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Detection of 2–4 GHz Continuum Emission from ϵ Eridani

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.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-4357/abc004DOIArticle
https://arxiv.org/abs/2010.05929arXivDiscussion Paper
ORCID:
AuthorORCID
Suresh, A.0000-0002-5389-7806
Chatterjee, S.0000-0002-2878-1502
Cordes, J. M.0000-0002-4049-1882
Bastian, T. S.0000-0002-0713-0604
Hallinan, G.0000-0002-7083-4049
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
Funders:
Funding AgencyGrant Number
NSFAAG-1815242
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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