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TOPIC: WD J1916+3938

Blobrana

L

Posts: 131433

Date: Jul 3 20:19 2015

KIC 4552982	Permalink

Title: KIC 4552982: Outbursts and Asteroseismology from the Longest Pseudo-Continuous Light Curve of a ZZ Ceti Author: Keaton J. Bell, J. J. Hermes, A. Bischoff-Kim, Sean Moorhead, M. H. Montgomery, Roy Ostensen, Barbara G. Castanheira, D. E. Winget We present the Kepler light curve of KIC 4552982, the first ZZ Ceti (hydrogen-atmosphere pulsating white dwarf star) discovered in the Kepler field of view. Our data span more than 1.5 years with a 86% duty cycle, making it the longest pseudo-continuous light curve ever recorded for a ZZ Ceti. This extensive data set provides the most complete coverage to-date of amplitude and frequency variations in a cool ZZ Ceti. We detect 20 independent frequencies of variability in the data that we compare with asteroseismic models to demonstrate that this star has a mass M_* > 0.6 solar masses. We identify a rotationally split pulsation mode and derive a probable rotation period for this star of 17.47 ± 0.04 hr. In addition to pulsation signatures, the Kepler light curve exhibits sporadic, energetic outbursts that increase the star's relative flux by 2-17%, last 4-25 hours, and recur on an average timescale of 2.7 days. These are the first detections of a new dynamic white dwarf phenomenon that we believe may be related to the pulsations of this relatively cool (T_eff = 10,860 ± 120 K) ZZ Ceti star near the red edge of the instability strip. Read more (1650kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Dec 21 12:38 2011

WD J191643.83+393849.7	Permalink

Title: A first asteroseismological analysis on WD J1916+3938, the ZZ Ceti star discovered in the Kepler mission field Authors: Alejandro H. Córsico, Alejandra D. Romero, Leandro G. Althaus, Marcelo M. Miller Bertolami Asteroseismology of DAV stars (ZZ Ceti variables) can provide valuable clues about the origin, structure and evolution of DA (atmospheres rich in H) white dwarfs. Recently, a new DAV star, WD J191643.83+393849.7, has been discovered in the field of the Kepler spacecraft. It is expected that further monitoring of this star in the next years will enable astronomers to obtain the best lightcurve of a pulsating DA white dwarf ever recorded, and thus to know with unprecedented precision the hidden details of the internal structure of this star. In this paper, we perform a first asteroseismological analysis of WD J191643.83+393849.7 on the basis of fully evolutionary DA white-dwarf models. Specifically, we employ a complete set of evolutionary DA white-dwarf structures covering a wide range of effective temperatures, stellar masses, and H envelope thicknesses. These models have been obtained on the basis of a complete treatment of the evolutionary history of progenitors stars. We compute g-mode adiabatic pulsation periods for this set of models and compare them with the pulsation periods exhibited by WD J191643.83+393849.7. Based on a tentative estimation of the mean period spacing of the star, we find that the stellar mass should be substantially large (\gtrsim 0.80 solar masses), in agreement with the spectroscopically derived stellar mass. Also, from period-to-period fits we find an asteroseismological model characterised by a low effective temperature, rather high stellar mass and a thin H envelope. The possibility that this rather massive pulsating white dwarf can be further monitored with Kepler with a high degree of detail turns the star WD J191643.83+393849.7 into a promising and unique object to study the physics of crystallisation and carbon/oxygen phase diagrams at high densities. Read more (59kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Sep 29 01:50 2011

WD J1916+3938	Permalink

Title: Discovery of a ZZ Ceti in the Kepler Mission Field Authors: J. J. Hermes, Fergal Mullally, R. H. Østensen, Kurtis A. Williams, John Telting, John Southworth, S. Bloemen, Steve B. Howell, Mark Everett, D. E. Winget We report the discovery of the first identified pulsating DA white dwarf in the field of the Kepler mission, WD J1916+3938 (Kepler ID 4552982). This ZZ Ceti star was first identified through ground-based, time-series photometry, and follow-up spectroscopy confirm it is a hydrogen-atmosphere white dwarf with an effective temperature = 11,129 ±115 K and log g = 8.34 ±0.06, placing it within the empirical ZZ Ceti instability strip. The object shows up to 0.5 percent amplitude variability at several periods between 800 -- 1450 s. Extended Kepler observations of this object could yield the best lightcurve, to-date, of any pulsating white dwarf, allowing us to directly study the interior of an evolved object representative of the fate of the majority of stars in our Galaxy. Read more (781kb, PDF) __________________

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