A method for the study of accretion disk emission in cataclysmic variables (original) (raw)
Related papers
A Method for the Study of Accretion Disk Emission in Cataclysmic Variables. I. The Model
Astrophysical Journal, 2011
We have developed a spectrum synthesis method for modeling the UV emission from the accretion disk from cataclysmic variables (CVs). The disk is separated into concentric rings, with an internal structure from the Wade & Hubeny disk-atmosphere models. For each ring, a wind atmosphere is calculated in the co-moving frame with a vertical velocity structure obtained from a solution of the Euler equation. Using simple assumptions, regarding rotation and the wind streamlines, these 1D models are combined into a single 2.5D model for which we compute synthetic spectra. We find that the resulting line and continuum behavior as a function of the orbital inclination is consistent with the observations, and verify that the accretion rate affects the wind temperature, leading to corresponding trends in the intensity of UV lines. In general, we also find that the primary mass has a strong effect on the P-Cygni absorption profiles, the synthetic emission line profiles are strongly sensitive to the wind temperature structure, and an increase in the mass loss rate enhances the resonance line intensities. Synthetic spectra were compared with UV data for two high orbital inclination nova-like CVs - RW Tri and V347 Pup. We needed to include disk regions with arbitrary enhanced mass loss to reproduce reasonably well widths and line profiles. This fact and a lack of flux in some high ionization lines may be the signature of the presence of density enhanced regions in the wind, or alternatively, may result from inadequacies in some of our simplifying assumptions.
A study of accretion disk wind emission
Accretion disk wind has been the most accepted scenario to explain the strong emission lines and the P Cyg profiles detected in the ultraviolet spectra of non-magnetic cataclysmic variables (CV's). Due to the main characteristics of line profiles, it is commonly accepted that those winds are radiatively driven. Here, we present an alternative method to study the disk-wind that takes into account the structure of whole system (disk+wind), as well as the interface between the disk photosphere and wind. We calculated a set of 1D NLTE atmosphere wind models with a consistent velocity wind profile, and map them into a 2D model including a 3D velocity field. The synthetic spectrum is calculated by exactly solving the radiative transfer equation throughout the inner disk, interface region and wind, taking into account the Doppler shifts for each step. We found a modeled line profile behavior according with the observed one. We also found dependences between line profiles and disk parameters. When tested with UV data for two nova-like systems, the models shows a good agreement. However, we found a lack a flux for high ionization lines. It is possible that it is due to the influence of the inner disk radiation on the outer wind regions.
The Impact of Accretion Disk Winds on the Optical Spectra of Cataclysmic Variables
2015
Many high-state non-magnetic cataclysmic variables (CVs) exhibit blue-shifted absorption or P-Cygni profiles associated with ultraviolet (UV) resonance lines. These features imply the existence of powerful accretion disk winds in CVs. Here, we use our Monte Carlo ionization and radiative transfer code to investigate whether disk wind models that produce realistic UV line profiles are also likely to generate observationally significant recombination line and continuum emission in the optical waveband. We also test whether outflows may be responsible for the single-peaked emission line profiles often seen in high-state CVs and for the weakness of the Balmer absorption edge (relative to simple models of optically thick accretion disks). We find that a standard disk wind model that is successful in reproducing the UV spectra of CVs also leaves a noticeable imprint on the optical spectrum, particularly for systems viewed at high inclination. The strongest optical wind-formed recombinatio...
The impact of accretion disc winds on the optical spectra of cataclysmic variables
Monthly Notices of the Royal Astronomical Society
Many high-state non-magnetic cataclysmic variables (CVs) exhibit blueshifted absorption or P-Cygni profiles associated with ultraviolet (UV) resonance lines. These features imply the existence of powerful accretion disc winds in CVs. Here, we use our Monte Carlo ionization and radiative transfer code to investigate whether disc wind models that produce realistic UV line profiles are also likely to generate observationally significant recombination line and continuum emission in the optical waveband. We also test whether outflows may be responsible for the single-peaked emission line profiles often seen in high-state CVs and for the weakness of the Balmer absorption edge (relative to simple models of optically thick accretion discs). We find that a standard disc wind model that is successful in reproducing the UV spectra of CVs also leaves a noticeable imprint on the optical spectrum, particularly for systems viewed at high inclination. The strongest optical wind-formed recombination lines are H α and He II λ4686. We demonstrate that a higher density outflow model produces all the expected H and He lines and produces a recombination continuum that can fill in the Balmer jump at high inclinations. This model displays reasonable verisimilitude with the optical spectrum of RW Trianguli. No single-peaked emission is seen, although we observe a narrowing of the double-peaked emission lines from the base of the wind. Finally, we show that even denser models can produce a single-peaked H α line. On the basis of our results, we suggest that winds can modify, and perhaps even dominate, the line and continuum emission from CVs.
