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We report a study of the eclipse timing variations in contact binary systems, using long-cadence lightcurves from the Kepler archive. As a first step, observed minus calculated (O-C) curves were produced for both the primary and secondary eclipses of some 2000 Kepler binaries. We find ~390 short-period binaries with O-C curves that exhibit (1) random walk-like variations or quasi-periodicities, with typical amplitudes of ±200-300 s, and (2) anticorrelations between the primary and secondary eclipse timing variations. We present a detailed analysis and results for 32 of these binaries with orbital periods in the range of 0.35 ± 0.05 days. The anticorrelations observed in their O-C curves cannot be explained by a model involving mass transfer, which, among other things, requires implausibly high rates of ~0.01 Mʘ yr-1. We show that the anticorrelated behavior, the amplitude of the O-C delays, and the overall random walk-like behavior can be explained by the presence of a starspot that is continuously visible around the orbit and slowly changes its longitude on timescales of weeks to months. The quasi-periods of ~50-200 days observed in the O-C curves suggest values for k, the coefficient of the latitude dependence of the stellar differential rotation, of ~0.003-0.013. [ABSTRACT FROM AUTHOR]

Star-forming galaxies at redshifts z > 6 are likely responsible for the reionization of the universe, and it is important to study the nature of these galaxies. We present three candidates for z ~ 7 Lyman break galaxies (LBGs) from a 155 arcmin² area in the CANDELS/COSMOS field imaged by the deep FourStar Galaxy Evolution (ZFourGE) survey. The FourStar medium-band filters provide the equivalent of R ~ 10 spectroscopy, which cleanly distinguishes between z ~ 7 LBGs and brown dwarf stars. The distinction between stars and galaxies based on an object's angular size can become unreliable even when using Hubble Space Telescope imaging; there exists at least one very compact z ~ 7 candidate (FWHM ~ 0.5-1 kpc) that is indistinguishable from a point source. The medium-band filters provide narrower redshift distributions compared with broadband-derived redshifts. The UV luminosity function derived using the three z ~ 7 candidates is consistent with previous studies, suggesting an evolution at the bright end (MUV ~ -21.6 mag) from z ~ 7 to z ~ 5. Fitting the galaxies' spectral energy distributions, we predict Lyα equivalent widths for the two brightest LBGs, and find that the presence of a Lyα line affects the medium-band flux thereby changing the constraints on stellar masses and UV spectral slopes. This illustrates the limitations of deriving LBG properties using only broadband photometry. The derived specific star-formation rates for the bright LBGs are ~13 Gyr-1, slightly higher than the lower-luminosity LBGs, implying that the star-formation rate increases with stellar mass for these galaxies. [ABSTRACT FROM AUTHOR]

We discuss the structural and morphological properties of galaxies in a z = 1.62 proto-cluster using near-IR imaging data from Hubble Space Telescope Wide Field Camera 3 data of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). The cluster galaxies exhibit a clear color-morphology relation: galaxies with colors of quiescent stellar populations generally have morphologies consistent with spheroids, and galaxies with colors consistent with ongoing star formation have disk-like and irregular morphologies. The size distribution of the quiescent cluster galaxies shows a deficit of compact (≲1 kpc), massive galaxies compared to CANDELS field galaxies at z = 1.6. As a result, the cluster quiescent galaxies have larger average effective sizes compared to field galaxies at fixed mass at greater than 90% significance. Combined with data from the literature, the size evolution of quiescent cluster galaxies is relatively slow from z 1.6 to the present, growing as (1 + z)-0.6±0.1. If this result is generalizable, then it implies that physical processes associated with the denser cluster region seem to have caused accelerated size growth in quiescent galaxies prior to z = 1.6 and slower subsequent growth at z ≃ 1.6 compared to galaxies in the lower density field. The quiescent cluster galaxies at z = 1.6 have higher ellipticities compared to lower redshift samples at fixed mass, and their surface- brightness profiles suggest that they contain extended stellar disks. We argue that the cluster galaxies require dissipationless (i.e., gas-poor or "dry") mergers to reorganize the disk material and to match the relations for ellipticity, stellar mass, size, and color of early-type galaxies in z < 1 clusters. [ABSTRACT FROM AUTHOR]

