S Coronae Australis -- a T Tauri Twin

TL;DR

This study examines the binary T Tauri star system S CrA, analyzing spectral and photometric data to understand accretion, wind features, and stellar similarities, revealing a twin system with complex emission characteristics and inclination discrepancies.

Contribution

The paper provides detailed spectroscopic and photometric analysis of S CrA, modeling accretion and wind features, and discusses the surprising difference in inclination measurements from different methods.

Findings

Both stars are remarkably similar in stellar parameters and rotation.

Observed emission line profiles match models at an inclination of around 65 degrees.

Discrepancies exist between inclination estimates from different observational techniques.

Abstract

The star S CrA is a tight visual binary consisting of two classical T Tauri stars, both with outstanding spectral characteristics and brightness variations. High-resolution spectra were collected at ESO and photometric observations with the SMARTS telescope. Both stars undergo large variation in brightness caused mainly by variable foreground extinction. From the stellar parameters we conclude that the two stars are remarkably similar, and that S CrA can be regarded as a T Tauri twin. Rotational periods and inclinations are also similar. The stars differ, however, in terms of degree of veiling and emission line profiles. We compared observed Balmer emission line profiles with models including magnetospheric accretion and a disk wind. We found a good match between observed signatures of accreting gas, wind features, and rotational velocities with those resulting from our modelling for inclinations of around 65 degrees. At this orientation the trajectories of infalling gas just above the stellar surfaces are parallel to the line-of-sight, and accordingly we observe extended red-shifted absorption components extending to + 380 km/s, the estimated free-fall velocity at the surface. However, our so derived inclinations differ from those derived from interferometric near-infrared spectroscopy, and we discuss possible causes for this puzzling discrepancy.