Robert D. McClure

The binary nature of the barium and CH stars. III. Orbital parameters

Results are presented from a 10-year program to monitor the velocity variations of Ba II and CH stars, showing that all Ba II and CH stars are binaries. Radial-velocity observations for Ba II and CH binaries are given. Also, the results of orbit calculations and orbital element determinations are analyzed. It is shown that the eccentricities of Ba II star orbits are significantly lower than the eccentricities for a sample of normal G and K giants. In addition, the eccentricities of CH star orbits are significantly lower than those of Ba II stars, suggesting dissipation due to mass exchange, probably from a previous AGB star. The mass functions for Ba II and CH stars indicate that the stars come from samples of binary systems with a small dispersion in mass ratios. If the Ba II and CH stars are assumed to have masses of 1.5 and 0.8 solar mass, respectively, then their companions would have masses near 0.6 solar mass, similar to the values expected for white dwarfs. 45 refs.

The binary nature of the barium stars

We present radial-velocity spectrometer observations that indicate that Ba II stars are binary systems. The secondary stars of these systems have low masses, consistent with their being degenerate objects which have lost mass onto their primaries in a previous stage of evolution. It is suggested that the Population II equivalents, the CH stars, may also be binary systems. This may be related to the fact that they are found only in globular clusters of the lowest central concentration.

The nucleus of M33

We have obtained high-resolution surface photometry and velocity dispersion measurements of the semistellar nucleus of M33 to study its structure and to look for a central black hole. The images were obtained with the DAO/CFHT HR Camera; this uses a tip-tilt mirror to correct the motion component of seeing. Our best images have resolution σ * =0″.186 in the B band and σ * =0″.177 in R (σ * = Gaussian dispersion radius of the point spread function). The nucleus is unresolved. Its true core radius is r c ≤ 0″.10 ≃ 0.39 pc; this is as small as in core-collapsed globular clusters. The true central surface brightness is μ 0 < 11.3 R mag arcsec −2 , and the central density is ρ 0 ≥ 5 × 10 5 M ○ . pc −3 . Except for M32 and the nucleus of our Galaxy, this is the most compact galactic core known

WIYN Open Cluster Study. XXXII. Stellar Radial Velocities in the Old Open Cluster NGC 188

(Abridged) We present the results of our ongoing radial-velocity (RV) survey of the old (7 Gyr) open cluster NGC 188. Our WIYN 3.5m data set spans a time baseline of 11 years, a magnitude range of 12<=V<=16.5 (1.18-0.94 MSun), and a 1 deg. diameter region on the sky. With the addition of a Dominion Astrophysical Observatory (DAO) data set we extend our bright limit to V = 10.8 and, for some stars, extend our time baseline to 35 years. Our magnitude limits include solar-mass main-sequence stars, subgiants, giants, and blue stragglers (BSs), and our spatial coverage extends radially to 17 pc (~13 core radii). For the WIYN data we find a measurement precision of 0.4 km/s for narrow-lined stars. We have measured RVs for 1046 stars in the direction of NGC 188, finding 473 to be likely cluster members. We detect 124 velocity-variable cluster members, all of which are likely to be dynamically hard-binary stars. Using our single member stars, we find an average cluster RV of -42.36 +/- 0.04 km/s. We use our precise RV and proper-motion membership data to greatly reduce field-star contamination in our cleaned color-magnitude diagram, from which we identify six stars of note that lie far from a standard single-star isochrone. We find the binaries to be centrally concentrated, providing evidence for the presence of mass segregation in NGC 188. We observe the BSs to populate a bimodal spatial distribution that is not centrally concentrated, suggesting that we may be observing two populations of BSs in NGC 188, including a centrally concentrated distribution as well as a halo population. Finally, we find NGC 188 to have a global RV dispersion of 0.64 +/- 0.04 km/s. When corrected for unresolved binaries, the NGC 188 RV dispersion has a nearly isothermal radial distribution. We use this mean-corrected velocity dispersion to derive a virial mass of 2300 +/- 460 MSun.

