Space Weather & Heliophysics

First Millimeter Flares Detected from Epsilon Eridani with ALMA

By Keith Cowing
Press Release
October 23, 2022
Filed under , , , , ,
First Millimeter Flares Detected from Epsilon Eridani with ALMA
(left) Natural weighted image of continuum emission from the ACA. Millimeter emission is detected at the stellar position (center of the image) at 776 ± 103 µJy . The outer debris disk is seen surrounding the star at approximately 1600 . The contour levels are in steps of [−2, 2, 4, 6, 8…]× the rms noise of 94 µJy beam−1 . The grey ellipse in the lower left corner shows the beam size which is 7. 004 × 4. 005 (right) Primary beam corrected, natural weighted continuum image of Epsilon Eridani and the northern arc of its outer debris disk from the ALMA 12-m array. Millimeter emission at the stellar position, 794 ± 45 µJy. The contours are in steps of [−3, 3, 6, 9…]× the rms noise of 33 µJy beam−1 (primary beam corrected noise). The beam size is 1. 006 × 1. 001, as indicated by the grey ellipse in the lower left corner of the image. — astro-ph.EP

We report the detection of three large millimeter flaring events from the nearby Sun-like, ϵ Eridani, found in archival ALMA 12m and ACA observations at 1.33 mm taken from 2015 January 17-18 and 2016 October 24-November 23, respectively. This is the first time that flares have been detected from a Sun-like star at millimeter wavelengths.

The largest flare among our data was detected in the ALMA observations on 2015 January 17 from 20:09:10.4-21:02:49.3 (UTC) with a peak flux density of 28 ± 7 mJy and a duration of 9 sec. The peak brightness of the largest flare is 3.4±0.9×1014 erg s−1Hz−1, a factor of >50× times brighter than the star’s quiescent luminosity and >10× brighter than solar flares observed at comparable wavelengths.

We find changes in the spectral index (Fν∝να) at the flare peak, with α = 1.81 ± 1.94 and a lower limit on the fractional linear polarization |Q/I|= 0.08 ± 0.12. This positive spectral index is more similar to millimeter solar flares, differing from M dwarf flares also detected at millimeter wavelengths that exhibit steeply negative spectral indices.

Kiana Burton, Meredith A. MacGregor, Rachel A. Osten

Comments: 9 pages, 4 figures, 1 table, accepted for publication in ApJL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2210.10818 [astro-ph.SR] (or arXiv:2210.10818v1 [astro-ph.SR] for this version)
Submission history
From: Meredith MacGregor
[v1] Wed, 19 Oct 2022 18:10:04 UTC (2,240 KB)

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