scholarly journals Some Aspects of the Evolutionary Status Of W Ursae Majoris Binaries Deduced from Observational Data

1982 ◽  
Vol 69 ◽  
pp. 301-304
Author(s):  
Walter Van Hamme
Keyword(s):  
Observational Data ◽  
Spectral Type ◽  
Main Sequence ◽  
Type A ◽  
Type Systems ◽  
Primary Component ◽  
Main Sequence Star ◽  
Evolutionary Status ◽  
Evolutionary Stage ◽  
Evolutionary State

AbstractWe have developed a test for the evolutionary state of W Ursae Majoris binaries by comparing the observed spectral type of 31 of these systems (14 of type W and 17 of type A) with the expected one when their primary component is an unevolved main sequence star. It appears that both the W- and A-type systems have a primary with a mass and radius too large to be compatible with the observed spectral type,so there is no indication that each type should mark a different evolutionary stage.

scholarly journals The Unusual Evolutionary State of Nova Scorpii 1994

2002 ◽  
Vol 187 ◽  
pp. 373-378
Author(s):  
Christopher A. Tout ◽  
Enikő Regős ◽  
Dayal Wickramasinghe
Keyword(s):  
Black Hole ◽  
Main Sequence ◽  
Main Sequence Star ◽  
Chemical Pollution ◽  
Evolutionary Status ◽  
Low Velocity ◽  
Alternative Scenario ◽  
X Ray ◽  
The Core ◽  
Evolutionary State

AbstractWe have investigated possible models for the evolutionary status of the black-hole soft X-ray transient Nova Scorpii. We propose that it is a main-sequence star in which convective overshooting, or some equivalent mixing, occurs at the core-envelope boundary. Recent detections of chemical pollution on the surface of the secondary suggest that the black hole formed in a supernova whose ejecta left and fell back at a sufficiently low velocity to accrete on to the secondary. We examine the effects of increased opacity, increased metallicity and reduced hydrogen abundance on the evolution of the secondary in the hope that these might lead to an alternative scenario. All these only exacerbate the problem.

scholarly journals The Subdwarf Eclipsing Binary LB3459 (AA Dor)

1982 ◽  
Vol 69 ◽  
pp. 455-456
Author(s):  
R.W. Hilditch ◽  
Graham Hill ◽  
D. Kilkenny
Keyword(s):  
Light Curve ◽  
Observational Data ◽  
Spectroscopic Data ◽  
Main Sequence ◽  
Primary Component ◽  
Curve Analysis ◽  
Current Status ◽  
Evolutionary Models ◽  
Light Curve Analysis ◽  
Normal Composition

A review was presented of the currently available observational data on this evolved system, namely, uvby photometry (Kilkenny et al. 1978; paper II) radial velocities (Kilkenny et al. 1981; paper III) and a non-LTE atmosphere analysis of the primary component (Kudritski et al. 1981). Kudritski et al. conclude that T(pr) = 40000 ± 2500°K and log g = 5.3 ± 0.2 and from the spectroscopic data and light curve analysis (papers II, III) derive masses and radii for the primary and secondary components of M(pr) ≃ 0.25 M⊙, M(sec) ≃ 0.04 M⊙, R(pr) ≃ 0.16R⊙, R(sec) ≃ 0.09R⊙ respectively. Thus the primary component is a normal sd0 star whilst the secondary component is a most enigmatic object, perhaps a normal composition degenerate dwarf but of too low a mass to be on the main sequence, perhaps an evolved degenerate object but then the radius is too large. The published evolutionary models for this system (Paczynski 1980; Conti et al 1981) do not adequately describe its current status.

scholarly journals The Present Data Situation for Stars in Open Clusters. II

1980 ◽  
Vol 85 ◽  
pp. 129-133
Author(s):  
J.-C. Mermilliod
Keyword(s):  
Present State ◽  
Spectral Type ◽  
Main Sequence ◽  
Open Clusters ◽  
Photometric Data ◽  
Main Sequence Star ◽  
The Sun ◽  
Previous Version

The present state of astrometric, spectroscopic and photometric data for stars in 63 open clusters nearer to the Sun than 750 pc is summarized. Table I reports the limits of the available data in terms of the apparent V magnitude, in the same way as the previous version (Mermilliod 1977). Information on the apparent V magnitude of the brightest main sequence star (Vbr) and on the number of stars brighter than V=10 (n∗) has been included. In addition, the bluest spectral type on the main sequence has been used as an age estimator (TS).

scholarly journals The evolutionary stage of five southern Galactic unclassified B[e] stars

