Radio emission and mass loss rate limits of four young solar-type stars

• Main Authors: Fichtinger, Bibiana, Güdel, Manuel, Mutel, Robert L, Hallinan, Gregg, Gaidos, Eric, Skinner, Stephen L, Lynch, Christene, Gayley, Kenneth G
• Format: Journal Article
• Language: English
• Published: 27-02-2017
• Subjects: Physics - Solar and Stellar Astrophysics
• DOI: 10.48550/arxiv.1702.08393

A&A 599, A127 (2017) Observations of free-free continuum radio emission of four young
main-sequence solar-type stars (EK Dra, Pi1 UMa, Chi1 Ori; and Kappa1 Cet) are
studied to detect stellar winds or at least to place upper limits on their
thermal radio emission, which is dominated by the ionized wind. These stars are
excellent proxies for representing the young Sun. Upper limits on mass loss
rates are calculated using their observational radio emission. Our aim is to
re-examine the faint young Sun paradox by assuming that the young Sun was more
massive in its past, and hence to find a possible solution for this famous
problem. The observations of our sample are performed with the Karl G. Jansky
VLA with excellent sensitivity, using the C-band and the Ku-band. ALMA
observations are performed at 100 GHz. For the estimation of the mass loss
limits, spherically symmetric winds and stationary, anisotropic, ionized winds
are assumed. We compare our results to 1) mass loss rate estimates of
theoretical rotational evolution models, and 2) to results of the indirect
technique of determining mass loss rates: Lyman-alpha absorption. We are able
to derive the most stringent direct upper limits on mass loss so far from radio
observations. Two objects, EK Dra and Chi1 Ori, are detected at 6 and 14 GHz
down to an excellent noise level. These stars are very active and additional
radio emission identified as non-thermal emission was detected, but limits for
the mass loss rates of these objects are still derived. The stars Pi1 UMa and
Kappa1 Cet were not detected in either C-band or in Ku-band. For these objects
we give upper limits to their radio free-free emission and calculate upper
limits to their mass loss rates. Finally, we reproduce the evolution of the Sun
and derive an estimate for the solar mass of the Sun at a younger age.