Radio continuum emission from winds, chromospheres, and coronae of cool giants and supergiants

The results of a sensitive VLA radio survey of the single cool-wind giants and super giants stars, having spectral types in the range (G0-M5), are presented. The survey was carried out at 6 cm using the NRAO VLA. The results of the observations are discussed in the context of the various mechanisms which might be producing radio emission in the cool stars. One coronal giant was detected as well as six cool-wind giants in the range 2-6 cm at levels of 0.1-2 mJy. The six-cm emission of the coronal giant alpha Aurigae is shown to be optically thin having free-free emission from the corona of energy 10 to the 7th K. The 2-cm emission from alpha Aur also contains contribution of about 65 percent from the stellar disk of one or both stars. The radio emission from all other sources is explained as optically thick emission from stellar winds. The inferred ionized mass-los rates for the cool wind stars was about 10 to the 10th solar mass per year for MK III-type stars and 10 to the -9th solar mass per year for MK II type stars.