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Photoelectric Photometry of Stars in the Orion Standard Region
Magnitudes and color indices in the Vilnius seven-color photometricsystem are given for 108 stars in the Orion standard region around theOrion Belt and the star lambda Orionis. New spectral and luminosityclasses, estimated from the photometric data, are given for some of thestars.
| Lithium and chromospherically active single giants
Nine chromospherically active single K giants were identified fromsurveys of chromospherically active stars. The stars have v sin i'sranging from 6 to 46 km/sec. Such large velocities are not explained byscenarios of main sequence to giant star evolution. Fluxes of theultraviolet emission lines of these stars are substantially less thanthose of FK Comae. Many of these giants have a moderate or stronglithium line strongly suggesting that these stars recently evolved fromrapidly rotating A or early F stars as is suggested by their spacemotions. Thus, they are not spun down FK Com stars. The characteristicsof these stars are such that they may be confused with pre-main sequencestars. The primary difference may be that the post main sequence starshave strong H alpha absorption lines while the pre-main sequence starsappear to have a weak H alpha absorption line or possibly H alpha inemission above the continuum.
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