A Statistical Study of Accretion Disk Model Spectra for Cataclysmic Variables
Astronomical Journal, 2007
We have performed a statistical test of the currently used accretion disk models for cataclysmic variables (CVs) using a set of 33 CVs with steady disks (10 old novae and 23 nova-like systems). The mass transfer rate (Ṁ ) for each system was also calculated. Ultraviolet (UV ) data were fitted by model spectra using a multiparametric optimization method, aiming to constrain theṀ values. It was verified that these accretion disk models fail to fit both color and flux simultaneously, as previously noted when composite stellar atmosphere models were fitted to the UV spectra of CVs by Wade. By applying such models to a sample of novae and nova-like CVs, we confirm that the limb-darkening effect must be taken into account when estimating mass transfer rates, especially for high-inclination systems. Important fitting degeneracies of the basic disk parameters are analyzed. Our simulations suggest that to reproduce the observations a revision of the temperature profile, at least in the innermost parts of the disk, seems to be required, and possibly the vertical distribution of the viscosity should be revised. In addition, an optically thin layer or an extended disk component should be considered. This component may be physically represented by a disk wind and/or a chromosphere. A physical description of the emission-line profiles may help to break the degeneracies that appear when only the continuum is analyzed. The average value ofṀ found for nova-like systems is 9:3;10Aˋ9MyrAˋ1,while9:3 ; 10 À9 M yr À1 , while 9:3;10Aˋ9MyrAˋ1,while1:3 ; 10 À8 M yr À1 is found for old classical novae. No clear evidence is found for either the presence or absence of a correlation betweenṀ and the orbital period. Such correlation analysis was performed for high accretion rate systems (15 nova-like systems and 10 old novae), but we were not able to find a well-defined correlation as found by Patterson. By measuring the equivalent width of the emission lines (C iv k1550 and He ii k1640) we found a lack of systems with lowṀ and strong UV emission lines. A correlation between the equivalent width of such lines and the orbital inclination (i) was also confirmed.
The Extreme Ultraviolet Emission Lines of Some Cataclysmic Variables at Outburst
Turkish Journal of Physics, 2007
Using spectral technique, analyses of some astrophysical data from the EUVE satellite in the Extreme Ultraviolet region on accretion disk of some cataclysmic variable were carried out. A number of strong emission lines in 14 CVs were discovered. Most CVs follow a similar trend in the number of ionized elements present in their spectrum while some have very few or no ionized elements in their spectrum. The AM Herculis star, which has the weakest magnetic field of all seven magnetic CVs studied, contain no ionized elements in its EUVE spectroscopy. However, for the rest of the CVs, there is sufficient evidence to conclude that the accretion disks of CVs are highly ionized. This implies also that the accretion disks of other astrophysical objects could be equally highly ionized. This result is in agreement with the suggestion that the most promising candidate for providing the angular momentum transport mechanism during the outburst is magneto hydrodynamics turbulence.
Monthly Notices of the Royal Astronomical Society, 2017
New time-resolved optical spectroscopic echelle observations of the nova-like cataclysmic variable RW Sextantis were obtained, with the aim of studying the properties of emission features in the system. The profile of the H α emission line can be clearly divided into two ('narrow' and 'wide') components. Similar emission profiles are observed in another novalike system, 1RXS J064434.5+33445, for which we also reanalysed the spectral data and redetermined the system parameters. The source of the 'narrow', low-velocity component is the irradiated face of the secondary star. We disentangled and removed the 'narrow' component from the H α profile to study the origin and structure of the region emitting the wide component. We found that the 'wide' component is not related to the white dwarf or the wind from the central part of the accretion disc, but is emanated from the outer side of the disc. Inspection of literature on similar systems indicates that this feature is common for some other long-period nova-like variables. We propose that the source of the 'wide' component is an extended, lowvelocity region in the outskirts of the opposite side of the accretion disc, with respect to the collision point of the accretion stream and the disc.