Galaxies with stellar masses near M* contain the majority of stellar mass in the universe, and are therefore of special interest in the study of galaxy evolution. The Milky Way (MW) and Andromeda (M31) have present-day stellar masses near M*, at 5 × 1010M☼ (defined here to be MW-mass) and 1011M☼ (defined to be M31-mass). We study the typical progenitors of these galaxies using the FOURSTAR Galaxy Evolution Survey (ZFOURGE). ZFOURGE is a deep medium-band near-IR imaging survey, which is sensitive to the progenitors of these galaxies out to z ∼ 3. We use abundance-matching techniques to identify the main progenitors of these galaxies at higher redshifts. We measure the evolution in the stellar mass, rest-frame colors, morphologies, far-IR luminosities, and star formation rates, combining our deep multiwavelength imaging with near-IR Hubble Space Telescope imaging from Cosmic Near-IR Deep Extragalactic Legacy Survey (CANDELS), and Spitzer and Herschel far-IR imaging from Great Observatories Origins Deep Survey-Herschel and CANDELS-Herschel. The typical MW-mass and M31-mass progenitors passed through the same evolution stages, evolving from blue, star-forming disk galaxies at the earliest stages to redder dust-obscured IR-luminous galaxies in intermediate stages and to red, more quiescent galaxies at their latest stages. The progenitors of the MW-mass galaxies reached each evolutionary stage at later times (lower redshifts) and with stellar masses that are a factor of two to three lower than the progenitors of the M31-mass galaxies. The process driving this evolution, including the suppression of star formation in present-day M* galaxies, requires an evolving stellar-mass/halo-mass ratio and/or evolving halo-mass threshold for quiescent galaxies. The effective size and SFRs imply that the baryonic cold-gas fractions drop as galaxies evolve from high redshift to z ∼ 0 and are strongly anticorrelated with an increase in the Sérsic index. Therefore, the growth of galaxy bulges in M* galaxies corresponds to a rapid decline in the galaxy gas fractions and/or a decrease in the star formation efficiency. [ABSTRACT FROM AUTHOR]

We report on the discovery of stellar occultations, observed with Kepler, which recur periodically at 15.685 hr intervals, but which vary in depth from a maximum of 1.3% to a minimum that can be less than 0.2%. The star that is apparently being occulted is KIC 12557548, a V = 16 mag K dwarf with Teff, s ≃ 4400 K. The out-of-occultation behavior shows no evidence for ellipsoidal light variations, indicating that the mass of the orbiting object is less than ∼3 MJ (for an orbital period of 15.7 hr). Because the eclipse depths are highly variable, they cannot be due solely to transits of a single planet with a fixed size. We discuss but dismiss a scenario involving a binary giant planet whose mutual orbit plane precesses, bringing one of the planets into and out of a grazing transit. This scenario seems ruled out by the dynamical instability that would result from such a configuration. We also briefly consider an eclipsing binary, possibly containing an accretion disk, that either orbits KIC 12557548 in a hierarchical triple configuration or is nearby on the sky, but we find such a scenario inadequate to reproduce the observations. The much more likely explanation—but one which still requires more quantitative development—involves macroscopic particles escaping the atmosphere of a slowly disintegrating planet not much larger than Mercury in size. The particles could take the form of micron-sized pyroxene or aluminum oxide dust grains. The planetary surface is hot enough to sublimate and create a high-Z atmosphere; this atmosphere may be loaded with dust via cloud condensation or explosive volcanism. Atmospheric gas escapes the planet via a Parker-type thermal wind, dragging dust grains with it. We infer a mass-loss rate from the observations of order 1 M⊕ Gyr–1, with a dust-to-gas ratio possibly of order unity. For our fiducial 0.1 M⊕ planet (twice the mass of Mercury), the evaporation timescale may be ∼0.2 Gyr. Smaller mass planets are disfavored because they evaporate still more quickly, as are larger mass planets because they have surface gravities too strong to sustain outflows with the requisite mass-loss rates. The occultation profile evinces an ingress-egress asymmetry that could reflect a comet-like dust tail trailing the planet; we present simulations of such a tail. [ABSTRACT FROM AUTHOR]