Stellar Flares from the First Tess Data Release: Exploring a New Sample of M-dwarfs


Flare frequency distributions (FFD) in the context of prebiotic chemistry (green area) and ozone sterilization (red areas). The x-axis shows the are energy, as bolometric energy E are;bol: on the lower ticks, and U-band energy E are;U on the upper ticks. The y-axis shows the cumulative rate of ares per day, i.e. how often a are with at least a certain energy appears. Di erent panels show F, G and K stars (orange), early M dwarfs (red) and late M dwarfs (black), separated into photometric rotators ( lled circle) and others (un lled circle). Solid lines are linear ts to the double-logarithmic FFD of each star, extrapolating into regimes that could not be observed. The green area denotes the minimum are rate and energy required to trigger prebiotic chemistry on a potential exoplanet (expanded from Rimmer et al. 2018, see Section 5.1). The di erent green shadings show each threshold for each star, which depends on the stellar radius and e ective temperature (Eq. 10). In the red shaded region derived from Tilley et al. (2017), intense ares are frequent enough that ozone layers cannot survive, and planet surfaces may be sterile (see Section 5.5). We mark two ozone sterilization regions: a permissive threshold for are rates  0:1 per day (lighter red area), and a conservative threshold for are rates  0:4 per day (darker red area). 71 stars, including 47 early M-dwarfs and 15 late M-dwarfs, in the TESS sample ful ll the criteria of prebiotic chemistry. On the other hand, potential exoplanets around 28 stars, including only 3 M-dwarfs, might su er from ozone depletion.Flare frequency distributions (FFD) in the context of prebiotic chemistry (green area) and ozone sterilization (red areas). The x-axis shows the are energy, as bolometric energy E are;bol: on the lower ticks, and U-band energy E are;U on the upper ticks. The y-axis shows the cumulative rate of ares per day, i.e. how often a are with at least a certain energy appears. Di erent panels show F, G and K stars (orange), early M dwarfs (red) and late M dwarfs (black), separated into photometric rotators ( lled circle) and others (un lled circle). Solid lines are linear ts to the double-logarithmic FFD of each star, extrapolating into regimes that could not be observed. The green area denotes the minimum are rate and energy required to trigger prebiotic chemistry on a potential exoplanet (expanded from Rimmer et al. 2018, see Section 5.1). The di erent green shadings show each threshold for each star, which depends on the stellar radius and e ective temperature (Eq. 10). In the red shaded region derived from Tilley et al. (2017), intense ares are frequent enough that ozone layers cannot survive, and planet surfaces may be sterile (see Section 5.5). We mark two ozone sterilization regions: a permissive threshold for are rates  0:1 per day (lighter red area), and a conservative threshold for are rates  0:4 per day (darker red area). 71 stars, including 47 early M-dwarfs and 15 late M-dwarfs, in the TESS sample ful ll the criteria of prebiotic chemistry. On the other hand, potential exoplanets around 28 stars, including only 3 M-dwarfs, might su er from ozone depletion.

We perform a study of stellar flares for the 24,809 stars observed with 2 minute cadence during the first two months of the TESS mission.

Flares may erode exoplanets' atmospheres and impact their habitability, but might also trigger the genesis of life around small stars. TESS provides a new sample of bright dwarf stars in our galactic neighborhood, collecting data for thousands of M-dwarfs that might host habitable exoplanets. Here, we use an automated search for flares accompanied by visual inspection. Then, our public allesfitter code robustly selects the appropriate model for potentially complex flares via Bayesian evidence. We identify 763 flaring stars, 632 of which are M-dwarfs. Among 3247 flares in total, the largest superflare increased the stellar brightness by a factor of 15.7. Bolometric flare energies range from 10^31 to 10^38.7 erg, with a median of 10^32.8 erg.

Furthermore, we study the flare rate and energy as a function of stellar type and rotation period. We solidify past findings that fast rotating M-dwarfs are the most likely to flare, and that their flare amplitude is independent of the rotation period. Finally, we link our results to criteria for prebiotic chemistry, atmospheric loss through coronal mass ejections, and ozone sterilization. Four of our flaring M-dwarfs host exoplanet candidates alerted on by TESS, for which we discuss how these effects can impact life.

With upcoming TESS data releases, our flare analysis can be expanded to almost all bright small stars, aiding in defining criteria for exoplanet habitability.

Maximilian N. Günther, Zhuchang Zhan, Sara Seager, Paul B. Rimmer, Sukrit Ranjan, Keivan G. Stassun, Ryan J. Oelkers, Tansu Daylan, Elisabeth Newton, Edward Gillen, Saul Rappaport, George R. Ricker, David W. Latham, Joshua N. Winn, Jon M. Jenkins, Ana Glidden, Michael Fausnaugh, Alan M. Levine, Jason A. Dittmann, Samuel N. Quinn, Akshata Krishnamurthy, Eric B. Ting
(Submitted on 2 Jan 2019)

Comments: 19 pages, 10 figures, 2 tables, submitted to AAS journals
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1901.00443 [astro-ph.EP] (or arXiv:1901.00443v1 [astro-ph.EP] for this version)
Submission history
From: Maximilian Günther
[v1] Wed, 2 Jan 2019 16:18:56 UTC (918 KB)
https://arxiv.org/abs/1901.00443
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