scholarly journals Evolution of an Accretion Disk in the Symbiotic Binary CI Cyg

1996 ◽  
Vol 158 ◽  
pp. 335-338
Author(s):  
Joanna Mikołajewska
Keyword(s):  
Boundary Layer ◽  
Accretion Disk ◽  
Main Sequence ◽  
Activity Cycle ◽  
Thin Disk ◽  
Photometric Data ◽  
Disk Accretion ◽  
Main Sequence Stars ◽  
Full Activity ◽  
Classical Boundary

AbstractWe have combined IUE spectra with optical spectroscopic and photometric data collected over a few orbits of the symbiotic binary CI Cyg to follow the evolution of a disk and boundary layer during a full activity cycle. Our results indicate an extended optically thin disk during quiescent periods, which evolves into an optically thick state in an eruption; a classical boundary layer at the inner edge of the disk ionizes a surrounding H II region in quiescence, and this emission fades during the rise to visual maximum in outburst. This evolution of Ṁ rivals that observed in classical CVs and pre-main sequence stars, so symbiotic systems like CI Cyg represent another opportunity to study the physics of disk accretion.

scholarly journals Boundary Layers in Cataclysmic Variables and Pre-Main-Sequence Stars

1997 ◽  
Vol 163 ◽  
pp. 230-240
Author(s):  
Robert Popham
Keyword(s):  
Boundary Layer ◽  
Accretion Disk ◽  
Main Sequence ◽  
Layer Structure ◽  
Cataclysmic Variables ◽  
Vertical Direction ◽  
Main Sequence Stars ◽  
Region I ◽  
Boundary Layer Region ◽  
Layer Region

AbstractThe boundary layer region, where the accretion disk meets the accreting star, is crucial to understanding the spectra and evolution of accretion disk systems. Recent numerical modeling of the flow of the accreting material and radiation in the boundary layer has provided a better understanding of this region. I will describe the “standard” boundary layer structure predicted by the models for the case where the boundary layer is optically thick and geometrically thin in the vertical direction. Large variations in this structure can occur when the boundary layer becomes optically thin or geometrically thick. Boundary layer models have been applied to cataclysmic variables and accreting pre-main-sequence stars. I will discuss the boundary layer spectra predicted by the models and how well they agree with observations of these objects. The boundary layer also controls the transfer of angular momentum and energy between the disk and star. This can have important effects upon pre-main-sequence stellar evolution.

Hydrodynamic ejection of intrinsically bipolar flows

1986 ◽  
Vol 64 (4) ◽  
pp. 514-519 ◽  
Author(s):  
Michael V. Torbett
Keyword(s):  
Boundary Layer ◽  
Main Sequence ◽  
Cataclysmic Variables ◽  
Hydrostatic Equilibrium ◽  
General Mechanism ◽  
Density Structure ◽  
Disk Accretion ◽  
Main Sequence Stars ◽  
Massive Black Holes ◽  
Vertical Density

A general mechanism is presented for generating pressure-driven winds, which are intrinsically bipolar, from objects undergoing disk accretion. The energy liberated in a boundary-layer shock as disk matter impacts the central object makes the vertical density structure of the boundary layer go out of hydrostatic equilibrium by large factors. The resultant expansion in the direction of the density gradient, i.e., perpendicular to the disk, converts accretion energy into P dV work and is shown to be capable of ejecting a fraction β ~ 10−2–10−1 of the accreted mass from the system. The ejection of these flows, accelerated within [Formula: see text], can account for the jets observed from pre-main-sequence stars and cataclysmic variables. Unless an analogous boundary-layer shock develops during accretion onto massive black holes, however, this mechanism does not seem to be applicable to jets from galaxies.

scholarly journals Circumstellar Disks and Star Formation

1992 ◽  
Vol 9 ◽  
pp. 377-380
Author(s):  
L. Hartmann ◽  
M. Gomez ◽  
S.J. Kenyon
Keyword(s):  
Star Formation ◽  
Spectral Region ◽  
Main Sequence ◽  
Circumstellar Disks ◽  
Central Star ◽  
Disk Accretion ◽  
Main Sequence Stars ◽  
Excess Emission ◽  
Infrared Spectral ◽  
The Masses

