Multivariate Characterization of Hydrogen Balmer Emission in Cataclysmic Variables
Gordon E. Sarty A B D and Kinwah Wu B CA Departments of Psychology and Physics & Engineering Physics, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5A5, Canada
B Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Surrey RH5 6NT, UK
C TIARA, Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan
D Corresponding author. E-mail: gordon.sarty@usask.ca
Publications of the Astronomical Society of Australia 23(3) 106-118 https://doi.org/10.1071/AS06011
Submitted: 11 April 2006 Accepted: 14 August 2006 Published: 24 November 2006
Abstract
The ratios of hydrogen Balmer emission line intensities in cataclysmic variables are signatures of the physical processes that produce them. To quantify those signatures relative to classifications of cataclysmic variable types, we applied the multivariate statistical analysis methods of principal components analysis and discriminant function analysis to the spectroscopic emission data set of Williams (1983). The two analysis methods reveal two different sources of variation in the ratios of the emission lines. The source of variation seen in the principal components analysis was shown to be correlated with the binary orbital period. The source of variation seen in the discriminant function analysis was shown to be correlated with the equivalent width of the Hβ line. Comparison of the data scatterplot with scatterplots of theoretical models shows that Balmer line emission from T CrB systems is consistent with the photoionization of a surrounding nebula. Otherwise, models that we considered do not reproduce the wide range of Balmer decrements, including ‘inverted’ decrements, seen in the data.
Keywords: accretion: accretion discs
Acknowledgments
G.E.S. is supported by a discovery grant from the Natural Sciences and Engineering Research Council of Canada (NSERC). G.E.S. also thanks the MSSL for their hospitality during his visits in 2005 and 2006. Conversations with Laszlo Kiss about T CrB spectra are gratefully acknowledged. K.W. thanks TIARA for their hospitality during his visit there and for support through a Visiting Fellowship. TIARA is operated under Academia Sinica and the National Science Council Excellence Projects programs in Taiwan administrated through grant number NSC 94-2752-M-007-001.
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1 It should be noted that interstellar reddening is a possible source of variance for all groups, but this should not affect the difference in variances either between dwarf novae and other CVs or between dwarf novae and magnetic CVs.
