Emergent polarization structure in spectral lines from rotating stars of spectral type B

1984 ◽  
Vol 107 (1) ◽  
pp. 61-69 ◽  
Author(s):  
Sean J. McKenna
Keyword(s):  
Spectral Type ◽  
Spectral Lines ◽  
Rotating Stars ◽  
Type B ◽  
Polarization Structure

scholarly journals Accuracy of Spectral Classification

1983 ◽  
Vol 62 ◽  
pp. 118-119
Author(s):  
Helmut A. Abt
Keyword(s):  
Spectral Type ◽  
Quantitative Information ◽  
Spectral Lines ◽  
Spectral Classification ◽  
Signal To Noise ◽  
Independent System ◽  
Visual Systems ◽  
Other Information

A knowledge of the spectral types of visual components is still basic to most intensive studies of visual systems. Although there are photoelectric techniques that give good quantitative information on certain classes of stars, the only way at present to identify most classes of stars, from mercury-manganese stars to barium stars, is by obtaining their spectra. The spectra can be obtained from objective prisms, slit spectrographs, or spectrum scans, but the important things are that they (1) show a large portion of the spectra, preferrably in the blue-violet for most classes of stars, (2) have sufficient resolution and signal-to-noise to identify many spectral lines, and (3) be standardized as an independent system. The last is important because if spectral type standards are changed so that they will agree with other information, such as colors, we lose the benefits of a comparison, such as deriving interstellar reddening.

scholarly journals NLTE-Analysis of Three Extremely Helium-Rich O-Type Subdwarfs

1985 ◽  
Vol 87 ◽  
pp. 353-357
Author(s):  
C. Husfeld ◽  
U. Heber ◽  
J.S. Drilling
Keyword(s):  
Spectral Type ◽  
White Dwarf ◽  
Asymptotic Giant Branch ◽  
Evolutionary Status ◽  
Type B ◽  
Hot Stars ◽  
Upper Limits ◽  
Helium Stars ◽  
Effective Temperatures

AbstractThree extremely helium-rich sdO stars (LSE 153, LSE 259 and LSE 263) were analyzed spectroscopically by means of detailed NLTE model atmospheres. These stars are very hot, with effective temperatures ranging from 70000 to 75000 K and gravities between log g = 4.4 and 4.9. Upper limits for the hydrogen abundance were also derived. The evolutionary status of the sdO stars is discussed and it is concluded that they evolve from the asymptotic giant branch towards the white dwarf stage. A possible evolutionary link between these hot stars and the extreme helium stars of spectral type B is discussed.

scholarly journals Simulation of the small-scale magnetism in main-sequence stellar atmospheres

2018 ◽  
Vol 614 ◽  
pp. A78 ◽  
Author(s):  
R. G. Salhab ◽  
O. Steiner ◽  
S. V. Berdyugina ◽  
B. Freytag ◽  
S. P. Rajaguru ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Spectral Type ◽  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Small Scale ◽  
Positive Contribution ◽  
The Sun ◽  
Free Atmosphere ◽  
Paper Properties

Context. Observations of the Sun tell us that its granular and subgranular small-scale magnetism has significant consequences for global quantities such as the total solar irradiance or convective blueshift of spectral lines. Aims. In this paper, properties of the small-scale magnetism of four cool stellar atmospheres, including the Sun, are investigated, and in particular its effects on the radiative intensity and flux. Methods. We carried out three-dimensional radiation magnetohydrodynamic simulations with the CO5BOLD code in two different settings: with and without a magnetic field. These are thought to represent states of high and low small-scale magnetic activity of a stellar magnetic cycle. Results. We find that the presence of small-scale magnetism increases the bolometric intensity and flux in all investigated models. The surplus in radiative flux of the magnetic over the magnetic field-free atmosphere increases with increasing effective temperature, Teff, from 0.47% for spectral type K8V to 1.05% for the solar model, but decreases for higher effective temperatures than solar. The degree of evacuation of the magnetic flux concentrations monotonically increases with Teff as does their depression of the visible optical surface, that is the Wilson depression. Nevertheless, the strength of the field concentrations on this surface stays remarkably unchanged at ≈1560 G throughout the considered range of spectral types. With respect to the surrounding gas pressure, the field strength is close to (thermal) equipartition for the Sun and spectral type F5V but is clearly sub-equipartition for K2V and more so for K8V. The magnetic flux concentrations appear most conspicuous for model K2V owing to their high brightness contrast. Conclusions. For mean magnetic flux densities of approximately 50 G, we expect the small-scale magnetism of stars in the spectral range from F5V to K8V to produce a positive contribution to their bolometric luminosity. The modulation seems to be most effective for early G-type stars.

