Geometry Diagnostics of a Stellar Flare from Fluorescent X-Rays
Abstract
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 lesssim 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2008
- DOI:
- 10.1086/533461
- arXiv:
- arXiv:0801.3857
- Bibcode:
- 2008ApJ...675L..97T
- Keywords:
-
- hydrodynamics;
- plasmas;
- stars: coronae;
- X-rays: stars;
- Astrophysics
- E-Print:
- accepted for publication on the Astrophysical Journal Letters