ROSAT X-ray observations of late-type evolved stars: On the relationship between coronal temperatures and luminosities

Details ROSAT X-ray observations of late-type evolved stars: On the relationship between coronal temperatures and luminosities ROSAT X-ray observations of late-type evolved stars: On the relationship between coronal temperatures and luminosities

Sep 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...432..701m&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 432, no. 2, p. 701-709

Astronomy and Astrophysics

Astronomy

14

Late Stars, Main Sequence Stars, Spectrum Analysis, Stellar Evolution, Stellar Luminosity, X Ray Astronomy, X Ray Spectra, Emission Spectra, Rosat Mission, Stellar Coronas

Scientific paper

We present ROSAT Position Sensitive Proportional Counters (PSPC) X-ray observations of three near-solar-mass stars, in different evolutionary phases beyond the main sequence: eta Sco (F3 III-IV), iota Vir (F6 III), and HD 74772 (G5 III). All three of these nearby, presumably single stars have been detected, and we have collected enough counts to perform a detailed analysis of their soft X-ray spectra. While the X-ray spectra of eta Sco and HD 74772 can be fitted with Raymond-Smith thermal models with temperatures around 2 x 106 K, the high signal-to-noise spectrum of iota Vir provides unambiguous evidence of a multitemperature plasma, with a two-temperature best-fit model with components at approximately 2 x 106 K and 8 x 106 K. Evidence of some hot plasma (T approximately 107 K) has been also found for HD 74772. The present data, compared with spectral fitting results for other late-type stars observed with the Einstein Observatory, indicate that the low X-ray luminosity giants (Lx is less than 5 x 1028 ergs/s) do not share with the higher X-ray luminosity stars of the same class the property of having substantial amount of 107 K plasma. Moreover, our results confirm the trend of increasing X-ray luminosities with increasing coronal temperatures.

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