The Implications of M Dwarf Flares on the Detection and Characterization of Exoplanets at Infrared Wavelengths

Abstract

We present the results of an observational campaign which obtained high time cadence, high precision, simultaneous optical and IR photometric observations of three M dwarf flare stars for 47 hours. The campaign was designed to characterize the behavior of energetic flare events, which routinely occur on M dwarfs, at IR wavelengths to milli-magnitude precision, and quantify to what extent such events might influence current and future efforts to detect and characterize extrasolar planets surrounding these stars. We detected and characterized four highly energetic optical flares having U -band total energies of ∼7.8 x 10 30 to ∼1.3 x 10 32 ergs, and found no corresponding response in the J, H, or Ks bandpasses at the precision of our data. For active dM3e stars, we find that a ∼1.3 x 10 32 erg U -band flare (∆U max ∼1.5 mag) will induce <8.3 (J ), <8.5 (H ), and <11.7 (Ks) milli-mags of a response. A flare of this energy or greater should occur less than once per 18 hours. For active dM4.5e stars, we find that a ∼5.1 x 10 31 erg U-band flare (∆U max ∼1.6 mag) will induce <7.8 (J ), <8.8 (H ), and <5.1 (Ks) milli-mags of a response. A flare of this energy or greater should occur less than once per 10 hours. No evidence of stellar variability not associated with discrete flare events was observed at the level of ∼3.9 milli-mags over 1 hour time-scales and at the level of ∼5.6 milli-mags over 7.5 hour time-scales. We therefore demonstrate that most M dwarf stellar activity and flares will not influence IR detection and characterization studies of M dwarf exoplanets above the level of ∼5-11 milli-mags, depending on the filter and spectral type. We speculate that the most energetic megaflares on M dwarfs, which occur at rates of once per month, are likely to be easily detected in IR observations with sensitivity of tens of milli-mags. We also discuss how recent detections of line flux enhancements during M dwarf flares could influence IR transmission spectroscopic observations of M dwarf exoplanets.

Periodic variability of spotted M dwarfs in WTS

“…This magnitude of flare is in contrast to the results of Tofflemire et al [17] who expect to find flaring events in the J band occurring on mmag scales, and would transform to a u-band response of > 6, which by extrapolation of the frequencies of flaring events per magnitude found by Davenport et al [9] would be expected to be observed less than once a year.…”

The habitability of planets orbiting M-dwarf stars

“…Stellar flares in light curves can potentially complicate the search for transits, and have even been observed during transit events themselves (Kundurthy et al, 2011). However, studies of M dwarf photometric variability on the timescales of transits conclude that stellar activity should not meaningfully affect the detection of exoplanets (Tofflemire et al, 2012;Goulding et al, 2012) (though they caution that this depends upon photometric filter and spectral type).…”

Influence of Stellar Flares on the Chemical Composition of Exoplanets and Spectra

“…∼ 5 h), a more realistic time scale and close to the maximum duration between flares observed by Pettersen et al (1984) on AD Leo. We chose this upper value, which is more likely to be representative of the occurence of flares observed by Tofflemire et al (2012); Hunt-Walker et al (2012) and of the one in lower spectral type (M0-M3) stars due to their lower magnetic activity (Kowalski et al 2009;Davenport et al 2012). We simulate a repetition of 47 flare cycles (representing ∼10 6 s s or ∼11 years).…”