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

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.

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Constraining convection parameters from the light curve shapes of pulsating white dwarf stars: the cases of EC 14012-1446 and WD 1524-0030

Journal of Physics Conference Series ◽

10.1088/1742-6596/118/1/012057 ◽

2008 ◽

Vol 118 ◽

pp. 012057 ◽

Cited By ~ 1

Author(s):

G Handler ◽

J L Provencal ◽

M H Montgomery ◽

E Romero-Colmenero ◽

K Sanchawala ◽

...

Keyword(s):

Light Curve ◽

White Dwarf ◽

Dwarf Stars ◽

White Dwarf Stars

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The Whole Earth Telescope

International Astronomical Union Colloquium ◽

10.1017/s0252921100099371 ◽

1989 ◽

Vol 114 ◽

pp. 109-114 ◽

Cited By ~ 1

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.

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2571 ◽

2019 ◽

Vol 490 (2) ◽

pp. 1803-1820 ◽

Cited By ~ 3

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.

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

International Astronomical Union Colloquium ◽

10.1017/s0252921100036800 ◽

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.

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Resistive switching kinetics and second-order effects in parylene-based memristors

Applied Physics Letters ◽

10.1063/5.0030069 ◽

2020 ◽

Vol 117 (24) ◽

pp. 243501

Author(s):

Anna N. Matsukatova ◽

Andrey V. Emelyanov ◽

Anton A. Minnekhanov ◽

Aleksandr A. Nesmelov ◽

Artem Yu. Vdovichenko ◽

...

Keyword(s):

Resistive Switching ◽

Second Order ◽

Order Effects ◽

Second Order Effects

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

International Astronomical Union Colloquium ◽

10.1017/s0252921100099759 ◽

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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