A statistical study of accretion disk model spectra for cataclysmic variables

Raúl E. Puebla, Marcos P. Diaz, Ivan - Hubeny

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

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 (M) for each system was also calculated. Ultraviolet (UV) data were fitted by model spectra using a multiparametric optimization method, aiming to constrain the M 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 of M found for nova-like systems is ∼9.3 × 10-9 M yr-1, while ∼1.3 × 10-8 M yr-1 is found for old classical novae. No clear evidence is found for either the presence or absence of a correlation between M 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 λ1550 and He II λ1640) we found a lack of systems with low M and strong UV emission lines. A correlation between the equivalent width of such lines and the orbital inclination (i) was also confirmed.

Original languageEnglish (US)
Pages (from-to)1923-1933
Number of pages11
JournalAstronomical Journal
Volume134
Issue number5
DOIs
StatePublished - Nov 2007

Fingerprint

cataclysmic variables
novae
accretion disks
accretion
mass transfer
inclination
limb darkening
orbitals
stellar atmospheres
statistical tests
vertical distribution
ultraviolet emission
chromosphere
ultraviolet spectra
temperature profile
temperature profiles
limb
estimating
viscosity
continuums

Keywords

  • Accretion, accretion disks
  • Novae, cataclysmic variables
  • Ultraviolet: general

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

A statistical study of accretion disk model spectra for cataclysmic variables. / Puebla, Raúl E.; Diaz, Marcos P.; Hubeny, Ivan -.

In: Astronomical Journal, Vol. 134, No. 5, 11.2007, p. 1923-1933.

Research output: Contribution to journalArticle

Puebla, Raúl E. ; Diaz, Marcos P. ; Hubeny, Ivan -. / A statistical study of accretion disk model spectra for cataclysmic variables. In: Astronomical Journal. 2007 ; Vol. 134, No. 5. pp. 1923-1933.
@article{e81cdf8630ff440096c6d3fbb3fba0b6,
title = "A statistical study of accretion disk model spectra for cataclysmic variables",
abstract = "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 (M) for each system was also calculated. Ultraviolet (UV) data were fitted by model spectra using a multiparametric optimization method, aiming to constrain the M 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 of M found for nova-like systems is ∼9.3 × 10-9 M⊙ yr-1, while ∼1.3 × 10-8 M⊙ yr-1 is found for old classical novae. No clear evidence is found for either the presence or absence of a correlation between M 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 λ1550 and He II λ1640) we found a lack of systems with low M and strong UV emission lines. A correlation between the equivalent width of such lines and the orbital inclination (i) was also confirmed.",
keywords = "Accretion, accretion disks, Novae, cataclysmic variables, Ultraviolet: general",
author = "Puebla, {Ra{\'u}l E.} and Diaz, {Marcos P.} and Hubeny, {Ivan -}",
year = "2007",
month = "11",
doi = "10.1086/522112",
language = "English (US)",
volume = "134",
pages = "1923--1933",
journal = "Astronomical Journal",
issn = "0004-6256",
publisher = "IOP Publishing Ltd.",
number = "5",

}

TY - JOUR

T1 - A statistical study of accretion disk model spectra for cataclysmic variables

AU - Puebla, Raúl E.

AU - Diaz, Marcos P.

AU - Hubeny, Ivan -

PY - 2007/11

Y1 - 2007/11

N2 - 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 (M) for each system was also calculated. Ultraviolet (UV) data were fitted by model spectra using a multiparametric optimization method, aiming to constrain the M 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 of M found for nova-like systems is ∼9.3 × 10-9 M⊙ yr-1, while ∼1.3 × 10-8 M⊙ yr-1 is found for old classical novae. No clear evidence is found for either the presence or absence of a correlation between M 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 λ1550 and He II λ1640) we found a lack of systems with low M and strong UV emission lines. A correlation between the equivalent width of such lines and the orbital inclination (i) was also confirmed.

AB - 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 (M) for each system was also calculated. Ultraviolet (UV) data were fitted by model spectra using a multiparametric optimization method, aiming to constrain the M 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 of M found for nova-like systems is ∼9.3 × 10-9 M⊙ yr-1, while ∼1.3 × 10-8 M⊙ yr-1 is found for old classical novae. No clear evidence is found for either the presence or absence of a correlation between M 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 λ1550 and He II λ1640) we found a lack of systems with low M and strong UV emission lines. A correlation between the equivalent width of such lines and the orbital inclination (i) was also confirmed.

KW - Accretion, accretion disks

KW - Novae, cataclysmic variables

KW - Ultraviolet: general

UR - http://www.scopus.com/inward/record.url?scp=36048973223&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=36048973223&partnerID=8YFLogxK

U2 - 10.1086/522112

DO - 10.1086/522112

M3 - Article

AN - SCOPUS:36048973223

VL - 134

SP - 1923

EP - 1933

JO - Astronomical Journal

JF - Astronomical Journal

SN - 0004-6256

IS - 5

ER -