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Published June 20, 2014 | Published + Submitted
Journal Article Open

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


We present the first detections of thermal radio emission from the atmospheres of solar-type stars τ Cet, η 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 μJy at combinations of 10.0, 15.0, and 34.5GHz. τ Cet, η Cas A, and 40 Eri A are all detected at 34.5GHz 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 τ Cet and 1.6 for η Cas A, at the 95% confidence level. The measured 34.5-GHz flux densities correspond to stellar disk-averaged brightness temperatures of roughly 10,000K, 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.

Additional Information

© 2014 American Astronomical Society. Received 2014 January 17; accepted 2014 April 23; published 2014 May 29. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No.DGE-1144469. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. This research benefited from the web page "Basic Astronomical Data for the Sun"7 created by Eric Mamajek of the University of Rochester. J.V. thanks Stephen White and Jeffrey Linsky for giving helpful feedback on the paper and additionally thanks Stephen White for information on the quiescent solar microwave brightness temperature spectrum.

Attached Files

Published - 0004-637X_788_2_112.pdf

Submitted - 1405.2341v1.pdf


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August 20, 2023
October 26, 2023