Contribution à l'étude des spectres composites. VIII. HD 174016-7, une étoile Ap associée à une géante G Contribution to the study of composite spectra VIII. HD 174016-7, an Ap star with a giant G

Abstract

HD 174016-7, listed by \cite[Hynek (1938)]{Hynek} as a star having a composite spectrum, was on our observing programmes of such objects carried out both at the Cambridge Observatories and at the Observatoire Midi-Pyrénées. Most of the observations were made with the CORAVEL spectrovelocimeter of the Swiss telescope at the Observatoire de Haute-Provence. We find that this star is a long-period spectroscopic binary with two correlation dips; we obtain the following orbital elements: P = 3097.9 days; T = JD 2450605.2; omega = 204fdg 8; e = 0.600; K_1 = 12.95 km s^-1; K_2 = 15.14 km s^-1; V_0 = -1.65 km s^-1; a_1 sin i = 441.1 Gm; a_2 sin i = 516.0 Gm; M_1 sin ³i = 1.967 M_sun; M_2sin ³i = 1.681 M_sun. The primary is a giant star of spectral type near G6III, and the hot dwarf secondary is found to be a peculiar A star of type A0p Sr, Cr, Eu, Si; so HD 174016-7 is, to our knowledge, the second discovered composite-spectrum binary with a Ap-type hot component. A confrontation with Hipparcos data suggests M_{v_1} = 0 and m_v = 0.6 mag. On the basis of very accurate masses of main sequence stars by \cite[Andersen (1991),]{Andersen} we estimate the mass, M_1 = 2.8 M_sun, of the giant primary, the orbital inclination, i = 63^o, and the mean linear separation of the components, a = 7.2 AU. The evolutionary status of the system is discussed using \cite[Schaller et al. (1992)]{Schaller} M_bol / T_eff diagram for stars of solar metallicity. Theoretical masses suggested by this diagram confirm the proposed model. Étude effectuée à partir d'observations faites aux Observatoires de Haute-Provence et de Cambridge.