Exploring the pulsational properties of two ZZ Ceti stars

Bognár, Zs.; Kalup, Cs.; Sódor, Á.

doi:10.1051/0004-6361/202140338

Cited by 7 publications

(5 citation statements)

References 46 publications

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“…TESS has provided extensive photometric observations of the 200 000 brightest stars in 85% of the sky in the first part of the mission, each observation with a time base of about 27 days per sector observed. In the context of pulsating WDs and pre-WDs, the high-quality observations of TESS, combined with ground-based observations, are able to provide a very important input to the asteroseismology of DBVs (Bell et al 2019;Bognár et al 2021), DAVs (Bognár et al 2020), pre-ELMVs (Wang et al 2020Hong et al 2021), and GW Vir stars (Córsico et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Pulsating hydrogen-deficient white dwarfs and pre-white dwarfs observed with TESS

Uzundag

Córsico

Althaus

et al. 2021

A&A

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Context. The Transiting Exoplanet Survey Satellite (TESS) mission is revolutionizing the blossoming area of asteroseismology, particularly of pulsating white dwarfs and pre-white dwarfs, thus continuing the impulse of its predecessor, the Kepler mission. Aims. In this paper, we present the observations from the extended TESS mission in both 120 s short-cadence and 20 s ultra-short-cadence mode of two pre-white dwarf stars showing hydrogen deficiency. We identify them as two new GW Vir stars, TIC 333432673 and TIC 095332541. We apply the tools of asteroseismology with the aim of deriving their structural parameters and seismological distances. Methods. We carried out a spectroscopic analysis and a spectral fitting of TIC 333432673 and TIC 095332541. We also processed and analyzed the high-precision TESS photometric light curves of the two target stars, and derived their oscillation frequencies. We performed an asteroseismological analysis of these stars on the basis of PG 1159 evolutionary models that take into account the complete evolution of the progenitor stars. We searched for patterns of uniform period spacings in order to constrain the stellar mass of the stars. We employed the individual observed periods to search for a representative seismological model. Results. The analysis of the TESS light curves of TIC 333432673 and TIC 095332541 reveals the presence of several oscillations with periods ranging from 350 to 500 s associated to typical gravity (g)-modes. From follow-up ground-based spectroscopy, we find that both stars have a similar effective temperature (Teff = 120 000 ± 10 000 K) and surface gravity (log g = 7.5 ± 0.5), but a different He/C composition of their atmosphere. On the basis of PG 1159 evolutionary tracks, we derived a spectroscopic mass of M⋆ = 0.58−0.08+0.16 M⊙ for both stars. Our asteroseismological analysis of TIC 333432673 allowed us to find a constant period spacing compatible with a stellar mass M⋆ ∼ 0.60 − 0.61 M⊙, and an asteroseismological model for this star with a stellar mass M⋆ = 0.589 ± 0.020 M⊙, as well as a seismological distance of d = 459−156+188 pc. For this star, we find an excellent agreement between the different methods to infer the stellar mass, and also between the seismological distance and that measured with Gaia (dGaia = 389−5.2+5.6 pc). For TIC 095332541, we have found a possible period spacing that suggests a stellar mass of M⋆ ∼ 0.55 − 0.57 M⊙. Unfortunately, we have not been able to find an asteroseismological model for this star. Conclusions. Using the high-quality data collected by the TESS space mission and follow-up spectroscopy, we have been able to discover and characterize two new GW Vir stars. The TESS mission is having, and will continue to have, an unprecedented impact on the area of white-dwarf asteroseismology.

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Section: Introductionmentioning

confidence: 99%

Pulsating hydrogen-deficient white dwarfs and pre-white dwarfs observed with TESS

Uzundag

Córsico

Althaus

et al. 2021

A&A

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“…PM J22299+3024 (G = 16.21 mag, α 2000 = 22 h 29 m 58 s , δ 2000 = +30 d 24 m 10 s ) was found to be a variable candidate by our research group in 2018 July (Bognár et al 2019a). We performed survey observations to find new bright white dwarf pulsators for the TESS (Ricker et al 2015) all-sky survey space mission.…”

