Day 496

Friday.  Still a week behind.

1308.4683
Hot-dust (690K) luminosity density and its evolution in the last 7.5 Gyr
Messias, Mobasher, Alfonso

Study the contribution of hot-dust to the luminosity density of galaxies and its evolution with cosmic time.  Using the Spitzer IRAC data in the COSMOS field, estimate the contribution from hot-dust at rest-frame 4.2 um (from ~0<z<~0.2 up to ~0.5<z<~0.9).  This wavelength corresponds to BB temperature of ~690K.  The contribution due to stellar emission is estimated from the rest-frame 1.6 um luminosity (assumed to result from stellar emission alone) and subtracted from the MIR luminosity of galaxies to measure hot-dust emission.  In order to attempt the study of the 3.3um-PAH feature, use the rest-frame 4.2um to infer the hot-dust flux at 3.3um.  This study is performed for different spectral types of galaxies: early-type, late-type, starburst, and IR-selected AGN.  Find: (a) the decrease of the hot-dust luminosity density since ~0.5<z<~1 is steeper (by at least ~0.5 dex) compared to that of the cold-dust, giving support to the scenario where galaxy obscuration increases with redshift, as already proposed in the literature; (b) hot-dust and PAH emission evolution seems to be correlated with stellar mass, where rest-frame 1.6um luminous non-AGN galaxies (i.e., massive systems) show a stronger decrement (with decreasing redshift) in hot-dust and PAH emission than the less luminous (less massive) non-AGN galaxies; (c) despite comprising <~3% of the total sample, AGN contribute as much as a third to the hot-dust luminosity density at z<1 and clearly dominate the bright-end of the total hot-dust Luminosity Density Function at ~0.5<z<~0.9; (d) at M_1.6 > -25, the dust-to-total and PAH-to-total luminosity ratios increase with decreasing luminosity, but deeper data is required to confirm this result.

1308.4728
An observational correlation between stellar brightness variations and surface gravity
Bastien, Stassun, Basri, Pepper

Surface gravity is a basic stellar property, but typical uncertainty of 25-50 per cent if measured spectroscopically and 90-150% photometrically.  Astroseismology measures gravity with an uncertainty of about 2%, but is restricted to relatively small samples of bright stars, most of which are giants.  The availability of high-precision measurements of brightness variations for >150,000 stars provides an opportunity to investigate whether the variations can be used to determine surface gravities.  The Fourier power of granulation on a star's surface correlates physically with surface gravity; if brightness variations on timescales of hours arise from granulation, then such variations should correlate with surface gravity.  Report an analysis of archival data that reveals an observational correlation between surface gravity and the root-mean-square brightness variations on timescales of less than eight hours for stars with temperatures of 4500-6750K, log of surface gravities of 2.5-4.5 (cgs units), and having overall brightness variations <3 pp thousand.  A straightforward observation of optical brightness variations therefore allows a determination of the surface gravity with a precision of <25% for inactive Sun-like stars at main-sequence to giant stages of evolution.

1308.4887
Evolution towards and beyond accretion-induced collapse of massive white dwarfs and formation of millisecond pulsars
Tauris, Sanyal, Yoon, Langer

Millisecond pulsars (MSPs) are generally believed to be old neutron stars (NSs), formed via type Ib/c core-collapse SNe, which have been spun up to high rotation rates via accretion from a companion star in a low-mass X-ray binary (LMXB).  In an alternative formation channel, NSs are produced via the accretion-induced collapse (AIC) of massive WD in a close binary.  Investigate binary evolution leading to AIC and examine if NSs formed in this way can subsequently be recycled to form MSPs and, if so, how they can observationally be distinguished from pulsars formed via the standard core-collapse SN channel in terms of their masses, spins, orbital periods and space velocities.  Numerical calculations with a detailed stellar evolution code were used for the first time to study the combined pre- and post-AIC evolution of close binaries.  Investigate the mass transfer onto a massive WD in 240 systems with 3 different types of non-degenerate donor stars: MS stars, red giants, and helium stars.  When the WD is able to accrete sufficient mass (depending on the mass-transfer rate and the duration of the accretion phase) assumed it collapses to form a NS and study the dynamical effects of this implosion on the binary orbit.  Subsequently, follow the mass-transfer epoch which resumes once the donor star refills its Roche lobe and calculate the continued LMXB evolution until the end.  Demonstrate that the final properties of these MSPs are, in general, remarkably similar to those of MSPs formed via the standard core-collapse SN channel.  However, the resultant MSPs created via the ACI channel preferentially form in certain orbital period intervals.  Finally, discuss the link between AIC and young NSs in globular clusters.  Calculations are applicable to progenitor binaries of SNe Ia under certain conditions.