14396627
Deep Optical Photometry of Six Fields in the Andromeda Galaxy
Using the Advanced Camera for Surveys on the Hubble Space Telescope, we have obtained deep optical images reaching well below the oldest main-sequence turnoff in six fields of the Andromeda Galaxy. The fields fall at four positions on the southeast minor axis, one position in the giant stellar stream, and one position on the northeast major axis. These data were obtained as part of three large observing programs designed to probe the star formation history of the stellar population in various structures of the galaxy. In this paper, we present the images, catalogs, and artificial star tests for these observing programs as a supplement to the analyses published previously. These high-level science products are also archived at the Multimission Archive at the Space Telescope Science Institute.
67759178
THE FIRST DETECTION OF BLUE STRAGGLER STARS IN THE MILKY WAY BULGE
We report the first detections of Blue Straggler Stars (BSS) in the bulge of the Milky Way. Proper motions from extensive space-based observations along a single sight line allow us to separate a sufficiently clean and well-characterized bulge sample such that we are able to detect a small population of bulge objects in the region of the color-magnitude diagram commonly occupied by young objects and blue stragglers. Variability measurements of these objects clearly establish that a fraction of them are blue stragglers. Out of the 42 objects found in this region of the color-magnitude diagram, we estimate that at least 18 are genuine BSS. We normalize the BSS population by our estimate of the number of horizontal branch stars in the bulge in order to compare the bulge to other stellar systems. The BSS fraction is clearly discrepant from that found in stellar clusters. The blue straggler population of dwarf spheroidals remains a subject of debate; some authors claim an anticorrelation between the normalized blue straggler fraction and integrated light. If this trend is real, then the bulge may extend it by three orders of magnitude in mass. Conversely, we find that the genuinely young (<5 Gyr) population in the bulge, must be at most 3.4% under the most conservative scenario for the BSS population.
119330474
100 Times Faster and 3 Times Sharper: Background-Dominated Observations of Stellar Populations with an 8-meter Optical-UV Space Telescope
An 8 m successor to the Hubble Space Telescope (HST) would make incredible gains in the study of stellar populations, especially in the Local Group. If diffraction-limited at 0.5 microns, the "Next HST" could produce high-resolution imaging of faint sources over a wide field in 1 percent of the time needed with the HST. With these capabilities, photometry of the ancient main sequence could be obtained for many sight-lines through Local Group galaxies, thus determining directly the ages of their structures and providing a formation history for the Local Group populations.
14120815
The Star Formation History in the Andromeda Halo
I present the preliminary results of a program to measure the star formation history in the halo of the Andromeda galaxy. Using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope, we obtained the deepest optical images of the sky to date, in a field on the southeast minor axis of Andromeda, 51 arcmin (11 kpc) from the nucleus. The resulting color-magnitude diagram (CMD) contains approximately 300,000 stars and extends more than 1.5 mag below the main sequence turnoff, with 50% completeness at V=30.7 mag. We interpret this CMD using comparisons to ACS observations of five Galactic globular clusters through the same filters, and through chi-squared fitting to a finely-spaced grid of calibrated stellar population models. We find evidence for a major (approximately 30%) intermediate-age (6-8 Gyr) metal-rich ([Fe/H] > -0.5) population in the Andromeda halo, along with a significant old metal-poor population akin to that in the Milky Way halo. The large spread in ages suggests that the Andromeda halo formed as a result of a more violent merging history than that in our own Milky Way.
