High-Cadence DST/ROSA Observations of the NUV/Blue Continuum Radiation in a Solar Flare

Abstract:

Radiative-hydrodynamic models of solar flares provide sophisticated predictions of the ultraviolet and optical continuum shape and strength on shorter than 1 s timescales covering a broad wavelength range. However, most optical observations of solar flares in the modern era are not obtained at fast cadence and are not optimized at blue continuum wavelengths, which provide a critical constraint on the heating properties at large column mass. To rectify this major gap in our knowledge of solar flare spectra, custom Balmer jump filters were designed for the ROSA instrument at the Dunn Solar Telescope. Unprecedented observations at 7.5 - 30 frames per second were obtained covering the C9.7 flare SOL20141025T15:52 in NOAA AR 12192 during the NSO’s Service Mode operations (and provided by the F-CHROMA solar flare database). We report on how the flare response in the 350 nm and 417 nm ROSA filters constrains several common assumptions employed in modern flare modeling, such as the duration of individual heating bursts. We also report on the Balmer jump properties in this flare and compare to several M dwarf flares, which have been observed in identical filters using the ULTRACAM and ARCTIC instruments on the 4.2m WHT, the 3.6m NTT, and the 3.5m ARC telescope. We compare the light curves to radiative-hydrodynamic model predictions of the 350 nm brightness evolution on short timescales.