Semidetached systems of spectral type B : BF Aurigae, mu*1 Scorpii and V Puppis.

1979 ◽  
Vol 84 ◽  
pp. 236 ◽  
Author(s):  
D. P. Schneider ◽  
J. J. Darland ◽  
K.-C. Leung
Keyword(s):  
Spectral Type ◽  
Type B

scholarly journals Rotation Broadening and the Shapes of W Ursae Majoris Stars

1980 ◽  
Vol 88 ◽  
pp. 485-489
Author(s):  
Lawrence Anderson ◽  
Malcolm Raff ◽  
Frank H. Shu
Keyword(s):  
Fourier Transform ◽  
Fast Fourier Transform ◽  
Spectral Type ◽  
Preliminary Data ◽  
Rotating Stars ◽  
Mass Ratio ◽  
Global Features ◽  
The Third ◽  
Limb Darkening ◽  
Rotation Function

We extract rotation broadening functions from the spectra of W Ursae Majoris Stars. Using a fast Fourier transform we deconvolve photographic spectra, covering some 500 A including dozens of strong lines, with equivalent spectra from non-rotating stars of similar spectral type. The resulting rotation functions contain information about global features such as the shape of the stellar surface (e.g. mass ratio and degree of contact), gravity brightening and limb darkening. We present preliminary data on the stars VW Cep and ER Vul. The rotation function of the former reveals the presence of the third component found visually by Heintz (1975), while that of the latter shows it to be detached and have mass ratio 0.9.

scholarly journals Star-streaming from the Stars of Spectral Type B

1954 ◽  
Vol 114 (4) ◽  
pp. 460-466
Author(s):  
T. R. Tannahill
Keyword(s):  
Spectral Type ◽  
Type B

scholarly journals The Determination and Interpretation of the Rotation Parameter v sin i

2004 ◽  
Vol 215 ◽  
pp. 3-16 ◽  
Author(s):  
George W. Collins
Keyword(s):  
Rotation Period ◽  
Rotation Parameter ◽  
Spectral Lines ◽  
Rotating Stars ◽  
Stellar Rotation ◽  
Indirect Methods ◽  
Stellar Spectroscopy ◽  
Rapidly Rotating Stars

In this paper we review the development of the concept of the stellar rotation parameter commonly known as v sin i. We emphasize that the interpretation of the parameter in terms of physical characteristics of the star always depends on comparison with a model that is intended to represent the physical properties of the star. To that end we will trace the development of such models along with the observational means of determining the parameter. Emphasis will be place on the traditional methods involving stellar spectroscopy, but some attention will be place on indirect methods involving direct measurement of the rotation period and recent interferometric determination of stellar oblatness. In addition we will comment on recent techniques involving the simultaneous measurement of many spectral lines and synthetic spectra to improve the accuracy of rotational half-widths.The natural desire for simplicity of such models has often resulted in erroneous values for stellar parameters. This is particularly the case for the most rapidly rotating stars generally of early spectral type, but may also be present in some giants and supergiants where rapid rotation is difficult to detect. Finally, we will comment on the possibilities of improving the quality of both the measurement and interpretation of this important stellar rotation parameter.

The genetic control of the two types of mannan produced by Saccharomyces cerevisiae

1971 ◽  
Vol 17 (11) ◽  
pp. 1451-1454 ◽  
Author(s):  
J. F. T. Spencer ◽  
P. A. J. Gorin ◽  
G. H. Rank
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Magnetic Resonance ◽  
Genetic Control ◽  
Spectral Type ◽  
Proton Magnetic Resonance ◽  
Side Chains ◽  
Type B ◽  
Complex Type ◽  
Mendelian Gene ◽  
Different Strains

The two mannans formed by different strains of Saccharomyces cerevisiae give proton magnetic resonance spectra (spectral types A and B), which suggests that they differ principally in the presence of a-(1 → 3)-linked mannopyranosyl end units of the side chains of the more complex type (giving spectral type B). The presence or absence of such end units was under the control of a single mendelian gene, since the two types of mannan segregated independently during sporulation. The gene controlling this type of mannan produced was apparently not linked to those controlling the requirements for adenine, uracil, leucine, or histidine. The implications of the findings concerning the mechanism of biosynthesis of yeast mannan are discussed.

Sign in / Sign up

Export Citation Format

Share Document