The galactic distribution and subtype evolution of Wolf-Rayet stars

1988 ◽  
pp. 152-153
Author(s):  
B. Hidayat ◽  
A. G. Admiranto ◽  
K. R. Supelli ◽  
K. A. van der Hucht
Keyword(s):  
Galactic Distribution

scholarly journals The Galactic Distribution of Electron Density Microstructure Inferred from Radio Scattering Observations

2001 ◽  
Vol 182 ◽  
pp. 11-16
Author(s):  
James Cordes
Keyword(s):  
Interstellar Medium ◽  
Radio Wave ◽  
Electron Density ◽  
Wave Scattering ◽  
Galactic Model ◽  
Dispersion Measures ◽  
Pulse Broadening ◽  
Galactic Distribution

AbstractI first review the observables and optics of interstellar seeing associated with radio wave scattering in the interstellar medium. I then describe the Galactic distribution of electron density and its fluctuations, as inferred from a number of observables, including angular and pulse broadening, diffractive scintillations, and dispersion measures. Propects for improving the Galactic model are outlined.

The Correlation of PN Morphology and Parameters

2003 ◽  
Vol 209 ◽  
pp. 431-438
Author(s):  
Arturo Manchado
Keyword(s):  
Stellar Population ◽  
Planetary Nebulae ◽  
Stellar Mass ◽  
Galactic Latitude ◽  
Complete Sample ◽  
Chemical Abundances ◽  
Galactic Distribution ◽  
Pn Morphology

The morphology of a complete sample of 255 northern planetary nebulae (PNe) was studied and correlated with the nebular parameters. PNe were classified according to the following scheme: round (R, 25%), elliptical (E, 58% of the sample), and bipolar (B, 17%). Bipolars include the quadrupolar subsample. A subclass of pointsymmetric and multiple shell PNe was also found. Nine per cent of ellipticals and 46% of bipolars were found to be pointsymmetric. Thirty-five per cent of the round and 22% of the elliptical PNe were found to be multiple shell PNe (MSPNe). Galactic latitude was found to be different for each morphological class (|b| = 8°, 5° and 2° for types R, E, and B, respectively). Galactic height was also found to vary: 〈z〉 = 647, 276, and 100 pc for categories R, E, and B, respectively. Segregation according to the chemical abundances was also found, with helium abundances of 0.10, 0.12, and 0.14 and N/O of 0.21, 0.31, and 1.33 for types R, E, and B, respectively. Both galactic distribution and chemical abundances point to a different stellar population for each morphological class, the round and bipolar types being the result of low and high stellar mass progenitor evolution, respectively.

scholarly journals Wolf-Rayet Binaries: Evolutionary Causes for their Distribution in the Galaxy

1984 ◽  
Vol 80 ◽  
pp. 175-190
Author(s):  
Bambang Hidayat ◽  
A. Gunawan Admiranto ◽  
Karel A. Van Der Hucht
Keyword(s):  
Galactic Plane ◽  
Small Mass ◽  
The Sun ◽  
Relative Importance ◽  
Galactocentric Distance ◽  
Evolutionary Scenario ◽  
The Galaxy ◽  
Binary Evolution ◽  
Mass Functions ◽  
Galactic Distribution

AbstractOn the basis of the most recent data, the fraction of known Wolf-Rayet binaries is 0.22. In the solar neighbourhood (d < 2.5 kpc) this fraction is 0.34In order to assess the relative importance of massive binary evolution as one of the ways to produce WR stars, the galactic distribution of WR binaries is compared with that of single WR stars using improved intrinsic parameters and new data for the fainter WR stars.In the galactic plane the increase of the binary frequency with galactocentric distance is confirmed.In a direction perpendicular to the galactic plane it is demonstrated at all distances from the Sun that the single-line spectroscopic WR binaries with small mass functions have definitely larger |z|-distances than the ‘single’ WR stars and the WR binaries with massive companions. This is consistent with the evolutionary scenario for massive binaries summarized by van den Heuvel (1976). Among the ‘single’ WR stars the fraction of those with large |z|-distances is increasing with galactocentric distance, like the fraction of the known binaries. This implies that among the high-ļzļ ‘single’ WR stars as well as among the WR stars with lower |z|-values many binaries are still to be discovered.The total WR binary frequency in the Galaxy could be well above 50 %.

