Search Publications
A "cool" PG 1159 star discovered by the Hamburg Schmidt Survey: NLTE analysis of HS 0704+6153.
Werner, K.; Dreizler, S.; Jordan, S. +1 more
The discovery of a new PG 1159 star by follow-up spectroscopy of candidates selected from objective-prism plates of the Hamburg Schmidt Survey is presented. From a NLTE model atmosphere analysis an effective temperature of 65 000 K and a surface gravity of logg=7.0 is determined, which together with the extreme helium abundance (H/He<1 by numbe…
Intersystem Transitions of Interstellar Carbon Monoxide toward zeta Ophiuchi
Federman, S. R.; Lambert, David L.; Cardelli, Jason A. +2 more
Absorption from seven intersystem (triplet-singlet) transitions of interstellar (12)CO were detected in ultraviolet spectra of zeta Oph. The observed equivalent widths are approximately consistent with the transitions' predicted f-values and the (12) CO column density derived from the weakest of the observed A-X bands. These unsaturated intersyste…
Interstellar Gas and Dust in the Young Cluster IC 348
Snow, Theodore P.; Hanson, Margaret Murray; Seab, Gregory C. +1 more
We have completed a multiband absorption- and emission-line study of a star embedded in the young cluster IC 348, to determine the environmental effect of star formation on the interstellar medium (ISM) local to the region. The hottest and youngest star in IC 348 is BD +31 deg 643, a B5 V star which samples the inner bright nebular region. The nea…
An Ultraviolet and Visible Spectroscopic Study of a Pulsational Cycle of RY Sagittarii
Cottrell, P. L.; Lawson, W. A.; Clayton, Geoffrey C. +3 more
High-dispersion visible and ultraviolet spectra and UBVRI photometry, covering a complete pulsation of the R Coronae Borealis star RY Sgr, have been obtained. The UV spectra were the first high-dispersion data ever obtained for the star. Together these observations comprise the most complete data set covering an RCB star pulsation cycle. The cycle…
Gradients in Giant Branch Morphology in the Core of 47 Tucanae
Bailyn, Charles D.
I describe an algorithm which uses the high spatial resolution of the Hubble Space Telescope to complement the high spatial-to-noise, approximately symmetric point response function, relatively large spatial coverage, and standard filters available from ground based images of crowded fields. Applying this technique to the central regions of the gl…
Ultraviolet and optical spectroscopy of a B supergiant star in M 31.
Massey, Philip; Hutchings, J. B.; Bianchi, Luciana +4 more
We present and discuss the UV spectrum of the supergiant star in NGC206-277 in M 31, obtained with the Faint Object Spectrograph (FOS) on Hubble Space Telescope. Customised extraction of the data was used to properly correct for the background light in the FOS. An optical blue spectrum taken at KPNO is also shown. From the optical and UV line spec…
X-Ray Spectral Study of Two X-Ray Binaries: 4U 1957+11 and 2S 1543-624
Kraft, Ralph P.; Apparao, Krishna M. V.; Singh, Kulinder P.
The X-ray observations of two binary systems, 4U 1957+11 and 2S 1543-624, by the High Eccentric Lunar Occultation Satellite (EXOSAT) satellite are analyzed. The continuum spectra are best fitted by a superposition of a blackbody spectrum (kT approximately = 1 keV) and emission from a Comptonized region, consistent with the spectra of low-mass X-ra…
Astrometry with Hubble Space Telescope Fine Guidance Sensor Number 3: Position Mode Stability and Precision
Benedict, G. F.; Franz, O. G.; Hemenway, P. D. +11 more
We report results from a test exploring the long- and short-term astrometric stability of Hubble Space Telescope Fine Guidance Sensor #3. A test field was observed 40 times over 522 days to determine the precision and accuracy of FGS astrometry and to measure the character and magnitude of possible secular scale changes. We examine the astrometric…
AL iii, SI iv, and C IV Absorption toward zeta Ophiuchi: Evidence for Photoionized and Collisionally Ionized Gas
Jenkins, Edward B.; Sembach, Kenneth R.; Savage, Blair D.
We present Goddard High-Resolution Spectrograph observations at 3.5 km/s resolution and signal-to-noise ratios of 30 to 60 for the Al III, Si IV, and N V absorption lines in the far-ultraviolet spectrum of the O9.5 V star zeat Ophiuchi. The measurement reveal three types of highly ionized gas along the 140 pc line of sight. (1) Narrow components o…
A Model for the Spectroscopic Variations of the Peculiar Symbiotic Star MWC 560
Michalitsianos, A. G.; Shore, Steven N.; Aufdenberg, Jason P.
In this note, we show that the ultraviolet and optical spectroscopic variability of this unique symbiotic star can be understood in terms of a time variable collimated stellar wind with a rapid acceleration near the source. Using the radial velocities observed during the ultraviolet bright phase, we find that a variation in the mass loss rate of a…