Quiescent and flare analysis for the chromospherically active star Gl355 (LQHya)

We discuss ROSAT and ASCA observations of the young active star Gl355}. During the ROSAT observation a strong flare was detected with a peak flux more than an order of magnitude larger than the quiescent level. Spectral analysis of the data allows us to study the temperature and emission measure dis...

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Bibliographic Details
Published in:arXiv.org 2001-03
Main Authors: Covino, S, Panzera, M R, Tagliaferri, G, Pallavicini, R
Format: Article
Language:English
Subjects:
Abundance
Coronas
Emission analysis
High temperature
Metallicity
Photosphere
Stellar flares
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Summary:We discuss ROSAT and ASCA observations of the young active star Gl355}. During the ROSAT observation a strong flare was detected with a peak flux more than an order of magnitude larger than the quiescent level. Spectral analysis of the data allows us to study the temperature and emission measure distribution, and the coronal metal abundance, for the quiescent phase and, in the case of ROSAT, also during the evolution of the flare. The global coronal metallicity \(Z/Z_{\odot} \sim 0.1\) derived from both ROSAT and ASCA data is much lower than solar and presumably also much lower than the photospheric abundance expected for this very young star. The temperature structure of the quiescent corona was about the same during the various observations, with a cooler component at \(T_1 \sim 7\) MK and a hotter component (to which only ASCA was sensitive) at \(T_2 \sim 20\) MK. During the flare, the low temperature component remained approximately constant and equal to the quiescent value, while the high-temperature component was the only one that varied. We have modeled the flare with the hydrodynamic-decay sustained-heating approach of Reale at al. (1997) and we have derived a loop semi--length of the order of \(\sim 1.5\) stellar radii, i.e. much larger than the dimensions of flares on the Sun, but comparable with the typical dimensions inferred for other stellar flares. We have compared the derived loop size with that estimated with a simpler (but physically inconsistent) approach, finding that for this, as well for several other stellar flares, the two methods give comparable loop sizes. Possible causes and consequences of this result are discussed.
ISSN:2331-8422
DOI:10.48550/arxiv.0103473