Search

The TESS and Gaia missions are both collecting data of exquisite quality for RR Lyrae-type pulsating stars. We combine light curve shape information from TESS with distances and brightnesses from Gaia to build a detailed classification scheme that is able to filter out intrinsically fainter binaries and rotational variables as well as short-period Cepheids that otherwise have light curves very similar to that of RR Lyrae stars, while preserving targets with unusual light curve shapes. We build a clean sample from the RR Lyrae stars in the vicinity of the Sun, out to 5-10 kpc distances. Based on the TESS light curves we find that a large fraction of RR Lyrae stars exhibit various additional low-amplitude modes. The distribution of extra modes in period is markedly different from that of stars within the bulge and globular clusters, signaling a metallicity dependence in the mode periods and excitation mechanisms. We also detect a possible dependence of extra modes from color and hence effective temperatures in overtone RRc stars. While these new results have brought us closer to true asteroseismic analysis of RR Lyrae stars, we show through new échelle-type diagrams that mode identification is still hindered by the strong influence of the radial mode(s) dominating the pulsation., {"references":["Bovy, J., et al., 2016, ApJ, 818, 130","Gaia Collaboration, 2021, A&A, 649, 1","Jurcsik, J., et al., 2015, ApJS, 219, 25","Molnár, L., et al., 2017, EpJ WoC, 160, 04008","Netzel, H., et al., 2019, MNRAS, 487, 5584","Pál, A., 2012, MNRAS, 421, 1825","Smolec, R., et al., 2017, MNRAS, 467, 2349"]}

TESS has a significant advantage in variable star classification over all-sky surveys that work with sparsely sampled photometric data. Beyond the classical problem of misidentified eclipsing and rotational variables among the pulsating stars, confusion between Cepheid types also exists. Here we focus on the anomalous Cepheid type of stars that lie in between Type I and II Cepheids regarding masses and luminosities. They represent the most metal poor and the least numerous type of Cepheids, for which evolutionary channels are a matter of debate. Their observed pulsation periods range between 0.3 to 2.7 days overlapping with the other Cepheids types and RR Lyrae stars, and their light curve shapes are very similar to each other. Photometric data alone are often not adequate to distinguish them, therefore only a handful of variable catalogs list anomalous Cepheids as an independent type. In this study we explore the potential of TESS in the validation of anomalous Cepheid candidates by investigating full-frame image light curves prepared with our differential photometric pipeline.