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NASA NTRS1984

The remarkable ultraviolet spectrum of the planetary nebula Abell 30

Abell 30 has been identified as a planetary nebula in which the nucleus has experienced a final helium shell flash after ejection of the original, outer envelope. Around the central star of the nebula, four knots of material are observed. In view of the importance of the chemical composition of the ejected material for studies of advanced stages of stellar evolution, clarification of the physical conditions in the knots is vital. Data obtained of Abell 30 with the aid of the International Ultraviolet Explorer (IUE) satellite are discussed along with aspects of extinction, the He II flux, ionic abundances, the C II lambda 4267 line, questions regarding the existence of a carbon-rich core in the knot, the heating of the nebular gas, the central star, and heating by suprathermal particles from the stellar wind. The UV spectrum of the inner nebulosity of Abell 30 indicates that an extraordinary amount of energy is being deposited in the gas.

Harrington, J. P.↗

NASA NTRS1984

The high-energy X-ray spectrum of Centaurus XR-3 observed from OSO 8

Observations of the X-ray binary Cen XR-3 in the 20-120 keV energy range by means of OSO 8's high energy X-ray spectrometer, during July 16-19, 1975, and July 5-14 and 28-29, 1978, indicate that the source was in a high luminosity state during 1975 and a low luminosity one in 1978. While mean orbital light curves appear similar in shape in both years, orbit-to-orbit intensity variations are noted. Spectral, luminosity, and the 4.84 sec modulation are characterized. Cen XR-3 may be a system in which mass transfer by Roche lobe overflow, and by accretion from a stellar wind, are both effective in the production of observable X-ray radiation.

Dolan, J. F.↗

NASA NTRS1984

Sigma Geminorum (K1 III + ?) - Variability of the ultraviolet emission lines near conjunction

Far-ultraviolet IUE echelle spectra of the moderate-period RS CVn system Sigma Geminorum (K1 III + ?) are reported. Despite the location of the red-giant primary of Sigma Gem in a portion of the H-R diagram where cool stellar winds are common, no evidence for circumstellar absorption features or blueward asymmetries is found in the chromospheric O I (or Mg I and Mg II) emission cores. However, observations on two consecutive days indicate significant changes in the profiles of high-excitation species such as Si IV and C IV which likely were produced by the rotation of a large-scale active region (Fried et al., 1983) off the visible hemisphere of the primary.

Ayres, T. R.↗

NASA NTRS1984

The evolution of cataclysmic and low-mass X-ray binaries

The observational data for the 124 cataclysmic and low-mass X-ray binaries of known orbital period are compiled. It is found that the eruption properties are very well correlated with the orbital periods, in a manner that suggests that the mass transfer is the all-important determinant of evolution and of the eruptive behavior. Transfer rates of 10 to the -11th to 10 to the -7th solar mass/year are found, which are well correlated with orbital period. It is concluded that the mechanism which drives these systems is the magnetic braking of the secondary's rotation by its own stellar wind, coupled with the enforcement of synchronous rotation by tidal friction. This permits CVs to lose sufficient angular momentum to begin mass transfer in a reasonable time and drives the mass transfer at a high rate once it begins. An account of the long-lived phases of CV evolution is given.

Patterson, J.↗

NASA NTRS1983

Observational Basis for Velocity Fields in Stellar Atmospheres, Workshop, Trieste, Italy, August-September 1982, Proceedings

Solar and stellar winds and mass-loss phenomena are discussed in reviews of recent observations and current theory. Topics examined include mass loss from the sun, the O-type stars, Wolf-Rayet stars, the Parker theory, B stars, T Tauri stars, Balmer line emission from Be stars, novae, symbiotic stars, planetary nebulae, and dwarf novae. Graphs, tables, diagrams, sample spectra, and extensive discussion on each contribution are provided.

Stalio, R.↗

NASA NTRS1984

X-rays from Eta Carinae

X-ray observations of Eta Car obtained with the high-resolution imager and solid-state spectrometer of the Einstein observatory are reported and interpreted in terms of a two-shell model. A soft component with temperature 5 million K is located in the expanding outer shell, and the hard core component with temperature 80 million K is attributed to the interaction of a high-velocity stellar wind from the massive central object with the inner edge of a dust shell. Model calculations based on comparison with optical and IR data permit estimation of the mass of the outer shell (0.004 solar mass), the mass of the dust shell (3 solar mass), and the total shell expansion energy (less than 2 x 10 to the 49th ergs).

