Nonlinear behavior of the pulsating white dwarf GD 358

Vuille, François

doi:10.1515/astro-2000-0109

Cited by 4 publications

(4 citation statements)

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“…Combination frequencies potentially contain a wealth of astrophysical information, which we are only just beginning to explore (e.g. see Wu 1998 andVuille 1999). As a further step in this direction, we will make a detailed comparison of our observations with the model by Wu (1998Wu ( , 2001, hereinafter "Wu's model") 1 .…”

Section: Combination Frequenciesmentioning

confidence: 99%

The unusual pulsation spectrum of the cool ZZ Ceti star HS 0507+0434B

Handler

Romero-Colmenero

Montgomery

2002

Monthly Notices of the Royal Astronomical Society

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We present the analysis of one week of single-site high-speed CCD photometric observations of the cool ZZ Ceti star HS 0507+0434B. Ten independent frequencies are detected in the star's light variations: one singlet and three nearly-equally spaced triplets. We argue that these triplets are due to rotationally split modes of spherical degree l=1. This is the first detection of consistent multiplet structure in the amplitude spectrum of a cool ZZ Ceti star and it allows us to determine the star's rotation period: 1.70 +/- 0.11 d. We report exactly equal frequency, not period, spacings between the detected mode groups. In addition, certain pairs of modes from the four principal groups have frequency ratios which are very close to 3:4 or 4:5; while these ratios are nearly exact (within one part in 10^4), they still lie outside the computed error bars. We speculate that these relationships between different frequencies could be caused by resonances. One of the three triplets may not be constant in amplitude and/or frequency. We compare our frequency solution for the combination frequencies (of which we detected 38) to Wu's (1998, 2001) model thereof. We obtain consistent results when trying to infer the star's convective thermal time and the inclination angle of its rotational axis. Theoretical combination-frequency amplitude spectra also resemble those of the observations well, and direct theoretical predictions of the observed second-order light-curve distortions were also reasonably successful assuming the three triplets are due to l=1 modes. Attempts to reproduce the observed combination frequencies adopting all possible l=2 identifications for the triplets did not provide similarly consistent results, supporting their identification with l=1.Comment: Accepted for publication in MNRAS; 12 pages, 8 figure

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Section: Combination Frequenciesmentioning

confidence: 99%

The unusual pulsation spectrum of the cool ZZ Ceti star HS 0507+0434B

Handler

Romero-Colmenero

Montgomery

2002

Monthly Notices of the Royal Astronomical Society

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“…In order to better describe the combination frequencies and their origin, their relative phases and amplitudes were analysed. Following Buchler et al (1997) and Vuille (2000), they are defined as and…”

Section: Nonlinear Frequency Lockingmentioning

confidence: 99%

Evidence for nonlinear resonant mode coupling in the $\mathsf{\beta}$ Cephei star HD 180642 (V1449 Aquilae) from CoRoT photometry

Degroote¹,

Briquet²,

Catala

et al. 2009

A&A

120

159

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Context. We present the CoRoT light curve of the β Cep star HD 180642, assembled during the first long run of the space mission, as well as archival single-band photometry. Aims. Our goal is to analyse the detailed behaviour present in the light curve and interpret it in terms of excited-mode frequencies. Methods. After describing the noise properties in detail, we use various time series analyses and fitting techniques to model the CoRoT light curve, for various physical assumptions. We apply statistical goodness-of-fit criteria that allow us to select the most appropriate physical model fit to the data. Results. We conclude that the light-curve model based on nonlinear resonant frequency and phase locking provides the best representation of the data. Interpretation of the residuals is dependent on the chosen physical model used to prewhiten the data. Conclusions. Our observational results constitute a fruitful starting point for detailed seismic stellar modelling of this large-amplitude and evolved β Cep star.

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“…Linear combinations of frequencies have been observed in DAVs and in DBVs. It is the case of the DAV star GD 154 (Pfeiffer et al 1996) and the DBVs stars GD 358 (Vuille et al 2000;Kepler et al 2003). The physical causes of the nonlinear behavior are not well understood.…”

Section: Linear Combinations Of Frequenciesmentioning

confidence: 99%

The pulsation modes of the pre-white dwarf PG 1159-035

Costa¹,

Kepler²,

Winget³

et al. 2007

A&A

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Context. PG 1159-035, a pre-white dwarf with T eff 140 000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. Analyzing the periods of pulsation, it is possible to measure the stellar mass, the rotational period and the inclination of the rotation axis, to estimate an upper limit for the magnetic field, and even to obtain information about the inner stratification of the star. Aims. We have three principal aims: to increase the number of detected and identified pulsation modes in PG 1159-035, study trapping of the star's pulsation modes, and to improve or constrain the determination of stellar parameters. Methods. We used all available WET photometric data from 1983, 1985, 1989, 1993 and 2002 to identify the pulsation periods. Results. We identified 76 additional pulsation modes, increasing to 198 the number of known pulsation modes in PG 1159-035, the largest number of modes detected in any star besides the Sun. From the period spacing we estimated a mass M/M = 0.59 ± 0.02 for PG 1159-035, with the uncertainty dominated by the models, not the observation. Deviations in the regular period spacing suggest that some of the pulsation modes are trapped, even though the star is a pre-white dwarf and the gravitational settling is ongoing. The position of the transition zone that causes the mode trapping was calculated at r c /R = 0.83 ± 0.05. From the multiplet splitting, we calculated the rotational period P rot = 1.3920 ± 0.0008 days and an upper limit for the magnetic field, B < 2000 G. The total power of the pulsation modes at the stellar surface changed less than 30% for = 1 modes and less than 50% for = 2 modes. We find no evidence of linear combinations between the 198 pulsation mode frequencies. PG 1159-035 models have not significative convection zones, supporting the hypothesis that nonlinearity arises in the convection zones in cooler pulsating white dwarf stars.Key words. stars: oscillations -stars: individual: PG 1159-035 -stars: interiors -stars: white dwarfs IntroductionThe star PG 1159-035 was identified by Green in 1977 in a survey for objects with ultraviolet excess, known as the PalomarGreen Survey (Green et al. 1986). The presence of lines of He II in the PG 1159-035 spectrum suggested a high superficial temperate (McGraw et al. 1979). The analysis of the far ultraviolet flux distribution -from ∼1200 Å to the Lyman limit at 912 Å -obtained with the Voyager 2 ultraviolet spectrophotometer indicated an effective temperature above 100 000 K (Wegner et al. 1982). Later analysis with the IUE and EXOSAT show that PG 1159-035 is one of the hottest stars known (Sion et al. 1985;Barstow et al. 1986); the current estimated temperature for PG 1159-035 is 140 000 ± 5000 K (Werner et al. 1991;Dreizler et al. 1998;and Jahn et al. 2007) and log g(cgs) = 7.0 ± 0.5 Tables 12-17 a...

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Nonlinear behavior of the pulsating white dwarf GD 358

Cited by 4 publications

References 0 publications

The unusual pulsation spectrum of the cool ZZ Ceti star HS 0507+0434B

The unusual pulsation spectrum of the cool ZZ Ceti star HS 0507+0434B

Evidence for nonlinear resonant mode coupling in the $\mathsf{\beta}$ Cephei star HD 180642 (V1449 Aquilae) from CoRoT photometry

The pulsation modes of the pre-white dwarf PG 1159-035

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