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Astron. Astrophys. 319, 637-647 (1997)

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The spectrum of Coronae Borealis in the lithium region

M. Hack 1, N.S. Polosukhina 2, V.P. Malanushenko 2 and F. Castelli 3

1 Dipartimento di Astronomia, via G.B.Tiepolo 11, I-34131 Trieste, Italy
2 Crimean Astrophysical Observatory, p/o Nauchny, 334413 Crimea, Ukraine
3 CNR-Gruppo Nazionale Astronomia and Osservatorio Astronomico, via G.B. Tiepolo 11, I-34131 Trieste, Italy

Received 22 March 1996 / Accepted 5 August 1996

Abstract

Results from spectroscopic observations in the Li region of the binary CP star [FORMULA]  CrB (HD 137909, HR 5747, F0p) are presented. The observations were carried out at the Crimean Observatory from 1993 to 1995 with the coudé spectrograph equipped with a CCD detector, R=45000.

We have analyzed the 6693-6721 Å  region by means of the spectral synthesis method by assuming a model with parameters [FORMULA] = [FORMULA] K, [FORMULA], and [FORMULA]. We derived abundances for the elements with lines in the studied range. The observed feature at 6708 Å  is not well fitted by the Li doublet even by assuming an isotopic ratio 10 times the terrestrial value and an overabundance of lithium of 2.6 dex; a very good fit is obtained assuming a blend with V I at 6708.094 Å, in the hypothesis that Vanadium is in excess by a factor larger than [FORMULA] (a value which is not confirmed by other abundance determinations). It is more probable that the Li feature is blended with some unidentified line due to some overabundant heavy element.

The ultraviolet excess for [FORMULA] [FORMULA] 1600 Å  is discussed. It could be explained either by assuming that the companion is a [FORMULA] Boo star having a metal deficiency [FORMULA] and [FORMULA] [FORMULA], or by assuming that [FORMULA]  CrB is Si deficient, so that the Si I discontinuities at 1514.34 Å  and at 1674.03 Å  disappear. However, there is no clear evidence of underabundances of this element with respect to the solar value.

The main results of this paper are: the variability of the lithium blend with the period of rotation of the star; the relations between rotational radial velocity, line intensity [FORMULA] and FWHM variations for the Li blend and other lines of different elements - Fe , Gd , Ce - which show similar variations.

Key words: stars: abundances – stars: chemically peculiar – lines: identification – individual star: fi CrB

Send offprint requests to: M. Hack

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998
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