Probing the Flare Atmospheres of M Dwarfs Using Infrared Emission Lines

• Published in: The Astrophysical journal Vol. 745; no. 1; pp. 14 - 10
• Main Authors: Schmidt, Sarah J, Kowalski, Adam F, Hawley, Suzanne L, Hilton, Eric J, Wisniewski, John P, Tofflemire, Benjamin M
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 20-01-2012; IOP
• Subjects: ABSORPTION SPECTROSCOPY; Astronomy; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Atmospheres; CHROMOSPHERE; Earth, ocean, space; Emission spectroscopy; Exact sciences and technology; Flares; Infrared; INFRARED SPECTRA; Infrared spectroscopy; Lead (metal); PHOTOMETRY; STAR EVOLUTION; STARS; Energetics; Infrared spectroscopy; Optical spectrometry; Late type stars; Line formation; H-gamma lines; Infrared photometry; stars: flare; stars: chromospheres; line: formation; stars: late-type; One dimensional model; Stellar chromospheres; Radiative transfer; Emission line; Stellar activity; Flare stars; stars: activity
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/745/1/14

We present the results of a campaign to monitor active M dwarfs using infrared spectroscopy, supplemented with optical photometry and spectroscopy. We detected 16 flares during nearly 50 hr of observations on EV Lac, AD Leo, YZ CMi, and VB 8. The three most energetic flares also showed infrared emission, including the first reported detections of P beta , P gamma , He I [lambda]10830, and Br gamma during an M dwarf flare. The strongest flare ( Delta u = 4.02 on EV Lac) showed emission from H gamma , H delta , He I [lambda]4471, and Ca II K in the UV/blue and P beta , P gamma , P delta , Br gamma , and He I [lambda]10830 in the infrared. The weaker flares ( Delta u = 1.68 on EV Lac and Delta U = 1.38 on YZ CMi) were only observed with photometry and infrared spectroscopy; both showed emission from P beta , P gamma , and He I [lambda]10830. The strongest infrared emission line, P beta , occurred in the active mid-M dwarfs with a duty cycle of ~3%-4%. To examine the most energetic flare, we used the static NLTE radiative transfer code RH to produce model spectra based on a suite of one-dimensional model atmospheres. Using a hotter chromosphere than previous one-dimensional atmospheric models, we obtain line ratios that match most of the observed emission lines.