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Einstein Observatory survey of X-ray emission from solar-type stars - The late F and G dwarf stars
Results of a volume-limited X-ray survey of stars of luminosity classesIV and V in the spectral range F7-G9 observed with the EinsteinObservatory are presented. Using survival analysis techniques, thestellar X-ray luminosity function in the 0.15-4.0 keV energy band forboth single and multiple sources. It is shown that the difference inX-ray luminosity between these two classes of sources is consistent withthe superposition of individual components in multiple-componentsystems, whose X-ray properties are similar to those of thesingle-component sources. The X-ray emission of the stars in our sampleis well correlated with their chromospheric CA II H-K line emission andwith their projected equatorial rotational velocity. Comparison of theX-ray luminosity function constructed for the sample of the dG stars ofthe local population with the corresponding functions derived elsewherefor the Hyades, the Pleiades, and the Orion Ic open cluster confirmsthat the level of X-ray emission decreases with stellar age.
| An empirical H-gamma luminosity calibration for class V-III stars
The W(H-gamma)-M(v) relation for spectral types O to early A of theluminosity classes III-V is calibrated, on the basis of highsignal/noise Reticon spectra for 87 members of eight open clusters andassociations as well as 37 reliable parallax stars, to a mean probabledispersion of + or - 0.28 mag. Although no spectral type corrections arerequired, stellar evolution probably affects the construction of the newcalibration, so care should be exercised in determinations of distancemoduli from slightly evolved cluster sequences. Systematic departuresfrom the calibration may be present for stars with V sin i not less than220-250 km/sec. A comparison of the new calibration with otherearly-type ones shows that it is 1.2 mag brighter than Petrie's (1965)H-gamma calibration at spectral type O6, and 0.7 mag brighter at A3.
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