O, Fernrohr!

Kepler, Johannes

doi:10.1007/978-3-322-88802-0_108

Cited by 7 publications

(9 citation statements)

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“…Fundamental properties of the stars, such as mass, can be derived from just a few pulsation periods (Fontaine et al 1991; Bradley & Winget 1994). If many modes are excited, the structure and composition of the white dwarfs can be determined in detail and with high precision (Winget et al 1994; Kepler et al 2003). Since they constitute the evolutionary end point of 95–98 per cent of all stars, information on their internal structure and composition provide a critical test for stellar evolution models, including the double shell burning phase at the asymptotic giant branch and mass‐loss rates.…”

Section: Introductionmentioning

confidence: 99%

Seismological studies of ZZ Ceti stars - I. The model grid and the application to individual stars

Castanheira¹,

Kepler²

2008

Monthly Notices of the Royal Astronomical Society

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We calculate and explore an extensive adiabatic model grid for pulsating white dwarfs with hydrogen‐dominated atmospheres, the ZZ Ceti stars. We also compared the computed modes with the observed ones for five ZZ Ceti stars that are a representative sample of the whole class of pulsators. We describe our new approach for seismological studies, using the relative observed amplitudes to give weights for the periods in the fit and the external mass and temperature determinations as a guide. Our seismological study is clear evidence that seismology is indeed a powerful tool in the study of stellar structure and evolution.

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Section: Introductionmentioning

confidence: 99%

Seismological studies of ZZ Ceti stars - I. The model grid and the application to individual stars

Castanheira¹,

Kepler²

2008

Monthly Notices of the Royal Astronomical Society

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“…Since the mechanism that converts mechanical movement of stellar material to luminosity variations at the surface appears to be non‐linear, both harmonics and combinations of the basic mode frequencies can be expected to appear in the light curve. At least, this is the conclusion of many previous studies of the pulsating white dwarfs – especially the large amplitude pulsators, such as DBV GD 358 (Kepler et al 2003).…”

Section: Fourier Analysismentioning

confidence: 53%

“…As is clear from Fig. 7, such a pattern was detected in GD 358 (Winget et al 1994; Kepler et al 2003), and they were all readily interpreted as having spherical degree ℓ= 1 due to the fact they displayed clear triplet (rotational) splitting. This conclusion was possible, in spite of the complicated nature of the GD 358 pulsation behaviour.…”

Section: Comparison With Modelsmentioning

confidence: 79%

“…Their 20 h of photometry over a four month period in 1994 revealed a total of eight pulsation frequencies and showed that the object was a low‐amplitude DBV variable that appeared to be quite stable; this is in complete contrast (on both counts) to the class prototype, GD 358. In fact GD 358 is a large amplitude variable which also exhibits considerable changes in its observed pulsation spectrum over various time‐scales ranging from days to years (Kepler et al 2003).…”

Section: Introductionmentioning

confidence: 99%

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Whole Earth Telescope observations of the hot helium atmosphere pulsating white dwarf EC 20058−5234

Sullivan¹,

Metcalfe²,

O’Donoghue³

et al. 2008

Monthly Notices RAS

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We present the analysis of a total of 177 h of high‐quality optical time‐series photometry of the helium atmosphere pulsating white dwarf (DBV) EC 20058−5234. The bulk of the observations (135 h) were obtained during a WET campaign (XCOV15) in 1997 July that featured coordinated observing from four southern observatory sites over an 8‐d period. The remaining data (42 h) were obtained in 2004 June at Mt John Observatory in NZ over a one‐week observing period. This work significantly extends the discovery observations of this low‐amplitude (few per cent) pulsator by increasing the number of detected frequencies from 8 to 18, and employs a simulation procedure to confirm the reality of these frequencies to a high level of significance (1 in 1000). The nature of the observed pulsation spectrum precludes identification of unique pulsation mode properties using any clearly discernable trends. However, we have used a global modelling procedure employing genetic algorithm techniques to identify the n, ℓ values of eight pulsation modes, and thereby obtain asteroseismic measurements of several model parameters, including the stellar mass (0.55 M⊙) and Teff (∼28 200 K). These values are consistent with those derived from published spectral fitting: Teff∼ 28 400 K and log g∼ 7.86. We also present persuasive evidence from apparent rotational mode splitting for two of the modes that indicates this compact object is a relatively rapid rotator with a period of 2 h. In direct analogy with the corresponding properties of the hydrogen (DAV) atmosphere pulsators, the stable low‐amplitude pulsation behaviour of EC 20058 is entirely consistent with its inferred effective temperature, which indicates it is close to the blue edge of the DBV instability strip. Arguably, our most significant result from this work is the clear demonstration that EC 20058 is a very stable pulsator with several dominant pulsation modes that can be monitored for their long‐term stability.

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“…In some cases, we encounter strange, sudden, short‐term variations in the pulsational behaviours of stars: for example the ‘sforzando’ effect observed in the DBV star GD 358 in 1996, where the non‐linear light curve of the star changed into a high amplitude, remarkably sinusoidal one for a short period of time (Kepler et al 2003; Provencal et al 2009). In the case of PG 1456+103 its luminosity variations almost disappeared just before the Whole Earth Telescope (WET; Nather et al 1990) run started on the star (Handler 2003a).…”

Section: Introductionmentioning

confidence: 99%

Characterizing the pulsations of the ZZ Ceti star KUV 02464+3239

Bognár

Paparó

Bradley

et al. 2009

Monthly Notices of the Royal Astronomical Society

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We present the results on period search and modeling of the cool DAV star KUV 02464+3239. Our observations resolved the multiperiodic pulsational behaviour of the star. In agreement with its position near the red edge of the DAV instability strip, it shows large amplitude, long period pulsation modes, and has a strongly non-sinusoidal light curve. We determined 6 frequencies as normal modes and revealed remarkable short-term amplitude variations. A rigorous test was performed for the possible source of amplitude variation: beating of modes, effect of noise, unresolved frequencies or rotational triplets. Among the best-fit models resulting from a grid search, we selected 3 that gave l=1 solutions for the largest amplitude modes. These models had masses of 0.645, 0.650 and 0.680 M_Sun. The 3 `favoured' models have M_H between 2.5x10^-5 - 6.3x10^-6 M_* and give 14.2 - 14.8 mas seismological parallax. The 0.645 M_Sun (11400 K) model also matches the spectroscopic log g and T_eff within 1 sigma. We investigated the possibility of mode trapping and concluded that while it can explain high amplitude modes, it is not required.Comment: 11 pages, 8 figures, accepted for publication in MNRA

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O, Fernrohr!

Cited by 7 publications

References 0 publications

Seismological studies of ZZ Ceti stars - I. The model grid and the application to individual stars

Seismological studies of ZZ Ceti stars - I. The model grid and the application to individual stars

Whole Earth Telescope observations of the hot helium atmosphere pulsating white dwarf EC 20058−5234

Characterizing the pulsations of the ZZ Ceti star KUV 02464+3239

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