Geometry Diagnostics of a Stellar Flare from Fluorescent X-Rays

Testa, Paola; Drake, Jeremy J.; Ercolano, Barbara; Reale, Fabio; Huenemoerder, David P.; Affer, Laura; Micela, Giuseppina; Garcia-Alvarez, David
Referencia bibliográfica

The Astrophysical Journal, Volume 675, Issue 2, pp. L97-L100.

Fecha de publicación:
3
2008
Número de autores
8
Número de autores del IAC
0
Número de citas
19
Número de citas referidas
17
Descripción
We present evidence of Fe fluorescent emission in the Chandra HETGS spectrum of the single G-type giant HR 9024 during a large flare. In analogy to solar X-ray observations, we interpret the observed Fe Kα line as being produced by illumination of the photosphere by ionizing coronal X-rays, in which case, for a given Fe photospheric abundance, its intensity depends on the height of the X-ray source. The HETGS observations, together with three-dimensional Monte Carlo calculations to model the fluorescence emission, are used to obtain a direct geometric constraint on the scale height of the flaring coronal plasma. We compute the Fe fluorescent emission induced by the emission of a single flaring coronal loop that well reproduces the observed X-ray temporal and spectral properties according to a detailed hydrodynamic modeling. The predicted Fe fluorescent emission is in good agreement with the observed value within observational uncertainties, pointing to a scale height <~0.3R*. Comparison of the HR 9024 flare with that recently observed on II Peg by Swift indicates the latter is consistent with excitation by X-ray photoionization.