Spectra of high-velocity giants.

Abstract

view Abstract Citations (5) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectra of high-velocity giants. Keenan, P. O. ; Morgan, W. W. ; Münch, G. Abstract From a comparison of Yerkes, McDonald and Perkins spectrograms it is found that the characteristic differences between high-velocity giants (space motion > 75 km/sec) and the ordinary giants assigned to population I by Baade are: (I) In types G and K the bands of CN are definitely weaker in high-velocity stars than in ordinary stars of the same luminosity. The stronger metallic lines appear nearly normal in the high-velocity stars. The Balmer lines of H and the G-band (N4300) of CH are at least as strong as in ordinary stars and may be slightly strengthened in high-velocity stars. (2) Among the carbon stars (Type R) the high-velocity (?nes are marked by such tremendous strengthening of the G-band that they have been called CH-stars. The CN-bands appear on the average to be somewhat weaker than in ordinary carbon stars. The Balmer lines and N4554 of Ba+ are slightly strengthened. In both of these groups the peculiarities shown by the high-velocity stars are more pronounced in molecular features (CH, CN) than in atomic lines. The elements most affected are H, C, N and possibly 0 (because of the great influence of CO abundance upon the equilibrium concentration of CN). It is significant that these are among the abundant light elements the concentration of which appears to be a determining factor in the structure of a star. Twenty stars of types C and K having space motions estimated at more than 75 km/sec in Miczaika's catalogue were examined on the Yerkes spectrograms. Sixteen of them definitely showed the peculiarities, while, in the spectra of the remaining four, differences from normal stars could not be established with certainty. When revised spectroscopic absolute magnitudes were estimated from the new plates, however, the corresponding space velocities for these four stars were reduced to less than 75 km/sec, and their assignment to the high-velocity group was accordingly thrown into doubt. It is concluded that the appearance of the peculiarities to at least some degree is a quite general feature of the spectra of high-velocity stars. If the metallic lines are used in preference to the N42 15 band of CN, fairly reliable spectroscopic absolute magnitudes can be found for the high-velocity stars. For this purpose sp3ctro- grams of moderate dispersion appear most efficient. On the other hand, the fact that the peculiarities become more conspicuous on smallscale spectrograms suggests that objective-prism plates can be used to discover faint stars having the high-velocity characteristics. Perksns Observatory, Delaware, Ohio, and Yerkes Observatory, Wittianis Bay, Wis. Publication: The Astronomical Journal Pub Date: January 1948 DOI: 10.1086/106117 Bibcode: 1948AJ.....53Q.194K full text sources ADS |