Imaging the Radio Photospheres of Mira Variables

TL;DR

This study used the VLA at 43 GHz to image radio photospheres and SiO maser emissions of Mira variables, revealing their sizes, shapes, and temperature characteristics, and comparing radio and infrared observations.

Contribution

It provides high-resolution radio images of Mira variables' photospheres and SiO masers, establishing their coextensive nature and morphological features for the first time.

Findings

Radio photospheres have diameters around 5.6 AU.

Infrared molecular layers are coextensive with radio photospheres.

SiO masers form partial rings near 8 AU.

Abstract

We have used the VLA at 43 GHz to image the radio continuum emission from o Ceti, R Leo, and W Hya and to precisely locate their SiO maser emission with respect to the star. The radio continuum emission region for all three stars has a diameter close to 5.6 AU. These diameters are similar to those measured at infrared wavelengths in bands containing strong molecular opacity and about twice those measured in line-free regions of the infrared spectrum. Thus, the radio photosphere and the infrared molecular layer appear to be coextensive. The 43 GHz continuum emission is consistent with temperatures near 1600 K and opacity from H-minus free-free interactions. While the continuum image of o Ceti appears nearly circular, both R Leo and W Hya display significant elongations. The SiO masers for all three stars show partial rings with diameters close to 8 AU.