scholarly journals Models for symbiotic stars in the light of the data

1982 ◽  
Vol 70 ◽  
pp. 253-267
Author(s):  
Michael Friedjung
Keyword(s):  
Accretion Disks ◽  
Radial Velocities ◽  
Symbiotic Stars ◽  
Single Star ◽  
Cool Component ◽  
Cool Star ◽  
Star Models ◽  
Excess Heating

AbstractDifferent single and binary models of symbiotic stars are examined. Single star models encounter a number of problems, and binary models are probable. There are however difficulties in the interpretation of radial velocities. Accretion disks play a role in some cases, but winds especially from the cool component must be taken into account in realistic models. There is some evidence of excess heating of the outer layers of the cool component. Outbursts may be related to sudden changes in the characteristics of the cool star wind.

scholarly journals Symbiotic Stars

1984 ◽  
Vol 80 ◽  
pp. 101-125
Author(s):  
David A. Allen
Keyword(s):  
Current Knowledge ◽  
Gas Flows ◽  
Symbiotic Stars ◽  
Single Star ◽  
Star Models ◽  
Activity Cycles ◽  
Optical Wavelengths ◽  
Orbital Periods ◽  
Future Work ◽  
Coherent Picture

AbstractI review our current knowledge of symbiotic stars. A great many papers have graced the literature in the fifty years of their study, and many data are available on the spectral variations at optical wavelengths these stars undergo. I do not give extensive references to those data, for previous reviews have done so quite adequately. Rather, I concentrate on the extensive widening of the wavebands within which symbiotic stars have been studied over the past few years, and attempt to synthesise the data into a coherent picture.Symbiotic stars are most readily explained as interacting binaries, though single star models may still be tenable for some systems. They are made much more complex than most other interacting binaries by the variety of accreting stars, and because gas flows may be highly structured. Moreover, their study is more difficult than that of dwarf novae because the orbital periods are long compared to the activity cycles of the accretion phenomena.Our data base has expanded enormously with our present spectral Catholicism. But there remains much valuable work to be done with even simple equipment on small telescopes. I suggest in a final section areas for future work.

Relaxation Oscillations in Red-Giant Envelopes and the Symbiotic Stars

1973 ◽  
Vol 2 (4) ◽  
pp. 198-200 ◽  
Author(s):  
P. R. Wood
Keyword(s):  
Absorption Spectrum ◽  
Light Curves ◽  
Emission Lines ◽  
Symbiotic Star ◽  
Symbiotic Stars ◽  
Relaxation Oscillations ◽  
Cool Component ◽  
Cool Star ◽  
Red Giant ◽  
Eruptive Behaviour

The spectrum of a symbiotic star consists of an M-type absorption spectrum, a B-type shell spectrum and nebula emission lines, the relative contributions of these three components varying with time. The light curves of the symbiotic stars vary with a semi-regular period typically 200-800 days while larger eruptions occur on a timescale of ~ 3.5 years. Some suggestions which have been advanced to explain the combination spectrum, variability and eruptive behaviour of the symbiotic stars are: (a)the symbiotic stars are binaries consisting of a hot and cool component.(b)the symbiotic stars consist of a single hot star surrounded by a large optically thick envelope giving the appearance of a hot continuum with the absorption spectrum of a cool star superimposed on it.(c)the symbiotic stars are single stars surrounded by a shock wave heated chromosphere.Although some of the symbiotic stars are undoubtedly binaries (for example, T Coronae Borealis), observatienal evidence suggests that others may be explained by hypothesis (c) above. The calculations described below provide an explanation of the symbiotic stars in conjunction with hypothesis (c).

scholarly journals Properties Of Cool Stellar Components in S-Type Symbiotic Stars