2003 ◽  
Vol 212 ◽  
pp. 154-155 ◽  
Author(s):  
Marcelo Borges Fernandes ◽  
Francisco X. de Araújo ◽  
H. Lamers
Keyword(s):  
Chemical Composition ◽  
Main Sequence ◽  
Planetary Nebulae ◽  
The Other ◽  
Special Focus ◽  
Evolutionary Status ◽  
Evolutionary Stage ◽  
Circumstellar Material ◽  
Physical Conditions ◽  
Evolutionary Phase

The spectra of stars with the B[e] phenomenon are dominated by features that are related to physical conditions of circumstellar material around these objects and are not intrinsic to the stars. Because of this, they form a very heterogeneous group. This group contains objects with different evolutionary stages. Lamers et al. (1998) have suggested a new designation with five sub-groups, which indicate the evolutionary stage. They are: supergiants, pre-main sequence or Herbig Ae/Be, compact planetary nebulae, symbiotic and unclassified. The unclassified group has many objects that need a better study to resolve their evolutionary status. Forbidden lines can be a useful tool to solve this problem. They can give informations about chemical composition, ionization and density of the circunstellar medium and probably the evolutionary phase of these objects. We analize spectra of some galactic objects, obtained with the feros and b&c spectrographs at the 1.52m telescope in ESO (La Silla-Chile), with a special focus on the forbidden lines. We have studied the spectra of five B[e] stars of uncertain evolutionary stage. We find that one of them is a pre-WN star, the other four are supergiant B[e] stars.

scholarly journals Protoplanetary Material Around Nearby Stars

1985 ◽  
Vol 112 ◽  
pp. 43-50
Author(s):  
Hartmut H. Aumann
Keyword(s):  
Statistical Analysis ◽  
Solar System ◽  
Spectral Type ◽  
Main Sequence ◽  
Type A ◽  
Main Sequence Stars ◽  
Infrared Excess ◽  
Working Hypothesis ◽  
Sufficient Distance ◽  
Nearby Stars

A statistical analysis of IRAS observations indicates that about 20% of the nearby main sequence stars, and probably a similar fraction of main sequence stars not detectable by IRAS, shows evidence of significant infrared excess beyond 12 microns. Spectral type A dwarfs are predominant, but not exclusive in showing large 60 micron excesses. Our solar system, when viewed from sufficient distance, appears to have, in contrast to this, less than 1% of cool infrared excess. These observational facts are consistent with the working hypothesis that cold infrared excess in stable main sequence stars is due to proto-planetary material, observable during the accretion phase in the evolution of a solar system.

scholarly journals Absolute Dimensions of Algol Binary Systems

1989 ◽  
Vol 107 ◽  
pp. 341-342
Author(s):  
J.M. Garcia ◽  
A. Gimenez
Keyword(s):  
Binary Systems ◽  
Main Sequence ◽  
Primary Component ◽  
Eclipsing Binaries ◽  
Evolutionary Status ◽  
Radial Velocity Curve ◽  
Orbital Inclination ◽  
Reliable Determination ◽  
Absolute Dimensions

In order to check the evolutionary status and theoretical models of eclipsing binaries of Algol type, a reliable determination of their absolute dimensions is needed. In this communication, we compare the most commonly used methods to derive absolute parametors in single-lined aclipsing binaries. Let us first assume that the mass function, f(m), is known from the analysis of the radial velocity curve while the relative radii and orbital inclination are derived from the light curve. The determination of absolute parameters is then equivalent to the obtention of the mass ratio, q = m2/m1. The following methods are available to estimate q from observed parameters — over-all errors being estimated for observational uncertainties of the order of 5 % in relative radii and temperatures and 15 % in f(m) —:1.qs: It is assumed that the primary component follows the mass-luminosity relation for main-sequence stars. This procedure provides qs with an uncertainty of about 10 %.2.qsD: It is assumed that the secondary component fills its Roche lobe. Errors of at least 15 to 20 % are expected from this procedure mainly due to its high sensitivity to small variations in the observed value of r2, particularly if r2 > 0.2.Both methods can be used together when f(m) is doubtful, or completely unknown, but errors can not be expected to be better than in case 2.3.qn: It is assumed that the primary component rotates synchronously in a circular orbit. This assumption is difficult to adopt due to the expected transfer of angular momentum through mass transfer and the value of qn is estimated with about 20 to 30 % error.4.qED: It is assumed that the primary component, is well reproduced by standard evolutionary models within the main sequence. Adopting a grid of models for a given chemical composition, an iterative procedure in the log Ti,.–log g plane permits the determination of m1 and thus q. This method is equivalent to (1) but avoids errors due to evolution from the ZAMS to the TAMS, not taken into account in the previous method, and allows to reach a higher accuracy, around 5 %, except for those primary stars located around the TAMS, where the determination of mi is not unique.