scholarly journals The Galactic Distribution of OH/IR Stars

1977 ◽  
Vol 42 ◽  
pp. 399-433
Author(s):  
H.J. Habing
Keyword(s):  
Present Status ◽  
Line Emission ◽  
Microwave Line ◽  
Late Type ◽  
Maser Emission ◽  
Long Period ◽  
Ir Stars ◽  
Long Period Variables ◽  
Recent Compilation ◽  
Galactic Distribution

In 1967 Wilson and Barrett (1968, 1970) discovered that some long period variables, very red and apparently very late type stars, emit OH microwave line emission that is especially strong in the 1612 MHz line at 18 cm. At present some 65 such OH-emitting stars have been identified - for a recent compilation see Bowers and Kerr (1977, M giants) and Baudry et al. (1977, M supergiants). Several stars show maser emission in H2O and SiO as well. At this colloquium Winnberg will review the present status of our knowledge of these stars.

scholarly journals Galactic Distribution, Kinematics, Locations in Clusters and H-R Diagrams, and Duplicity of Be Stars (Review Paper)

1987 ◽  
Vol 92 ◽  
pp. 470-485 ◽  
Author(s):  
Helmut A. Abt
Keyword(s):  
Be Stars ◽  
Orbital Elements ◽  
Constant Frequency ◽  
B Stars ◽  
Star Catalogue ◽  
Solar Motion ◽  
Observational Techniques ◽  
Mass Functions ◽  
Galactic Distribution ◽  
Contraction Stage

AbstractThe locations of 143 B0e-B7e III-V stars listed in the Bright Star Catalogue are similar to those of the early-B Gould Belt stars. Therefore the Be stars have roughly the same ages and origins as early B stars. The frequency of runaway Be stars must be less than several percent. The radial velocities of Be stars show primarily the reflex of solar motion and show no evidence for systematically negative velocities attributable to mass-loss effects upon the absorption profiles. The scatter in the residual velocities is such that there is unlikely to be many undetected binaries with orbital amplitudes greater than 10 km s-l. We are unable to state whether or not Be stars tend to occur during the overall contraction stage, but we do observe Be stars in roughly constant frequency in clusters of all ages. About 18% of the field B0-B7 III-V stars are Be stars. Clusters show both lower and higher frequencies that may be real or may be due to different observational techniques. The frequencies and distribution of binary periods for Be stars is the same as for non-emission B stars except for the lack of periods less than 10-1 yr. Statistically the 12 classical Be stars with known orbital elements have mass functions indicating that their secondaries are more massive than neutron stars and their secondary mass distribution is like that of normal B stars. We observe 35 companions for 100 Be primaries, so after correction for undetected companions, it seems likely that most Be stars have companions, mostly with periods of years.

scholarly journals The galactic distribution of OH/IR stars

1979 ◽  
Vol 84 ◽  
pp. 29-34
Author(s):  
B. Baud ◽  
H. J. Habing ◽  
J. H. Oort
Keyword(s):  
Spectral Type ◽  
Velocity Difference ◽  
Double Peak ◽  
Strong Emission ◽  
Long Period ◽  
Ir Stars ◽  
Long Period Variables ◽  
Galactic Distribution

Through systematic surveys (Johansson et al., Caswell and Haynes, Bowers, Baud, Caswell et al.) some 200 OH masers have been detected that are presumably associated with long period variables of very late spectral type (>M5). Tentatively these stars will be called “OH/IR stars”. They are characterized by their strong emission in the 1612 MHz line which shows a double peak due to the expansion of the shell surrounding these stars. The velocity difference ΔV between the peaks is generally between 10 and 50 km s−1.

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