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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Mass flow in the O7f binary UW Canis Majoris. II

The far-ultraviolet spectrum of UW CMa was obtained from the telescope spectrometer on the Copernicus satellite at about phase 0.25 in order to supplement earlier observations of the same kind made near phase 0.75. Analysis of the data shows that the high-temperature gas giving rise to the P Cygni features in the far-ultraviolet spectrum is located primarily around the entire binary system and does not share in the motion of either component. The effects of radiation pressure on the Roche (Jacobian) equipotential surfaces and in generating a stellar wind are discussed.

Mccluskey, G. E., Jr.↗
NASA NTRS1976

Coordinated X-ray optical and radio observations of YZ Canis Minoris

Coordinated X ray, optical, and radio observations of the flare star YZ CMi are reported. Twenty-two minor optical flares and twelve radio events were recorded. No major optical flares, greater than 3 magnitudes, were observed. Although no flare related X ray emission was observed, the measured upper limits in this band enable meaningful comparisons with published flare star models. Three of the five models predicting the relative X ray to optical or radio flare luminosities are in serious disagreement with the observations. For the largest optical flare with coincident X ray coverage, the 3 sigma upper limit on X ray emission in the 0.15 to 0.8 keV band is 8.7 x 10 to the 28th power erg/s, corresponding to a ratio of X ray to B-band luminosity of less than 0.3. Based on the present results, the contribution of the flares UV Ceti flare stars to the galactic component of the diffuse soft X ray background is less than 0.2 percent.

Karpen, J. T.↗
NASA NTRS1977

The ultraviolet spectra of Alpha Aquilae and Alpha Canis Minoris

Scans of Alpha Aql (A7 IV, V) and Alpha CMi (F5 IV-V) obtained with the Copernicus satellite spectrometer over the wavelength range from 2100 to 3200 A are presented along with a spectrum of the integrated solar disk over the same range procured during a calibrated rocket flight. About 1500 fairly strong absorption lines in the Alpha CMi spectrum between 2400 and 2961 A are identified by comparison with a solar atlas and by using a theoretical spectrum synthesized from a blanketed LTE model with an effective temperature of 6500 K and a surface gravity of 10,000 cm/sec per sec. The Mg II resonance doublet at 2795.528 and 2802.704 A is found to be present in all three stars together with a discontinuity at 2635 A due to Fe II, Fe I, Cr I, and Mn II. It is concluded that the Mg II resonance lines and the 2635-A continuum break would be the best spectral features for estimating the redshift of a galaxy observed at low resolution provided the redshift is not less than about 0.75.

Morton, D. C.↗
NASA NTRS1978

Heavy element abundances in Ap stars from ultraviolet data. I - The bright reference stars Alpha Lyrae and Alpha Canis Majoris A

Curve-of-growth analysis is used to derive chemical abundances in Alpha Lyr and Alpha CMa, based on ultraviolet spectra obtained with Copernicus. This analysis is part of a program to study the abundances of the heavy elements mercury and platinum and the short-lived element technetium in the atmospheres of Ap and Am stars. Ultraviolet Fe II lines are used to establish the curves of growth for Alpha Lyr and Alpha CMa A; abundances of a variety of elements, along with upper limits on Hg, Pt, and Tc, are derived. In cases where previous studies based on visual spectra have included elements in common with the present analysis, the agreement is good within the known uncertainties. One new element, cadmium, is observed for these two stars. The upper limits on Pt and Hg, as well as Tc, show that these elements are probably not enhanced in Alpha CMa A by more than about one order of magnitude.

Boiarchuk, A. A.↗
NASA NTRS1978

Very long baseline interferometric observations of the hydroxyl masers in VY Canis Majoris

Results are presented for spectral-line VLBI observations of the OH emission from VY CMa. The main-line (1665 and 1667 MHz) emission was mapped with an angular resolution of 0.02 arcsec by analyzing interferometer phase data. The main-line emission comes from many maser components of apparent size less than 0.03 arcsec which are separated by up to 0.5 arcsec. New maser features near the center of the OH spectra were detected and found to lie within the region encompassed by the low-velocity OH emission. The 1612-MHz emission was mapped by Fourier inversion of the VLBI data from two baselines. All spatially isolated maser components appeared smaller than 0.15 arcsec; however, the maser emission is very complex at most velocities. Maser components within a velocity range of 1.3 km/s are often separated by more than 1 arcsec, while components more than 10 km/s apart in each emission complex are often coincident to 0.2 arcsec.

Reid, M. J.↗
NASA NTRS1978

The eight micron band of silicon monoxide in the expanding cloud around VY Canis Majoris

Observations of vibration-rotation transitions of silicon monoxide in VY CMa show that the lines originate in accelerating, expanding, and cool (600 K) layers of a circumstellar cloud at a distance of roughly 0.15 minutes from the central star. The central stellar velocity, as estimated from observed SiO P Cygni line profiles, is somewhat redshifted from the midpoint of the maser emission features. Most of the silicon is probably in the form of dust grains. The isotopic ratios of silicon are nearly terrestrial.