35491181
A SPECTROSCOPIC SEARCH FOR LEAKING LYMAN CONTINUUM AT z ∼ 0.7*
We present the results of rest-frame, UV slitless spectroscopic observations of a sample of 32 z ~ 0.7 Lyman break galaxy (LBG) analogs in the COSMOS field. The spectroscopic search was performed with the Solar Blind Channel on the Hubble Space Telescope. We report the detection of leaking Lyman continuum (LyC) radiation from an active galactic nucleus-starburst composite. While we find no direct detections of LyC emission in the remainder of our sample, we achieve individual lower limits (3σ) of the observed non-ionizing UV-to-LyC flux density ratios, f -ν (1500 A)/f _ν(830 A) of 20 to 204 (median of 73.5) and 378.7 for the stack. Assuming an intrinsic Lyman break of 3.4 and an intergalactic medium transmission of LyC photons along the line of sight to the galaxy of 85%, we report an upper limit for the relative escape fraction in individual galaxies of 0.02-0.19 and a stacked 3σ upper limit of 0.01. We find no indication of a relative escape fraction near unity as seen in some LBGs at z ~ 3. Our UV spectra achieve the deepest limits to date at any redshift for the escape fraction in individual sources. The contrast between these z ~ 0.7 low escape fraction LBG analogs with z ~ 3 LBGs suggests that either the processes conducive to high f esc are not being selected for in the z 1 samples or the average escape fraction is decreasing from z ~ 3 to z ~ 1. We discuss possible mechanisms that could affect the escape of LyC photons
18506635
THE WFC3 GALACTIC BULGE TREASURY PROGRAM: A FIRST LOOK AT RESOLVED STELLAR POPULATION TOOLS
When the Wide Field Camera 3 (WFC3) is installed on the Hubble Space Telescope (HST), the astronomical community will have access to powerful new capabilities for investigating resolved stellar populations. The WFC3 Galactic Bulge Treasury program will obtain deep imaging in five photometric bands on four low-extinction fields. These data will have no proprietary period, and will enable a variety of science investigations not possible with previous data sets. To aid in planning for the use of these data and for future observing proposals, we provide an introduction to the Treasury program, its photometric system, and the associated calibration effort. The observing strategy is based upon a new photometric system employing five WFC3 bands spanning the UV, optical, and near-infrared: F390W, F555W, F814W, F110W, and F160W (analogous but not identical to the ground-based filters Washington C, V, I, J, and H). With these bands, one can construct reddening-free indices of temperature and metallicity. Using this photometric system, the program will target six fields in well studied star clusters, spanning a wide range of metallicity, and four fields in low-extinction windows of the Galactic bulge. The cluster data serve to calibrate the reddening-free indices, provide empirical population templates, and correct the transformation of theoretical isochrone libraries into the WFC3 photometric system. The bulge data will shed light on the bulge formation history, and will also serve as empirical population templates for other studies. One of the fields includes 12 candidate hosts of extrasolar planets. Color-magnitude diagrams (CMDs) are the most popular tool for analyzing resolved stellar populations. However, due to degeneracies among temperature, metallicity, and reddening in traditional CMDs, it can be difficult to draw robust conclusions from the data. The five-band system used for the bulge Treasury observations will provide reddening-free indices that are roughly orthogonal in temperature and metallicity, and we argue that model fitting in an index-index diagram will make better use of the information than fitting separate CMDs. We provide some results from simulations to show the expected quality of the data and their potential for differentiating between different star formation histories.
122947911
Reaction rate sensitivity of 44Ti production in massive stars and implications of a thick target yield measurement of 40Ca(alpha,gamma)44Ti
We evaluate two dominant nuclear reaction rates and their uncertainties that affect 44Ti production in explosive nucleosynthesis. Experimentally we develop thick target yields for the 40Ca(α, γ)44Ti reaction at E α = 4.13, 4.54, and 5.36 MeV using γ-ray spectroscopy. At the highest beam energy, we also performed an activation measurement which agrees with the thick target result. From the measured yields a stellar reaction rate was developed that is smaller than current statistical-model calculations and recent experimental results, which would suggest lower 44Ti production in scenarios for the α-rich freezeout. Special attention has been paid to assessing realistic uncertainties of stellar reaction rates produced from a combination of experimental and theoretical cross sections. With such methods, we also develop a re-evaluation of the 44Ti(α, p)47V reaction rate. Using these two rates we carry out a sensitivity survey of 44Ti synthesis in eight expansions representing peak temperature and density conditions drawn from a suite of recent supernova explosion models. Our results suggest that the current uncertainty in these two reaction rates could lead to as large an uncertainty in 44Ti synthesis as that produced by different treatments of stellar physics.
