# The Be Phenomenon in the Mono-Periodic STEREO Star; 13 Tau

## TL;DR

This study analyzes five years of photometric and spectroscopic data of star 13 Tau, revealing its mono-periodic variability and linking it to the Be phenomenon, with observed changes in light variation and spectral features.

## Contribution

It provides the first detailed analysis of 13 Tau's variability and its connection to the Be phenomenon using combined photometric and spectroscopic data.

## Key findings

- 13 Tau exhibits mono-periodic light variation at 1.80487 cd$^{-1}$.
- The frequency and amplitude of light variation vary annually.
- Spectroscopic Hα line equivalent widths also vary, correlating with photometric changes.

## Abstract

13\,Tau is a rarely studied bright B9V type star ({\sl V} = 5.68 mag), which shows a weak and double-peaked H{$\alpha$} emission profile in its spectra. In this study, we presented high-precision photometric data of 13\,Tau taken by the {\sl STEREO} satellite between 2007 and 2011, and compared the results to the spectroscopic findings to shed light on the Be phenomenon in the star. From the frequency analysis of the five-year data, we detected that 13\,Tau has exhibited a mono-periodic light variation ($f$ = 1.80487(1) cd$^{-1}$; A $\sim$ 2.76(8) mmag). The analysis revealed that frequency and amplitude values of the seasonal light curves varied from one year to another. From the spectroscopic data, we figured out that the equivalent widths of the H{$\alpha$} lines also showed variability, which seemed connected to the changes seen in both frequency and amplitude.