Geballe, T. R.↗
NASA NTRS1979

The 8 micron band of silicon monoxide in the expanding cloud around VY Canis Majoris

Observations of vibration-rotation transitions of silicon monoxide in VY CMa show that the lines originate in accelerating, expanding, and cool (about 600 K) layers of a circumstellar cloud at a distance of approximately 0.15 arcsec from the central star. The central stellar velocity, as estimated from observed SiO P Cygni line profiles, is somewhat redshifted from the midpoint of the maser emission features. Most of the silicon is probably in the form of dust grains. The isotopic ratios of silicon are nearly terrestrial.

Geballe, T. R.↗
NASA NTRS1979

Mass flow and evolution of UW Canis Majoris

The far-UV spectrum of the eclipsing binary UW CMa (O7f + O-B) had earlier been utilized to derive a mass-loss rate of about 0.000001 to 0.00001 solar mass per year. The mass flow seems to be basically in the form of a stellar wind emanating from the O7f primary component, with radiation pressure as the controlling factor. The main characteristics that make UW CMa a possible progenitor of a Wolf-Rayet system are discussed.

Kondo, Y.↗
NASA NTRS1980

Mass flow analysis of the ultraviolet spectrum of UW Canis Majoris

The ultraviolet spectrum of the close binary UW CMa, obtained with the Copernicus (OAO-3) and IUE satellites in the wavelength region from 1010 to 1510 A and from 1200 to 3000 A, respectively, is analyzed. The observed P Cygni line profiles are compared with theoretically predicted profiles formed by isotropic and coherent scattering in a spherically symmetric expanding circumstellar envelope. Tables illustrate the identified stellar lines, laboratory wavelengths, and line strengths in terms of peak height for emission or central depth for absorption components, normalized to the local stellar continuum.

Drechsel, H.↗
NASA NTRS1981

Phase-correlated P Cygni profile variations of the C III multiplet in UW Canis Majoris

The interacting close binary system UW CMa has been observed, in the wavelength range from 1161 to 1188 A, continuously during a complete orbital cycle in 1979 with the Copernicus (OAO-3) U2 spectrometer. The C III multiplet at 1175 A, observed as a P Cygni feature, exhbits a clear dependence on the orbital phase of the binary; the radial velocity variation of this feature lags behind that of the O7 primary component by 0.1 orbital phase, which agrees with the anticipations in an earlier study by the same authors. The radiation-driven matter, flowing out of the binary, originates in the primary component.

Drechsel, H.↗
NASA NTRS1981

The ultraviolet spectrum of UW Canis Majoris

High resolution spectra of the eclipsing binary UW CMa have been obtained in the wavelength range 950 to 3200 A with the Copernicus (OAO-3) and IUE satellites. UW CMa is an interacting system, consisting of an 07f Ia primary and an O-B secondary. The spectra have been used to compile a list of stellar and interstellar lines. Identifications together with position and laboratory wavelengths are given. The spectra are dominated by envelope (P Cygni) lines. Numerous, but less conspicuous photospheric absorption lines from the 07f component are present. In addition, a wealth of interstellar lines appear.

Drechsel, H.↗
NASA NTRS1985

Activity-driven structure variations as a cause of period changes in RS Canis Venaticorum-like systems

Magnetic activity cycles of a convective star in a close binary system may lead to orbit period changes through tidal spin-orbit coupling. An increase in the mean magnetic field throughout the convection zone provides an additional pressure support and increases the star's moment of inertia. In order for the system to conserve angular momentum instantaneously, the convective star must reduce its rotation rate. When this happens, the system is no longer synchronous; in particular, the equilibrium tide now suffers a phase lag. A tidal torque must act, transferring angular momentum from the star's rotation to the orbit, lengthening the period. When the field decays, these events reverse and the period shortens. Observed period changes in RS CVn-like systems are of the order delta p/p = 10 to the -6th, implying variations in the mean field strength at the base of the convection zone of approximately 1000 G over time scales of 10-30 yr. It is predicted that the strength of magnetic activity indicators will track orbital period changes in a given system: the period will be largest during the active portion of the magnetic cycle and smallest during the quiescent part.

Van Buren, D.↗
NASA NTRS1987

IUE observations of the dwarf nova HL Canis Majoris and the winds of cataclysmic variables

An observational and theoretical study is conducted of the P Cygni profiles of cataclysmic variables, with attention to the profiles of the dwarf nova HL CMa, in light of the ionization structure of the wind for a given geometry. It is found that a spherically symmetric wind is capable of generating the observed profile shapes when the accretion disk is limb-darkened, provided that the acceleration of the wind is very low and that the wind represents a mass-loss rate of about 10 to the -11th/C IV ionization fraction of the solar mass per year; a wind of this magnitude, however, cannot be driven by radiation pressure.

Mauche, Christopher W.↗
NASA NTRS1988

Recent unusual activity in the Be star FY Canis Majoris

Unusual activity observed in the circumstelar envelope of FY CMa during April-May, 1987 is reported. Nightly CCD observations from April 16-20 revealed an invariant H-alpha emission feature and a simple absorption profile for He I 6678 with very weak double emission components. Similar observations on May 2, however, showed that the V lobe of the H-alpha feature had increased in strength by 30 percent and that the He I line had developed into a structured inverse P Cygni profile.

Peters, Geraldine J.↗