scholarly journals Probing the Extraordinary Ends of Ordinary Stars: White Dwarf Seismology with the Whole Earth Telescope

1995 ◽  
Vol 155 ◽  
pp. 81-91
Author(s):  
Steven D. Kawaler
Keyword(s):  
White Dwarf ◽  
High Speed ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Dense Cores ◽  
Photometric Observations ◽  
Nuclear Burning ◽  
Stellar Seismology ◽  
Composition Changes ◽  
Whole Earth

AbstractDuring the final evolution of most stars, they shed their outer skin and expose their core of the hot ashes of nuclear burning. As these hot and very dense cores cool into white dwarf stars, they go through episodes of multiperiodic, nonradial g-mode pulsation. The tools of stellar seismology allow us to use the pulsation spectra as powerful probes into the deep interiors of these stars. Progress in white dwarf seismology has required significant international cooperation, since another consequence of the complex pulsations of these stars is decoding the true pulsation frequencies requires a coordinated global effort involving high-speed photometric observations. Through one such effort, the Whole Earth Telescope project, we have located subsurface composition changes, detected differential rotation and magnetic fields, and measured fundamental quantities such as stellar mass, luminosity, and distance to extraordinary accuracy.

scholarly journals Interacting Binary White Dwarf Stars

1992 ◽  
Vol 151 ◽  
pp. 461-464
Author(s):  
J.-E. Solheim
Keyword(s):  
White Dwarf ◽  
Structural Changes ◽  
Light Curves ◽  
Physical Parameters ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Test Models ◽  
Radial Pulsations ◽  
Whole Earth

This group of stars consists of 4 systems, also called helium cataclysmics. Three of them show photometric variations and have been studied by the Whole Earth Telescope (WET), which have revealed multiperiodic light curves showing the signature of g-mode non-radial pulsations on the accreting star. The combination of accretion and g-mode pulsations gives a unique opportunity to test models for the accreator's structural changes in response to accretion. IUE-spectra provide additional physical parameters.

scholarly journals Amplitude and frequency variability of the pulsating DB white dwarf stars KUV 05134+2605 and PG 1654+160 observed with the Whole Earth Telescope

2003 ◽  
Vol 340 (3) ◽  
pp. 1031-1038 ◽  
Author(s):  
G. Handler ◽  
D. O'Donoghue ◽  
M. Muller ◽  
J.- E. Solheim ◽  
J. M. Gonzalez-Perez ◽  
...  
Keyword(s):  
White Dwarf ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Whole Earth

scholarly journals The Whole Earth Telescope

1989 ◽  
Vol 114 ◽  
pp. 109-114 ◽  
Author(s):  
R. Edward Nather
Keyword(s):  
Star Formation ◽  
Light Curve ◽  
Early Universe ◽  
White Dwarf ◽  
Dwarf Stars ◽  
Detailed History ◽  
White Dwarf Stars ◽  
Observational Technique ◽  
History Of ◽  
Whole Earth

AbstractThe history of our galaxy and the detailed history of star formation in the early universe is written in the white dwarf stars. Recently we have learned how to reach beneath their exposed surfaces by observing white dwarfs that are intrinsic variables. We use the stellar equivalent of seismology to probe their interiors, and thus to unravel the history they hold inside. We have designed and placed into operation an observational technique that uses the whole earth as a telescope platform, defeating the effects of daylight which, until now, had seriously limited the length of a single light curve, and therefore the amount of information we could hope to extract from it. This paper describes our new telescope and presents preliminary results from our first observing run in March, 1988.

scholarly journals Ground-based observation of ZZ Ceti stars and the discovery of four new variables

2019 ◽  
Vol 490 (2) ◽  
pp. 1803-1820 ◽  
Author(s):  
Alejandra D Romero ◽  
L Antunes Amaral ◽  
T Klippel ◽  
D Sanmartim ◽  
L Fraga ◽  
...  
Keyword(s):  
White Dwarf ◽  
Signal To Noise Ratio ◽  
Structural Parameters ◽  
Instability Strip ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Photometric Observations ◽  
Best Fitting ◽  
New Variables

