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New Pulsating DB White Dwarf Stars from the Sloan Digital Sky Survey
A. Nitta, S. J. Kleinman, J. Krzesinski +8
We are searching for new He atmosphere white dwarf pulsators (DBVs) based on the newly found white dwarf stars from the spectra obtained by the Sloan Digital Sky Survey. DBVs pulsa…
Pulsating White Dwarf Stars and Precision Asteroseismology
D. E. Winget, S. O. Kepler
Galactic history is written in the white dwarf stars. Their surface properties hint at interiors composed of matter under extreme conditions. In the forty years since their discove…
SDSS J142625.71+575218.3, a Prototype for a New Class of Variable White Dwarf
M. H. Montgomery, Kurtis A. Williams, D. E. Winget +3
We present the results of a search for pulsations in six of the recently discovered carbon-atmosphere white dwarf ("hot DQ") stars. Based on our theoretical calculations, the star…
Whole Earth Telescope observations of the hot helium atmosphere pulsating white dwarf EC 20058-5234
WET Collaboration, D. J. Sullivan, T. S. Metcalfe +22
We present the analysis of a total of 177h of high-quality optical time-series photometry of the helium atmosphere pulsating white dwarf (DBV) EC 20058-5234. The bulk of the observ…
Limits on Planets Around White Dwarf Stars
F. Mullally, D. E. Winget, Steven Degennaro +3
We present limits on planetary companions to pulsating white dwarf stars. A subset of these stars exhibit extreme stability in the period and phase of some of their pulsation modes…
The pulsation modes of the pre-white dwarf PG 1159-035
J. E. S. Costa, S. O. Kepler, D. E. Winget +74
PG 1159-035, a pre-white dwarf with T_eff=140,000 K, is the prototype of both two classes: the PG1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-0…
Strong limits on the DFSZ axion mass with G117-B15A
A. Bischoff-Kim, M. H. Montgomery, D. E. Winget
We compute rates of period change (Pdots) for the 215s mode in G117-B15A and the 213s mode in R548, first for models without axions, and then for models with axions of increasing m…
Fine Grid Asteroseismology of R548 and G117-B15A
A. Bischoff-Kim, M. H. Montgomery, D. E. Winget
We now have a good measurement of the cooling rate of G117-B15A. In the near future, we will have equally well determined cooling rates for other pulsating white dwarfs, including…
White Dwarf Luminosity and Mass Functions from Sloan Digital Sky Survey Spectra
Steven DeGennaro, Ted von Hippel, D. E. Winget +4
We present the first phase in our ongoing work to use Sloan Digital Sky Survey (SDSS) data to create separate white dwarf (WD) luminosity functions for two or more different mass r…
Mean ZZ Ceti pulsation period gauges stellar temperature
Anjum S. Mukadam, M. H. Montgomery, A. Kim +3
The mean pulsation period of ZZ Ceti stars increases with decreasing effective temperature as we traverse from the blue to the red edge of the instability strip. This well-establis…
New Techniques to Determine Ages of Open Clusters Using White Dwarfs
E. J. Jeffery, T. von Hippel, W. H. Jefferys +3
Currently there are two main techniques for independently determining the ages of stellar populations: main sequence evolution theory (via cluster isochrones) and white dwarf cooli…
A Spitzer White Dwarf Infrared Survey
F. Mullally, Mukremin Kilic, William T. Reach +4
We present mid-infrared photometry of 124 white dwarf stars with Spitzer Space Telescope. Objects were observed simultaneously at 4.5 and 8.0um with sensitivities better than 1 mJy…
Towards a pure ZZ Ceti instability strip
B. G. Castanheira, S. O. Kepler, A. F. M. Costa +8
We have observed again two stars inside the ZZ Ceti instability strip that were previously classified as not-observed-to-vary (NOV) by Mukadam et al. (2004) and found them to be lo…
Spitzer White Dwarf Planet Limits
F. Mullally, Ted von Hippel, D. E. Winget
We present preliminary limits on the presence of planets around white dwarf stars using the IRAC photometer on the Spitzer space telescope. Planets emit strongly in the mid-infrare…
Further Evidence for Variable Synchrotron Emission in XTE J1118+480 in Outburst
R. I. Hynes, E. L. Robinson, K. J. Pearson +7
We present simultaneous multicolor infrared and optical photometry of the black hole X-ray transient XTE J1118+480 during its short 2005 January outburst, supported by simultaneous…
Debris Disks Around White Dwarfs: The DAZ Connection
Mukremin Kilic, Ted von Hippel, S. K. Leggett +1
We present near-infrared spectroscopic observations of 20 previously known DAZ white dwarfs obtained at the NASA Infrared Telescope Facility. Two of these white dwarfs (G29-38 and…
Inverting Color-Magnitude Diagrams to Access Precise Star Cluster Parameters: A Bayesian Approach
Ted von Hippel, William H. Jefferys, James Scott +5
We demonstrate a new Bayesian technique to invert color-magnitude diagrams of main sequence and white dwarf stars to reveal the underlying cluster properties of age, distance, meta…
The Mystery Deepens: Spitzer Observations of Cool White Dwarfs
Mukremin Kilic, Ted von Hippel, Fergal Mullally +4
We present 4.5m and 8m photometric observations of 18 cool white dwarfs obtained with the Spitzer Space Telescope. Our observations demonstrate that four white dwarfs with T_…
Discovery of eleven new ZZ Ceti stars
B. G. Castanheira, S. O. Kepler, F. Mullally +8
We report the discovery of eleven new ZZ Cetis using telescopes at OPD (Observatório do Pico dos Dias/LNA) in Brazil, the 4.1 m SOAR (Southern Astrophysical Research) telescope at…
The Dust cloud around the White Dwarf G 29-38
William T. Reach, Marc J. Kuchner, Ted von Hippel +4
We present new observations of the white dwarf G 29-38 with the camera (4.5 and 8 microns), photometer (24 microns), and spectrograph (5.5-14 microns) of the Spitzer Space Telescop…
The White Dwarf Luminosity Function from SDSS Imaging Data
Hugh C. Harris, Jeffrey A. Munn, Mukremin Kilic +16
A sample of white dwarfs is selected from SDSS DR3 imaging data using their reduced proper motions, based on improved proper motions from SDSS plus USNO-B combined data. Numerous S…
Driving in ZZ Ceti stars - Problem solved?
A. Kim, D. E. Winget, M. H. Montgomery +1
There is a fairly tight correlation between the pulsation periods and effective temperatures of ZZ Ceti stars (cooler stars have longer periods). This seems to fit the theoretical…
Excess Infrared Radiation from a Massive DAZ White Dwarf: GD362 - a Debris Disk?
Mukremin Kilic, Ted von Hippel, S. K. Leggett +1
We report the discovery of excess K-band radiation from a massive DAZ white dwarf star, GD362. Combining infrared photometric and spectroscopic observations, we show that the exces…
Faint Blue Objects in the Hubble Deep Field South Revealed: White Dwarfs, Subdwarfs, and Quasars
Mukremin Kilic, R. A. Mendez, Ted von Hippel +1
We explore the nature of the faint blue objects in the Hubble Deep Field South. We have derived proper motions for the point sources in the Hubble Deep Field South using a 3 year b…