Mira's Wind Explored in Scattering Infrared CO Lines

Abstract

We have observed the intermediate regions of the circumstellar envelope of Mira (ο Ceti) in photospheric light scattered by three vibration-rotation transitions of the fundamental band of CO, from low-excited rotational levels of the ground vibrational state, at an angular distance of β~2^''-7" away from the star. The data were obtained with the Phoenix spectrometer mounted on the 4 m Mayall telescope at Kitt Peak. The spatial resolution is approximately 0.5" and seeing limited. Our observations provide absolute fluxes, leading to an independent new estimate of the mass-loss rate of approximately 3×10^-7 M_solar yr^-1, as derived from a simple analytic wind model. We find that the scattered intensity from the wind of Mira for 2^''<~β<~7^'' decreases as β^-3, which suggests a time constant mass-loss rate, when averaged over 100 yr, over the past 1200 yr.