Abstract
Ultraviolet low resolution spectra of most of the B stars observed with the S2/68 experiment onboard the TD1 satellite in the spectral range 1350 A - 2500 A are computer-investigated in order to define a grid of standard behaviors (J.M. Vreux and J.P. Swings, 1976 Astron. Astrophys., in press). The behavior of the relative intensities of the Balmer and Paschen continua is studied as a function of the spectral type and the visible photometric index Q: both relations are shown to be luminosity dependent. A comparison to theoretical predictions and to previous studies is also presented. A measure of the slope of the pseudo-continuum drawn between ~ λ 1660 A and ~ λ 2550 A is studied in the same way: the effect of luminosity is discussed in connection with recently proposed temperature scales for super-giants. The behavior of the depths of the absorption features at λλ 1550 A, 1940 A, 2000 A, 2055 A, 2105 A, 2340 A and 2395 A with respect to the spectral type, the Q index and the luminosity class is also briefly presented. Special emphasis is given to the absorption features at λ 1550 A in connection to the discussion of the Felll lines in the ultraviolet spectra of early B stars by J.P. Swings, M. Klutz, J.M. Vreux and E. Peytremann (1976, Astron. Astrophys. Suppl. 25, 193). Preliminary results of a study of high resolution Copernicus spectra in the A 1550 A region are also presented: it is shown that the role of Felll remains predominant for stars of spectral type as early as about BIII - BIIII (J.P. Swings and J.M. Vreux, to be published).
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