Mira’s Wind Explored in Scattering Infrared CO Lines

We have observed the intermediate regions of the circumstellar envelope ofMira (o Ceti) in photospheric light scattered by three vibration-rotationtransitions of the fundamental band of CO, from low-excited rotational levelsof the ground vibrational state, at an angular distance of beta = 2"-7" awayfrom the star. The data were obtained with the Phoenix spectrometer mounted onthe 4 m Mayall telescope at Kitt Peak. The spatial resolution is approximately0.5" and seeing limited. Our observations provide absolute fluxes, leading toan independent new estimate of the mass-loss rate of approximately 3e-7Msun/yr, as derived from a simple analytic wind model. We find that thescattered intensity from the wind of Mira for 2" < beta < 7" decreases asbeta^-3, which suggests a time constant mass-loss rate, when averaged over 100years, over the past 1200 years.Comment: accepted for publication in the Astrophysical Journa