Time-Resolved Properties and Global Trends in dMe Flares from Simultaneous Photometry and Spectra

摘要

We present a homogeneous survey of line and continuum emission fromnear-ultraviolet (NUV) to optical wavelengths during twenty M dwarf flares withsimultaneous, high cadence photometry and spectra. These data were obtained tostudy the white-light continuum components at bluer and redder wavelengths thanthe Balmer jump. Our goals were to break the degeneracy between emissionmechanisms that have been fit to broadband colors of flares and to provideconstraints for radiative-hydrodynamic (RHD) flare models that seek toreproduce the white-light flare emission. The main results from the continuumanalysis are the following: 1) the detection of Balmer continuum (in emission)that is present during all flares and with a wide range of relativecontributions to the continuum flux at bluer wavelengths than the Balmer jump;2) a blue continuum at flare maximum that is linearly decreasing withwavelength from \lambda = 4000-4800\AA, matched by the spectral shape of hot,blackbody emission with typical temperatures of T_{BB}~9000-14,000 K; 3) aredder continuum apparent at wavelengths longer than H\beta\ (\lambda >4900\AA) which becomes relatively more important to the energy budget duringthe late gradual phase. We calculate Balmer jump flux ratios and compare to RHDmodel spectra. The model ratios are too large and the blue-optical (\lambda =4000-4800\AA) slopes are too red in both the impulsive and gradual decay phasesof all twenty flares. This discrepancy implies that further work is needed tounderstand the heating at high column mass during dMe flares. (Abridged)