G 207-9 and LP 133-144: light-curve analysis and asteroseismology of two ZZ Ceti stars

Bognár, Zs.; Paparó, M.; Molnár, L.; Pápics, P. I.; Plachy, E.; Verebélyi, Erika; Sódor, Á.

doi:10.1093/mnras/stw1597

Cited by 16 publications

(13 citation statements)

References 31 publications

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“…References. -(0) This work; (1) Giammichele et al (2016); (2) Dolez et al (2006); (3) Fu et al (2013); (4) Su et al (2014); (5) Pfeiffer et al (1996); (6) Bognár et al (2016); (7) Bradley (2001); (8) Castanheira et al (2013); (9) Kepler et al (1995); (10) Pech & Vauclair (2006); (11) Fu et al (2007); (12) Bond et al (1996); (13) Charpinet et al (2009); (14) Vauclair et al (2002); (15) Kawaler et al (1995); (16) Østensen et al (2011); (17) Hermes et al (2017b); (18) Bell et al (2015); (19) Greiss et al (2014); (20) icantly simplifies mode identification and affords us the opportunity to probe internal rotation for 20 of the 27 DAVs we present here. For example, Figure 1 shows the five dipole (ℓ = 1) modes in EPIC 201802933 (SDSSJ1151+0525) identified from their splittings.…”

Section: Rotation Ratesmentioning

confidence: 99%

White Dwarf Rotation as a Function of Mass and a Dichotomy of Mode Line Widths: Kepler Observations of 27 Pulsating DA White Dwarfs through K2 Campaign 8

Hermes

Gänsicke

Kawaler

et al. 2017

ApJS

199

226

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We present photometry and spectroscopy for 27 pulsating hydrogen-atmosphere white dwarfs (DAVs, a.k.a. ZZ Ceti stars) observed by the Kepler space telescope up to K2 Campaign 8, an extensive compilation of observations with unprecedented duration (>75 days) and duty cycle (>90%). The space-based photometry reveals pulsation properties previously inaccessible to ground-based observations. We observe a sharp dichotomy in oscillation mode linewidths at roughly 800 s, such that white dwarf pulsations with periods exceeding 800 s have substantially broader mode linewidths, more reminiscent of a damped harmonic oscillator than a heat-driven pulsator. Extended Kepler coverage also permits extensive mode identification: We identify the spherical degree of 61 out of 154 unique radial orders, providing direct constraints of the rotation period for 20 of these 27 DAVs, more than doubling the number of white dwarfs with rotation periods determined via asteroseismology. We also obtain spectroscopy from 4m-class telescopes for all DAVs with Kepler photometry. Using these homogeneously analyzed spectra we estimate the overall mass of all 27 DAVs, which allows us to measure white dwarf rotation as a function of mass, constraining the endpoints of angular momentum in low-and intermediate-mass stars. We find that 0.51 − 0.73 M ⊙ white dwarfs, which evolved from 1.7 − 3.0M ⊙ ZAMS progenitors, have a mean rotation period of 35 hr with a standard deviation of 28 hr, with notable exceptions for higher-mass white dwarfs. Finally, we announce an online repository for our Kepler data and follow-up spectroscopy, which we collect at k2wd.org.

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Section: Rotation Ratesmentioning

confidence: 99%

White Dwarf Rotation as a Function of Mass and a Dichotomy of Mode Line Widths: Kepler Observations of 27 Pulsating DA White Dwarfs through K2 Campaign 8

Hermes

Gänsicke

Kawaler

et al. 2017

ApJS

199

226

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“…With this publication on PM J22299+3024 and LP 119-10, we continue our efforts to introduce the results of our long-term ground-based observations on pulsating white dwarf stars in a series of papers (see e.g. Bognár et al 2009Bognár et al , 2014Bognár et al , 2016Bognár et al , 2019bPaparó et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Exploring the pulsational properties of two ZZ Ceti stars