1988 ◽  
Vol 103 ◽  
pp. 37-41
Author(s):  
O.G. Taranova ◽  
B.P. Yudin
Keyword(s):  
Spectral Type ◽  
Dust Emission ◽  
Roche Lobe ◽  
Red Giants ◽  
Symbiotic Stars ◽  
Cool Component ◽  
Cool Star ◽  
Type D ◽  
Red Giant

In 1975 Webster and Allen (1975) divided all symbiotic stars into two groups-those in which the 1-4μm continuum show only the presence of a cool star (type S),and those in which dust emission dominates (type D). With the exception of some of yellow symbiotic stars, the dust presence in others correlates with the spectral type of their cool components. That is why one can say that S-type symbiotics contain red giants with spectral type earlier than M6-M7.At the IAU Colloq. N 7Q Allen (1982) noted that it is difficult to escape the conclusion that symbiotic stars contain normal cool giants. Nowadays it is certaiu to be correct because the modern observations of S-type symbiotic stars have not yet discovered any specific distinctions between their cool stellar components and normal red giants. At the same time it should be noted that some of these, for example, Z And, CI Cyg may be interacting binaries in which the cool component apparently fields its Roche lobe and unstable accretion of gas from the red giant onto its hot companion leads to the out bursts of the latter (Kenyon and Webbink 1984; Yudin 1987).

scholarly journals The effects of surface fossil magnetic fields on massive star evolution: III. The case of τ Sco

2021 ◽  
Author(s):  
Z Keszthelyi ◽  
G Meynet ◽  
F Martins ◽  
A de Koter ◽  
A David-Uraz
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Massive Star ◽  
Slow Rotation ◽  
Single Star ◽  
Surface Magnetic Field ◽  
Fundamental Parameters ◽  
Chemical Enrichment ◽  
Star Models ◽  
Nitrogen Excess

Abstract τ Sco, a well-studied magnetic B-type star in the Uτer Sco association, has a number of surprising characteristics. It rotates very slowly and shows nitrogen excess. Its surface magnetic field is much more complex than a purely dipolar configuration which is unusual for a magnetic massive star. We employ the cmfgen radiative transfer code to determine the fundamental parameters and surface CNO and helium abundances. Then, we employ mesa and genec stellar evolution models accounting for the effects of surface magnetic fields. To reconcile τ Sco’s properties with single-star models, an increase is necessary in the efficiency of rotational mixing by a factor of 3 to 10 and in the efficiency of magnetic braking by a factor of 10. The spin down could be explained by assuming a magnetic field decay scenario. However, the simultaneous chemical enrichment challenges the single-star scenario. Previous works indeed suggested a stellar merger origin for τ Sco. However, the merger scenario also faces similar challenges as our magnetic single-star models to explain τ Sco’s simultaneous slow rotation and nitrogen excess. In conclusion, the single-star channel seems less likely and versatile to explain these discrepancies, while the merger scenario and other potential binary-evolution channels still require further assessment as to whether they may self-consistently explain the observables of τ Sco.

scholarly journals Carbon Depletion in Case B Mass Transfer Algol-Type Binaries

1992 ◽  
Vol 151 ◽  
pp. 355-358
Author(s):  
Tae S. Yoon ◽  
Kent Honeycutt
Keyword(s):  
Mass Transfer ◽  
Mass Loss ◽  
Similar Type ◽  
Single Star ◽  
Star Models ◽  
Promising Tool ◽  
Carbon Abundance ◽  
Processed Material ◽  
C And N ◽  
Larger Sample

The surface carbon abundances of Algol secondaries are known to be low compared to field stars of similar type. The C and N anomalies of these G and K subgiants are undoubtedly due to the exposure of CN cycle processed material as mass transfer removes the outer layers of the star. Therefore the carbon abundance is a promising tool for helping fix the evolutionary state of Algols, particularly the amount of mass which has been lost from the secondary. We report here the carbon abundance of 12 Algol secondaries as deduced from the g-band in spectra obtained during photometric totality. We compare the abundances to those from models of single stars of appropriate age and mass. The values of log ∊(C) for this sample fall 0.25–0.75 dex below field G and K giants, and 1.25–1.75 dex above “stripped” single star models. This larger sample supports the conclusions of Parthasarthy et al. regarding mixing and mass loss, which they deduced from a smaller sample of carbon abundances.

