exotic magnetic O stars the radial wind outflow is strongly perturbed by the presence of the field, forming a structured, dynamic magnetosphere. Although recent observational investigations exploiting optical spectroscopy and spectropolarimetry have advanced our understanding of the winds of magnetized O stars significantly, basic conflicts with the predictions of radiation magnetohydrodynamic (MHD) simulations remain - conflicts that require UV data to be resolved. Systematic HST UV spectroscopy of the rare magnetic Of?p stars has revealed a variety of surprising phenomena, leading to new insights concerning the kinematics and ionization structure of their winds and magnetospheres. Since 2011 we have obtained (or are currently obtaining) STIS and COS observations of 4 of the 5 known Of?p stars in the Galaxy: HD 108, HD 191612, CPD -28 2561 and NGC 1624-2. In this talk we present a summary of the results of these investigations, including a sneak peek at remarkable first results for CPD -28 2561 and NGC 1624-2 - the latter being the most strongly magnetized O-type star currently known.

Bradley Whitmore: STScI

The Hubble Data Archives: Past and Future

Since the beginning of the mission, the Hubble archives has revolutionized the way astronomers do science. Twenty five years ago an astronomer would have to go to the telescope themselves. With the advent of the Hubble archive, suddenly astronomers had access to all Hubble data (after the 1 year proprietary time), the data was already calibrated (greatly reducing redundant work and enhancing uniformity), and the data was shipped to them at their home institution. But that was just the beginning. Over the years both the storage medium (tapes to internet) and products (raw data to high level science products) have changed drastically. As importantly, the tools for accessing the data have evolved. The importance of the Hubble archives has grown with time, with more than half of the paper written using Hubble data now coming from the archives. With the advent of the internet, a whole new set of capabilities and opportunities became possible. This talk will highlight three examples: the Hubble Legacy Archive - (http://hla.stsci.edu), the Hubble Source Catalog - (http://archive.stsci.edu/hst/hsc), and the MAST Discovery Portal - (http://mast.stsci.edu/explore). Using these facilities, we are only now beginning to realize the true potential of the Hubble archives, both for the present, and for decades into the future.

Rogier Windhorst: Arizona State University-School of Earth & Space Exploration

HST Observations of Escaping Lyman Continuum Radiation from Galaxies and Weak AGN at z=2.3--6: (How) Did they Reionize the Universe?

We present tentative detections of the redshift-dependent amount of Lyman Continuum (LyC) radiation escaping from galaxies with reliably measured spectroscopic redshifts at 2.3 < z < 6. For this, we analyzed reprocessed Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS) mosaics of the Early Release Science (ERS) field in four filters that sample LyC over this redshift range. Hubble's WFC3 UV-channel was specifically designed for experiments like this. With our best current assessment of the WFC3 systematics, we find that the LyC emission of faint galaxies at =2.37, 2.65, 3.45, and 5.23 is detected at the >2.2--4 sigma level, on average, in typical image stacks of 11-40 objects in the WFC3/UVIS F225W, F275W, F336W, and ACS/WFC F435W filters, respectively. The LyC flux of weak AGN are detected at similar levels, but with fewer objects. The measured signal corresponds to total LyC fluxes of 29 < AB < 30.5 mag. With SED-fitting of the UV-continuum longwards of Lya, the observed flux corresponds to an average LyC escape fraction of order f_esc = 4--23% in these four redshift bins, respectively. Our results suggest that faint galaxies collectively, and to some extent also weak AGN, may have measurably contributed to maintaining cosmic reionization at redshifts 2.3 < z < 6, although their average LyC escape fractions are relatively low. The available data is consistent with a possible trend of f_esc = (0.021+/-0.008) x (1+z)^{1.0+/-0.5}. Complete reionization at z=6--7 may additionally require: a steep faint-end of the galaxy luminosity function at higher redshifts, integration to very faint luminosities (M > -14 AB-mag), and possibly also that f_esc increases at fainter luminosities and/or lower metallicities at higher redshifts than sampled here.