Ultraviolet emission-line ratios of cataclysmic variables

Journal Article · Sat Mar 01 04:00:00 EST 1997 · Astrophysical Journal

DOI:https://doi.org/10.1086/303717· OSTI ID:544374

Mauche, C W ^[1]; Lee, Y P ^[2]; Kallman, T R ^[3]

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1. Lawrence Livermore National Laboratory, L-41, P.O. Box 808, Livermore, California 94550 mauche (at) cygnus.llnl.gov
2. Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
3. Laboratory for High Energy Astrophysics, NASA/Goddard Space Flight Center, Code 665, Greenbelt, Maryland 20771 tim (at) xstar.gsfc.nasa.gov

We present a statistical analysis of the ultraviolet emission lines of cataclysmic variables (CVs) based on {approx}430 ultraviolet spectra of 20 sources extracted from the {ital International Ultraviolet Explorer} Uniform Low Dispersion Archive. These spectra are used to measure the emission-line fluxes of NV, SiIV, CIV, and HeII and to construct diagnostic flux ratio diagrams. We investigate the flux ratio parameter space populated by individual CVs and by various CV subclasses (e.g., AM Her stars, DQ Her stars, dwarf novae, nova-like variables). For most systems, these ratios are clustered within a range of {approximately}1 decade for logSi IV/C IV{approx}{minus}0.5 and logHe II/C IV{approx}{minus}1.0 and {approximately}1.5 decades for logH V/C IV{approx}{minus}0.25. These ratios are compared to photoionization and collisional ionization models to constrain the excitation mechanism and the physical conditions of the line-emitting gas. We find that the collisional models do the poorest job of reproducing the data. The photoionization models reproduce the SiIV/CIV line ratios for some shapes of the ionizing spectrum, but the predicted NV/CIV line ratios are simultaneously too low by typically {approximately}0.5 decades. Worse, for no parameters are any of the models able to reproduce the observed HeII/CIV line ratios; this ratio is far too small in the collisional and scattering models and too large by typically {approximately}0.5 decades in the photoionization models. {copyright} {ital 1997} {ital The American Astronomical Society}

• Research Organization: Lawrence Livermore National Laboratory
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 544374
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 477; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
CARBON
ELEMENT ABUNDANCE
EMISSION SPECTRA
HELIUM
NITROGEN
PHOTOIONIZATION
SILICON
STAR EVOLUTION
ULTRAVIOLET SPECTRA
VARIABLE STARS