scholarly journals Non-Linear Radial Pulsation Models for the Early-Type Helium Stars V652 Her and BX Cir

2002 ◽  
Vol 185 ◽  
pp. 438-441
Author(s):  
P. Montañés Rodríguez ◽  
C.S. Jeffery
Keyword(s):  
Linear Models ◽  
High Surface ◽  
Radial Pulsation ◽  
Early Type ◽  
Helium Stars ◽  
Non Linear ◽  
Early Type Stars ◽  
Hydrodynamic Code ◽  
Work Supports ◽  
Good Agreement

AbstractHydrogen-deficient early-type stars have an extremely high surface helium abundance (> 98% by number) and have represented a considerable challenge to stellar evolution theory. Recent work supports the view that they are the product of a merger between two white dwarfs.All very luminous stars (log L/M > 4) are believed to pulsate, but at effective temperatures around 20 000 K, helium stars with lower luminosities (log-L/M < 3) are also known to pulsate due to iron-group bump instability. The two known cases are V652 Her and BX Cir. Their observed periods are in good agreement with linear theory. Recently high-resolution Spectroscopic observations were used to measure the stellar dimensions and radial velocity curves with high precision.A hydrodynamic code including recent OPAL opacity data has been used to construct non-linear models of the pulsations of these two stars. The results impose additional constraints on those stellar dimensions, including mass, which remain poorly determined by observation.

scholarly journals Non-linear radial pulsation models for the early-type helium stars V652 Her and BX Cir

2002 ◽  
Vol 384 (2) ◽  
pp. 433-440 ◽  
Author(s):  
P. Montañés Rodríguez ◽  
C. S. Jeffery
Keyword(s):  
Radial Pulsation ◽  
Early Type ◽  
Helium Stars ◽  
Non Linear

scholarly journals Comparison between model atmospheres and spectra from early-type stars

1965 ◽  
Vol 23 ◽  
pp. 147-161 ◽  
Author(s):  
E. H. Avrett ◽  
S. E. Strom
Keyword(s):  
Grey Model ◽  
Line Profiles ◽  
Early Type ◽  
Ultraviolet Continuum ◽  
Preliminary Calculation ◽  
Effective Temperatures ◽  
Early Type Stars ◽  
Hydrogen Lines ◽  
Good Agreement

To assist in the interpretation of ultraviolet continuum observations, we present observational features of a grid of non-grey model atmosphères in strict radiative equilibrium which have effective temperatures in the range 10000 °K to 20000 °K and surface gravities 103 and 104. For three models, we add the blended wings of the higher Balmer and Lyman hydrogen lines and include in an approximate way further effects of line blanketing in the ultraviolet. Finally, we present a preliminary calculation of the effect of departures from L. T. E. on the continuous flux.To examine the validity of the models, we compare the predicted continuous flux and predicted line profiles with the corresponding observed quantities for Vega and Sirius.We consider the question of discrepancies between theory and observations in the ultraviolet from the viewpoint of these new calculations, and find generally good agreement with recent observations made by T. Stecher.

scholarly journals The Metallicity Dependence of the Mass Loss of Early-Type Massive Stars

2007 ◽  
Vol 3 (S250) ◽  
pp. 39-46
Author(s):  
Alex de Koter
Keyword(s):  
Mass Loss ◽  
Metal Content ◽  
Massive Stars ◽  
Magellanic Clouds ◽  
Stellar Winds ◽  
Early Type ◽  
The Galaxy ◽  
Early Type Stars ◽  
Good Agreement ◽  
Comprehensive Study

AbstractWe report on a comprehensive study of the wind properties of 115 O- and early B-type stars in the Galaxy and the Large Magellanic Clouds. This work is part of the VLT/FLAMES Survey of Massive Stars. The data is used to construct the empirical dependence of the mass-loss in stellar winds on the metal content of their atmospheres. The metal content of early-type stars in the Magellanic Clouds is discussed. Assuming a power-law dependence of mass loss on metal content, Ṁ ∝ Zm, we find m = 0.83 ± 0.16 from an analysis of the wind momentum luminosity relation (Mokiem et al. 2007b). This result is in good agreement with the prediction m = 0.69 ± 0.10 by Vink et al. (2001). Though the scaling agrees, the absolute empirical value of mass loss is found to be a factor of two higher than predictions. This may be explained by a modest amount of clumping in the outflows of the objects studied.

Some results of the Barbier-Chalonge-Divan system of stellar classification

1966 ◽  
Vol 24 ◽  
pp. 77-90 ◽  
Author(s):  
D. Chalonge
Keyword(s):  
Early Type ◽  
Parameter System ◽  
Early Type Stars ◽  
Two Parameter

Several years ago a three-parameter system of stellar classification has been proposed (1, 2), for the early-type stars (O-G): it was an improvement on the two-parameter system described by Barbier and Chalonge (3).

G Optimal Design in Non linear Models to Increase Silicon Oxide Purity Levels and Electrical Conductivity

2018 ◽  
pp. 150-155
Author(s):  
Muklas Rivai
Keyword(s):  
Electrical Conductivity ◽  
Optimal Design ◽  
Linear Models ◽  
Silicon Oxide ◽  
Information Matrix ◽  
Relevant Information ◽  
Non Linear

Optimal design is a design which required in determining the points of variable factors that would be attempted to optimize the relevant information so that fulfilled the desired criteria. The optimal fulfillment criteria based on the information matrix of the selected model.

Radio Continuum Measurements of Southern Early‐Type Stars. III. Nonthermal Emission from Wolf‐Rayet Stars

1999 ◽  
Vol 518 (2) ◽  
pp. 890-900 ◽  
Author(s):  
Jessica M. Chapman ◽  
Claus Leitherer ◽  
Barbel Koribalski ◽  
Roderick Bouter ◽  
Michelle Storey
Keyword(s):  
Radio Continuum ◽  
Early Type ◽  
Nonthermal Emission ◽  
Early Type Stars

Preliminary Observations of Interstellar Sodium D-Line Absorption towards the Carina Nebula

1980 ◽  
Vol 4 (1) ◽  
pp. 95-97 ◽  
Author(s):  
J. B. Whiteoak ◽  
F. F. Gardner
Keyword(s):  
High Resolution ◽  
Hii Regions ◽  
Early Type ◽  
Interstellar Clouds ◽  
Carina Nebula ◽  
Line Absorption ◽  
General Investigation ◽  
Early Type Stars ◽  
Resolution Study

As part of a general investigation of interstellar clouds associated with southern HII regions we have begun a high-resolution study of the sodium D-line absorption in the directions of early-type stars that are likely to be associated with or located behind the clouds.

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