Search Publications
The Nature of the Recurrent Nova T Coronae Borealis: Ultraviolet Evidence for a White Dwarf Accretor
Cassatella, Angelo; Gilmozzi, Roberto; Selvelli, Pier L.
Data from eleven years of IUE observations of T CrB during its quiescent phase suggest that a white dwarf accretor rather than a main-sequence star is the hot component of the system. The spectroscopic and photometric behavior of T CrB during the 1946 outburst actually supports the interpretation of a thermonuclear runaway event on a massive white…
Evolving, Dynamical Models for Collapsed-Core Globular Clusters: M15 and NGC 6624
Cohn, Haldan N.; Lugger, Phyllis M.; Murphy, Brian W. +1 more
The stellar populations of the collapsed-core globular clusters M15 and NGC 6624 are investigated by fitting observed surface-brightness and projected velocity-dispersion profiles. The present evolving cluster models were generated by the direct Fokker-Planck method and incorporate realistic stellar mass spectra and energy input from binaries form…
Spherically Symmetric, Expanding, Non--LTE Model Atmospheres for Novae during Their Early Stages
Hauschildt, P. H.; Starrfield, S.; Wehrse, R. +1 more
In the continuum and line-blanketed models presented here, nova atmospheres are characterized by a very slow decrease of density with increasing radius. This feature leads to very large geometrical extensions so that there are large temperature differences between the inner and outer parts of the line-forming regions. The theoretical spectra show …
A Multiwavelength Study of Nova QU Vulpeculae 1984
Williams, Robert E.; Truran, James W.; Ferland, Gary J. +6 more
We have combined ground-based optical and satellite ultraviolet spectrophotometric data to study the ejected shell of Nova Vulpecula 1984 No. 2 (QU Vul). Substantial uncertainties concerning the nature of the ionizing continuum, and the role played by density inhomogeneities, now exist. Because of these uncertainties, the chemical composition is d…
Fractionation of CO in the Diffuse Clouds toward zeta Ophiuchi
Federman, S. R.; Lambert, David L.; Cardelli, Jason A. +1 more
An analysis of CO A-X bands in diffuse clouds toward Zeta Ophiuchi is presented. The results provide isotopic ratios that constitute the strongest observational evidence for highly localized isotopic fractionation of CO in diffuse portions of an interstellar cloud. The value of the fractionation implies that selective photodissociation is the cont…
Ultraviolet, Optical, and Infrared Observations of the High-Latitude Molecular Cloud toward HD 210121
Welty, Daniel E.; Fowler, James R.
Low-resolution UV spectra of the B3 V star HD 210121, located behind the high-latitude molecular cloud DBB 80, yield an extinction curve exhibiting a far-UV rise that is among the steepest known. The apparently simple line of sight affords an excellent opportunity for investigating the absorption and emission characteristics of a single, isolated …
Eclipse Studies of the Dwarf Nova HT Cassiopeiae. II. White Dwarf and Accretion Disk
Horne, Keith; Wood, Janet H.; Vennes, Stephane
The white dwarf and accretion disk in the dwarf nova HT Cas are investigated by means of the simultaneous UBVR light curve presented by Horne et al. (1991). A temperature of 14,000 +/- 1000 K and a distance of 125 +/- 8 pc for E(B - V) = 0.0 are found. A blackbody fit to the UBVR fluxes yields T(W) of 13,600 +/- 1000 K and D of 140 +/- 12 pc. Thes…
Search for Partial Systemic Lyman Edges in Nearby Quasars
Koratkar, A. P.; Bohlin, R. C.; Kinney, A. L.
The Lyman edge region (912 A) of quasars is thought to be formed by thermally emitting accretion disks and would be affected by broad-line region (BLR) clouds. The Lyman edge discontinuities in disk models are predicted both in absorption (<= 80%) and in emission (<= 30%). For BLR clouds, the predictions range from complete absorption at the…
The Origin of Broad Emission Lines in the Extragalactic Giant H II Region NGC 2363
Dufour, R. J.; McCall, Marshall L.; Roy, Jean-Rene +1 more
High signal-to-noise long-slit spectra have been obtained of the giant H II region NGC 2363 located in the dwarf SBm galaxy NGC 2366. A discovery of low-intensity broad spectral components (FWHM ~40 A or 2400 km s^-1^) in the bright nebular lines Hα, Hβ, and [O III) is reported. The broad spectral components are detected over a large spatial exten…
Detection of Fundamental and Harmonic Type III Radio Emission and the Associated Langmuir Waves at the Source Region
Stone, R. G.; Fainberg, J.; Reiner, M. J.
Type III radio emission generated in the vicinity of the Ulysses spacecraft has been detected at both the fundamental and harmonic of the local plasma frequency. The observations represent the first clear evidence of locally generated type III radio emission. This local emission shows no evidence of frequency drift, exhibits a relatively short ris…