Spectroscopic and photometric time series of the bright RRc star T Sex

TL;DR

This study provides detailed spectroscopic and photometric analysis of the bright RRc star T Sex, revealing unique pulsation features, line distortions, and potential shock phenomena, contributing new insights into RRc star behavior from space and ground observations.

Contribution

First detailed spectroscopic and photometric analysis of T Sex, revealing unique pulsation frequencies and line distortion phenomena not previously observed in RRc stars from space data.

Findings

T Sex shows only the 0.5f_x pulsation frequency among RRc stars.

Spectroscopic data reveal a novel periodic distortion of the Hα line.

Detection of Na D line emission suggesting a weak shock wave.

Abstract

We present spectroscopic time series observations on one of the brightest northern RRc star, T Sex. Additionally, we also analysed extended photometric data sets, particularly the recent observations of the TESS space telescope. The main findings of our studies are as follows: T Sex, unlike all RRc stars whose space photometry has been analysed, shows only the $0.5f_x$ frequency as an additional pulsation frequency. With this, T Sex may be the first represent of such rare RRc stars found from space photometry. The spectroscopic data show a periodic distortion of the H$\alpha$ line with the pulsation phase. This phenomenon has not been reported for any RR Lyrae stars. The characteristic line distortion is probably caused by the turbulent convection, which resulted in higher macroturbulent velocity for T Sex than for typical RRab stars. Line doubling of the Na D line was observed between the 0.37 and 0.80 pulsation phases. The explanation of this phenomenon is that the two absorption components originate from different sources. The redder component comes from the pulsating atmosphere of the star, while the bluer one from the interstellar space. At phase 0.438, we detected emission on the Na D line, which may indicate a weak shock wave.