Results from the IRAS satellite showed that many pre-main sequence stars exhibited unexpectedly large fluxes in the infrared spectral region. Several studies have shown that the simplest and most satisfying explanation of this excess emission is that it arises in optically-thick, dusty, circumstellar disks (Rucinski 1985; Adams, Lada, and Shu 1987, 1988; Kenyon and Hartmann 1987; Bertout, Basri, and Bouvier 1988; Basri and Bertout 1989). The masses of these disks are estimated to range between 10-3M⊙ to 1M⊙ (Beckwith et al. 1990; Adams et al. 1990), large enough that disk accretion may have a significant effect on the evolution of the central star. Indeed, Mercer-Smith, Cameron, and Epstein (1984) suggested that stars are essentially completely accreted from disks, rather than formed from quasi-spherical accretion (Stabler 1983, 1988).

scholarly journals The Scatter of Metallicities of Stars in the Solar Neighbourhood

1996 ◽  
Vol 169 ◽  
pp. 431-432 ◽  
Author(s):  
B. Fuchs ◽  
C. Dettbarn ◽  
R. Wielen
Keyword(s):  
Main Sequence ◽  
Thin Disk ◽  
Thick Disk ◽  
Solar Neighbourhood ◽  
Data Sets ◽  
Main Sequence Stars ◽  
The Third ◽  
Nearby Stars ◽  
Velocity Dispersions

It is well known that the velocity dispersions of the stars in the solar neighbourhood increase with their ages (Wielen 1977). In Fig.1 we show |W| weighted velocity dispersions (cf. Wielen 1977) of the stars in the Third Catalog of Nearby Stars (Gliese and Jahreiß 1994). Open symbols indicate main sequence stars and crosses indicate McCormick stars, a kinematically unbiased subset of the CNS3, respectively, whereas the filled symbols are the Edvardsson et al. (1993) data. Stars older than 14 Gyr are not shown because they are probably thick disk stars (Freeman 1991). We have assumed a maximum age of the old thin disk stars of 12 Gyr as suggested by the Edvardsson et al. data. As can be seen from Fig.1 both data sets fit ideally together. The solid line indicates a σ ∝ τ1/2 law.

scholarly journals The rotational evolution of young low mass stars

2007 ◽  
Vol 3 (S243) ◽  
pp. 231-240 ◽  
Author(s):  
Jérôme Bouvier
Keyword(s):  
Angular Momentum ◽  
Accretion Disk ◽  
Main Sequence ◽  
Young Stars ◽  
Sequence Evolution ◽  
Main Sequence Stars ◽  
Low Mass Stars ◽  
Rotational Evolution ◽  
Low Mass

AbstractStar-disk interaction is thought to drive the angular momentum evolution of young stars. In this review, I present the latest results obtained on the rotational properties of low mass and very low mass pre-main sequence stars. I discuss the evidence for extremely efficient angular momentum removal over the first few Myr of pre-main sequence evolution and describe recent results that support an accretion-driven braking mechanism. Angular momentum evolution models are presented and their implication for accretion disk lifetimes discussed.

scholarly journals Microlensing evidence for super-Eddington disk accretion in quasars

2012 ◽  
Vol 8 (S290) ◽  
pp. 307-308
Author(s):  
Nikolai I. Shakura ◽  
Pavel Abolmasov
Keyword(s):  
Accretion Disk ◽  
Stellar Population ◽  
Thin Disk ◽  
Disk Accretion ◽  
Disk Model ◽  
Disk Structure ◽  
Gravitational Microlensing ◽  
Observational Manifestation

AbstractGravitational microlensing by the stellar population of lensing galaxies provides an important opportunity to spatially resolve the accretion disk structure in strongly lensed quasars. Some of the objects (like Einstein's cross) are reasonably consistent with the predictions of the standard accretion disk model. In other cases, the size of the emitting region is larger than predicted by the standard thin disk theory and practically independent on wavelength. This may be interpreted as an observational manifestation of an optically-thick scattering envelope possibly related to super-Eddington accretion with outflows.