14997883
Expected Planet and False Positive Detection Rates for the Transiting Exoplanet Survey Satellite
The proposed Transiting Exoplanet Survey Satellite (TESS) will survey the entire sky to locate the nearest and brightest transiting extrasolar planets with orbital periods up to about 36 days. Here we estimate the number and kind of astrophysical false positives that TESS will report, along with the number of extrasolar planets. These estimates are then used to size the ground-based follow-up observing efforts needed to confirm and characterize the planets. We estimate that the needed observing resources will be about 1400 telescope-nights of imaging with 0.5m to 1m-class telescopes, 300 telescope-nights with 1m to 2m-class telescopes for the classification of the host stars and for radial velocity measurements with roughly 1 km/s precision, and 380 telescope-nights with 2m to 4m-class telescopes for radial velocity studies with precision of a few m/s. Follow-up spectroscopy of the smallest planets discovered by TESS at the best possible velocity precision will be limited by the number of telescope nights available on 4m to 10m class telescopes with instruments such as HARPS and HIRES, but the pay-off of such efforts will be the determination of masses for Super Earths with sufficient accuracy to distinguish rocky desert planets from water worlds.
15724697
The Hubble Deep Field South - STIS imaging
We present the imaging observations made with the Space Telescope Imaging Spectrograph (STIS) of the Hubble Deep Field South. The field was imaged in four bandpasses: a clear CCD bandpass for 156 ks, a long-pass filter for 22–25 ks pixel-1 typical exposure, a near-UV bandpass for 23 ks, and a far-UV bandpass for 52 ks. The clear, visible image is the deepest observation ever made in the UV-optical wavelength region, reaching a 10 σ AB magnitude of 29.4 for an object of area 0.2 arcsec2. The field contains QSO J2233-606, the target of the STIS spectroscopy, and extends 50'' × 50'' for the visible images, and 25'' × 25'' for the ultraviolet images. We present the images, catalog of objects, and galaxy counts obtained in the field.
118405817
Stellar ages through the corners of the boxy bulge
Aims: In some scenarios for the formation of the Milky Way bulge, the stellar population at the edges of the boxy bulge may be younger than those on the minor axis or close to the Galactic center. So far the only bulge region where deep color-magnitude diagrams have been obtained is indeed along the minor axis. To overcome this limitation, we aim to age-date the bulge stellar populations far away from the bulge minor axis. 
Methods: Color-magnitude diagrams and luminosity functions have been obtained from deep near-IR VLT/HAWK-I images taken at the two Southern corners of the boxy bulge, i.e., near the opposite edges of the Galactic bar. The foreground disk contamination has been statistically removed using a pure disk field observed with the same instrument and located approximately at similar Galactic latitudes of the two bulge fields and ~30° in longitude away from the Galactic center. For each bulge field, mean reddening and distance are determined using the position of red clump stars, and the metallicity distribution is derived photometrically using the color distribution of stars in the upper red giant branch. 
Results: The resulting metallicity distribution function of both fields peaks around [Fe/H] ~ -0.1 dex, with the bulk of the stellar population having a metallicity within the range: -1 dex ≲ [Fe/H] ≲ +0.4 dex, quite similar to that of other inner bulge fields. As for the previously explored inner fields, the color-magnitude diagrams of the two bar fields are consistent with their stellar population being older than ~10 Gyr, with no obvious evidence of younger population. 
Conclusions: The stellar population of the corners of the boxy bulge appears to be coeval with those within the innermost ~4° from the Galactic center. 
Based on data taken at the ESO/VLT Telescope, within the observing program 081.B-0489(A).The derived photometric catalogs are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/559/A98
119293956
The Kepler Asteroseismic Investigation: Scientific goals and first results
Kepler is a NASA mission designed to detect exoplanets and characterize the properties of exoplanetary systems. Kepler also includes an asteroseismic programme which is being conducted through the Kepler Asteroseismic Science Consortium (KASC), whose 400 members are organized into 13 working groups by type of variable star. So far data have been available from the first 7 month of the mission containing a total of 2937 targets observed at a 1-min cadence for periods between 10 days and 7 months. The goals of the asteroseismic part of the Kepler project is to perform detailed studies of stellar interiors. The first results of the asteroseismic analysis are orders of magnitude better than seen before, and this bodes well for how the future analysis of Kepler data for many types of stars will impact our general understanding of stellar structure and evolution (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)