Stellar spectra in the region of the obscuring clouds of Ophiuchus and Scorpius.

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view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Stellar spectra in the region of the obscuring clouds of Ophiuchus and Scorpius. Struve, Otto ; Rudkjobing, Mogens Abstract Joy's remarkable discovery of forty stars having strong emission lines in the vicinity of the great obscuring clouds of Taurus has in- spired a study of the faint stars in the region of the dark nebulae in Ophiuchus and Scorpius. With the 8 -inch telescope of the McDonald Observatory the authors have observed the spectra of approximately twenty stars between photographic apparent magnitudes 12 and 15. TABLE 1. EMIS' No. (1948) 8(1948) Mag. 4 I6 2 8 24113 13 9 16 24.5 -24 14 12.5 10 i6 24.7 -24 i6 15 12 i6 24.1 -2434 13.5 13 i6 25.6 -24 20 12.5- -14.0 FAINT STARS OF EARLY TV 3 1623.0 -2428 13 5 1622.9 -23 50 13 16 1623.8 -23 50 13.5 Five of them were found to have strong emission lines and one of the five (number 13 in our list) is a variable star with a range of at least 1.5 mag. These five stars range in spectral type, as estimated from the absorption features, between K2 and M. They are thus similar to the majority of Joy's stars in Taurus, presumably belonging to the main sequence and having in addition a superposed spectrum of strong emission lines which make them stand out among the ordinary dMe and the dKe stars which are occassionally found among ordinary stellar populations. An interesting feature of the stars 9, 12, and 13 is the great strength of the blend of Caii H and HE which seems to be abnormal since it exceeds the sum of the intensities to be expected in the two blended components. It is possible that this excessive strength of the Caii H line m y be explained by inelastic collisions between Caii ions in the ground state and H atoms in the seventh quantum state. The occurence of dwarf stars with strong emission lines in cosmic dust clouds again raises the problem of the origin of their peculiar spectra. A computation based upon Hoyle's expression for the accretion of mass of a star which rests within a nebula leads to the following ratio of the energy released by the infall of particles to the energy of radiation of the star = I0-iN( 3) 31 It may be reasonable to suppose that the number of atoms per cubic centimeter of the dust cloud is is the order of the 101 or I0 and that the tempera- ON LINE STARS Sp. Description K5 Very strong H and Caii and perhaps weak HeI. The absorption lines are systematically weaker than normal. K2 Fairly strong and very broad H, strong and sharp Caii. Caii H very much stronger than CaiI K. K? Very strong H and Caii, moderately strong FeII. Spectral type estimated from the continuous spectrum because the emission lines overlie the absorption features. M Moderate H and Caii, perhaps weak FeiI. Caii H very much stronger than Caii K. Has TiO absorption bands. Very strong H and weak Cail. HE$ ? Caii H is much stronger than H . Continuous spectrum too weak. E ITHOUT EMISSION LINES Ao Fairly sharp absorption of H. A Very weak and shallow absorption lines of H. ture of the thermal motions of these atoms in the vicinity `of the star may be of the order of I0 . In that case it is reasonable to expect fairly strong emission lines in the spectra of those stars which do not have enough radiation pressure to drive away the dust particles. In addition to the five emission line stars, three faint stars of type A were found within the densest regions of the nebula. Their spectra have no emission lines and only number 16 looks abnormal because of the weakness of its hydrogen absorption lines. This may be an underluminous A star or possibly even a white dwarf. The rest of the stars have normal spectra of types K and M. Most of them are probably foreground stars while a few, near the edges of the nebula may be distant objects shining through the thinner portions of the cloud. Table I gives a list of the more interesting objects. Ferkes Observatory, Williams Bay, Wis., and McDonald Observatory, Fort Davis, Tex. Publication: The Astronomical Journal Pub Date: October 1948 DOI: 10.1086/106193 Bibcode: 1948AJ.....54...51S full text sources ADS |