# STEREO observations of HD 90386 (RX Sex): a Delta Scuti or a hybrid star?

## TL;DR

This study analyzes four years of high-precision photometric data of HD 90386, a bright A2V star, revealing multiple pulsation frequencies, period variations, and suggesting it may be a hybrid Delta Scuti and Gamma Dor star.

## Contribution

The paper provides the first detailed frequency analysis of HD 90386 using STEREO data, indicating its potential hybrid pulsation nature and contributing to understanding of its internal structure.

## Key findings

- Detected at least six pulsation frequencies between 1 and 15 c/d.
- Identified dominant frequencies at around 10.25 and 12.40 c/d.
- Suggested HD 90386 may be a hybrid Delta Scuti and Gamma Dor star.

## Abstract

HD 90386 is a rarely studied bright A2V type Delta Scuti star (V = 6.66 mag). It displays short-term light curve variations which are originated due to either a beating phenomenon or a non-periodic variation. In this paper, we presented high-precision photometric data of HD 90386 taken by the STEREO satellite between 2007 and 2011 to shed light on its internal structure and evolution stage. From the frequency analysis of the four-year data, we detected that HD 90386 had at least six different frequencies between 1 and 15 c~d$^{-1}$. The most dominant frequencies were found at around 10.25258 c~d$^{-1}$ (A $\sim$ 1.92 mmag) and 12.40076 c~d$^{-1}$ (A $\sim$ 0.61 mmag). Based on the ratio between these frequencies, the star was considered as an overtone pulsator. The variation in pulsation period over 35 years was calculated to be dP/Pdt = 5.39(2) x 10$^{-3}$ yr$^{-1}$. Other variabilities at around 1.0 c~d$^{-1}$ in the amplitude spectrum of HD90386 were also discussed. In order to explain these variabilities, possible rotational effects and Gamma Dor type variations were focused. Consequently, depending on the rotation velocity of HD 90386, we speculated that these changes might be related to Gamma Dor type high-order g-modes shifted to the higher frequencies and that HD 90386 might be a hybrid star.