Publications of the Astronomical Society of the Pacific

Friel, E.; Kraft, R. P.; Suntzeff, N. B.; Carbon, D. F.

doi: 10.1086/131078pmid: N/A

Image dissector scanner low resolution spectra have been obtained for giants in the remote NGC 7006 and Pal 13 globular clusters which yield mean iron-peak metallicities of -1.45 and -1.9, respectively. These two clusters are often considered to be 'second parameter' clusters, exhibiting anomalously red branches for their metallicities. While the Pal 13 giants in the present sample exhibit the modest carbon depletions and nitrogen enhancements distinguishing stars in the classical second parameter cluster M3, the giants of NGC 7006 have C and N abundances that are intermediate between those of M3 and M13 giants. Recent suggestions that anomalous overabundances of elements in the CNO group are responsible for the second parameter effect in NGC 7006 are not supported by the present results.

Kron, R. G.; Albert, C. E.

doi: 10.1086/131079pmid: N/A

A comparison of large scale images of supergiant galaxy cores with those of associated galaxies is presented, giving attention to apparent central surface brightness and the frequency of close companions in order to better constrain models for the origin and evolution of cD galaxies. It is found that, in four out of five nearby, rich cD clusters, the central surface brightness of the cD galaxy appears to be less than, or comparable to, that of neighboring giant ellipticals

Gaskell, C. M.

doi: 10.1086/131080pmid: N/A

The reliability of the narrow line Balmer decrement as an indicator of reddening is examined. Estimates of the reddening and electron density of the narrow line regions of a number of active galaxies are made by using the trans-auroral/nebular line ratios of forbidden line S II and O II. The derived densities agree with published estimates from the S II forbidden line 6717 A/6731 A ratios, and reddenings derived by this and other methods agree with those predicted from Balmer decrements. It is concluded that the intrinsic narrow-line Balmer decrement is close to the Menzel-Baker case B values, and that observations of the narrow line Balmer decrement do give a reliable indication of the reddening.

Flower, P. J.

doi: 10.1086/131081pmid: N/A

The principal aim of the paper is to determine the ages of two Large Magellanic Cloud star clusters, NGC 2058 and NGC 2065. Photoelectric and photographic photometry was used to obtain color-magnitude diagrams of both clusters and a nearby star field. A grid of evolutionary tracks was computed for masses bracketing those of the cluster giants. Both the red-giant distribution and the main-sequence termination were compared to the models, and yielded an age of 120 million yr for both clusters. The field stars were found to be composed of a young population of stars with the same age as the clusters and an older population with an age of about one billion yr. It is concluded that reliable cluster ages can be obtained without requiring photometry faint enough to reach the unevolved main sequence.

Sullivan, W. T.

doi: 10.1086/131082pmid: N/A

Given that a large fraction of young supernovae which occur in the Galaxy are probably too much obscured by dust to be detected optically and that little suitable radio monitoring now takes place, the chances of an accidental radio detection are estimated. Using young extragalactic supernovae recently detected at radio wavelengths as a model, the expected flux density of a young supernova occurring on the opposite side of the Milky Way at a distance of 30 kpc is as strong as the half-dozen strongest sources now in the sky. An analysis of the characteristics and programs of the world's radio telescopes then indicates for several reasons that wavelengths in the 2- to 20-cm range are much more likely than others to make such a discovery, typically within 1-2 yr of the appearance of the new source. Older but still active microwave dishes, such as the Kraus-type reflector at Ohio State University, are the best candidates for an accidental discovery.

Adler, D. S.; Janes, K. A.

doi: 10.1086/131083pmid: N/A

A preliminary color-magnitude diagram of the distant open cluster Tombaugh 2 shows it to bear a close resemblance to the well known, metal-poor cluster NGC 2158. From this, it is deduced that To 2 has a reddening of 0.08, a distance modulus of 15.6, and a main sequence turn-off color of 0.27. To 2 is approximately 18.5 kpc from the galactic center, and -1.69 kpc from the galactic plane, therefore representing one of the most distant open clusters from both the galactic plane and center.

Bonnell, J.; Wu, C. -C.; Bell, R. A.; Hutchinson, J. L.

doi: 10.1086/131084pmid: N/A

Photometric observations of RR Lyr in the ultraviolet have been obtained using the Astronomical Netherlands Satellite. The observations are compared with theoretical light curves calculated using synthetic spectra and angular diameters determined as a function of phase for RR Lyr by Manduca et al. from photometry at longer wavelengths. A good agreement is found. A bump in the observed light curves in the phase range 0.6 to 0.8 supports the existence of a shock as predicted by Hutchinson, Hill, and Lillie.

Bruch, A.

doi: 10.1086/131085pmid: N/A

A radial velocity curve derived from spectroscopic observations of the old nova HR Del indicates that the currently adopted binary period is too small, the improved orbital period being 0.2141674 d. The measurements and the canonical model for cataclysmic variables yield 0.9 and 0.58 solar masses for the binary components, and an orbital inclination of 41 deg. The spectral type of the secondary is estimated to be near K8, and it is noted that the intensity of the Balmer emission lines and He II 4686 A may vary during the cycle. It is estimated that the Roche lobe of the primary is almost filled by the accretion disk.

Chambliss, C. R.

doi: 10.1086/131086pmid: N/A

AF Gem is an Algol-type eclipsing binary with a period of 1.2435 days. The period is found to have decreased slightly over the years that this object has been under observation. Approximately 800 observations in UBV have been analyzed by the Wood (1972) method, and orbital elements have been obtained. The primary eclipse is a transit, and the eclipses are partial. The spectral types of the components are estimated to be B9 V and G0 IV. AF Gem has a faint visual companion situated about 2 arcsec from the eclipsing pair. It is most probable that this star is a member of the system.

Radick, R. R.; Mihalas, D.; Hartmann, L.; Worden, S. P.; Africano, J. L.; Klimke, A.; Tyson, E. T.

doi: 10.1086/131087pmid: N/A

The young main sequence stars in the Pleiades and Hyades clusters, and old disk stars in the Malmquist Field near the north galactic pole, have been observed by precision photometry in order to determine the prevalance of variability among solar type stars. Significant variations have been found in at least five, and possibly ten, of 44 Hyades stars, and possibly one of the 41 stars in the Malmquist Field, all of which are of spectral type F8 V-K2 V.