Chlebowski, T.↗

NASA NTRS1984

Spectral formation in compact X-ray sources

The gas flows responsible for X-ray spectral emission in compact X-ray sources are complex and likely to be optically thick. In galactic sources these flows include: stellar wind, accretion disk and corona, magnetosphere, and shock at the compact object surface. Active galactic nuclei are surrounded by many dense clouds responsible for the broad optical and UV emission lines. The nature of these flows can be discovered through observations of their X-ray spectra and time variability. Theoretical models for the formation of line and continuum spectra in these sources are described, emphasizing atomic photoabsorption, line emission, and Comptonization. Current observations of X-ray and UV spectra of compact galactic sources and active galactic nuclei are interpreted in terms of these models. Great advances in the understanding of these systems will result from future missions capable of observing their spectra at higher resolution. Observations of the complex of iron K-alpha lines at 6.4-6.7 keV will be particularly valuable.

Mccray, R.↗

NASA NTRS1984

Ultraviolet high-resolution spectroscopy of the X-ray binary Sk 160/SMC X-1

High-resolution IUE spectra of Sk 160, the optical counterpart of the X-ray source SMC X-1, show substantial variations with orbital phase of the resonance P Cygni profiles. These variations are ascribed to the changing ionization state in the stellar wind caused by the X-rays emitted by the companion, as suggested by Hatchett and McCray and first established for the galactic X-ray binary Vela X-1. Furthermore, the profile observed during X-ray eclipse differs significantly from profiles of similar stars in the absence of X-ray ionization.

Hammerschlag-Hensberge, G.↗

NASA NTRS1985

Spectroscopic observations of selected stellar systems

Spectra of very luminous, high temperature stars, the o-type stars with the largest masses among stars, and the Wolf-Rayet (W-R) stars are studied. These stars are characterized by strong stellar winds which produce signiicant mass loss. The nature and evolution of these winds are studied to learn the densities, velocity structue, ionization balance, and composition. The IUE satellite provides the best way to study these phenomena because many of the most important ground state and excited state lines of common highly ionized species are found in the spectral range.

Conti, P. S.↗

NASA NTRS1985

Combined ultraviolet studies of astronomical sources

Ultraviolet studies of various astronomical entities are reported. Among the specific phenomena examined were supernova remnants, dwarf novae, red giant stars, stellar winds, binary stars, and galaxies.

Dupree, A. K.↗

NASA NTRS1985

The Formation of Preplanetary Disks from the Collapse of Rotating Molecular Cloud Cores

Solutions that describe the collapse of a molecular cloud core that is initially in unstable equilibrium, embedded within an envelope of uniform density, and rotating at the same rate as the envelope are given. Hydrodynamic equations, including self gravity, are deduced to a set of ordinary differential equations, which are solved by the method of matched asymptotic expansions. Results of these calculations are: (1) the range of stellar masses derived seems to correspond to realistic ranges of observed stellar masses and interstellar cloud parameters, (2) the proper measure of dissipation rate is the ratio of accretion time to viscous diffusion time, and (3) the pressure distribution on the surface of an accreting protostar is nonuniform in a way that favors the channeling of a stellar wind into a bipolar flow directed along the rotation axis.

Cassen, P.↗

NASA NTRS1985

Excess gamma-rays in the direction of the rho Ophiuchi cloud: An exotic object?

The COS-B X-ray data in the direction of the rho Oph dark cloud show an extended structure; at the same time, the region of highest intensity has a spatial distribution compatible with a localized source; 2CG353+16 which is designated Oph gamma. The possibility of an excess gamma ray flux over what is expected on the basis of the interaction of average density cosmic rays with an estimated cloud mass of 2 to 4 000 M is still open, pending an extended CO survey matching the gamma ray data. Estimates for this excess factor are in the range 2 to 4. While the cloud mass may be underestimated, it should be noted that an excess of the same order appears to be present in the nearby Oph-Sag area, well surveyed in CO with the Columbia dish. Possible reasons for a gamma ray excess, in view of two recent observational developments: an Einstein X-ray survey and a VLA radio survey, both covering the approx 2 deg diameter Oph gamma error box. Current interpretations link the gamma ray excess to the cloud gas, in which some active agent is present: stellar winds, or interaction with the North Polar Spur.

