Context. The collection of high-quality photometric data by space telescopes, such as the completed Kepler mission and the ongoing TESS program, is revolutionizing the area of white-dwarf asteroseismology. Among the different kinds of pulsating white dwarfs, there are those that have He-rich atmospheres, and they are called DBVs or V777 Her variable stars. The archetype of these pulsating white dwarfs, GD 358, is the focus of the present paper. Aims. We report a thorough asteroseismological analysis of the DBV star GD 358 (TIC 219074038) based on new high-precision photometric data gathered by the TESS space mission combined with data taken from the Earth. Methods. We reduced TESS observations of the DBV star GD 358 and performed a detailed asteroseismological analysis using fully evolutionary DB white-dwarf models computed accounting for the complete prior evolution of their progenitors. We assessed the mass of this star by comparing the measured mean period separation with the theoretical averaged period spacings of the models, and we used the observed individual periods to look for a seismological stellar model. We detected potential frequency multiplets for GD 358, which we used to identify the harmonic degree ( ℓ ) of the pulsation modes and rotation period. Results. In total, we detected 26 periodicities from the TESS light curve of this DBV star using standard pre-whitening. The oscillation frequencies are associated with nonradial g (gravity)-mode pulsations with periods from ∼422 s to ∼1087 s. Moreover, we detected eight combination frequencies between ∼543 s and ∼295 s. We combined these data with a huge amount of observations from the ground. We found a constant period spacing of 39.25 ± 0.17 s, which helped us to infer its mass ( M ⋆ = 0.588 ± 0.024 M ⊙ ) and constrain the harmonic degree ℓ of the modes. We carried out a period-fit analysis on GD 358, and we were successful in finding an asteroseismological model with a stellar mass ( M ⋆ = 0.584 −0.019 +0.025 M ⊙ ), compatible with the stellar mass derived from the period spacing, and in line with the spectroscopic mass ( M ⋆ = 0.560 ± 0.028 M ⊙ ). In agreement with previous works, we found that the frequency splittings vary according to the radial order of the modes, suggesting differential rotation. Obtaining a seismological model made it possible to estimate the seismological distance ( d seis = 42.85 ± 0.73 pc) of GD 358, which is in very good accordance with the precise astrometric distance measured by Gaia EDR3 ( π = 23.244 ± 0.024, d Gaia = 43.02 ± 0.04 pc). Conclusions. The high-quality data measured with the TESS space telescope, used in combination with data taken from ground-based observatories, provides invaluable information for conducting asteroseismological studies of DBV stars, analogously to what happens with other types of pulsating white-dwarf stars. The currently operating TESS mission, together with the advent of other similar space missions and new stellar surveys, will give an unprecedented boost to white dwarf asteroseismology.
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Bridging the Gap—The Disappearance of the Intermediate Period Gap for Fully Convective Stars, Uncovered by New ZTF Rotation Periods
Abstract The intermediate period gap, discovered by Kepler, is an observed dearth of stellar rotation periods in the temperature–period diagram at ∼20 days for G dwarfs and up to ∼30 days for early-M dwarfs. However, because Kepler mainly targeted solar-like stars, there is a lack of measured periods for M dwarfs, especially those at the fully convective limit. Therefore it is unclear if the intermediate period gap exists for mid- to late-M dwarfs. Here, we present a period catalog containing 40,553 rotation periods (9535 periods >10 days), measured using the Zwicky Transient Facility (ZTF). To measure these periods, we developed a simple pipeline that improves directly on the ZTF archival light curves and reduces the photometric scatter by 26%, on average. This new catalog spans a range of stellar temperatures that connect samples from Kepler with MEarth, a ground-based time-domain survey of bright M dwarfs, and reveals that the intermediate period gap closes at the theoretically predicted location of the fully convective boundary ( G BP − G RP ∼ 2.45 mag). This result supports the hypothesis that the gap is caused by core–envelope interactions. Using gyro-kinematic ages, we also find a potential rapid spin-down of stars across this period gap.
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- Award ID(s):
- 2108251
- NSF-PAR ID:
- 10413457
- Date Published:
- Journal Name:
- The Astronomical Journal
- Volume:
- 164
- Issue:
- 6
- ISSN:
- 0004-6256
- Page Range / eLocation ID:
- 251
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Context. The recent arrival of continuous photometric observations of unprecedented quality from space missions has strongly promoted the study of pulsating stars and caused great interest in the stellar astrophysics community. In the particular case of pulsating white dwarfs, the TESS mission is taking asteroseismology of these compact stars to a higher level, emulating or even surpassing the performance of its predecessor, the Kepler mission. Aims. We present a detailed asteroseismological analysis of six GW Vir stars that includes the observations collected by the TESS mission. Methods. We processed and analyzed TESS observations of RX J2117+3412 (TIC 117070953), HS 2324+3944 (TIC 352444061), NGC 6905 (TIC 402913811), NGC 1501 (TIC 084306468), NGC 2371 (TIC 446005482), and K 1−16 (TIC 233689607). We carried out a detailed 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 constrained the stellar mass of these stars by comparing the observed period spacing with the average of the computed period spacings, and we employed the individual observed periods to search for a representative seismological model when possible. Results. In total, we extracted 58 periodicities from the TESS light curves of these GW Vir stars using a standard prewhitening procedure to derive the potential pulsation frequencies. All the oscillation frequencies that we found are associated with g -mode pulsations, with periods spanning from ∼817 s to ∼2682 s. We find constant period spacings for all but one star (K 1−16), which allowed us to infer their stellar masses and constrain the harmonic degree ℓ of the modes. Based on rotational frequency splittings, we derive the rotation period of RX J2117+3412, obtaining a value in agreement with previous determinations. We performed period-to-period fit analyses on five of the six analyzed stars. For four stars (RX J2117+3412, HS 2324+3944, NGC 1501, and NGC 2371), we were able to find an asteroseismological model with masses that agree with the stellar mass values inferred from the period spacings and are generally compatible with the spectroscopic masses. Obtaining seismological models allowed us to estimate the seismological distance and compare it with the precise astrometric distance measured with Gaia . Finally, we find that the period spectrum of K 1−16 exhibits dramatic changes in frequency and amplitude that together with the scarcity of modes prevented us from meaningful seismological modeling of this star. Conclusions. The high-quality data collected by the TESS space mission, considered simultaneously with ground-based observations, provide very valuable input to the asteroseismology of GW Vir stars, similar to the case of other classes of pulsating white dwarf stars. The TESS mission, in conjunction with future space missions and upcoming surveys, will make impressive progress in white dwarf asteroseismology.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3847/1538-3881/ac9bee
