Spitzer, Lyman; Zabriskie, Franklin R.
doi: 10.1086/132199pmid: N/A
This paper is reproduced from Publ. Astron. Soc. Pac., Vol. 71, p. 417 - 420 (1959) to celebrate the centenary of the Publications. See also 004.112.
doi: 10.1086/132200pmid: N/A
Copernicus and IUE observations of UV absorption lines of interstellar gas (IG) are reviewed. The historical context, major findings, and IG observation proposals presented in a paper by Spitzer and Zabriskie (1959) are recalled and compared with the campaigns actually undertaken and their results. Consideration is given to the performance of the satellite instruments, the observed IG depletion of most atomic species relative to hydrogen, the dominance of H2 over atomic H in dense molecular clouds, the presence of hot gas in the Galactic disk, D/H abundance ratios, neutral H distributions, and the distribution of IG in the solar vicinity. Problems encountered in interpreting UV absorption data are discussed, and the important role of the IG in the evolution of galaxies is indicated.
doi: 10.1086/132201pmid: N/A
Surface photometry of galaxies has undergone a great advance recently with the development of fast digital plate-measuring machines, powerful computers to process the huge amount of data from them, and efficient image-processing software. Further, the recent advent of charge-coupled devices (CCDs) has made the technique effective even with relatively small telescopes. Because of their very high sensitivity, especially in the red wavelength region, CCDs have opened a new era of surface photometry. The methodology of surface photometry of galaxies is reviewed and recent results are summarized. Future prospects of the technique in galaxy research are briefly discussed.
Reed, B. Cameron; Hesser, James E.; Shawl, Stephen J.
doi: 10.1086/132202pmid: N/A
Observed integrated colors, spectral types, and E(B-V) color excesses for 50 Galactic globular clusters are used to calibrate the relationship between intrinsic UBVRI colors and integrated spectral types. Color excesses are then estimated from Reed's averages of observed (B-V) colors for 93 clusters with integrated spectral types on the Hesser and Shawl system. The authors find that the R and I colors add little reddening information. Mean colors of five spectral-type groupings are presented. Clusters of the latest spectral type (i.e., most metal rich) are particularly easy to identify in the (U-V)0, (V-I)0 diagram. Distributions of the inferred reddenings and intrinsic colors with Galactic longitude and latitude are presented.
doi: 10.1086/132203pmid: N/A
This review examines the present status of searches for star clusters in nearby galaxies and comments on problems of completeness in each case. To facilitate the discussion, an attempt is made to redefine the terminology used to classify star clusters, and a simple but fairly universally applicable scheme is adopted. Nonuniformities are found in the formation rates of clusters as a function of time and from galaxy to galaxy. The median ages of clusters in different galaxies are different and may be related to the mass and perhaps structure of the galaxy.
doi: 10.1086/132204pmid: N/A
An analysis of age estimates for nearly complete samples of LMC clusters in 12 different fields shows that LMC clusters have much longer life expectancies than their Galactic counterparts. The median age for LMC clusters is 1.1 Gyr, compared to the value of 0.2 Gyr for the Galaxy. Cluster-formation histories show nonuniform rates that depend on position in the Cloud. It is calculated that the present mean cluster-formation rate is 270 clusters formed per 108^ years.
Bopp, Bernard W.; Dempsey, Robert C.; Africano, John L.; Goodrich, Bret D.
doi: 10.1086/132205pmid: N/A
BV photometry of the rapidly-rotating M dwarf Gliese 890 (dM2e) obtained in 1983-84 is presented. The long-term photometric behavior of the star is examined, and evidence is found for the presence of persistent polar active regions, as has been proposed by Young at al. (1987). In an attempt to detect additional rapidly-rotating field M dwarfs similar to Gliese 890, four dM stars suspected by Cowley and Hartwick (1982) to show broadened absorption lines are observed. CCD spectra with 1-A resolution fail to show any evidence for line broadening. The H-alpha line is in absorption in all four stars.
Heller, Clayton H.; Kramer, Karen S.
doi: 10.1086/132206pmid: N/A
Several northern Ap stars have been monitored to search for short-period (P less than 15 min) photometric variations. It was not possible to confirm the low-amplitude variability of HR 2977 and HR 5156 reported by Matthews and Wehlau (1985). HR 5747 was observed near magnetic maximum; it showed no sign of rapid variations. No evidence of variability was found in HD 165474, HD 188471, and HD 191742 over several days of observation. Of the seven Ap stars observed, only HR 7167 (10 Aql) showed evidence of rapid light variability, with a period of 11.4 minutes and a peak-to-peak B amplitude of about 0.55 mmag. This detection is considered only tentative; further observations are needed to confirm the variability of HR 7167.
doi: 10.1086/132207pmid: N/A
A study of the O-C diagrams of FN Aql and RX Aur revealed sinusoidal variations in the pulsation period of both Cepheids. An interpretation in terms of the binary nature of these variable stars is suggested because both stars have an unusual color index that may be caused by an unresolved companion. The orbital period and some other parameters are determined. Radial-velocity studies are strongly recommended in order to get decisive information on the existence of the companion.
doi: 10.1086/132208pmid: N/A
Spectroscopic, time-resolved observations of the accretion disk in the long-period Algol system RY Gem during eclipse are presented. It is shown that the disk is non-Keplerian and has asymmetries between the leading and trailing sides of the accretion disk similar to those seen in the transient disks of the short-period Algol systems. There is about 50 km/s difference in the rotational velocity between the leading and trailing sides of the disk. The rotational velocity of the leading side appears to be sub-Keplerian. The linewidths on the trailing side are larger than expected for a rotationally broadened line and they do not vary during eclipse. Similar linewidths are seen from a portion of the leading side. Taken together this suggests the presence of turbulence like that proposed to exist in the transient disk systems. At least a portion of the gas stream from the secondary star strikes the trailing side of the accreting star. Apparently this collision and the subsequent interaction of the gas circling the star with the incoming stream produce a structure very similar to a transient disk.
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