Astron. Astrophys. Suppl. Ser. 130, 415-419

Contribution à l'étude de la binarité des étoiles de type Am

I. HD 125273, binaire spectroscopique à raies doubles
HD 125273, a double-lined spectroscopic binary

N. Ginestet et J.-M. Carquillat

Laboratoire d'Astrophysique (UMR 5572), Observatoire Midi-Pyrénées, 14 avenue Edouard Belin, 31400 Toulouse, France e-mail: Carquillat@obs-mip.fr, Ginestet@obs-mip.fr

Reçu le 25 mars; accepté le 17 décembre 1997

Abstract:

We present an observing program undertaken at Observatoire de Haute-Provence, for the search and study of spectroscopic binaries among Am stars. HD 125273 was recognized as an Am star some time ago (Olsen 1980; Abt 1984); observations, carried out with the CORAVEL spectrovelocimeter, show that this star is a double-lined spectroscopic binary; its orbital elements are as follows: P = 7.482664 days; T = 2448665.660 JD; $\omega_1 = 355.3^{\rm \circ}$; e = 0.071; K₁ = 49.82 km/s; K₂ = 51.75  km/s; V₀ = -17.42 km/s; $a_1\,{\rm sin}i = 5.113$ Gm; $a_2\,{\rm sin}i = 5.311$ Gm; $M_1\,{\rm sin}^3i = 0.412\, M_\odot;\; M_2 \,{\rm sin}^3i = 0.396\, M_\odot$.

Strömgren photometry of the star (Olsen 1983) permits us to estimate the following mean physical parameters for the components of the binary: $T_{\rm eff} = 7500$ K; log g = 3.70; M_v = 1.24; $M = 2.1\, M_\odot;\; R = 3.2\, R_\odot$, and to specify the evolutionary status of the system.

Assuming the above mass for the components, we found $i\sim 35^{\rm \circ}$ and $a \sim 26 \,R_\odot$. This system is thus a detached one without possibility of eclipses. It is likely that the two components are Am stars of very close characteristics.

The $v\,{\rm sin}i$ values, determined from the correlation dips given by CORAVEL, are near 11 km/s for both components. We retain for this binary the hypothesis of rotation-revolution synchronism, because it leads to a value of the radius of the stars in agreement both with the above value and the results of a previous study by Kitamura & Kondo (1978) of similar, but eclipsing, systems. The ratio of the correlation dip areas indicates a magnitude difference $\Delta m_v \sim 0.2$ mag. As expected in detached systems of main sequence stars, such as Am's, HD 125273 obeys the mass-luminosity law.

Key words: : stars: individual: HD 125273; binaries: spectroscopic -- stars: fundamental parameters