16998214
Understanding the Relationship Between Observations and Stellar Parameters in an Eclipsing Binary System
We would like to investigate the information contained in our observations and to what extent each of them contributes individually to constraining the physical parameters of the system we are investigating. To do this, we present a study involving the technique of Singular Value Decomposition using as a simple example a detached eclipsing binary system. We intend to apply an extension of this technique to asteroseismic measurements of Delta~Scuti stars that are members of eclipsing binary systems.
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)
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.
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.
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.
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.
119452243
The Extended Star Formation History of the Andromeda Spheroid at Twenty One Kiloparsecs on the Minor Axis
Using the HST ACS, we have obtained deep optical images of a southeast minor-axis field in the Andromeda Galaxy, 21 kpc from the nucleus. In both star counts and metallicity, this field represents a transition zone between the metal-rich, highly-disturbed inner spheroid that dominates within 15 kpc and the metal-poor, diffuse population that dominates beyond 30 kpc. The color-magnitude diagram reaches well below the oldest main-sequence turnoff in the population, allowing a reconstruction of the star formation history in this field. Compared to the spheroid population at 11 kpc, the population at 21 kpc is ~1.3 Gyr older and ~0.2 dex more metal-poor, on average. However, like the population at 11 kpc, the population at 21 kpc exhibits an extended star formation history; one third of the stars are younger than 10 Gyr, although only a few percent are younger than 8 Gyr. The relatively wide range of metallicity and age is inconsistent with a single, rapid star-formation episode, and instead suggests that the spheroid even at 21 kpc is dominated by the debris of earlier merging events likely occurring more than 8 Gyr ago.
18259911
Evidence for a Significant Intermediate-Age Population in the M31 Halo from Main Sequence Photometry
We present a color-magnitude diagram (CMD) for a minor-axis field in the halo of the Andromeda galaxy (M31), 51' (11 kpc) from the nucleus. These observations, taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope, are the deepest optical images yet obtained, attaining 50% completeness at mV = 30.7 mag. The CMD, constructed from ~3 × 105 stars, reaches more than 1.5 mag fainter than the old main-sequence turnoff. Our analysis is based on direct comparisons to ACS observations of four globular clusters through the same filters, as well as χ2 fitting to a finely spaced grid of calibrated stellar-population models. We find that the M31 halo contains a major (~30% by mass) intermediate-age (6-8 Gyr) metal-rich ([Fe/H] > -0.5) population, as well as a significant globular cluster age (11-13.5 Gyr) metal-poor population. These findings support the idea that galaxy mergers played an important role in the formation of the M31 halo.
17530033
UV emission from elliptical galaxies near and far
The far-ultraviolet is the most rapidly evolving portion of the spectrum in both very young galaxies and very old galaxies. The “UV upturn” in the spectra of elliptical galaxies shortward of 2000 A offers a promising probe of the ages and chemical evolution of very old galaxies. In early-type non-active galaxies with the bluest 1550—V colors, the bulk of the emission arises from Extreme Horizontal Branch (EHB) stars, along their evolution from the zero-age HB to the white-dwarf cooling curve. The strength of the UV-upturn is governed by the fraction of stars that evolve through the EHB phase, which is in turn governed by age, metallicity, helium abundance, and other parameters such as stellar rotation and binarity that might influence the amount of mass loss on the RGB. Spectral constraints on the nature of the hot stellar population from Astro-2 are reviewed, and new imaging results from the HST Faint Object Camera are presented. Attempts to measure evolution through observations of high-redshift ellipti...
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.