Section: Pm J22299+3024mentioning

confidence: 82%

“…This makes the search for new pulsators among white dwarfs an important effort. This is why we have initiated a survey searching for new pulsating white dwarf targets for the TESS (Transiting Exoplanet Survey Satellite) space telescope (Bognár et al 2018(Bognár et al , 2019a. One of our new discoveries was PM J22299+3024, a new pulsator candidate (Bognár et al 2019a).…”

Section: Introductionmentioning

confidence: 99%

Exploring the pulsational properties of two ZZ Ceti stars

Bognár,

Kalup,

Sódor

2021

Preprint

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Context. We continued our ground-based observing project with the season-long observations of ZZ Ceti stars at 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 (Transiting Exoplanet Survey Satellite) space telescope in 120-second cadence mode. Aims. Our main aims are to characterise the pulsation properties of the targets, and extract pulsations modes from the data for asteroseismic investigations. Methods. We performed standard Fourier analysis of the daily, weekly, and the whole 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. 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. The temperature is ≈ 800 K higher, while the mass of the model star is exactly the same as it 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, while our best model solutions give M * = 0.70 M ⊙ mass for this target, near to the spectroscopic value of 0.65 M ⊙ , likewise in the case of PM J22299+3024. The seismic distances of our best-fitting 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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“…For our target, this geometric distance is d Gaia = 33.939 +0.027 −0.030 pc (Bailer-Jones et al 2021), which is based on the Gaia early third release EDR3 (Gaia Collaboration et al 2021). The method we followed to determine the seismic distances of the selected models utilising the luminosity of the given model and the apparent visual magnitude of the star is detailed, for instance, in Bell et al (2019) and Bognár et al (2021). For the apparent visual magnitude of GD 99, the fourth US Naval Observatory CCD Astrograph Catalog (Zacharias et al 2012) gives m V = 14.584 ± 0.06 mag.…”

Section: T Eff [K]mentioning

confidence: 99%

“…Thus, we selected this target for further, long-term and ground-based photometric observations, as one of the targets in our observing programme aimed at obtaining measurements as well as (in many cases) carrying out an asteroseismological investigation of our target objects (see e.g. Bognár et al 2009;Paparó et al 2013;Bognár et al 2014Bognár et al , 2016Bognár et al , 2018Bognár et al , 2019Bognár et al , 2021Kalup et al 2021).…”

Section: Introductionmentioning

confidence: 99%

GD 99: Re-investigation of an old ZZ Ceti companion

Bognár

Sódor

Mező

2023

A&A

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Context. Thanks to photometric space missions, we have access to more and more information on the properties of white dwarf stars, especially pulsating ones. In the case of pulsators, we have the opportunity to get an insight into their otherwise hidden interiors by the means of asteroseismology. In addition to space-based observations, we also take advantage of the opportunity to study the pulsations of white dwarf stars from the ground, either as observations that are complementary to space-based measurements or individual observing runs on selected targets across long timescales. Aims. We aim to investigate long-term, single-site observations of the bright, yet scarcely studied ZZ Ceti star, GD 99. Our main goals are to determine as many eigenmodes for asteroseismology as possible and then to carry out a seismic analysis of this target. Methods. We performed a Fourier analysis of the light curves obtained in different epochs. After finding the normal modes of the pulsation, we ran the 2018 version of the White Dwarf Evolution Code to build model grids for the period fits. We compared the seismic distance of the best-fit model with the geometric value provided by Gaia measurements. Results. We find that GD 99 is rich in pulsation modes in the ∼ 200 − 1100 s period range, as we detected seven new periods. Together with the literature data, we were able to use 11 modes for the asteroseismic fits. We accepted an asteroseismic model solution with T eff = 13 500 K and M * = 0.80 M ⊙ as a best fit, however, this suggests a hotter and more massive star than we might have expected based on the spectroscopic values. We also estimated the rotational rate of the star to be 13.17 h, based on TESS observations.

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Exploring the pulsational properties of two ZZ Ceti stars

Cited by 7 publications

References 46 publications

Pulsating hydrogen-deficient white dwarfs and pre-white dwarfs observed with TESS

Pulsating hydrogen-deficient white dwarfs and pre-white dwarfs observed with TESS

Exploring the pulsational properties of two ZZ Ceti stars

GD 99: Re-investigation of an old ZZ Ceti companion

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