We present a detailed analysis of a large spectroscopic and photometric sample of DZ white dwarfs based on our latest model atmosphere calculations. We revise the atmospheric parameters of the trigonometric parallax sample of Bergeron, Leggett, & Ruiz (2001, Cat. <J/ApJS/133/413>, 12 stars) and analyze 147 new DZ white dwarfs discovered in the SDSS. The inclusion of metals and hydrogen in our model atmosphere calculations leads to different atmospheric parameters than those derived from pure helium models.
Based on our intensive spectroscopic campaign with the GoldCam spectrograph on the Kitt Peak National Observatory (KPNO) 2.1-m telescope, we have constructed the first catalogue of E+A galaxies with spectroscopic companion galaxies, and investigated a probability that an E+A galaxy has close companion galaxies. We selected 660 E+A galaxies with 4.0{AA}<H{delta} EW at a redshift of <0.167 from the Data Release 5 of the Sloan Digital Sky Survey (SDSS). We selected their companion candidates from the SDSS imaging data, and classified them into true companions, fore/background galaxies and companion candidates using the SDSS and our KPNO spectra. We observed 26 companion candidates of E+A galaxies at the KPNO to measure their redshifts. Their spectra showed that 17 targets are true companion galaxies.
We present results of a study of E+A galaxies in the cluster Cl0939+472 (z=0.41). We have used a series of narrow-band filters (FWHM~=90-200A) covering the range from 3800 to 9200A, and broad band B, R, I filters to obtain low resolution spectra for all galaxies brighter than R=22.5mag in a 5'x5' cluster field. Two of the narrow-band filters have been chosen to measure the 4000A-break index, and 3 filters were centered on the H_{beta}_, H_{gamma}_ and H_{delta}_ lines which are indicators of recent star formation.
A sample of 70 E+A galaxies is selected from 37206 galaxies in the second data release of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). This sample is selected according to the criteria for E+A galaxies defined by Goto, and each of these objects is further visually identified. In this sample, most objects are low redshift E+A galaxies with z<0.25, and are located in an area of the sky with high Galactic latitude and magnitude from 14 to 18mag in the g, r and i bands. A stellar population analysis of the whole sample indicates that the E+A galaxies are characterized by both young and old stellar populations (SPs), and the metal-rich SPs have relatively higher contributions than the metal-poor ones. Additionally, a morphological classification of these objects is performed based on images taken from the Sloan Digital Sky Survey.
This paper presents results from a continuum radio survey of a complete sample of 248 southern E and S0 galaxies. All the galaxies were observed at 2.7GHz (11cm) with the Parkes radio telescope, and those detected were reobserved at 5.0 GHz (6 cm). Thirty-seven galaxies were detected above a level of 25-30mJy, and a consideration of the background source density at 2.7GHz indicates that no more than two or three of these detections are due to background sources.
We present a seismic analysis of the pulsating hot B subdwarf KPD 1943+4058 (KIC 005807616) on the basis of the long-period, gravity-mode pulsations recently uncovered by Kepler. This is the first time that g-mode seismology can be exploited quantitatively for stars on the extreme horizontal branch, all previous successful seismic analyses having been confined so far to short-period, p-mode pulsators. We demonstrate that current models of hot B subdwarfs can quite well explain the observed g-mode periods, while being consistent with independent constraints provided by spectroscopy. We identify the 18 pulsations retained in our analysis as low-degree ({l}=1 and 2), intermediate-order (k=-9 through -58) g-modes. The periods (frequencies) are recovered, on average, at the 0.22% level, which is comparable to the best results obtained for p-mode pulsators. We infer the following structural and core parameters for KPD 1943+4058 (formal fitting uncertainties only): T_eff_=28050+/-470K, logg=5.52+/-0.03, M_*_=0.496+/-0.002M_{sun}_, log(M_env_/M*)=-2.55+/-0.07, log(1-M_core_/M_*_)=-0.3+/-0.01, and X_core_(C+O)=0.261+/-0.008. We additionally derive the age of the star since the zero-age extended horizontal branch 18.4+/-1.0Myr, the radius R=0.203+/-0.007R_{sun}_, the luminosity L=22.9+/-3.13L_{sun}_, the absolute magnitude M_V_=4.21+/-0.11, the reddening index E(B-V)=0.094+/-0.017, and the distance d=1180+/-95pc.
