Spatial heterodyne interferometry of VY Canis Majoris, Alpha Orionis, Alpha Scorpii, and R Leonis at 11 microns
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Sution, E. C.↗
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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.↗
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.↗
Ultraviolet photometry from the Orbiting Astronomical Observatory. XXXI - The shape and atmospheric structure of the primary component of UW Canis Majoris
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Eaton, J. A.↗
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.↗
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.↗
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.↗
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.↗
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.↗
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.↗
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.↗
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.↗
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.↗
Pre-main-sequence disk accretion in Z Canis Majoris
It is suggested that the pre-main-sequence object Z CMa is a luminous accretion disk, similar in many respects to the FU Orionis variables. Z CMa shows the broad, doubled optical absorption lines expected from a rapidly rotating accretion disk. The first overtone CO absorption detected in Z CMa is blue-shifted, suggesting line formation in a disk wind. Accretion at rates about 0.001 solar mass/yr over 100 yr is required to explain the luminosity of Z CMa. The large amount of material accreted (0.1 solar mass/yr) indicates that Z CMa is in a very early stage of stellar evolution, possibly in an initial phase of massive disk accretion.
Hartmann, L.↗
A rotating, expanding disk in the Wolf-Rayet star EZ Canis Majoris?
The discovery of linear polarization changes across the extended wings of He II lines, mainly the strong 4-3 transition at 4686 A, in the WN5 star EZ CMa, is reported. When the polarization across the line profiles is plotted in the Stokes parameters plane, it traces loops clockwise from the blue wing through line center to the red, rather than straight lines. Such polarization loops are reminiscent of what is observed in the Balmer lines of Be stars. The continuum polarization in EZ CMa can be understood by an axisymmetric, electron-scattering envelope, with the decrease in polarization in He II being caused by an increase in absorptive opacity in the lines and dilution by unpolarized line emission, while the variations in position angle are due to the Doppler-shifted absorptive opacity and/or scattered line photons. As the sense of rotation in the loops is also independent of phase of this alleged Wolf-Rayet + compact binary, the polarized line profiles are the signature of a rotating, expanding wind geometry around a single star.
Schulte-Ladbeck, R. E.↗
The interstellar tunnel of neutral-free gas toward Beta Canis Majoris
Using high-resolution sodium absorption observations of early-type stars to determine the distribution of neutral interstellar gas in the direction of the star Beta CMa, the contours of a large feature in the local interstellar medium, some 50 pc in diameter and 300 pc long, that appears to be virtually free of neutral gas have been mapped. This rarefied 'interstellar tunnel' is an extension of a region of very low gas density surrounding the sun called the Local Bubble, which may well have been formed by the interaction of expanding interstellar cavities produced by multiple supernova events. This large region of unusually low gas density will be a prime area for study in the soft X-ray and EUV spectral regions.
Welsh, Barry Y.↗
On the wind geometry of the Wolf-Rayet star EZ Canis Majoris
Recent models of Wolf-Rayet star winds have been tailored to EZ CMa, and make predictions of the envelope structure and location of line-emitting regions. It is discussed how the wind structure of EZ CMa can be probed observationally through electron distribution integrals as measured by spectropolarimetry, and then present, analyze, and interpret a time-dependent spectropolarimetric data set of EZ CMa. The observations further the view of an electron-scattering wind that is axisymmetric, rotating, and expanding, with a variable mass-loss rate being responsible for the quasi-periodic polarimetric variability. It is demonstrated that the emission lines of EZ CMa are partially polarized, indicating that line photons are electron-scattered in the wind. The polarization in N V lambda 4945 and N IV lambda 4058 is observed to be larger than that of He II lambda 4686 and He I lambda 5876, as expected from ionization stratification.
Schulte-Ladbeck, R. E.↗
An infrared companion to Z Canis Majoris
New near-infrared speckle observations of Z CMa reveal it to be a double star with a separation 0.1 arcsec at P.A. 120 deg. The northwest component is an infrared object whose broadband spectrum is reminiscent of the infrared companions to several T Tauri stars. The southeast component has the spectral energy distribution expected for a circumstellar disk whose luminosity is dominated by gravitational accretion. The far-infrared and millimeter-wave photometric fluxes suggest the presence of a massive second disk large enough to surround both components; this may be the reservoir from which the material accreted by the first disk is drawn.
Koresko, Chris D.↗