Evidence for Steep Luminosity Functions in Clusters of Galaxies

Luminosity Functions have been obtained for very faint dwarf galaxies in the cores of four rich clusters of galaxies (Abell 2052, 2107, 2199 and 2666). It is found that the luminosity function of dwarf galaxies rises very steeply in these clusters, with a power-law slope of \alpha -2.2 (down to absolute limiting magnitudes M_I = -13 and M_B = -11 for H_0 = 75 km/s/Mpc). A steepening of the luminosity function at faint magnitudes may in fact be a common feature of both cluster and field populations. Such a result may explain the observed excess counts of faint, intermediate redshift galaxies in the Universe, without resorting to more exotic phenomena. An alternate explanation is that star formation in dwarf galaxies is less affected by gas loss in the richest clusters, because of the dense, hot intracluster medium found in such environments.

High-resolution imaging of distant clusters. I : Close pairs, interactions, and the Butcher-Oemler' effect at z=0.4

We present new ground-based high-resolution images of 23 blue galaxies whose membership has been confirmed spectroscopically in the two distant rich clusters Abell 370 and Cl 0024+1654. The images, taken with the High Resolution Camera on the CFHT, have a stellar FWHM=0.45 arcsec. Ten of these blue galaxies are found to have close companions, with separations on the scale of 1 to 2 arcsec. These multiple systems represent 45% of the confirmed blue galaxy population in the two clusters. Several of the remaining blue galaxies also have peculiar morphologies and features, such as tidal tails, suggestive of interactions/mergers

THE R STARS: CARBON STARS OF A DIFFERENT KIND

After ~16 years of radial-velocity observations of a sample of 22 R-type carbon stars, no evidence for binary motion has been detected in any of them. This is surprising considering that approximately 20% of normal late-type giants are spectroscopic binaries, and the fraction is close to 100% in barium, CH, and subgiant/dwarf CH and barium stars. It is suggested, therefore, that a process that has caused the mixing of carbon to the surface of these stars cannot act in a wide binary system. Possibly, the R stars were once all binaries, but with separations that would not allow them to evolve completely up the giant and asymptotic giant branchs without coalescing. This coalescence may be the agent which causes carbon produced in the helium-core flash to be mixed outwards to a region where convection zones can bring it to the surface of the star.

The supernova rate in Shapley-Ames galaxies

A visual search for SNs in 748 Shapley-Ames galaxies during the 5-year period from November 1, 1980 to October 31, 1985 has yielded SN rates of 0.3h-squared, 0.4h-squared, and 1.1h-squared for objects of types Ia, Ib, and II, respectively. These data are judged to imply that Tammanns (1974, 1982) SN rates are probably too high by a factor of about 3. For a Galactic luminosity of 2 x 10 to the 10th solar L(B), the predicted SN rates in the Milky Way system are 0.6h-squared, 0.8h-squared, and 2.2h-squared/century, respectively, for the three aforementioned types. 29 references.

THE BARIUM STARS.

The barium stars are Population I G-K giants that have enhanced abundances of carbon and s-process elements, and are probably related in their peculiarities to several other carbon enhanced red-giant types such as CH, R, N, and S stars. Since the abundance anomalies in the barium stars are likely the result of mixing of processed material from deep within a stellar interior, and since they are numerous with many bright examples suitable for detailed observations, these stars provide very valuable information on nucleosynthesis, and the advanced stages of stellar evolution. A clue to the origin of the anomalous abundances in the barium stars is the recent discovery that they are likely all members of binary systems.

Revised supernova rates in Shapley-Ames galaxies

Les observations de 855 galaxies Shapley-Ames effectuees durant la periode 1 novembre 1980-31 octobre 1988, combinees avec des luminosites ameliorees des supernovae, sont utilisees pour etablir la frequence des supernovae de differents types