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Title: 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 Ca 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 34.5 GHz. τ Cet, η 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 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 10,000 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 Atacama Large Millimeter/Submillimeter Array observations, willmore » enable the construction of temperature profiles of their chromospheres and lower transition regions.« less
Authors:
; ;  [1] ;  [2] ;  [3]
  1. Department of Astronomy, California Institute of Technology, 1200 E. California Ave., Pasadena, CA 91125 (United States)
  2. Department of Astrophysics, University of Vienna, Türkenschanzstrasse 17, A-1180 Vienna (Austria)
  3. National Radio Astronomy Observatory, Socorro, NM 87801 (United States)
Publication Date:
OSTI Identifier:
22356608
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 788; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BRIGHTNESS; CHROMOSPHERE; COSMIC RADIO SOURCES; DETECTION; EMISSION; FLUX DENSITY; LUMINOSITY; SENSITIVITY; SIGNAL-TO-NOISE RATIO; STELLAR ATMOSPHERES; SUN; X RADIATION