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Detection of 2−4 GHz Continuum Emission from ε Eridani
The nearby star ϵ Eridani has been a frequent target of radio surveys for stellar emission and extraterrestial intelligence. Using deep 2−4 GHz observations with the Very Large Array, we have uncovered a 29 μJy compact, steady continuum radio source coincident with ϵ Eridani to within 0.06 arcseconds (≲2σ; 0.2 au at the distance of the star).
Combining our data with previous high frequency continuum detections of ϵ Eridani, our observations reveal a spectral turnover at 6 GHz. We ascribe the 2−6 GHz emission to optically thick, thermal gyroresonance radiation from the stellar corona, with thermal free-free opacity likely becoming relevant at frequencies below 1 GHz. The steep spectral index (α≃2) of the 2−6 GHz spectrum strongly disfavors its interpretation as stellar wind-associated thermal bremsstrahlung (α≃0.6).
Attributing the entire observed 2−4 GHz flux density to thermal free-free wind emission, we thus, derive a stringent upper limit of 3×10−11 M⊙ yr−1 on the mass loss rate from ϵ Eridani. Finally, we report the non-detection of flares in our data above a 5σ threshold of 95 μJy. Together with the optical non-detection of the most recent stellar maximum expected in 2019, our observations postulate a likely evolution of the internal dynamo of ϵ Eridani.
Akshay Suresh, Shami Chatterjee, James M. Cordes, Timothy S. Bastian, Gregg Hallinan
Comments: 13 pages, 4 figures, accepted to ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2010.05929 [astro-ph.SR] (or arXiv:2010.05929v1 [astro-ph.SR] for this version)
From: Akshay Suresh
[v1] Mon, 12 Oct 2020 18:00:13 UTC (74 KB)