118553175
Photometric Variability in Kepler Target Stars. II. An Overview of Amplitude, Periodicity, and Rotation in First Quarter Data
We provide an overview of stellar variability in the first quarter data from the Kepler mission. The intent of this paper is to examine the entire sample of over 150,000 target stars for periodic behavior in their light curves and relate this to stellar characteristics. This data set constitutes an unprecedented study of stellar variability given its great precision and complete time coverage (with a half hour cadence). Because the full Kepler pipeline is not currently suitable for a study of stellar variability of this sort, we describe our procedures for treating the raw pipeline data. About half of the total sample exhibits convincing periodic variability up to two weeks, with amplitudes ranging from differential intensity changes of less than 10?4 up to more than 10%. K and M dwarfs have a greater fraction of period behavior than G dwarfs. The giants in the sample have distinctive quasi-periodic behavior, but are not periodic in the way we define it. Not all periodicities are due to rotation, and the most significant period is not necessarily the rotation period. We discuss properties of the light curves, and in particular look at a sample of very clearly periodic G dwarfs. It is clear that a large number of them do vary because of rotation and starspots, but it will take further analysis to fully exploit this.
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)
9685561
Hubble Space Telescope and Ground-based Optical and Ultraviolet Observations of GRB 010222
We report on Hubble Space Telescope (HST) Wide Field Planetary Camera 2 optical and Space Telescope Imaging Spectrograph (STIS) near-ultraviolet MAMA observations and ground-based optical observations of GRB 010222, spanning 15 hr to 71 days. The observations are well described by a relativistic blast wave model with a hard electron energy distribution, p = 1.57, and a jet transition at t* = 0.93 days. These values are slightly larger than previously found as a result of a correction for the contribution from the host galaxy to the late-time ground-based observations and the larger temporal baseline provided by the HST observations. The host galaxy is found to contain a very compact core (size <025), which coincides with the position of the optical transient. The STIS near-ultraviolet MAMA observations allow for an investigation of the extinction properties along the line of sight to GRB 010222. We find that the far-ultraviolet curvature component c4 is rather large. In combination with the low optical extinction, AV = 0.110 mag, when compared with the hydrogen column inferred from X-ray observations, we suggest that this is evidence for dust destruction.
119288725
Observational detection of eclipses of J5 Amalthea by the Galilean satellites
Aims. We carried out observations of the small jovian satellite Amalthea (J5) as it was being eclipsed by the Galilean satellites near the 2009 equinox of Jupiter in order to apply the technique of mutual event photometry to the astrometric determination of this satellite’s position. Methods. The observations were carried out during the period 06/2009−09/2009 from the island of Maui, Hawaii and Siding Spring, Australia with the 2m Faulkes Telescopes North and South respectively. We observed in the near-infrared part of the spectrum using a PanStarrs-Z filter with Jupiter near the edge of the field in order to mitigate against the glare from the planet. Frames were acquired at rates >1/min during eclipse times predicted using recent JPL ephemerides for the satellites. Following subtraction of the sky background from these frames, differential aperture photometry was carried out on Amalthea and a nearby field star. Results. We have obtained three lightcurves which show a clear drop in the flux from Amalthea, indicating that an eclipse took place as predicted. These were model-fitted to yield best estimates of the time of maximum flux drop and the impact parameter. These are consistent with Amalthea’s ephemeris but indicate that Amalthea is slightly ahead of, and closer to Jupiter than, its predicted position by approximately half the ephemeris uncertainty in these directions. We argue that a ground-based campaign of higher-cadence photometry accurate at the 5% level or better during the next season of eclipses in 2014-15 should yield positions to within 0. �� 05 and affect a corresponding improvement in Amalthea’s ephemeris.
118530564
DISCOVERY OF A RED GIANT WITH SOLAR-LIKE OSCILLATIONS IN AN ECLIPSING BINARY SYSTEM FROM KEPLER SPACE-BASED PHOTOMETRY
Oscillating stars in binary systems are among the most interesting stellar laboratories, as these can provide information on the stellar parameters and stellar internal structures. Here we present a red giant with solar-like oscillations in an eclipsing binary observed with the NASA Kepler satellite. We compute stellar parameters of the red giant from spectra and the asteroseismic mass and radius from the oscillations. Although only one eclipse has been observed so far, we can already determine that the secondary is a main-sequence F star in an eccentric orbit with a semi-major axis larger than 0.5 AU and orbital period longer than 75 days.
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.
