Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995sao..rept.....b&link_type=abstract
In Smithsonian Astrophysical Observatory, 8 p (SEE N96-14306 03-90)
Astronomy and Astrophysics
Astronomy
Cool Stars, Electron Density (Concentration), Emission Spectra, Extreme Ultraviolet Radiation, Radiation Dosage, Spaceborne Astronomy, Spectrum Analysis, Stellar Atmospheres, Ultraviolet Astronomy, Ultraviolet Spectra, Abundance, Atmospheric Temperature, Extreme Ultraviolet Explorer Satellite, Hydrogen, Iron, Low Temperature, Signal To Noise Ratios, Time Series Analysis
Scientific paper
Extreme ultraviolet spectra of Capella, obtained at various orbital phases over the past two years by the EUVE satellite, show strong emission lines from a continuous distribution of temperatures (approximately 105 -10(exp 7.3 K). In addition to the strong He II lambda 303.8, the spectra are dominated by emission lines of highly ionized iron. Strong lines of Fe IX, XV, XVI, and XVIII-XXIV are used to construct emission measure distributions for the individual pointings, which show several striking features, including a minimum near 106 K and a local maximum at 106.8 K. Furthermore, intensities of the highest temperature lines (Te is greater than 107 K) show variations (factors of 2-3) at different orbital phases, while the lower temperature Fe lines show variations of about 30% or less. The low variability of most of the strong low temperature features motivates a detailed analysis of the summed spectrum. With approximately 280 ksec of total exposure time, we have measured over 200 emission features with S/N greater than or equal to 3.0 in the summed spectrum. We report here initial results from the analysis of this spectrum. We can now identify lines of Fe VIII and X-XIV, as well as a number of electron density and abundance diagnostic lines. We also report here the first direct measurement of the continuum flux around approximately 100 A in a cool star atmosphere with EUVE. The continuum flux can be predicted from the emission measure model based on Fe line emission, and demonstrates that the Fe/H abundance ratio is dose to the solar photospheric value.
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