Time-Resolved Near-Ultraviolet Flare Spectra with the Hubble Space Telescope / Cosmic Origins Spectrograph

Kowalski, Adam F.; Hawley, Suzanne L.; Johns-Krull, Christopher M.; Schmidt, Sarah J.; Brown, Alexander; Wisniewski, John P.; Davenport, James R. A.; Farina, Cecilia; Pietro Gentile Fusillo, Nicola; Xilouris, Manolis; Mathioudakis, Mihalis; Osten, Rachel A.; Holtzman, Jon A.; Phan-Bao, Ngoc; Valenti, Jeff A.; Walkowicz, Lucianne
American Astronomical Society, AAS Meeting #225, #449.03 (2015).


A large amount of the radiated energy during solar and stellar flares is emitted as white-light continuum emission, extending through the ultraviolet and optical wavelength regimes. Broadband photometry and optical spectral observations of M dwarf flares suggest that the white-light peak is located in the near-ultraviolet wavelength regime similar to a blackbody with T ~ 10,000 K, whereas radiative-hydrodynamic models using a solar-type flare heating mechanism (nonthermal electrons with a flux ~ 1011 erg / s / cm2 accelerated in the corona) predict that the peak lies at redder wavelengths at the head of the Balmer continuum. We have completed a successful flare monitoring campaign on the dM4e star GJ 1243, in order to constrain the time-evolution of the peak of the white-light continuum. The campaign took place over 12 hours on Aug 31/Sept 1, 2014, and included optical monitoring from nine ground-based telescopes as the Hubble Space Telescope recorded time-tagged spectra in the near-ultraviolet (2450-2840 Å) with the Cosmic Origins Spectrograph. Two flares occurred during the HST observations, and we show preliminary results relating the continuum and line (Fe II and Mg II) emission to the simultaneous ground-based optical spectra and photometry. This dataset provides new constraints for radiative-hydrodynamic modeling of the lower flaring atmosphere in addition to input for models of the effects of flares on biomarkers and habitability around M dwarfs.