Suresh, A. and Chatterjee, S. and Cordes, J. M. and Bastian, T. S. and Hallinan, G. (2020) Detection of 2–4 GHz Continuum Emission from ϵ Eridani. Astrophysical Journal, 904 (2). Art. No. 138. ISSN 1538-4357. https://resolver.caltech.edu/CaltechAUTHORS:20201204-110357143
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Abstract
The nearby star epsilon Eridani has been a frequent target of radio surveys for stellar emission and extraterrestrial 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 epsilon Eridani to within 0."06 (⩽2σ; 0.2 au at the distance of the star). Combining our data with previous high-frequency continuum detections of epsilon 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 epsilon Eridani. Finally, we report the nondetection of flares in our data above a 5σ threshold of 95 μJy. Together with the optical nondetection of the most recent stellar maximum expected in 2019, our observations postulate a likely evolution of the internal dynamo of epsilon Eridani.
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Alternate Title: | Detection of 2–4 GHz Continuum Emission from epsilon Eridani | ||||||||||||
Additional Information: | © 2020. The American Astronomical Society. Received 2020 August 14; revised 2020 October 2; accepted 2020 October 8; published 2020 November 27. All authors thank J. Villadsen for initial conversations that motivated this work. A.S. thanks P. Nicholson and R. J. Jennings for useful thought-provoking discussions. A.S., S.C., and J.M.C. acknowledge support from the National Science Foundation (AAG 1815242). The VLA observations presented here were obtained as part of program VLA/19A−283, PI: A. Suresh. The VLA is operated by the National Radio Astronomy Observatory, a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Facility: VLA. - Software: CASA (McMullin et al. 2007), Python 3 (http://www.python.org), Astropy (Price-Whelan et al. 2018), NumPy (van der Walt et al. 2011), Matplotlib (Hunter 2007), SciPy (Virtanen et al. 2020). | ||||||||||||
Group: | Astronomy Department | ||||||||||||
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Subject Keywords: | Stellar coronae ; K stars ; Radio continuum emission ; Stellar atmospheres | ||||||||||||
Issue or Number: | 2 | ||||||||||||
Classification Code: | Unified Astronomy Thesaurus concepts: Stellar coronae (305); K stars (878); Radio continuum emission (1340); Stellar atmospheres (1584) | ||||||||||||
Record Number: | CaltechAUTHORS:20201204-110357143 | ||||||||||||
Persistent URL: | https://resolver.caltech.edu/CaltechAUTHORS:20201204-110357143 | ||||||||||||
Official Citation: | A. Suresh et al 2020 ApJ 904 138 | ||||||||||||
Usage Policy: | No commercial reproduction, distribution, display or performance rights in this work are provided. | ||||||||||||
ID Code: | 106914 | ||||||||||||
Collection: | CaltechAUTHORS | ||||||||||||
Deposited By: | George Porter | ||||||||||||
Deposited On: | 05 Dec 2020 00:47 | ||||||||||||
Last Modified: | 09 Dec 2020 19:09 |
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