AAVSO: American Association of Variable Star Observers

A Spectroscopic Study of the Variable Star T Centauri Over a 91-day Cycle, and the Effects of Titanium Oxide on Its Atmosphere

Volume 49 number 1 (2021)

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Julian F. West
Astronomical Association of Queensland (AAQ), P. O. Box 6101, St. Lucia, Queensland 4067, Australia; spectroscopy@aaq.org.au
Benedict Pace
54 Bowley Street, Hendra, Queensland 4011, Australia; ben_penny1@bigpond.com

Abstract

We observed spectra of the large amplitude semiregular variable T Centauri during a complete 91-day period, which were subsequently combined with contemporaneous photometric data from the AAVSO International Database. The analysis of these data, together with other reference material, has enabled us to estimate a mean photospheric radius of T Centauri at ~ 94 Rsun, and to develop a simple model reflecting the effects of the formation of titanium oxide in the star’s atmosphere as it cools through minimum brightness. Our model incorporated the variation in atmospheric opacity due to TiO and, in comparison with the observed magnitudes, indicated an increase of 20–40% in the apparent stellar radius, as observed in the visual and near-infrared bands as the star cooled mid-phase.