Massive Star Population in the Sextans A Dwarf Galaxy from HST UV Photometry

TL;DR

This study creates a catalog of massive stars in Sextans A using HST UV photometry, employing a novel FE interpolation method to estimate stellar properties and uncertainties.

Contribution

Introduces a new FE interpolation approach for deriving stellar properties from UV CMDs, enhancing accuracy and uncertainty estimation in low-metallicity environments.

Findings

Catalog contains 655 massive stars, with the most massive at 58±11 M_sun.

Good agreement between UV CMD estimates and spectral classifications for O-type stars.

Minimal overlap between UV photometry catalog and ground-based spectroscopic census.

Abstract

We build a catalog of massive (M>$8~$M$_\odot$) main sequence stars in the \mbox{metal-poor} ($\sim0.1~$Z$_\odot$) dwarf irregular galaxy Sextans A. HST WFC3 UV photometry in the 275 and 336 nm wideband filters is arranged in a Color-Magnitude Diagram (CMD), and overlaid on top of stellar evolutionary tracks from the MIST library. The star properties (mass, age, etc.) are computed with a Finite Element (FE) interpolation of the stellar tracks. The FE method, originally developed for solid mechanics problems, provides a general framework for interpolating fields inside domains of complex geometry. Besides the interpolated properties, the algorithm computes their gradients with respect to the photometry. These sensitivities provide a direct an efficient estimate of the associated uncertainties. Our catalog contains 655 stars, with the most massive one estimated at $58\pm11~$M$_\odot$. A comparison with a ground-based spectroscopic census of OB stars yields only 8 matches, evidencing the minimal overlap between both datasets. The mass estimates derived from the UV CMD and the spectral classification are in good agreement for the majority of O-type stars found in both datasets. Our catalog provides an extensive list of candidates for followup spectroscopic observation, which could improve our understanding of the early evolutionary stages of massive \mbox{low-metallicity} stars.