ABSTRACT We perform ground-based photometric observations of 22 DA white dwarf stars, 10 already known ZZ Cetis and 12 candidates with atmospheric parameters inside the classical instability strip. We report on the discovery of four new variable DA white dwarf stars. Two objects are near the middle of the instability strip, SDSS J082804.63+094956.6 and SDSS J094929.09+101918.8, and two red edge pulsators, GD 195 and L495−82. In addition, we classified four objects as possible variables, since evidence of variability was detected in the light curve, but the signal-to-noise ratio was not sufficient to establish a definite detection. Follow-up observations were performed for 10 known ZZ Ceti stars to verify period stability and search for new periodicities. For each confirmed variable, we perform a detailed asteroseismological fit and compare the structural parameters obtained from the best-fitting models with those obtained from spectroscopy and photometry from Gaia. Finally we present a study of the asteroseismological properties of a sample of 91 ZZ Ceti stars.

scholarly journals Seismological investigations of compact stars

1988 ◽  
Vol 123 ◽  
pp. 305-324
Author(s):  
D. E. Winget†
Keyword(s):  
White Dwarf ◽  
Mode Selection ◽  
Physical Structure ◽  
Compact Stars ◽  
Future Research ◽  
Underlying Structure ◽  
Rapid Progress ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Stellar Seismology

Since Landolt's discovery of the first ZZ Ceti star, the ranks of the compact pulsators have swollen to include planetary nebula nuclei, hot pre-white dwarf stars, hot and cool white dwarf stars, and possibly even neutron stars. The discovery of multi-periodic variations in these objects has helped to usher in a new era of rapid progress in the field of stellar seismology. For the compact stars this rapid progress is the result of a combination of four fortunate circumstances: their physical structure is relatively simple; typical amplitudes are small enough to be both readily observable and amenable to linear analysis; the wealth of observed periods in each object provides many independent clues to the underlying structure of the compact stars; and the periods are short enough that we can observe many cycles in a night, thereby completely resolving the period structure in many of these stars.In this review I will discuss the current state of our understanding of these objects, with special emphasis on their distribution in the H-R diagram, range of pulsation properties, possible mode selection mechanisms, excitation of the pulsations, problems of convection, and particularly the measurement and interpretation of period changes. In addition to the results of recent research, I will review the techniques used to obtain them, pointing out both their strengths and weaknesses. I will close with a discussion of some of the important problems facing us in the study of these objects, and attempt to identify potentially fruitful directions for future research.

scholarly journals White Dwarf.Org - Establishing a Permanent Endowment for the Whole Earth Telescope

2003 ◽  
Vol 12 (2) ◽  
Author(s):  
Travis S. Metcalfe
Keyword(s):  
White Dwarf ◽  
Fund Raising ◽  
Current Status ◽  
Dwarf Stars ◽  
Non Profit ◽  
White Dwarf Stars ◽  
Funding Sources ◽  
Governmental Funding ◽  
Whole Earth

AbstractWhite Dwarf Research Corporation is a non-profit organization dedicated to scientific research and public education on topics relevant to white dwarf stars. It was founded in 1999 in Austin, Texas to help fulfill the need for an alternative research center where scarce funding dollars could be used more efficiently, and to provide a direct link between astronomers who study white dwarf stars and the general public. Due to its administrative simplicity, WDRC can facilitate the funding of multi-institutional and international collaborations, provide seamless grant portability, minimize overhead rates, and actively seek non-governmental funding sources. I describe the motivation for, and current status of, one of the long-term goals of WDRC: to establish a permanent endowment for the operation of the Whole Earth Telescope. I pay particular attention to fund-raising efforts through the website at http://WhiteDwarf.org/donate/.

scholarly journals The Internal Structure of White Dwarf Stars Using the Whole Earth Telescope

