First Detection of Thermal Radio Emission from Solar-Type Stars with the Karl G. Jansky Very Large Array

Jackie Villadsen, Gregg Hallinan, Stephen Bourke, Manuel Güdel, Michael Rupen

(Submitted on 9 May 2014)

We present the first detections of thermal radio emission from the atmospheres of solar-type stars {\tau} Cet, {\eta} Cas A, and 40 Eri A. These stars all resemble the Sun in age and level of magnetic activity, as indicated by X-ray luminosity and chromospheric emission in calcium-II H and K lines. We observed these stars with the Karl G. Jansky Very Large Array with sensitivities of a few {\mu}Jy at combinations of 10.0, 15.0, and 34.5 GHz. {\tau} Cet, {\eta} Cas A, and 40 Eri A are all detected at 34.5 GHz with signal-to-noise ratios of 6.5, 5.2, and 4.5, respectively. 15.0-GHz upper limits imply a rising spectral index greater than 1.0 for {\tau} Cet and 1.6 for {\eta} Cas A, at the 95% confidence level. The measured 34.5-GHz flux densities correspond to stellar disk-averaged brightness temperatures of roughly 10,000 K, similar to the solar brightness temperature at the same frequency. We explain this emission as optically- thick thermal free-free emission from the chromosphere, with possible contributions from coronal gyroresonance emission above active regions and coronal free-free emission. These and similar quality data on other nearby solar-type stars, when combined with ALMA observations, will enable the construction of temperature profiles of their chromospheres and lower transition regions.

Comments: 9 pages, 2 figures. Accepted for publication in ApJ

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Cite as: arXiv:1405.2341 [astro-ph.SR] (or arXiv:1405.2341v1 [astro-ph.SR] for this version)

Submission history

From: Jackie Villadsen 

[v1] Fri, 9 May 2014 20:01:18 GMT (156kb)