THE COLORS AND LUMINOSITIES OF WHITE DWARFS.Eggen, O. J.
doi: 10.1086/131659pmid: N/A
Photoelectrically determined color indices of white dwarfs are reviewed with particular emphasis on the possibility that a large percentage of these objects in the solar neighborhood are members of the Hyades and Sirius superclusters. The astrometric, photometric, and spectroscopic data now available for the best-established cases of such membership are discussed. The color-luminosity array obtained from supercluster members is tested against that obtained with trigonometric parallaxes determined at the U.S. Naval Observatory.
AN ASSESSMENT OF RESEARCH DONE AT THE NATIONAL OPTICAL OBSERVATORIESAbt, H. A.
doi: 10.1086/131660pmid: N/A
We know that the national optical observatories produce hundreds of papers yearly but we wonder whether these include a reasonable share of major studies because some practices at those observatories, especially before 1982, seemed to be biased against major long-term studies. We considered the papers published in 1980 and 1981 and based on data obtained primarily from four large telescopes, two at national and two at university observatories. The former telescopes produce more papers, but are they as useful to astronomy as judged by citation counts? There is statistically no significant differences in the average citations per paper for the four telescopes and the 5% most-cited papers came from all four telescopes in statistically equal numbers.
METAL ABUNDANCES AND RADIAL VELOCITIES OF SHORT-PERIOD VARIABLE STARS IN THE DIRECTION OF THE LARGE MAGELLANIC CLOUD.Smith, H. A.
doi: 10.1086/131661pmid: N/A
Spectra have been obtained for five short-period (P is less than 1d) variable stars in the direction of the Large Magellanic Cloud. Radial velocities and Delta S metallicity indices have been determined for the variables. Most of the variables appear to be foreground RR Lyrae stars of the Galaxy and not members of the LMC. The stars range in forbidden line ratio Fe/H from 0.6 to -1.7. The radial velocities of these variables and those of two similar variables observed by Connolly (1980) are discussed. The line-of-sight velocity dispersion for these stars is consistent with both spherical and cylindrical descriptions of the halo velocity dispersion.
IMPLICATIONS OF THE DWARF SPHEROIDAL GALAXY MASS-METALLICITY RELATION.Smith, G. H.
doi: 10.1086/131662pmid: N/A
The properties of the mass-metallicity relation among dwarf spheroidal galaxies are discussed in terms of a model which assumes that the internal chemical evolution of the dwarf spheroidals was promoted by supernova activity. The model can be used to explain the observed dwarf spheroidal mass-metallicity relation assuming the present mass of these systems Ms is proportional to their initial masses M as Ms varies according to a power-law index of exp 7/4. It is inferred from the power-law dependence of M on the proto-cloud radius that the most massive dwarf spheroids were formed from the densest clouds. The observed slope of the mass-metallicity relation for dwarf spheroidal galaxies is found to be significantly different from theoretical estimates of this slope for elliptical galaxies. It is suggested that the difference may imply that spheroidal dwarfs and elliptical galaxies had different formation histories, confirming Kormendy's (1985) observations of differences in the brightness and luminosity trends.
STELLAR ASSOCIATIONS IN THE GALAXY NGC 2403.Hodge, P.
doi: 10.1086/131663pmid: N/A
Stellar associations in the Sc galaxy NGC 2403 are identified and compared to similar samples in Local Group galaxies. Their properties, including the total number delineated, their sizes, the average number of supergiant stars they contain, and their radial distribution are tabulated and are shown to be similar to those of M33 and the LMC. The stellar associations have an exponential radial-density distribution, the scale length of which is 2.0±0.2 kpc, which is the same as that of the H II regions, larger than that of the blue background galaxian light, but considerably smaller than that of the H I distribution.
NOVA SERPENTIS 1983.Schlegel, E. M.; Honeycutt, R. K.; Kaitchuck, R. H.
doi: 10.1086/131665pmid: N/A
A spectrum of Nova Serpentis 1983 has been obtained using the IIDS spectrograph attached to the 2.1-meter telescope at Kitt Peak. A series of 10 spectra were co-added to produce a single spectrum covering the wavelengths in the range 4250-4950 A. The integration time was 300 seconds using an 8.4 arcsec aperture. The photometric and spectroscopic characteristics of the spectrum are discussed in detail. A table listing the spectral line emission intensities of H-beta, H-gamma, and N III in the spectrum of Nova Serpentis 1983 is given, and the photometric light curve is reproduced in graphic form.
CLASSICAL CEPHEID LIGHT CURVES REVISITED.Simon, N. R.; Moffett, T. J.
doi: 10.1086/131666pmid: N/A
Fourier decompositions are made of the B, V, R, and I classical Cepheid observations of Moffett and Barnes. The Fourier diagrams for V agree very well with the corresponding plots of Simon and Lee. The B, R, and I diagrams resemble the plots for V, but with small, systematic shifts in the phases φ21 and φ31. The 2.5-day star, DT Cyg, is confirmed as a likely overtone pulsator by its anomalous position in the Fourier plots. Finally, the authors study the Fourier phase quantity φ41, and introduce phase-phase diagrams to look at the Hertzsprung progression. Discontinuities in these diagrams support the idea that the long-period and short-period Cepheids may reach their limit cycles in different ways.
A NEW SPECTROSCOPIC ORBIT OF THE W URSAE MAJORIS SYSTEM U PEGASI.Lu, W.
doi: 10.1086/131667pmid: N/A
High-dispersion spectra have been obtained for the W UMa system U Peg. Time resolution was kept high by means of an image tube coupled to a Reticon. All the spectra were measured by cross-correlation techniques. The orbital elements for both components of the system have been determined to be: T0 = 2445956.983, V0 = 28.5 km/s, K1 = 77.6 km/s, K2 = 246.5 km/s. A circular orbit is adopted. From the semiamplitudes of the two components, an accurate mass ratio m1/m2 = 3.18 is deduced. Spectrophotometric measurements were also carried out from which the luminosity ratio (determined from line-strength ratios) is deduced to be 1.47, corresponding to a difference of 0.42 mag in the blue region of the spectrum. Both stars are found to be on the main sequence; their spectral types are each close to G2 with the secondary a little earlier.
OPTICAL STUDIES OF THE X-RAY TRANSIENT EXO 0748-676.Wade, R. A.; Quintana, H.; Horne, K.; Marsh, T. R.
doi: 10.1086/131668pmid: N/A
Identification of the optical counterpart of the transient X-ray source EXO 0748-676 is reported. The identification was made during a search of the X-ray error circle on March 1, 1985, when the optical counterpart was at 17th magnitude. The observations were carried out using the Charge-Coupled imaging Device (CCD) attached to the l-meter Yale telescope at CTIO. CCD images of the field containing the X-ray error circle are provided. Spectroscopic analysis of the CCD images showed absorption features in the wavelengths bands double lambda 7150-7400 (H2O), 7600-7700 (A band), and 8100-8400 (H2O). No absorption or emission features were found in excess of the statistical noise. CCD photometry of EXO 0748-676 is given in a table. It is argued that EXO 0748-676 almost certainly comprises a neutron star receiving matter from a secondary star in close orbit around it. The presence of an accretion disk is inferred from the longer duration of the optical eclipse as compared to the X-ray eclipse. The mass of the secondary star is estimated near a few times 0.1 solar mass. Some similarities between the optical spectrum EXO 0748-676 and the optical spectra of other low-mass binary X-ray transients and luminous cataclysmic variable stars are discussed.