scholarly journals Parameters Teff and L/L⊙ for a Group of λ Bootis Candidate Stars and their Evolutionary Status

1993 ◽  
Vol 138 ◽  
pp. 413-417
Author(s):  
M. Gerbaldi ◽  
J. Zorec ◽  
F. Castelli ◽  
R. Faraggiana
Keyword(s):  
Main Sequence ◽  
Flux Distribution ◽  
Evolutionary Status ◽  
Evolutionary Stage ◽  
Bolometric Luminosity ◽  
Colour Excess ◽  
Trigonometric Parallaxes ◽  
Abundance Anomalies ◽  
Definition Of

AbstractThe Teff value, according to the definition of this parameter, is computed with the procedure described; the observations are then compared with the flux distribution from Kurucz’ LTE blanketed models for various values of the metallicity parameter [Z/H].Then we derive the bolometric luminosity L/L⊙ by combining the stellar bolometric flux with the values of the trigonometric parallaxes and of the colour excess found in the literature. These luminosities are then plotted on evolutionary sequences; from the position of some λ Boo stars (ρ Vir and π1 Ori), we argue that their evolutionary stage, if interpreted as that of stars having left the main sequence, is too late to keep the λ Boo abundance anomalies.These same λ Boo stars, plotted on pre-main sequence evolutionary tracks, would indicate increasing λ Boo character when the stars are approaching the main sequence showing the strongest character in λ Boo and 29 Cyg, the two stars nearest the ZAMS.

scholarly journals Cataclysmic Variables: Structure and Evolution

1994 ◽  
Vol 147 ◽  
pp. 420-442
Author(s):  
J.-M. Hameury
Keyword(s):  
Equation Of State ◽  
Internal Structure ◽  
Observational Data ◽  
Main Sequence ◽  
Cataclysmic Variables ◽  
Main Sequence Star

AbstractI discuss the structure and evolution of cataclysmic variables, with a particular emphasis on the influence of the physics used in calculating the internal structure of the secondary. The available observational data is very rich, and can, in principle, be used to constrain the stellar physics. It is found that, in order to explain the lack of systems with periods in the range 2 – 3 hr, it is required that main sequence star become convective for masses below 0.3 M⊙. This has little consequences on the equation of state, but constrains the opacities and the treatment of subphotospheric layers.

scholarly journals Clusters rich in red supergiants

2015 ◽  
Vol 11 (A29B) ◽  
pp. 461-463
Author(s):  
Ignacio Negueruela
Keyword(s):  
Spectral Type ◽  
Milky Way ◽  
Strong Support ◽  
Evolutionary Status ◽  
Evolutionary Stage ◽  
Large Numbers ◽  
Large Populations ◽  
Red Supergiants ◽  
Stellar Properties ◽  
Stellar Masses

AbstractIn the past few years, several clusters containing large numbers of red supergiants have been discovered. These clusters are amongst the most massive young clusters known in the Milky Way, with stellar masses reaching a few 104M⊙. They have provided us, for the first time, with large homogeneous samples of red supergiants of a given age. These large populations make them, despite heavy extinction along their sightlines, powerful laboratories to understand the evolutionary status of red supergiants. While some of the clusters, such as the eponymous RSGC1, are so obscured that their members are only observable in the near-IR, some of them are easily accessible, allowing for an excellent characterisation of cluster and stellar properties. The information gleaned so far from these clusters gives strong support to the idea that late-M type supergiants represent a separate class, characterised by very heavy mass loss. It also shows that the spectral-type distribution of red supergiants in the Milky Way is very strongly peaked towards M1, while suggesting a correlation between spectral type and evolutionary stage.

scholarly journals Statistical Study of the Spin of Algols

1989 ◽  
Vol 107 ◽  
pp. 368-368
Author(s):  
Tan Huisong
Keyword(s):  
Spectral Type ◽  
Statistical Study ◽  
Type A ◽  
Type Systems ◽  
Type B ◽  
Synchronous Rotation

Synchronous rotational velocities have been calculated for 91 Algol-type systems for which the radii of the components and orbital inclinations have been published. New values of V sin i have been measured for some of these systems. The frequency of components rotating near synchronism (F less than 1.5) is found to be higher for unevolved than for evolved systems. For Algols with periods less than 10 days and radii greater than 0.2, synchronous rotation is found to be the rule. There are 50 components of spectral type B and 44 of spectral type A in systems with periods shorter than 10ḍ The shortest period in which synchronism is found is 4 days for the A-type components and 2 days for the B-type.

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