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Spectroscopy and Spectrophotometry of Cataclysmic Variable Stars


Wade, Richard Alan (1981) Spectroscopy and Spectrophotometry of Cataclysmic Variable Stars. Dissertation (Ph.D.), California Institute of Technology.


Distances and luminosities of individual cataclysmic variable stars (as opposed to statistical properties of the group as a whole) can best be acquired by studying the secondary stars of these short-period binary systems. Since the secondary stars are of late spectral type, observations in the near infrared are especially useful.

Spectrophotometry of the dwarf nova U Geminorum has been carried out from 0.3µ to 1µ using the Hale 5m telescope. The energy distribution can be interpreted as the sum of fluxes from an M4.5 or M5 star and a source giving a flat continuum. The M companion, referred to as U Gem B, is less dense than a main-sequence star of the same color index. The absolute spectrophotometry allows a distance modulus of 4.4 ± 0.8 mag to be derived for U Geminorum. The absolute visual magnitude of the quiescent system is about Mv = 10.3.

The Na I infrared doublet in the spectrum of U Geminorum has been observed at high resolution around the orbit. The velocity semi-amplitude of U Gem B is 283 ± 15 km s-1, and spectroscopic conjunction occurs before mid-eclipse of the bright spot. These results, combined with previous analysis of the emission-line velocity variations, have been used to deduce M1 = 1.01 ± 0.25 and M2 = 0.36 ± 0.10 (solar units) for the masses of the component stars. U Gem B is too cool and probably too large, compared to a zero-age main-sequence star of the same mass.

A spectrophotometric survey of about 30 cataclysmic variable stars has been carried out from 0.3µ to 1µ. Old novae, nova-like variables, and erupting dwarf novae are characterized by spectral energy distributions which are flat (fν = constant) or rising toward shorter wavelengths. These objects have Balmer jumps in absorption or else no Balmer jump at all. No trace of a red stellar spectrum is evident in these stars, except for the nova-like system RW Tri. Quiescent dwarf novae show emission Balmer jumps and emission lines of the Balmer series and He I. Some quiescent dwarf novae show no trace of the spectrum of the secondary star, while others show the secondary star with various degrees of observability.

These spectral energy distributions are analyzed to determine the spectral types of the secondary stars and the fraction of light contributed by the primary stars and their accretion disks. The analysis makes use of flux-ratio diagrams to eliminate those spectral decompositions which result in physically implausible energy distributions for the accretion disks. The Balmer jump is especially useful in eliminating unphysical distributions. Refined estimates of spectral type and fractional light contribution are made in favorable cases, using an interactive computer program. It is argued that the secondary stars in cataclysmic variable systems should be expected to deviate from the normal main-sequence relations among mass, radius, spectral type, and luminosity. The results of the analysis support previous workers' estimates of the absolute visual magnitudes of cataclysmic variable stars; the spectral types assigned to the secondary stars of individual systems on the basis of this work are generally later than those assigned by previous workers.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Astronomy
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Astronomy
Thesis Availability:Restricted to Caltech community only
Research Advisor(s):
  • Oke, J. Beverley
Thesis Committee:
  • Oke, J. Beverly (chair)
  • Greenstein, Jesse L.
  • Blandford, Roger D.
  • Young, Peter J.
Defense Date:23 October 1980
Funding AgencyGrant Number
Record Number:CaltechETD:etd-09082008-093158
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3388
Deposited By: Imported from ETD-db
Deposited On:12 Sep 2008
Last Modified:09 Feb 2018 00:17

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