1993 ◽  
Vol 139 ◽  
pp. 117-119
Author(s):  
P.A. Bradley
Keyword(s):  
Internal Structure ◽  
Stellar Evolution ◽  
White Dwarf ◽  
White Dwarfs ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
History Of ◽  
The Way ◽  
Whole Earth

AbstractWhite dwarfs are the final end state for the majority of stars, and hold clues to help solve many current pressing astrophysical problems. We can perform asteroseismology on the pulsating white dwarfs to better understand their internal structure and input physics, paving the way to a better understanding of astrophysics, stellar evolution, and the history of our Galaxy. I describe briefly the potential of asteroseismology by using it to infer the internal structure of PG1159-035.

scholarly journals Second-Order Effects due to Rotation in Pulsating Da White Dwarfs

1989 ◽  
Vol 114 ◽  
pp. 258-262
Author(s):  
P. Brassard ◽  
F. Vesemael ◽  
G. Fontaine
Keyword(s):  
Light Curve ◽  
White Dwarf ◽  
High Speed ◽  
Structural Parameters ◽  
Second Order ◽  
Order Effects ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Theoretical Predictions ◽  
Second Order Effects

The ZZ Ceti star L 19-2 is a stable pulsator whose light curve has now been deciphered with the help of over 300 hours of white light, high-speed photometry (O’Donoghue and Vamer 1982, 1987, hereafter ODV). The analysis indeed reveals the presence in the light curve of five coherent oscillations, with periods ranging from 113s to 350s. Among those, the 192s oscillation possesses three components, almost equally separated in frequency. Most importantly, the slight, but statistically significant, inequality in the frequency spacing of the triplet has been interpreted by these authors as second-order splitting of rotationally-perturbed g-mode oscillations. And indeed, the measured splitting appears consistent with the theoretical predictions of Chlebowski (1978), which are based on somewhat archaic white dwarf models. As pointed out by ODV, it is clearly of great interest to investigate 1) to what extent theoretical predictions based on more realistic, current-generation white dwarf models agree with ODVs identification, and 2) to what extent such second order effects can, eventually, be used to identify individual pulsation modes or constrain the structural parameters of variable white dwarf stars. Motivated by these questions, we have initiated a study of second-order effects due to rotation in ZZ Ceti stars, and we report here the first results of this program.

scholarly journals The Time Dependence of the Phases of the Harmonics Relative to the 1490 sec Fundamental in PG1346+082

1989 ◽  
Vol 114 ◽  
pp. 296-299
Author(s):  
J. L. Provencal ◽  
J. C. Clemens ◽  
G. Henry ◽  
B. P. Hine ◽  
R. E. Nather ◽  
...  
Keyword(s):  
White Dwarf ◽  
Compact Object ◽  
Detailed Knowledge ◽  
Line Profiles ◽  
Pressure Broadening ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Adequate Understanding ◽  
Magnitude Variation ◽  
Hydrogen Lines

White dwarf stars provide important boundary conditions for the understanding of stellar evolution. An adequate understanding of even these simple stars is impossible without detailed knowledge of their interiors. PG1346+082, an interacting binary white dwarf system, provides a unique opportunity to view the interior of one degenerate as it is brought to light in the accretion disk of the second star as the primary strips material from its less massive companion (see Wood et at. 1987).PG1346+082 is a photometric variable with a four magnitude variation over a four to five day quasi-period. A fast Fourier transform (FFT) of the light curve shows a complex, time-dependent structure of harmonics. PG1346+082 exhibits flickering – the signature of mass transfer. The optical spectra of the system contain weak emission features during minimum and broad absorption at all other times. This could be attributed to pressure broadening in the atmosphere of a compact object, or to a combination of pressure broadening and doppler broadening in a disk surrounding the compact accretor. No hydrogen lines are observed and the spectra are dominated by neutral helium. The spectra also display variable asymmetric line profiles.

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