Young (<600Myr) low-mass stars (M<~1M_{sun}_) of equal mass exhibit a distribution of rotation periods. At the very early phases of stellar evolution, this distribution is set by the star-disc locking mechanism, which forces stars to rotate at the same rate as the inner edge of the disc. The primordial disc lifetime and consequently the duration of the disc-locking mechanism, can be significantly shortened by the presence of a close companion, making the rotation period distribution of close binaries different from that of either single stars or wide binaries. We use new data to investigate and better constrain the range of ages, the components separation, and the mass ratio dependence at which the rotation period distribution has been significantly affected by the disc dispersal that is enhanced by close companions. We select a sample of close binaries in the Upper Scorpius association (age~8Myr) whose components have measured the separation and the rotation periods and compare their period distribution with that of coeval stars that are single stars. We find that components of close binaries have, on average, rotation periods that are shorter than those of single stars. More precisely, binaries with approximately equal-mass components (0.9<=M2/M1<=1.0) have rotation periods that are shorter than those of single stars by ~0.4d on average; the primary and secondary components of binaries with smaller mass ratios (0.8<M2/M1<0.9) have rotation periods that are shorter than those of single stars by ~1.9d and ~1.0d on average, respectively. A comparison with the older 25-Myr {beta} Pictoris association shows that whereas in the latter, all close binaries with projected separation {rho}<=80AU rotate faster than single stars, in the Upper Scorpius this is only the case for about 70% of stars. We interpret the enhanced rotation in close binaries with respect to single stars as the consequence of an early disc dispersal induced by the presence of close companions. The enhanced rotation suggests that disc dispersal timescales are longest for single stars and shorter for close binaries.
We present an early-phase g-band light curve and visual-wavelength spectra of the normal Type Ia supernova (SN) 2013gy. The light curve is constructed by determining the appropriate S-corrections to transform KAIT natural-system B- and V-band photometry and Carnegie Supernova Project natural-system g-band photometry to the Pan-STARRS1 g-band natural photometric system. A Markov chain Monte Carlo calculation provides a best-fit single power-law function to the first ten epochs of photometry described by an exponent of 2.16^+0.06^_0.06_ and a time of first light of MJD 56629.4^+0.1^_0.1_, which is 1.93^+0.12^_0.13_ days (i.e., <48hr) before the discovery date (2013 December 4.84 UT) and -19.10^+0.12^_0.13_ days before the time of B-band maximum (MJD 56648.50.1). The estimate of the time of first light is consistent with the explosion time inferred from the evolution of the SiII 6355 Doppler velocity. Furthermore, discovery photometry and previous nondetection limits enable us to constrain the companion radius down to Rc<=4R_{sun}_. In addition to our early-time constraints, we used a deep +235 day nebular-phase spectrum from Magellan/IMACS to place a stripped H-mass limit of <0.018M_{sun}_. Combined, these limits effectively rule out H-rich nondegenerate companions.
In 1900 E.E. Barnard published 37 visual observations of Variable 2 (V2) in the globular cluster M13 made in 1899 and 1900. A review of Barnard's notebooks revealed he made many additional brightness estimates up to 1911, and he had also recorded the variations of V1 starting in 1904. These data provide the earliest-epoch light curves for these stars and thus are useful for studying their period changes. This paper presents Barnard's observations of the M13 variables along with their derived heliocentric Julian dates and approximate V magnitudes. These include 231 unpublished observations of V2 and 94 of V1. How these data will be of value for determining period changes by these stars is described.
We present multicolor optical observations of long-duration {gamma}-ray bursts (GRBs) made over a three-year period with the robotic Palomar 60 inch telescope (P60). Our sample consists of all 29 events discovered by Swift for which P60 began observations less than 1hr after the burst trigger. We were able to recover 80% of the optical afterglows from this prompt sample, and we attribute this high efficiency to our red coverage. Like Melandri et al. (2008, Cat. J/ApJ/686/1209), we find that a significant fraction (~50%) of Swift events show a suppression of the optical flux with regard to the X-ray emission (the so-called "dark" bursts). Our multicolor photometry demonstrates this is likely due in large part to extinction in the host galaxy. We argue that previous studies, by selecting only the brightest and best-sampled optical afterglows, have significantly underestimated the amount of dust present in typical GRB environments.