Ground-Based Observations of the ZZ Ceti Star HS 1625+1231

We present the results of our detailed light curve analysis of the ZZ Ceti star HS 1625+1231. We collected photometric time series data at Konkoly Observatory on 14 nights, and performed Fourier analysis of these data sets. We detected 11 significant frequencies, where six of them are found to be independent pulsation modes in the 514-881 s period range. By utilizing these frequencies, we performed preliminary asteroseismic investigations to give constraints on the main physical parameters, and to derive seismic distances for the star. Finally, we compared the astrometric distance provided by the Gaia EDR3 data with those seismic distances. Our selected model, considering both the spectroscopic measurements and the distance value provided by Gaia, has Teff=11 000 K and M*=0.60 M⊙

TESS first look at evolved compact pulsators. Known ZZ Ceti stars of the southern ecliptic hemisphere as seen by TESS

Context. We present our findings on 18 previously known ZZ Ceti stars observed by the TESS space telescope in 120 s cadence mode during the survey observation of the southern ecliptic hemisphere. Aims: We focus on the frequency analysis of the space-based observations, comparing the results with findings of previous ground-based measurements. The frequencies detected by the TESS observations can serve as inputs for future asteroseismic analyses. Methods: We performed standard pre-whitening of the data sets to derive the possible pulsation frequencies of the different targets. In some cases, we fit term amplitude or phase variations that occurred during the TESS observations. Results: We detected more than 40 pulsation frequencies in seven ZZ Ceti stars observed in the 120 s cadence by TESS, with precision better than 0.1 μHz. We found that HE 0532-5605 may be a new outbursting ZZ Ceti. Ten targets do not show any significant pulsation frequencies in their Fourier transforms, due to a combination of their intrinsic faintness and/or crowding on the large TESS pixels. We also detected possible amplitude or phase variations during the TESS observations in some cases. Such behaviour in these targets was not previously identified from ground-based observations

Discovery of 74 new bright ZZ Ceti stars in the first three years of TESS

We report the discovery of 74 new pulsating DA white dwarf stars, or ZZ Cetis, from the data obtained by the Transiting Exoplanet Survey Satellite mission, from Sectors 1 to 39, corresponding to the first 3 cycles. This includes objects from the Southern hemisphere (Sectors 1-13 and 27-39) and the Northern hemisphere (Sectors 14-26), observed with 120 s- and 20 s-cadence. Our sample likely includes 13 low-mass and one extremely low-mass white dwarf candidate, considering the mass determinations from fitting Gaia magnitudes and parallax. In addition, we present follow-up time series photometry from ground-based telescopes for 11 objects, which allowed us to detect a larger number of periods. For each object, we analysed the period spectra and performed an asteroseismological analysis, and we estimate the structure parameters of the sample, i.e. stellar mass, effective temperature, and hydrogen envelope mass. We estimate a mean asteroseismological mass of ⟨Msis⟩ = 0.635 ± 0.015 M⊙, excluding the candidate low or extremely low-mass objects. This value is in agreement with the mean mass using estimates from Gaia data, which is ⟨Mphot⟩ = 0.631 ± 0.040 M⊙, and with the mean mass of previously known ZZ Cetis of ⟨M*⟩ = 0.644 ± 0.034 M⊙. Our sample of 74 new bright ZZ Cetis increases the number of known ZZ Cetis by ~20 per cent

Wandering near the red edge: photometric observations of three cool ZZ Ceti stars

We summarize our findings on three cool ZZ Ceti type pulsating white dwarfs. We determined eight independent modes in HS 0733+4119, of which seven are new findings. For GD 154, we detected two new eigenmodes, and the recurrence of the pulsational behaviour first observed in 1977. We discuss that GD 154 does not only vary its pulsations between a multiperiodic and a quasi-monoperiodic phase, but there are also differences between the relative amplitudes of the near-subharmonics observed in the latter phase. In the complex pulsator, Ross 808, we compared the pre- and post Whole Earth Telescope campaign measurements, and determined two new frequencies besides the ones observed during the campaign. Studying these stars can contribute to better understanding of pulsations close to the empirical ZZ Ceti red edge. All three targets are in that regime of the ZZ Ceti instability strip where short-term amplitude variations or even outbursts are likely to occur, which are not well-understood theoretically

GD358: Three Decades of Observations for the In-depth Asteroseismology of a DBV Star

