Contribution to the search of binaries among Am stars

Free access article

Issue		A&A Volume 369, Number 3, April III 2001


Page(s)		908 - 914
Section		Formation, structure and evolution of stars
DOI		http://dx.doi.org/10.1051/0004-6361:20010168

A&A 369, 908-914 (2001)
DOI: 10.1051/0004-6361:20010168

II. HD 81976 and HD 98880, double-lined spectroscopic binaries

J.-M. Carquillat, N. Ginestet and J.-L. Prieur

UMR 5572 d'Astrophysique, Observatoire Midi-Pyrénées -Centre National de la Recherche Scientifique, 14 avenue Édouard Belin, 31400 Toulouse, France

(Received 22 November 2000 / Accepted 15 January 2001 )

Abstract
We present the results of the observations of two Am stars of eighth magnitude, the double-lined spectroscopic binaries HD 81976 and HD 98880, carried out with the CORAVEL instrument at the Observatoire de Haute-Provence in order to determine their orbital elements. We found 1) for HD 81976: P = 5.655750 days, T = 2449785.941 HJD, $\omega = 341.4^{\circ}$ , e = 0.061, K₁ = 61.68 km s^-1, K₂ = 63.84 km s^-1, V₀ = 19.85 km s^-1, $a_1 \sin i = 4.788$ Gm, $a_2 \sin i = 4.956$ Gm, $M_1 \sin^3 i = 0.5875$ $M_\odot$ , $M_2 \sin^3 i = 0.5676$ $M_\odot$ , and 2) for HD 98880: P = 14.20783 days, T₀ = 2448682.883 HJD (ascending node), e = 0., K₁ = 42.47 km s^-1, K₂ = 49.16 km s^-1, V₀ = 2.40 km s^-1, $a_1 \sin i = 8.298$ Gm, $a_2 \sin i = 9.604$ Gm, $M_1 \sin^3 i = 0.6091$ $M_\odot$ , $M_2 \sin^3 i = 0.5262$ $M_\odot$ . The first of these two systems, HD 81976, is formed by two quasi-identical stars, and the Hipparcos data (M_V, B-V) are consistent with late A stars in effective temperature; it is likely that the components rotate synchronised with the orbital motion. A third body may be present in this system since (i) the orbit has a significant eccentricity despite its short period and (ii) the systemic velocity V₀ shows a possible drift. For the second system, HD 98880, we give $\Delta m_B = 1.25$ and we propose a simple model based upon Strömgren photometric indices and the HR theoretical diagram of Schaller et al (1992) in addition to orbital parameters and Hipparcos data: $T_{\rm eff} = 7000$ K, $\log_{10} g = 4.0$ , M₁ = 1.9 $M_\odot$ , M₂ = 1.6 $M_\odot$ , $\log_{10}({\rm age}) = 9.12$ . The components do not rotate synchronously contrary to HD 81976. Both binaries appear to be detached systems without possibility of eclipses.

Key words: stars: individual: HD 81976, HD 98880 -- binaries: spectroscopic -- stars: fundamental parameters

Offprint request: J.-M. Carquillat, jean-michel.carquillat@obs-mip.fr

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