Search Publications
On the Automatic Determination of Light-Curve Parameters for Cepheid Variables
Stetson, Peter B.
A computerized algorithm for the automatic detection of Cepheid variables and for the estimation of their periods, amplitudes, and mean magnitudes from sparse data sets is presented. It is intended to be suitable for use in such programs as the measurement of Cepheid distances to external galaxies, for example with the Hubble Space Telescope. The …
A Database for Galaxy Evolution Modeling
Walborn, Nolan R.; Parker, Joel Wm.; Robert, Carmelle +77 more
This paper represents a collective effort to provide an extensive electronic database useful for the interpretation of the spectra and evolution of galaxies. A broad variety of empirical and theoretical data are discussed here, and the data are made fully available in the AAS CD-ROM Series, Vo. 7. Several empirical stellar libraries are part of th…
A Supergiant-Dominated Starburst in the Nucleus of NGC 4569
Keel, William C.
The Virgo spiral NGC 4569 has a very compact optical nucleus whose spectrum is highly composite, which strong Balmer absorption indicating that A stars dominate the optical light. Recent HST imaging shows that the nucleus is extremely compact in the mid-ultraviolet, so that either there must be a central AGN or an extraordinarily luminous and comp…
The Spectrum of the Planetary Nebula NGC 6790
Feibelman, Walter A.; Hyung, Siek; Aller, Lawrence H.
International Ultraviolet Explorer (IUE) and optical region spectroscopic observations are presented for the medium excitation planetary nebula (PN), NGC 6790, which displays a rich spectrum permitting application of several diagnostic ratios and the calculation of a number of ionic concentrations, N(ion)/N(H+). NGC 6790 seems to be a relatively y…
The White-Dwarf Companions of 56 Persei and HR 3643
Bergeron, Pierre; Simon, Theodore; Landsman, Wayne
We have obtained low-dispersion IUE spectra of the stars 56 Persei (F4 V) and HR 3643 (F7 II), as part of a survey of late-type stars with a 1565A flux excess in the TD-1 ultraviolet sky survey. The IUE spectrum of each star reveals the presence of a hot white dwarf companion. We fit the Ly-alpha profile and ultraviolet continuum using pure hydrog…
An O VIII Sequence for Planetary Nebula Nuclei
Feibelman, Walter A.
The detection of O VIII emission lines in ultraviolet and optical spectra of high-excitation planetary nebula central stars suggests an "O VIII Sequence" for these object. Emission lines of O VII are also detected. Seven out of ten central stars for these planetaries are known to be nonradial g-mode pulsators. The stars form a narrow strip when pl…
The Diverse Optical/Ultraviolet Spectra of the Globular Cluster X-ray Sources in NGC 7078 and NGC 6712
Anderson, Scott F.; Margon, Bruce; Downes, Ronald A.
Among the about one dozen luminous X-ray bursters in the cores of globular clusters, only three have optical/UV counterparts unambiguously identified. We have observed two of these counterparts spectroscopically with the low resolution optical and UV gratings of the Faint Object Spectrograph (FOS) aboard the Hubble Space Telescope (HST), yielding …
Low Mass Stars in an Outer Field in NGC 6397
Casertano, Stefano; Ballester, Gilda E.; Crisp, David +13 more
We have imagined a field 10' from the center of the globular cluster NGC 6397 in the visible and I bands with WFPC-2 on the HST. AT a level which is severely limited by counting statistics in the small area so far studied, this field is richer in dwarfs with I > 21.5 than the 4.6' radius parallel field discussed by Paresce and colleagues. This …
The Iron Abundance of IOTA Herculis
Grigsby, James A.; Mulliss, Christopher L.; Baer, Gretchen M.
We have obtained coadded, high-resolution IUE spectra of Iota Herculis (B3 IV) in both the short-wavelength (SWP) and long-wavelength (LWP) regions. LTE synthetic spectra with a resolution identical to that of IUE were produced with the Kurucz model atmosphere and spectral synthesis codes ATLAS9/SYNTHE. Model parameters were chosen from the litera…
Formation of the Galaxy: Clues from Globular Cluster Ages and Abundances
Fullton, Laura Kellar
In an effort to bring more data to bear on the problem of the age and formation history of the inner regions of the Milky Way, I undertook a photometric and spectroscopic study of a small sample of globular clusters within 5 kpc of the Galactic center: NGC~6723, NGC~6352 and NGC~5927. The ages and chemical compositions of these clusters provide cl…