Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...278..499d&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 278, no. 2, p. 499-510
Astronomy and Astrophysics
Astrophysics
8
Electron Density (Concentration), Rotational Spectra, Stellar Flares, Astronomical Photometry, Iron, Iue, Solar Maximum Mission, Spectral Resolution, Spectrographs, Ultraviolet Spectroscopy
Scientific paper
During ultraviolet spectroscopic observations of the RS CVn star II Peg in September 1990 a long duration (greater than or = 3 hrs.) flare was observed. During the early stage of the event, a feature at 1354 A was present, however, within the spectral resolution of the data it is not possible to identify this line. A contribution from the hot coronal ion Fe XXI is suspected. From line diagnostic ratios, the electron pressure at flare peak was estimated to be 1017/cu cm K, decreasing to 1016/cu cm K towards the end of the flare. One other flare was observed with IUE, and three optical flares (unfortunately none of these were observed simultaneously). The chromospheric and transition region losses from the larger of the two IUE flares was approx. 3 x 1031 erg/s at flare maximum, with total chromospheric/transition region radiative losses over the duration of the event being approx. 1.5 x 1035 erg. Continuum radiative losses over the wavelength region 1150A to 1950A were approximately 3% of the above figure. At flare maximum, the N V 1240 A line showed an enhancement factor of approx. 3 over the preflare value compared to 9 for the C IV 1550 A line. We interpret this difference as due to an underabundance of nitrogen during the flare, possibly related to photoionization of lower chromospheric material by soft X-ray photons sometime prior to the flare. No evidence of rotational modulation was present in any of the transition region lines, although the chromospheric lines did show a phase variation. However, these lines (H-alpha, Ca II K and Mg II h&k) were not consistent with one another although it is clear that the H-alpha equivalent width showed variations faster than the star's rotation period, being perhaps related to the decay/activation of individual active regions.
Avgoloupis S.
Doyle Gerry J.
Mathioudakis Michail
Mavridis Lyssinmahos N.
Murphy H. M.
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