Multicolor variations of the ZZ Ceti stars

Robinson, E. L.; Kepler, S. O.; Nather, R. E.

doi:10.1086/160162

Cited by 116 publications

(121 citation statements)

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“…While nonlinear effects are well known for large observed amplitude pulsations, the present study reaches the surprising conclusion that the amplitudes and phases can be described fairly accurately by the linear theory as developed by Robinson et al (1982) for the fundamental and Wu (1998) for higher harmonics.…”

Section: Discussionsupporting

confidence: 49%

“…Robinson et al 1982) all terms with m = 0 do not contribute to a flux variation in the integrated light, because they are equivalent to a rotating pattern with respect to an axis directed to the observer. For the term with m = 0 the assumption of a constant phase over the stellar surface is valid and the Fourier coefficient a 0 is assumed to be constant over the surface by Eq.…”

Section: The Linear Assumptionmentioning

confidence: 99%

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Nonlinear effects in time-resolved spectra of DAVs

Ising

Koester

2001

A&A

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Abstract. Numerical simulations of light curves of variable DA white dwarfs (ZZ Ceti stars) predict flux amplitudes with surface distributions different from the spherical harmonics of the pulsation mode in deeper layers. In contrast to the results of the perturbation analysis by Goldreich and Wu, this is also true for the fundamental period of the flux variation. As a consequence, normalized amplitude spectra depend not only on the mode number l but also on pulsation amplitude and inclination. Another new result is that with increasing amplitude of the pressure variation below the convection zone, the flux variation at the surface goes through a maximum and then decreases again.

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Section: Discussionsupporting

confidence: 49%

Section: The Linear Assumptionmentioning

confidence: 99%

Nonlinear effects in time-resolved spectra of DAVs

Ising

Koester

2001

A&A

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“…7). The very important work by Robinson et al (1982) provided unequivocal theoretical support to the idea that the luminosity variations are entirely due to surface temperature variations, and that the variations of radius are as small as δ R * /R * ∼ 10 −4 . Note that the lineal theory of non-radial pulsations does not provide any clue about the value of the fractional change in radius, since the governing equations are homogeneous and the normalization of the eigenfunctions is arbitrary (Cox 1980).…”

Section: Brief History Of Discoverymentioning

confidence: 95%

Evolutionary and pulsational properties of white dwarf stars

Althaus

Córsico

Isern

et al. 2010

Astron Astrophys Rev

359

372

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White dwarf stars are the final evolutionary stage of the vast majority of stars, including our Sun. Since the coolest white dwarfs are very old objects, the present population of white dwarfs contains a wealth of information on the evolution of stars from birth to death, and on the star formation rate throughout the history of our Galaxy. Thus, the study of white dwarfs has potential applications to different fields of astrophysics. In particular, white dwarfs can be used as independent reliable cosmic clocks, and can also provide valuable information about the fundamental parameters of a wide variety of stellar populations, like our Galaxy and open and globular clusters. In addition, the high densities and temperatures characterizing white dwarfs allow to use these stars as cosmic laboratories for studying physical processes under extreme conditions that cannot be achieved in terrestrial laboratories. Last but not least, since many white dwarf stars undergo pulsational instabilities, the study of their properties constitutes a powerful tool for applications beyond stellar astrophysics. In particular, white dwarfs can be used to constrain fundamental properties of elementary particles such as axions and neutrinos, and to study problems related to the variation of fundamental constants.These potential applications of white dwarfs have led to a renewed interest in the calculation of very detailed evolutionary and pulsational models for these stars. In this work, we review the essentials of the physics of white dwarf stars. We enumerate the reasons that make these stars excellent chronometers and we describe why white dwarfs provide tools for a wide variety of applications. Special emphasis is placed on the physical processes that lead to the formation of white dwarfs as well as on the different energy sources and processes responsible for chemical abundance changes that occur along their evolution. Moreover, in the course of their lives, white dwarfs cross different pulsational instability strips. The existence of these instability strips provides astronomers with an unique opportunity to peer into their internal structure that would otherwise remain hidden from observers. We will show that this allows to measure with unprecedented precision the stellar masses and to infer their envelope thicknesses, to probe the core chemical stratification, and to detect rotation rates and magnetic fields. Consequently, in this work, we also review the pulsational properties of white dwarfs and the most recent applications of white dwarf asteroseismology.

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“…The mode identification is described by Kepler et al (2003). Robinson et al (1982) and Kepler (1984) demonstrated that the variable white dwarf stars pulsate in non-radial g-modes, with buoyancy providing the restoring force. They also show that the amplitudes change with wavelength but the phases do not, in the models with no non-adiabatic effects.…”

Section: Amplitude Variation With Wavelengthmentioning

confidence: 99%

HST observations of the pulsating white dwarf GD 358

Castanheira¹,

Nitta²,

Winget

et al. 2005

A&A

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Abstract. We used time-resolved ultraviolet spectroscopy obtained with the FOS and STIS spectrographs of the Hubble Space Telescope (HST), together with archival IUE observations to measure the effective temperature (T eff ), surface gravity (log g) and distance (d) of the pulsating DB white dwarf GD 358 with unprecedented accuracy, and to show that the temperature did not change during the 1996 sforzando, when the star changed basically to a single mode pulsator. We also measured for the first time for a DBV the spherical harmonic degree ( ) for two modes, with k = 8 and k = 9, which was only possible because the stellar light curve was dominated by a single mode in 1996. The independent spectra provide the following values: T eff = 24 100 ± 400 K, log g = 7.91 ± 0.26 and d = 42.7 ± 2.5 pc. The ultraviolet spectroscopic distance is in better agreement with the seismological value, than the one derived by parallax.

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Multicolor variations of the ZZ Ceti stars

Cited by 116 publications

References 0 publications

Nonlinear effects in time-resolved spectra of DAVs

Nonlinear effects in time-resolved spectra of DAVs

Evolutionary and pulsational properties of white dwarf stars

HST observations of the pulsating white dwarf GD 358

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