Colour excesses and absolute magnitudes for non-Cepheid F-G supergiants from uvbybeta photometry

Details Colour excesses and absolute magnitudes for non-Cepheid F-G supergiants from uvbybeta photometry Colour excesses and absolute magnitudes for non-Cepheid F-G supergiants from uvbybeta photometry

Nov 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990a%26a...239..205a&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 239, no. 1-2, Nov. 1990, p. 205-213.

Astronomy and Astrophysics

Astrophysics

37

F Stars, G Stars, Stellar Color, Stellar Magnitude, Stellar Spectrophotometry, Ubv Spectra, Calibrating, Interstellar Extinction, Stellar Luminosity, Supergiant Stars, Spectrophotometry, Stars: Cepheids, Stars: Colors Of, Stars: General, Luminosities Supergiant

Scientific paper

An extensive compilation of non-cepheid F0-G8 supergiants in open clusters and OB associations has been carried out. A group of these stars was critically selected to serve as calibrators for functional formulae to predict E (B - V) and Mν for luminous yellow supergiants, exclusively from uvbyβ colour indices. A reddening formula for F0-G3 supergiants is provided that predicts E(B- V) within ±0.03. It is demonstrated that such a formula also predicts cepheid reddenings within the same accuracy.
It is shown that luminous (Mν < -6) F-G supergiants are clearly separated from their counterparts cepheids on the [m1]-[c1] plane. On the basis of this, a group of luminous non-cepheids in open clusters and associations were selected as calibrators for the Mν-uvbyβ relationship. We offer a formula that predicts Mν with an estimated accuracy of ±0.5 for the most luminous F-G supergiants.
From the above calibrations, the membership of HD 97534 in NGC 3572 finds support. The case of the high galactic latitude supergiants UU Her, 89 Her and HD 161796 is addressed and found, from their photometric indices, that they are affected by moderate reddenings (E (B - V) = 0.1-0.3), probably of circumstellar origin and that they are luminous (Mν < -7.5). Why their colours lead to much higher luminosities than the expected ones from the evolutionary scenarios sketched from spectroscopic grounds is not yet understood.

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