Contribution to the study of composite spectra VIII. HD 174016-7, an Ap star with a giant G

HD 174016-7, listed by Hynek (1938) as a star having a composite spectrum, was on our observing programmes of such objects carried out both at the Cam bridge Observatories and at the Observatoire Midi-Pyrenees. Most of the obs ervations were made with the CORAVEL spectrovelocimeter of the Swiss telesc ope at the Observatoire de Haute-Provence. We find that this star is a long -period spectroscopic binary with two correlation dips; we obtain the follo wing orbital elements: P = 3097.9 days; T = JD 2450605.2; omega = 204.degre es 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(3) i = 1.967 M. ; M-2 sin(3) i = 1.681 M.. The primary is a giant star of spectral type nea r G6III, and the hot dwarf secondary is found to be a peculiar A star of ty pe A0p Sr, Cr, Eu, Si; so HD 174016-7 is, to our knowledge, the second disc overed composite-spectrum binary with a Ap-type hot component. A confrontat ion with Hipparcos data suggests M-upsilon 1 = 0 and m(upsilon) = 0.6 mag. On the basis of very accurate masses of main sequence stars by Andersen (19 91), we estimate the mass, M-1 = 2.8 M., of the giant primary, the orbital inclination, i = 63 degrees, and the mean linear separation of the componen ts, a = 7.2 AU. The evolutionary status of the system is discussed using Sc haller et al. (1992) M-bol/T-eff diagram for stars of solar metallicity. Th eoretical masses suggested by this diagram confirm the proposed model.