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 е) 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 S