15423004
Halos of Spiral Galaxies. II. Halo Metallicity-Luminosity Relation*
Using the Hubble Space Telescope, we have resolved individual red giant branch stars in the halos of eight nearby spiral galaxies. The fields lie at projected distances between 2 and 13 kpc along the galaxies' minor axes. The data set allows a first look at the systematic trends in halo stellar populations. We have found that bright galaxies tend to have broad red giant branch star color distributions with redder mean colors, suggesting that the heavy-element abundance spread increases with the parent galaxy luminosity. The mean metallicity of the stellar halo, estimated using the mean colors of red giant branch stars, correlates with the parent galaxy luminosity. The metallicity of the Milky Way halo falls nearly 1 dex below this luminosity-metallicity relation, suggesting that the halo of the Galaxy is more the exception than the rule for spiral galaxies; i.e., massive spirals with metal-poor halos are unusual. The luminosity-halo stellar abundance relation is consistent with the scaling relation expected for stellar systems embedded in dominant halos, suggesting that the bulk of the halo stellar population may have formed in situ.
119296037
HST/ACS Observations of RR Lyrae Stars in Six Ultra-Deep Fields of M31
We present HST/ACS observations of RR Lyrae variable stars in six ultra-deep fields of the Andromeda galaxy (M31), including parts of the halo, disk, and giant stellar stream. Past work on the RR Lyrae stars in M31 has focused on various aspects of the stellar populations that make up the galaxy's halo, including their distances and metallicities. This study builds upon this previous work by increasing the spatial coverage (something that has been lacking in previous studies) and by searching for these variable stars in constituents of the galaxy not yet explored. Besides the 55 RR Lyrae stars we found in our initial field located 11 kpc from the galactic nucleus, we find additional RR Lyrae stars in four of the remaining five ultra-deep fields as follows: 21 in the disk, 24 in the giant stellar stream, three in the halo field 21 kpc from the galactic nucleus, and five in one of the halo fields at 35 kpc. No RR Lyrae stars were found in the second halo field at 35 kpc. The RR Lyrae populations of these fields appear to be mostly of Oosterhoff I type, although the 11 kpc field appears to be intermediate or mixed. We will discuss the properties of these stars including period and reddening distributions. We calculate metallicities and distances for the stars in each of these fields using different methods and compare the results, to an extent that has not yet been done. We compare these methods not just on RR Lyrae stars in our M31 fields, but also on a data set of Milky Way field RR Lyrae stars.
10819395
Star formation histories in the Local Group
Deep color–magnitude diagrams extending to the main sequence provide the most direct measure of the detailed star formation history in a stellar population. With large investments of observing time, HST can obtain such data for populations out to 1 Mpc, but its field of view is extremely small in comparison to the size of Local Group galaxies. This limitation severely constrains our understanding of galaxy formation. For example, the largest galaxy in the Local Group, Andromeda, offers an ideal laboratory for studying the formation of large spiral galaxies, but the galaxy shows substructure on a variety of scales, presumably due to its violent merger history. Within its remaining lifetime, HST can only sample a few sight-lines through this complex galaxy. In contrast, a wide field imager could provide a map of Andromeda’s halo, outer disk, and tidal streams, revealing the spatially-dependent star formation history in each structure. The same data would enable many secondary studies, such as the age variation in Andromeda’s globular cluster system, gigantic samples of variable stars, and microlensing tracers of the galaxy’s dark matter distribution.
14525131
Far-UV Emission from Elliptical Galaxies at z=0.55
The restframe UV-to-optical flux ratio, characterizing the ``UV upturn'' phenomenon, is potentially the most sensitive tracer of age in elliptical galaxies; models predict that it may change by orders of magnitude over the course of a few Gyr. In order to trace the evolution of the UV upturn as a function of redshift, we have used the far-UV camera on the Space Telescope Imaging Spectrograph to image the galaxy cluster CL0016+16 at z=0.55. Our 25''x25'' field includes four bright elliptical galaxies, spectroscopically confirmed to be passively evolving cluster members. The weak UV emission from the galaxies in our image demonstrates that the UV upturn is weaker at a lookback time 5.6 Gyr earlier than our own, as compared to measurements of the UV upturn in cluster E and S0 galaxies at z=0 and z=0.375. These images are the first with sufficient depth to demonstrate the fading of the UV upturn expected at moderate redshifts. We discuss these observations and the implications for the formation history of galaxies.
16344850
Using M32 to Study Rapid Phases of Stellar Evolution
The compact elliptical galaxy M32 offers a unique testing ground for theories of stellar evolution. Because of its proximity, solar-blind UV observations can resolve the hot evolved stars in its center. Some of these late evolutionary phases are too rapid to study adequately in globular clusters, and their study in the Galactic field is often complicated by uncertainties in distance and reddening. Using the UV cameras on the Space Telescope Imaging Spectrograph, we have obtained a deep color-magnitude diagram (CMD) of the M32 center. Although the hot horizontal branch is well-detected, our CMD shows a striking scarcity of the brighter post-asymptotic giant branch (PAGB) and post-early AGB stars expected for a population of this size. This dearth suggests that the evolution to the white dwarf phase may be much more rapid than that predicted by canonical evolutionary tracks for low-mass stars.