Montmerle, T.↗

NASA NTRS1985

Possible origin of the anomalous component of cosmic rays

The possible origin of the anomalous cosmic rays (ACR) are studied in terms of stellar wind injection from O type stars and their acceleration in shock fronts of SNR's. It is assumed that a fraction of heavy ions will encounter interstellar shock fronts of SNR's and these are accelerated to about 5 to 100 MeV/N and give rise to ACR's. Typically these ions would travel a distance of the order of a few 1000 pc. Therefore it is estimated that O type stars in a volume of radius of a few Kpc around the solar system are contributing to the intensity of ACR in the local ISM. From observational data, the intensity of ACR in the local ISM is estimated. It is suggested that these ACR ions enter the solar system along the solar dipole field lines connected to the interplanetary magnetic field lines.

Biswas, S.↗

NASA NTRS1984

On the extended chromosphere of Alpha Orionis

A detailed examination of the extended chromosphere of Alpha Orionis was performed in an attempt to characterize the matter-emitting processes of red giants and supergiants. The problem was approached using an Alfven wave driven stellar wind model to compute the density, temperature, and velocity structure of the wind. It is shown that the mechanical energy fluxes necessary to maintain the observed chromospheric temperatures are commensurate with the momentum deposition necessary to extend the chromosphere. The chromospheric model constructed is, however, inconsistent with the kinematics of the observed symmetric profiles, which could correspond to a fountain-type model that described infalling, rather than escaping, ejected material such as He.

Hartmann, L.↗

NASA NTRS1984

Mass loss in O-type stars - Parameters which affect it

Newly determined mass loss rates are presented for sixteen O-type stars in three open clusters. Combining the data with that already in the literature, no evidence is found that the rates are different in clusters with differing galactocentric distances and compositions, at least near the sun. There is still appreciable dispersion in the relationship between the mass loss rate and the stellar luminosity. It may be that the mass loss depends additionally on the stellar mass and/or radius, but these data cannot unequivocally indicate which physical dependence is correct. Evidence is found that a stellar wind increases as a massive star evolves from the zero-age main sequence.

Garmany, C. D.↗

NASA NTRS1984

The galaxy as a self-regulated star-forming system - The case of the OB associations

It is proposed that the energy and momentum injected from OB associations can act as the regulators of high-mass star formation throughout the disk of a spiral galaxy. The mechanism, interacting blast waves driven by supernovae and stellar winds, leads to a generalized Schmidt law for the star formation rate and could explain in a natural way the galactic gradients of metals and star formation rate. The formation of massive stars is determined by the average ambient density in the disk while low-mass star formation is regulated by the density in molecular clouds. That is, there are two modes of star formation, but the physical mechanism is the same in both cases.

Franco, J.↗

NASA NTRS1984

Brackett-alpha line profiles of young stellar objects

Profiles of the Br-alpha line of H I at a velocity resolution of 45 km/s are presented for the compact imbedded infrared objects BN, S106/IRS 3, GLS 490, GL 961, GL 989, Mon. R2/IRS 2, and for the visible objects LkH-alpha 101, T Tau, and R Mon. A proportionality obtained between Br-alpha luminosity and bolometric luminosity is shown to extend over three orders of magnitude, supporting the idea that the physical conditions and gas motions in the circumstellar envelopes of stellar objects are closely related over a wide range of luminosities. The Br-alpha line strengths are compared to radio continuum flux densities in the context of stellar wind models. Momentum deposition rates deduced from Br-alpha or radio continuum fluxes are consistent with those available in the radiation fields, which appear capable of driving the ionized gas outflows in the vicinity of the core sources. The results of a comparison of the H-alpha and Br-alpha profiles for T Tau are discussed.

Persson, S. E.↗

NASA NTRS1984

Feige 24 - Wind/flare accretion by a hot DAZ1 degenerate

Model stellar envelopes have been constructed in order to represent the outer layers of the hot DAZ white dwarf component of the spectroscopic binary Feige 24. The results of the calculations show that the metals, discovered by Dupree and Raymond (1983) should diffuse rapidly into the interior unless a continuous source of these elements is present in the system. It is proposed that this source is a stellar wind from the red dwarf component of this detached close binary, and diffusion and accretion calculations are provided to support the hypothesis. Recent EXOSAT observations of Feige 24 provide additional evidence to test the accretion hypothesis. The accreting material may provide significant X-ray opacity for this object. This discussion is extended to other similar M dwarf-white dwarf close binary systems.

Sion, E. M.↗