Periodic variable A-F spectral type stars in the northern TESS continuous viewing zone

Abstract

Context. In the time of large space surveys that provide tremendous amounts of precise data, it is highly desirable to have a commonly accepted methodology and system for the classification of variable stars. This is especially important for A-F stars, which can show intrinsic brightness variations due to both rotation and pulsations. Aims. The goal of our study is to provide a reliable classification of the variability of A-F stars brighter than 11 mag located in the northern TESS continuous viewing zone. We also aim to provide a thorough discussion about issues in the classification related to data characteristics and the issues arising from the similar light-curve shape generated by different physical mechanisms. Methods. We used TESS long-and short-cadence photometric data and corresponding Fourier transform to classify the variability type of the stars. We also used spectroscopic observations to determine the projected rotational velocity of a few stars. Results. We present a clear and concise classification system that is demonstrated on many examples. We find clear signs of variability in 3025 of 5923 studied stars (51 %). For 1813 of these 3025 stars, we provide a classification; the rest cannot be unambiguously classified. Of the classified stars, 64.5 % are pulsating stars of g-mode γ Doradus (GDOR) and p-mode δ Scuti types and their hybrids. We realised that the long-and short-cadence pre-search data conditioning simple aperture photometry data can differ significantly not only in amplitude but also in the content of instrumental and data-reduction artefacts, making the long-cadence data less reliable. We identified a new group of stars that show stable light curves and characteristic frequency spectrum patterns (8.5 % of the classified stars). According to the position in the Hertzsprung-Russell diagram, these stars are likely GDOR stars but are on average about 200 K cooler than GDORs and have smaller amplitudes and longer periods. With the help of spectroscopic measurements of v sin i, we show that the variability of stars with unresolved groups of peaks located close to the positions of the harmonics in their frequency spectra (16 % of the classified stars) can be caused by rotation rather than by pulsations. We show that without spectroscopic observations it can be impossible to unambiguously distinguish between ellipsoidal variability and rotational variability. We also applied our methodology to three previous studies and find significant discrepancies in the classification. Conclusions. We demonstrate how difficult the classification of variable A-F stars can be when using only photometric data, how the residual artefacts can produce false positives, and that some types cannot actually be distinguished without spectroscopic observations. Our analysis provides collections that can be used as training samples for automatic classification.

Physical Parameters of 11,100 Short-period ASAS-SN Eclipsing Contact Binaries

“…This may be caused by the fact that some short-period ellipsoidal variable stars are usually classified as EW-type eclipsing binaries. Ellipsoidal variable stars and low-amplitude EW-type eclipsing binaries are not easily distinguished directly by light curves (Dal & Sipahi 2013;Li & Liu 2021;Skarka et al 2022). However, in this paper, the selection of our sample with amplitudes greater than 0.2 mag has led to the early exclusion of many ellipsoidal variable stars that have been misclassified as low-amplitude EW-type eclipsing binaries.…”

“…Based on the mean magnitude distribution of ASAS-SN (Jayasinghe et al 2018), we select targets with a mean V-band magnitude less than 15 mag; this includes the vast majority of targets. We also select targets with amplitudes greater than 0.2 mag because many ellipsoidal variable stars have amplitudes less than 0.2 mag and they are often mistaken for low-amplitude EW-type eclipsing binaries (Dal & Sipahi 2013;Li & Liu 2021;Skarka et al 2022). The Laflfler-Kinman string length (LKSL) statistic (Lafler & Kinman 1965;Clarke 2002) is a measure of scatter in the light curve of periodic variables.…”

Mode coupling coefficients between the convective core and radiative envelope of γ Doradus and slowly pulsating B stars

“…However, progress can be ensured by analyzing the thousands of light curves for the SPB and γ Dor candidates from TESS data assembled throughout the nominal and extended mission, covering more than five years. The catalogues from Pedersen et al (2019), Antoci et al (2019), andSkarka et al (2022) are only the tip of the iceberg in discovery space for TESS gravito-inertial asteroseismology.…”

Tidally perturbed g-mode pulsations in a sample of close eclipsing binaries

“…10 mmag) and dense pulsation spectra with typical periods between 0.3 and 3 d, the advent of space missions gave a large boost to the detection and observational analysis of g-mode pulsators (e.g. Tkachenko et al 2013;Van Reeth et al 2015b;Li et al 2020b;Garcia et al 2022;Skarka et al 2022).…”