X-ray and optical observations of HD 155638 : a remarkably active cool star.
Abstract
X-ray and optical observations of the 8.5-mag star HD 155638 are reported which reveal a remarkably active chromosphere and corona for the star. The object was first observed in soft X-rays with the HEAO 1 A2 low-energy detectors, and later reobserved with the HEAO 2 IPC. X-ray fluxes of about 2 x 10 to the -11th and 3 x 10 to the -12th ergs/sq cm per sec were obtained on the two occasions, indicative of source variability over the 2.5-year period between observations. SIT spectrographs taken in July-August 1980 show evidence of Ca II H and K core emission reversals and filled-in H alpha, while spectra taken in March and July 1981 show evidence of asymmetry and variability in the Ca II reversals. The spectral data are consistent with a G8 IV-V classification, from which is inferred a distance of 35-120 pc, and an X-ray luminosity from 4 x 10 to the 29th to 4 x 10 to the 31st ergs/sec. An absence of emission lines characteristic of mass transfer in binary systems indicates the X-rays to be coronal in origin. The properties of the star are noted to be similar to those of the RS CVn binaries.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 1981
- DOI:
- Bibcode:
- 1981ApJ...251L.105S
- Keywords:
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- Emission Spectra;
- Late Stars;
- Stellar Spectra;
- Stellar Spectrophotometry;
- Stellar Temperature;
- X Ray Sources;
- Calcium;
- Chromosphere;
- H Alpha Line;
- Heao 1;
- Heao 2;
- Light (Visible Radiation);
- Potassium;
- Stellar Evolution;
- Stellar Luminosity;
- Stellar Structure;
- Astronomy