scholarly journals A test for radial mixing using local star samples

2012 ◽  
Vol 10 (H16) ◽  
pp. 357-357
Author(s):  
Jincheng Yu ◽  
Jerry Sellwood ◽  
Carlton Pryor ◽  
Li Chen ◽  
Jinliang Hou
Keyword(s):  
Angular Momentum ◽  
Main Sequence ◽  
Milky Way ◽  
Galactic Center ◽  
Thin Disk ◽  
Main Sequence Stars ◽  
Radial Gradient ◽  
Stellar Temperature ◽  
Effective Temperatures ◽  
Constant Gradient

AbstractWe use samples of local main-sequence stars to show that the radial gradient of [Fe/H] in the thin disk of the Milky Way decreases with mean effective stellar temperature. We use the angular momentum of each star about the Galactic center to eliminate the effects of epicyclic motion, which would otherwise blur the estimated gradients. We use the effective temperatures as a proxy for mean age, and conclude that the decreasing gradient is consistent with the predictions of radial mixing due to transient spiral patterns. We find some evidence that the trend of decreasing gradient with increasing mean age breaks to a constant gradient for samples of stars whose main-sequence life-times exceed the likely age of the thin disk.

scholarly journals Local Variations of the Velocity Ellipsoid

1996 ◽  
Vol 169 ◽  
pp. 525-526
Author(s):  
M. Moreno ◽  
J. Torra ◽  
E. Oblak
Keyword(s):  
Main Sequence ◽  
Photometric Data ◽  
The Sun ◽  
Main Sequence Stars ◽  
Nearby Stars ◽  
Input Catalogue

We have analyzed the distribution of residual velocities of nearby stars (within 200 pc of the Sun) looking for space variations on the velocity ellipsoid. We used a sample of 1071 main sequence stars of spectral types B, A and F selected from the Hipparcos Input Catalogue [7] with uvbyHβ photometric data. Ages have been calculated following [1]. Six subsamples with 8.07 ≤ log(age) ≤ 9.45 have been considered.

scholarly journals The evolution of C and O abundances in stellar populations

2013 ◽  
Vol 9 (S298) ◽  
pp. 65-70 ◽  
Author(s):  
Poul E. Nissen ◽  
William J. Schuster
Keyword(s):  
High Resolution ◽  
Time Scale ◽  
Main Sequence ◽  
Stellar Populations ◽  
Thin Disk ◽  
Main Sequence Stars ◽  
Chemical Enrichment ◽  
Halo Stars ◽  
New Information ◽  
Atomic Lines

AbstractCarbon and oxygen abundances in F and G main-sequence stars ranging in metallicity from [Fe/H] = −1.6 to +0.5 are determined from a non-LTE analysis of C i and O i atomic lines in high-resolution spectra. Both C and O are good tracers of stellar populations; distinct trends of [C/Fe] and [O/Fe] as a function of [Fe/H] are found for high- and low-alpha halo stars and for thick- and thin-disk stars. These trends and that of [C/O] provide new information on the nucleosynthesis sites of carbon and the time-scale for the chemical enrichment of the various Galactic components.

scholarly journals Far-ultraviolet intensities of Orion stars

1970 ◽  
Vol 36 ◽  
pp. 100-108
Author(s):  
George R. Carruthers
Keyword(s):  
Wavelength Range ◽  
Main Sequence ◽  
Photometric Data ◽  
Orion Nebula ◽  
Main Sequence Stars ◽  
Spectral Class ◽  
Color Excess ◽  
Far Ultraviolet ◽  
Spectral Intensities ◽  
Good Agreement

Photometric data in the 1050–1180 Å and 1230–1350 Å wavelength ranges, and electronographic spectra in the 1000–1600 Å wavelength range, were obtained in an Aerobee rocket flight on January 30, 1969. The spectral intensities derived from these data for main-sequence stars are in good agreement with the model atmospheres of Morton and co-workers. Giant and supergiant stars, however, appear to be up to one magnitude weaker, at 1115 Å, than main-sequence stars of the same spectral class.The correction for interstellar reddening appears to be not inconsistent with a 1/λ extrapolation of earlier determinations of Smith (1967) and Stecher (1965), except in the case of θ Ori, in which the predicted color excess appears to be much too great, confirming the existence of a peculiar reddening law in the Orion Nebula region.

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