Contribution to the search of binaries among Am stars

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: days, HJD, , , km s-1 , km s-1 , km s-1 , Gm, Gm, , , and 2) for HD 98880: days, HJD (ascending node), , km s-1 , km s-1 , km s-1 , Gm, Gm, , . The first of these two systems, HD 81976, is formed by two quasi-identical stars, and the Hipparcos data (M 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 V 0 shows a possible drift. For the second system, HD 98880, we give and we propose a simple model based upon Stromgren photometric indices and the HR theoretical diagram of Schaller et al (1992) in addition to orbital parameters and Hipparcos data: K, , , , . The components do not rotate synchronously contrary to HD 81976. Both binaries appear to be detached systems without possibility of eclipses.