Multiwavelength Observations of Flares on AD Leonis

Abstract

We report results from a multiwavelength observing campaign conducted during 2000 March on the flare star AD Leo. Simultaneous data were obtained from several ground-and space-based observatories, including observations of eight sizable flares. We discuss the correlation of line and continuum emission in the optical and ultraviolet wavelength regimes, as well as the flare energy budget, and we find that the emission properties are remarkably similar even for flares of very different evolutionary morphology. This suggests a common heating mechanism and atmospheric structure that are independent of the detailed evolution of individual flares. We also discuss the Neupert effect, chromospheric line broadening, and velocity fields observed in several transition region emission lines. The latter show significant downflows during and shortly after the flare impulsive phase. Our observations are broadly consistent with the solar model of chromospheric evaporation and condensation following impulsive heating by a flux of nonthermal electrons. These data place strong constraints on the next generation of radiative hydrodynamic models of stellar flares.

M Dwarf Flare Continuum Variations on One-Second Timescales: Calibrating and Modeling of Ultracam Flare Color Indices*

“…In Hawley et al (2003), similarly small filling factors were found for ≈9000 K blackbody emission using broadband photometry of a ΔU=−1.8 mag event on AD Leo, and Lovkaya (2013) also used broadband colors to deduce T∼14,000 K blackbody components at the peaks of two moderate-amplitude events, ΔU=−1.65 and −1.76 mag, also on AD Leo. The simultaneous information from our spectra allow us to assess the excess Balmer continuum emission and obtain a more detailed view of the continuum during moderate-sized flares.…”

Abiotic Ozone and Oxygen in Atmospheres Similar to Prebiotic Earth

“…This highlights the need for contextual information and integrated models to thoroughly characterize extrasolar planets. Characterization and target star selection efforts will be greatly aided by knowledge of the stellar energy distribution incident upon the planet, and this strongly motivates future UV observations of different star types, in particular F-type stars and M dwarfs (e. g. Hawley et al 2003;Walkowicz et al 2008;France et al 2012). These results also motivate the broadest possible wavelength range for spectral observations of exoplanets.…”

A Unified Computational Model for Solar and Stellar Flares

“…Observations of flares on dMe stars (Hawley & Pettersen 1991;Hawley et al 2003;Kowalski et al 2010) and the Sun (Johns- Krull et al 1997) have shown that the hydrogen Balmer lines can become extremely broadened. These authors speculate the cause to be Stark broadening, and that conclusion is supported by the models of Allred et al (2006) and Paulson et al (2006).…”

“…Active dMe stars are known to have flares much larger than those on the Sun. These stars spin faster and generate much larger magnetic fields (Hawley et al 2014, and references therein) resulting in flares some 10 3 times more energetic than typical solar flares (e.g., Hawley & Pettersen 1991;Hawley et al 2003;Kowalski et al 2010). In addition, the background intensity of dMe stars is much smaller than that of the Sun.…”