scholarly journals Slow and Rapid Changes of the Radial Velocities in the Symbiotic Binary CH Cygni

1988 ◽  
Vol 103 ◽  
pp. 223-224
Author(s):  
A. Skopal
Keyword(s):  
Light Curve ◽  
Orbital Motion ◽  
Radial Velocities ◽  
Cool Component ◽  
Absorption Component ◽  
Middle Position ◽  
Rapid Changes ◽  
Red Wing

In the period 1982–1986, new 98 radial velocities (RVs) were determined (at the figures denoted by □). All spectrograms were obtained at the Toruń Observatory. RVs were measured at the Skalnaté Pleso Observatory. The main results are summarized in the figures 1-3. The phase is determined from the middle position of the hot component eclipse (JD 2 446 272) and from the minima difference observed in U light curve (5700d) (Mikolajewski et al., 1987).Slow changes of the RVs of the absorption components of ionized metals reflect the orbital motion of the hot component only between the phases 0.7 and 0.0. The rapid changes are observed mainly between the phases 0.8 and 0.9. They are created by combination of the emission red wing with the absorption component (Skopal et al., 1987). RVs of the cool component are in antiphase (Tomov and Luud, 1984).

scholarly journals Accretion Disks in Symbiotic Stars

1988 ◽  
Vol 103 ◽  
pp. 137-148
Author(s):  
Wolfgang J. Duschl
Keyword(s):  
Accretion Disks ◽  
Symbiotic Stars

AbstractWe give an overview over the theory of geometrically thin α-accretion disks: further we introduce the two different proposed mechanisms that can cause outbursts of accretion disks: and finally we compare the results of these models applied to symbiotic stars (=SS).

scholarly journals Details of the Classification of Symbiotic Stars: The Case of the Symbiotic Nova AG Peg

2016 ◽  
Vol 25 (3) ◽  
Author(s):  
A. A. Tatarnikova ◽  
M. A. Burlak ◽  
D. V. Popolitova ◽  
T. N. Tarasova ◽  
A. M. Tatarnikov
Keyword(s):  
Component Model ◽  
Symbiotic Stars ◽  
Cool Component ◽  
Photometric Observations

AbstractWe analyze archival and modern spectroscopic and photometric observations of the oldest known symbiotic nova AG Peg. Its new outburst (which began in 2015 June) differs greatly from the first one (which occurred in the mid-1850s). Fast photometric evolution of the new outburst is similar to that of Z And-type outbursts. However, the SED of AG Peg during the 2015 outburst, as well as during the quiescence, can be fitted by a standard three-component model (cool component + hot component + nebula), which is not common for an Z And-type outburst.

Velocity Variations in Beta Centauri

1968 ◽  
Vol 1 (3) ◽  
pp. 82-83 ◽  
Author(s):  
R.R. Shobbrook ◽  
J.W. Robertson
Keyword(s):  
Double Star ◽  
Radial Velocities ◽  
Spectral Lines ◽  
Single Star ◽  
Spectroscopic Evidence ◽  
Stellar Interferometer ◽  
Velocity Variations

This programme was undertaken because the preliminary observations of Beta Centauri with the Narrabri stellar interferometer (Hanbury Brown, Davis, Allen, and Rome) show that the correlation received is not consistent with that expected from a single star. The Lick Catalogue of Radial Velocities states that β Cen is a Bl II star. The Narrabri results are consistent with several models; in particular, it may be a double star with components of similar brightness, or it may have a very luminous, extended atmosphere or shell surrounding it. The latter possibility is perhaps unlikely on the spectroscopic evidence, as there are neither emission nor sharp absorption components in the spectral lines.

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