J/A+A/315/384 J/A+A/315/384 Binarity among B-stars in NGC 6231 D Raboud Astron. Astrophys. 315 384 1996 1996A&A...315..384R Binaries, spectroscopic Radial velocities binaries: general binaries: spectroscopic open clusters and associations: individual (NGC 6231) techniques: radial velocities We have measured radial velocities for 53 B-type stars, between B1 and B9, in the young open cluster NGC 6231 through a cross-correlation technique with synthetic spectra. Two measurements for 36 stars of the sample were obtained with a time separation of about two years. We derived a minimum binary fraction of 52% in the considered population. The velocity determination precisions were simulated and we analysed their dependence upon the S/N ratios of the spectra and upon the stellar rotational velocities. We discuss the selection of the templates for the correlation.

Number Star number from Seggewiss (1968VeBon..79....1S) --- Vmag V magnitude mag [B-V] Color index mag Teff Effective temperature calculated number=1 See Sect. 3.2.1 of the paper. K n_Teff Remark on Teff determination number=2 The question mark in brackets indicates that the determination is possibly outside the validity range of the Q parameter (see Sect. 3.2.1). --- Vsini Rough determination of Vsini number=3 See Sect. 3.2.2. km/s r_Teff Source of the photometry and Teff number=4 GE is for the Geneva photometry, pe for UBV photoelectric and pg for UBV photographic photometry. The digits have the following significations: 1 = Teff from Spectral Type estimated from equivalent widths (Didelon 1982A&AS...50..199D) 2 = V and [B-V] from Garrison & Schild (1979AJ.....84.1020G), Teff from Van Genderen et al. (1984A&AS...58..537V) 3 = Seggewiss (1968VeBon..79....1S) 4 = V and [B-V] from Seggewiss (1968VeBon..79....1S), Teff calculated from uvby photometry (Shobbrook 1983MNRAS.205.1229S) 5 = Garrison & Schild (1979AJ.....84.1020G) 6 = V and [B-V] from Garrison & Schild (1979AJ.....84.1020G), Teff calculated from uvby photometry (Shobbrook 1983MNRAS.205.1229S) 7 = V and [B-V] from Geneva photometry, Teff from Spectral Type (Kilian et al. 1994A&A...284..437K) and Vsini from Kilian et al. (1994A&A...284..437K) 8 = V and [B-V] from Garrison & Schild (1979AJ.....84.1020G), Teff from Spectral Type (Garrison & Schild 1979AJ.....84.1020G) 9 = Heske & Wendker (1984A&AS...57..205H) --- JD Julian Date of the observation --- RV Radial velocities km/s n_RV SBII characteristic of the star number=5 See Sect. 6.1.4. --- e_RV Radial velocity uncertainties number=6 Radial velocity uncertainties, obtained from the simulations described in Sect. 4, using a fixed B1 synthetic spectrum for all cases, and adapted in order to reproduce exactly the conditions of the radial velocity determinations for the two runs (i.e. without the region between 430 nm and 440 nm, see Sect. 3.3). km/s RVdiff1 Radial velocity differences number=7 Differences between radial velocities of column RV. km/s RVdiff2 Radial velocity differences number=7 Differences between radial velocities of column RV. km/s RVdiff3 Radial velocity differences number=8 Differential radial velocities obtained without any template (see text). km/s RVdiff4 Radial velocity differences number=8 Differential radial velocities obtained without any template (see text). km/s Raboud University of Lausanne Patricia Bauer CDS 1996May14Didier Raboud <Didier.Raboud@obs.unige.ch> J_A+A_315_384.xml