We report on the analysis of 34 years of photometric observations of the pulsating helium atmosphere white dwarf GD358. The complete data set includes archival data from 1982 to 2006, and 1195.2 hr of new observations from 2007 to 2016. From this data set, we extract 15 frequencies representing g-mode pulsation modes, adding 4 modes to the 11 modes known previously. We present evidence that these 15 modes are ℓ = 1 modes, 13 of which belong to a consecutive sequence in radial overtone k. We perform a detailed asteroseismic analysis using models that include parameterized, complex, carbon and oxygen core composition profiles to fit the periods. Recent spectroscopic analyses place GD358 near the red edge of the DBV instability strip, at 24,000 ± 500 K and a {log} {\\text{}}g of 7.8 ± 0.08 dex. The surface gravity translates to a mass range of 0.455─0.540 {M}ȯ . Our best-fit model has a temperature of 23,650 K and a mass of 0.5706 {M}ȯ . That is slightly more massive than what is suggested by the most recent spectroscopy. We find a pure helium layer mass of 10−5.50, consistent with the result of previous studies and the outward diffusion of helium over time

The first view of δ Scuti and γ Doradus stars with the TESS mission

We present the first asteroseismic results for δ Scuti and γ Doradus stars observed in Sectors 1 and 2 of the TESS mission. We utilize th 2-min cadence TESS data for a sample of 117 stars to classify thei Russell diagram using Gaia DR2 data. Included within our sample are th eponymous members of two pulsator classes, γ Doradus and SX Phoenicis Our sample of pulsating intermediate-mass stars observed by TESS als allows us to confront theoretical models of pulsation driving in th classical instability strip for the first time and show that mixin processes in the outer envelope play an important role. We derive a empirical estimate of 74 per cent for the relative amplitude suppressio factor as a result of the redder TESS passband compared to the Keple mission using a pulsating eclipsing binary system. Furthermore, ou sample contains many high-frequency pulsators, allowing us to probe th frequency variability of hot young δ Scuti stars, which were lacking i the Kepler mission data set, and identify promising targets for futur asteroseismic modelling. The TESS data also allow us to refine th stellar parameters of SX Phoenicis, which is believed to be a blu straggler

TESS cycle 1 observations of roAp stars with 2-min cadence data

We present the results of a systematic search for new rapidly oscillating Ap (roAp) stars using the 2-min cadence data collected by the Transiting Exoplanet Survey Satellite (TESS) during its Cycle 1 observations. We identify 12 new roAp stars. Amongst these stars we discover the roAp star with the longest pulsation period, another with the shortest rotation period, and six with multiperiodic variability. In addition to these new roAp stars, we present an analysis of 44 known roAp stars observed by TESS during Cycle 1, providing the first high-precision and homogeneous sample of a significant fraction of the known roAp stars. The TESS observations have shown that almost 60 per cent (33) of our sample of stars are multiperiodic, providing excellent cases to test models of roAp pulsations, and from which the most rewarding asteroseismic results can be gleaned. We report four cases of the occurrence of rotationally split frequency multiplets that imply different mode geometries for the same degree modes in the same star. This provides a conundrum in applying the oblique pulsator model to the roAp stars. Finally, we report the discovery of non-linear mode interactions in α Cir (TIC 402546736, HD 128898) around the harmonic of the principal mode - this is only the second case of such a phenomenon

Rotation periods and shape asphericity in asteroid families based on TESS S1-S13 observations

Here we present the analysis of the distribution of rotation periods and light curve amplitudes based on 2859 family asteroids in 16 Main Belt families based on 9912 TESS asteroid light curves in the TSSYS-DR1 asteroid light curve database. We found that the distribution of the light curve properties follow a family-specific character in some asteroid families, including the Hungaria, Maria, Juno, Eos, Eucharis, and Alauda families. While in other large families, these distributions are in general very similar to each other. We confirm that older families tend to contain a larger fraction of more spheroidal, low-amplitude asteroids. We found that rotation period distributions are different in the cores and outskirts of the Flora and Maria families, while the Vesta, Eos, and Eunomia families lack this feature. We also confirm that very fast spinning asteroids are close to spherical (or spinning top shapes), and minor planets rotating slower than approximate to 11 h are also more spherical than asteroids in the 4-8 h period range and this group is expected to contain the most elongated bodies