Steady State Accretion Disk Research Articles

Emission lines from the accretion disks of cataclysmic variables

The heating and radiative cooling of steady-state viscous accretion disks in close binary systems are studied. It is shown that the temperatures of the outer regions of disks do not fall below approx.6000 K over a wide range of conditions. Depending upon the mass accretion rate, the outer parts of disks in cataclysmic variables are optically thin in the optical continuum, and radiate a line spectrum which is superposed upon the thermal continuum emitted by the inner disk. The Balmer lines and Ca II H and K emission which are observed in dwarf novae at quiescence can be explained by the emission from the optically thin outer regions of the disks; however, the HeI and H II lines must be produced by a different mechanism. This theory predicts that the peak fluxes of the Balmer lines in cataclysmic variables should fall on a Planck curve of temperature approx.7000 K.

SS Cygni - The accretion disk in eruption and at minimum light

view Abstract Citations (84) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS SS CYG : the accretion disk in eruption and at minimum light. Kiplinger, A. L. Abstract Absolute spectrophotometric observations of the dwarf nova SS Cygni have been obtained at maximum light, during the subsequent decline, and at minimum light. In order to provide a critical test of accretion disk theory, a model for a steady-state α-model accretion disk has been constructed which utilizes a grid of stellar energy distributions to synthesize the disk flux. Physical parameters for the accretion disk at maximum light are set by estimates of the intrinsic luminosity of the system that result from a desynthesis of a composite minimum light energy distribution. At maximum light, agreements between observational and theoretical continuum slopes and the Balmer jump are remarkably good. The model fails, however, during the eruption decline and at minimum light. It appears that the physical character of an accretion disk at minimum light must radically differ from the disk observed at maximum light. Publication: The Astrophysical Journal Pub Date: December 1979 DOI: 10.1086/157584 Bibcode: 1979ApJ...234..997K Keywords: Astronomical Spectroscopy; Binary Stars; Dwarf Stars; Stellar Luminosity; Stellar Mass Accretion; Balmer Series; Disks (Shapes); Spectral Energy Distribution; Spectrum Analysis; Stellar Models; Stellar Rotation; Astrophysics full text sources ADS | data products SIMBAD (2)

Z Cam at Standstill and in Eruption

Absolute spectrophotometric observations of the prototype dwarf nova Z Cam have been obtained at standstill and during the course of an eruption. Optical continuum slopes during the final stages of the rise to maximum appear steeper (bluer) than those observed during decline and at standstill. The Balmer jump is observed to be in shallow absorption during decline and in deeper absorption during the rise to maximum and at standstill. A composite energy distribution constructed for Z Cam at standstill is compared with fluxes derived from steady state (a-raodel) accretion disk models which utilize a grid of stellar energy distributions to synthesize the disk fluxes. The most reasonable accretion disk fit to the observations at standstill suggests a mass transfer rate of ~3 × 1017 g sec-1. The steady state model does not fit the observations of Z Cam during decline, nor does any arbitrary linear combination of stellar energy distributions. The results suggest that the accretion disk of decline is time dependent and exhibits an emission character which differs from that seen at standstill.

Theory and Observations of Accretion Disc Spectra

Theoretical continua (3000 ≲ λ (Å) ≲ 20000), UBV colours and Balmer absorption line profiles (Hα – Hδ) have been computed for the optically thick parts of steady-state accretion discs around white dwarfs as a function of mass flow rate, mass of white dwarf and inclination angle. The uncertainties due to disc z-structure and outer radius and viscosity are considered.The theoretical results for continua and UBV colours are compared with the theoretical results of Schwarzenberg-Czerny and Rózyczka (1977) and Herter et al. (1979) and with results obtained using black bodies instead of stellar atmospheres (e.g. Lynden-Bell 1969). Where models can be directly compared the quantitative agreement is good.

Theoretical Continuum and Line Spectra of Accretion Discs

Abstract.Theoretical continuum and Balmer line spectra have been computed for steady-state accretion discs. Models can be found which are in good general agreement with the observed colours and hydrogen absorption line profiles of dwarf novae in outburst and UX UMa-type objects.