Radio emission from the extended chromosphere of Alpha Orionis

Abstract

The red supergiant Alpha Orionis (Betelgeuse) has been detected at 1.46, 4.89, 15.0, and 22.5 GHz with the VLA. These observations fit a radio spectrum described by 0.24 nu(1.32 GHz) mJy. All radio observations of this star reported since 1972 fit the same spectrum, except for two single dish measurements that are too low by a factor of 2. This spectrum can be modeled by thermal emission from a spherically symmetric, partially ionized, chromospheric region (electron temperature approximately 10,000 K) extending from 1 to 4 stellar radii, with an electron density radial power law of -3.59. Current wave-driven models for mass loss in late-type supergiants can account for the existence of such a region.