Bognár

Kalup

Sódor

2021

A&A

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Context. We continued our ground-based observing project with the season-long observations of ZZ Ceti stars at the Konkoly Observatory. Our present targets are the newly discovered PM J22299+3024 and the already known LP 119–10 variables. LP 119–10 was also observed by the TESS space telescope in 120-second cadence mode. Aims. Our main aims are to characterise the pulsation properties of the targets and extract pulsation modes from the data for asteroseismic investigations. Methods. We performed a standard Fourier analysis of the daily, weekly, and entire data sets, together with test data of different combinations of weekly observations. We then performed asteroseismic fits utilising the observed and the calculated pulsation periods. For the calculations of model grids necessary for the fits, we applied the 2018 version of the White Dwarf Evolution Code. Results. We derived six possible pulsation modes for PM J22299+3024 and five plus two TESS pulsation frequencies for LP 119–10. We note that further pulsation frequencies may be present in the data sets, but we found their detection ambiguous, so we omitted them from the final frequency list. Our asteroseismic fits of PM J22299+3024 give 11 400 K and 0.46 M⊙ for the effective temperature and the stellar mass, respectively. The temperature is ≈800 K higher, while the mass of the model star is exactly the same as was earlier derived by spectroscopy. Our model fits of LP 119–10 put the effective temperature in the range of 11 800−11 900 K, which is again higher than the spectroscopic 11 290 K value. Moreover, our best model solutions give M* = 0.70 M⊙ mass for this target, which is near to the spectroscopic value of 0.65 M⊙ and likewise in the case of PM J22299+3024. The seismic distances of our best-fit model stars agree with the Gaia astrometric distances of PM J22299+3024 and LP 119–10 within the errors, validating our model results.

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“…In particular, two main asteroseismological avenues have been employed: one considering stellar models harboring parametrized chemical composition profiles, and another involving fully evolutionary models characterized by chemical profiles resulting from all the processess experienced during the evolution of the WD progenitors. The former approach constitutes a powerful forward method with the flexibility of allowing a full exploration of the parameter space (the total mass, the mass of the H and He envelopes, the thickness of the chemical transition regions, the core chemical structure and composition, etc) to find an optimum asteroseismological model (see Bradley 1998Bradley , 2001Paparó et al 2013;Bognár et al 2016;Giammichele et al 2016Giammichele et al , 2017aGiammichele et al ,b, 2018. The weak point of this method is that given the lack of a large number of observed pulsations it can lead to asteroseismological solutions characterized by chemical structures that are not predicted by any scenario of WD evolution.…”

Section: Introductionmentioning

confidence: 99%

Pulsating low-mass white dwarfs in the frame of new evolutionary sequences

Calcaferro

Córsico

Althaus

et al. 2018

A&A

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Context. Some low-mass white-dwarf (WD) stars with H atmospheres currently being detected in our galaxy, show long-period g(gravity)-mode pulsations, and comprise the class of pulsating WDs called extremely low-mass variable (ELMV) stars. At present, it is generally believed that these stars have thick H envelopes. However, from stellar evolution considerations, the existence of low-mass WDs with thin H envelopes is also possible. Aims. We present a thorough asteroseismological analysis of ELMV stars on the basis of a complete set of fully evolutionary models that represents low-mass He-core WD stars harboring a range of H envelope thicknesses. Although there are currently nine ELMVs, here we only focus on those that exhibit more than three periods and whose periods do not show significant uncertainties. Methods. We considered g-mode adiabatic pulsation periods for low-mass He-core WD models with stellar masses in the range [0.1554–0.4352] M⊙, effective temperatures in the range [6000–10 000] K, and H envelope thicknesses in the interval −5.8 ≲ log(MH/M⋆)≲ −1.7. We explore the effects of employing different H-envelope thicknesses on the adiabatic pulsation properties of low-mass He-core WD models, and perform period-to-period fits to ELMV stars to search for a representative asteroseismological model. Results. We found that the mode-trapping effects of g modes depend sensitively on the value of MH, with the trapping cycle and trapping amplitude larger for thinner H envelopes. We also found that the asymptotic period spacing, ΔΠa, is longer for thinner H envelopes. Finally, we found asteroseismological models (when possible) for the stars under analysis, characterized by canonical (thick) and by thin H envelope. The effective temperature and stellar mass of these models are in agreement with the spectroscopic determinations. Conclusions. The fact that we have found asteroseismological solutions with H envelopes thinner than canonical gives a suggestion of the possible scenario of formation of these stars. Indeed, in the light of our results, some of these stars could have been formed by binary evolution through unstable mass loss.

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G 207-9 and LP 133-144: light-curve analysis and asteroseismology of two ZZ Ceti stars

Cited by 16 publications

References 31 publications

White Dwarf Rotation as a Function of Mass and a Dichotomy of Mode Line Widths: Kepler Observations of 27 Pulsating DA White Dwarfs through K2 Campaign 8

White Dwarf Rotation as a Function of Mass and a Dichotomy of Mode Line Widths: Kepler Observations of 27 Pulsating DA White Dwarfs through K2 Campaign 8

Exploring the pulsational properties of two ZZ Ceti stars

Pulsating low-mass white dwarfs in the frame of new evolutionary sequences

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