Space observations of AA Doradus provide consistent mass determinations. New HW-Vir systems observed with TESS

TL;DR

This study uses space-based TESS data and Gaia parallax to analyze the HW-Vir type eclipsing system AA Doradus, confirming its stellar parameters, orbital stability, and secondary mass near hydrogen burning limit, with no significant pulsations detected.

Contribution

First detailed analysis of AA Doradus using TESS and Gaia data, providing precise stellar parameters and orbital stability confirmation.

Findings

Orbital period is stable with an upper limit to period change of 5.75e-13 s/s.

Primary star's mass, radius, and luminosity are consistent with an evolved horizontal branch star.

Secondary's mass is at the hydrogen-burning limit.

Abstract

We present an overview of eclipsing systems of the HW-Virginis type, based on space observations from the TESS Mission. We perform a detailed analysis of the properties of AA Dor, which was monitored for almost a full year. This excellent time-series dataset permitted us to search for both stellar pulsations and eclipse timing variations. In addition, we used the high-precision trigonometric parallax from Gaia Early Data Release 3 to make an independent determination of the fundamental stellar parameters. No convincing pulsations were detected down to a limit of 76 parts per million, however we detected one peak with false alarm probability of 0.2%. 20 sec cadences being collected during Year 3 should confirm or reject our detection. From eclipse timing measurements we were able to confirm that the orbital period is stable, with an upper limit to any period change of 5.75 $\cdot$ 10$^{-13}$ s/s. The apparent offset of the secondary eclipse is consistent with the predicted R{\o}mer delay when the primary mass is that of a canonical extended horizontal branch star. Using parallax and a spectral energy distribution corroborates that the mass of the primary in AA Dor is canonical, and its radius and luminosity is consistent with an evolutionary state beyond core helium burning. The mass of the secondary is found to be at the limit of hydrogen burning.