Publications of the Astronomical Society of the Pacific

Carney, B. W.

doi: 10.1086/131443pmid: N/A

The paper discusses recent and continuing studies of the outer halo of our galaxy. A brief inventory is conducted of the stellar systems lying at distances exceeding 25 kpc from the galactic center. The spatial distributions of such systems and the field stars are reviewed, as well as the galactic mass estimates that follow from considerations of their kinematics. The question of a gradient in the halo's metallicity is addressed, plus the scant information available on the chemical abundance pattern of outer halo stars. Finally, the probability of differences in ages of outer halo systems is discussed.

Frogel, J. A.

doi: 10.1086/131444pmid: N/A

The article considers evidence for an old metal-poor population in the Magellanic Clouds corresponding to that of the Galactic halo, and evidence for subsequent star-forming episodes. Particular emphasis is placed on cluster research and on observations of bright giants in clusters and the field as a means to understand the past and present stellar content of the Clouds. The color-magnitude diagrams and luminosity functions for bright giants in clusters and in a selected field of the LMC are compared to see if the stellar content of the field can be reproduced by a superposition of clusters. The small, but growing body of data on the chemical enrichment history of the Clouds is considered. Finally, some remarks on the gaseous content of the Clouds, and the implication for present-day star formation, are made.

van den Bergh, S.; Lafontaine, A.

doi: 10.1086/131445pmid: N/A

Star counts have been performed for rings centered on the carbon star at 1 = 69 degrees, b = + 55 degrees at a distance of 60 kpc. The counts were performed in order to determine whether halo carbon stars might be situated in dwarf spheroidal galaxies which are too star-poor to have been recognized as galaxies. The counts were made on a IIIa-J plate baked in forming gas that was exposed for 40 minutes through a 2C filter with the Palomar 1.2-m Schmidt telescope. It is shown that the carbon star is not situated in a dwarf spheroidal galaxy brighter than MV = 5.7.

Geisler, D. P.; Smith, V. V.

doi: 10.1086/131446pmid: N/A

Abundances for a sample of giants in the old open cluster Melott 66 have been determined from Washington photometry. The mean cluster abundance of the forbidden line of Fe/H was -0.5 (+ or - 0.2) and CN appears to be enhanced. The implications of a comparison with previous abundance determinations are discussed.

Morbey, C. L.

doi: 10.1086/131447pmid: N/A

A number of first-ranked galaxies in poor and rich clusters have absolute magnitudes which correlate well with the richness classes of their parent clusters. The correlation is consistent with the statistical theory for the luminosities of first-ranked galaxies in clusters advocated by Geller and Peebles (1976). This does not rule out spectral process theories but suggests that, if special processes do occur, their effects may be somewhat nonuniform from cluster to cluster. It is shown that the commonly observed small dispersion in the absolute magnitudes of giant elliptical galaxies is a result of: (1) the size of the sampling aperture used and (2) the intrinsic gradients of their observed surface brightness profiles. Parameters associated with the dominant galaxies do not correlate well with Bautz-Morgan class.

van den Bergh, S.; Lafontaine, A.

doi: 10.1086/131448pmid: N/A

Intercomparison of the Michigan Catalogue of Two-Dimensional Spectral Types with a uniform survey of southern open clusters by van der Bergh and Hagen shows that about 6 percent of Fand G-type supergiants of luminosity classes la, Iab, and Ib are cluster members. The most-luminous supergiants are more likely to be cluster members than are less-luminous supergiants.

McWilliam, A.; Lambert, D. L.

doi: 10.1086/131449pmid: N/A

The strength of the CO 2.3 μm bands was measured photometrically in an attempt to identify extremely carbon poor M giants. Magnitudes of about 200 bright M stars were obtained through a J filter, and narrow filters centered on 2.17 μm, and 2.40 μm. No M giants with CO indices indicative of extremely low carbon abundances were positively identified. The tight correlation of CO index to effective temperature does not extend to the extremely late and variable M giants. The CO index in M giants defined by the 2.17 μm and 2.40 μm magnitudes was calibrated by a spectrum synthesis technique. The dependence of CO index upon carbon abundance, the 12C/13C ratio, surface gravity, effective temperature, and microturbulent velocity was investigated. Predicted and observed CO indices are in excellent agreement for stars with a spectroscopically determined carbon abundance.

Kunkel, W. E.; Liebert, J.; Boroson, T. A.

doi: 10.1086/131450pmid: N/A

Photometry and spectrophotometry of VB3, the distant companion to HR 3018, show it to be a white dwarf of low luminosity (Mv ≅ +15.6) and not an M dwarf. The pair provides the best available example of a very old white dwarf with a main-sequence star of sufficiently early type that a useful empirical limit may eventually be derivable for the ages of the oldest degenerate stars.

Bopp, B. W.

doi: 10.1086/131451pmid: N/A

The H-aplha and Na I D-line regions of the M6 giant star ZZ Canis Minoris (ZZ CMi) were observed with the Kitt Peak coude feed telescope and a CCD detector. It is shown that ZZ CMi has similar spectroscopic and photoproperties to the symbiotic star EG And. The data are used to argue for the classification of ZZ CMi as a symbiotic star despite its current listing in the General Catalog of Variable Stars (GCVS) as a semi-regular variable. The infrared magnitudes of ZZ CMi and the known symbiotic stars are compared in a table.

Bohm-Vitense, E.; Proffitt, C.

doi: 10.1086/131452pmid: N/A

The ultraviolet energy distribution of the metal-poor supergiant HD 112374 is analyzed based on observations from the International Ultraviolet Explorer (IUE) satellite for the region between 1200 and 2000 A. A discontinuity was found in the UV spectra at 2600 A which confirmed the low-abundance of heavy elements found by Luck et al. (1983). Values for effective temperature and log g in HD112374 were consistent with the star being a very luminous Population II semi-regular variable. The full observational results are presented in a table.