AAVSO: American Association of Variable Star Observers

Low Resolution Spectroscopy of Miras—X Octantis

Volume 47 number 1 (2019)

Recent AAVSO Volumes are restricted to AAVSO Members. Please consider joining

Bill Rea
6A Bygrave Place, Bishopdale, Christchurch, 8053, New Zealand; rea.william@gmail.com

Abstract

We present a photometric and spectroscopic study of X Oct and five selected comparison stars. We show that the changes in spectral classification of X Oct over the course of its pulsation cycle can be determined by comparison between its spectra and that of the five comparison stars. In particular, we conclude that the ratio between the counts at the continuum point at 754nm and the TiO absorption line at 719nm is the single most reliable feature for determining spectral type. We suggest that X Oct may cycle between M3 and M7 as it pulsates, rather than the published range of M3 to M6. We also undertook a frequency analysis of CQ Oct and report two significant pulsation periods of 52.9 and 37.4 days, respectively.