Exoplanets, -moons, -comets

Short-Term Balmer Line Emission Variability in M Dwarfs

By Keith Cowing
Status Report
astro-ph.SR
February 6, 2025
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Short-Term Balmer Line Emission Variability in M Dwarfs
Grid search results comparing 43 RADYN model fits to the Hα and Hβ lines during the peak of the largest flare in our sample, which was observed with OSMOS from TIC 415508270 on 2020-12-09 at 5:52 UT. The electron beams that give the lowest RSS fits the observed spectra are characterized by low electron fluxes and energies of 1–2×1011 erg s−1 cm2 and 17–37 keV, respectively. The flare area coverage versus RSS value points are color-coded by increasing beam intensity, with select models labeled in gray. The model labeled in red signifies the favored models based on our data. — astro-ph.SR

M Dwarfs make up the majority of stars, offering an avenue for discovering exoplanets due to their smaller sizes. However, their magnetic activity poses challenges for exoplanet detection, characterization, and planetary habitability. Understanding its magnetic activity, including surface starspots and internal dynamos, is crucial for exoplanet research.

In this study, we present short-term variability in four Balmer emission lines Hα, Hβ, Hγ, and Hδ for a sample of 77 M dwarfs of varying spectral types, and binarity. Stars were observed using the MDM Observatory’s Ohio State Multi-Object Spectrograph on the 2.4m Telescope and the Modular Spectrograph on the 1.3 m Telescope.

These data are combined with TESS photometry to explore the connection between spectroscopic and photometric variability. We observe sporadic short-term variability in Balmer lines for some stars, on timescale ≳ 15-min, but much shorter than the stellar rotation period.

We calculate periods for stars lacking those measurements, re-evaluated the relationship between amplitude (Rvar)-activity relation for the Hα line from Garc´ıa Soto et al. (2023), and extended our analysis to the Hβ, Hγ and Hδ lines, which indicates that the relation becomes increasingly dispersed for higher-order Balmer lines. This is consistent with increased intrinsic variability from lower to higher order lines.

Additionally, we compute the Balmer decrement, using Hβ as the fiducial, for stars where we could measure Hγ and/or Hδ. The Balmer decrement can show distinct patterns during white-light flares, with significant differences even for the same star. We also find evidence for dark spots on TIC 283866910.

Aylin Garcia Soto, Girish M. Duvvuri, Elisabeth R. Newton, Ward S. Howard, Alejandro Núñez

Comments: 19 Pages (3 are references), 10 Figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2502.02568 [astro-ph.SR] (or arXiv:2502.02568v1 [astro-ph.SR] for this version)
https://doi.org/10.48550/arXiv.2502.02568
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Submission history
From: Aylin Garcia Soto
[v1] Tue, 4 Feb 2025 18:41:55 UTC (4,450 KB)
https://arxiv.org/abs/2502.02568

Astrobiology

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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