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Title: M DWARF FLARE CONTINUUM VARIATIONS ON ONE-SECOND TIMESCALES: CALIBRATING AND MODELING OF ULTRACAM FLARE COLOR INDICES

We present a large data set of high-cadence dMe flare light curves obtained with custom continuum filters on the triple-beam, high-speed camera system ULTRACAM. The measurements provide constraints for models of the near-ultraviolet (NUV) and optical continuum spectral evolution on timescales of ≈1 s. We provide a robust interpretation of the flare emission in the ULTRACAM filters using simultaneously obtained low-resolution spectra during two moderate-sized flares in the dM4.5e star YZ CMi. By avoiding the spectral complexity within the broadband Johnson filters, the ULTRACAM filters are shown to characterize bona fide continuum emission in the NUV, blue, and red wavelength regimes. The NUV/blue flux ratio in flares is equivalent to a Balmer jump ratio, and the blue/red flux ratio provides an estimate for the color temperature of the optical continuum emission. We present a new “color–color” relationship for these continuum flux ratios at the peaks of the flares. Using the RADYN and RH codes, we interpret the ULTRACAM filter emission using the dominant emission processes from a radiative-hydrodynamic flare model with a high nonthermal electron beam flux, which explains a hot, T ≈ 10{sup 4} K, color temperature at blue-to-red optical wavelengths and a small Balmer jump ratio as observed in moderate-sized and large flaresmore » alike. We also discuss the high time resolution, high signal-to-noise continuum color variations observed in YZ CMi during a giant flare, which increased the NUV flux from this star by over a factor of 100.« less
Authors:
 [1] ;  [2] ; ;  [3] ;  [4] ;  [5] ;  [6] ;  [7]
  1. Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
  2. Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast, BT7 1NN (United Kingdom)
  3. Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States)
  4. HL Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W Brooks Street, Norman, OK 73019 (United States)
  5. Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH (United Kingdom)
  6. Department of Physics, Gibbet Hill Road, University of Warwick, Coventry CV4 7AL (United Kingdom)
  7. Laboratory for Atmospheric and Space Physics and Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, Colorado 80309 (United States)
Publication Date:
OSTI Identifier:
22518552
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 820; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CAMERAS; COLOR; DIAGRAMS; ELECTRON BEAMS; HYDRODYNAMICS; MASS; NEAR ULTRAVIOLET RADIATION; STARS; STELLAR FLARES; TIME RESOLUTION; ULTRAVIOLET RADIATION; VELOCITY; VISIBLE RADIATION