47 Tucanae: Radial Velocities and Spectral Types of Individual Stars

Abstract

A discussion is given of the radial velocities and spectral types of 32 stars in 47 Tuc determined from 64 plates. The spectral types of 23 red giants lie in the range of MK types G8–M2 and luminosity classes II–III. There is a slight CN discrepancy, but the spectra are much more normal than the extreme population II globular cluster stars. The metal/hydrogen ratio is unlikely to be less than 1/4 normal. The spectroscopic evidence suggests that the top of the giant branch lies below and to the red of that of other globular clusters in the HR diagram. One red giant, not known to be a variable star shows a variable spectrum. A mean velocity of –14.2 km/sec for the cluster is deduced. A dependence of radial velocity on spectral type is found. It is unlikely that this is due to the wavelength system employed. From the velocity dispersion of the red giants it is found that under almost any assumption the mass of 47 Tuc is unlikely to be greater than 6.0 × 10 5 solar masses and taking into account the dependence of velocity on type may well be less than 2.5 × 10 5 solar masses. The mass/light ratio (0.3 solar units) is much less than in intermediate spirals and elliptical galaxies. The membership and spectrum of a bright B8 III star is discussed. Two irregular and one semi-regular red variables have spectral types in the range M2–3 II–III; three regular (200 d ) red variables have types in the range M2–3 II–Ib, and are normal Me variables. The velocities of these stars are discussed. The distance modulus of 47 Tuc is deduced from the RR Lyrae member (HV 814). It is shown that a distance of 4.4 kpc, which follows if HV 814 has a median absolute visual magnitude of +0.5, fits best with the spectroscopic absolute magnitudes of the red giants, the red variables and the B-type member.