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White dwarfs

Citation

Shipman, Henry Longfellow (1971) White dwarfs. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-05132008-145722

Abstract

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The aim of this thesis is to use model-atmosphere techniques and intermediate-band photoelectric scans to determine the properties of white dwarfs. Model atmospheres have been calculated with [...] for solar composition and [...] for helium-rich (Y=1) models. Photoelectric scans of some 37 white dwarfs are the observational basis of the thesis.

The essential results for the program stars are that the DA stars have a mean radius of .013 [...]. With one or two exceptions, the program stars are on the upper sequence of the white dwarfs. The median mass is 0.58 [...]. One of the DA,F stars in the program L 870-2, has a radius of .04 [...]. The DA stars cover a wide range of effective temperature; the DB stars, with the exception of HZ 29, have 12,000°[...]18,000°K. The DA stars contain very little helium ([...]0.8% by number); and the DB stars contain very little metals. It is possible to interpret the spectrum of the one DC star in the program (L 1363-3) as a cooled-off DB star, since the helium lines fade out at [...].

The spectrum of Sirius B is analyzed; the hydrogen line profiles, combined with the mass of 1.02[...] (van den Bos 1960) and the visual magnitude of 8.29 (Lindenblad 1970) yield an effective temperature of 32,000°K and a surface gravity of 8.65, corresponding to a radius of 0.0078 [...]. These values are consistent with the measured gravitational redshift of +88 km/sec.

Using the program stars, I then define a U-V versus [...] relation for DA stars and for the DB and DC stars. Using this relation, and the [...] as measured by Graham (1969), I compute masses and radii for a much larger sample of white dwarfs than the program stars those with known distances. The median radius of these stars, which include quite a few on the lower sequence is 0.0095 [...]. Using these data, I find that the atmospherically derived masses of white dwarfs are in reasonable agreement with the mass-radius relation for degenerate stars and with the gravitational redshifts measured by Greenstein and Trimble (1967).

The effective temperatures of all the stars in the lists of Eggen and Greenstein were computed for the purpose of testing the convection-accretion theory of Strittmatter and Wickramasinghe (1971) which purports to account for the formation of DB stars. The results here contradict their prediction that there should be a shortage of DA stars with 15,000° [...] 18,000°K. I propose a modification of their theory which explains the existence of both the DA and the DB stars in the temperature ranges in which they are observed. This modification also explains the DC stars, and suggests a possible explanation for the 4670 stars.

The wavelength dependence of the circular polarization of Grw+70°8247 for 3000[...] 8000 [...] is explained in the context of radiative transfer theory.

Item Type:Thesis (Dissertation (Ph.D.))
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Astronomy
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Oke, J. Beverley
Thesis Committee:
  • Unknown, Unknown
Defense Date:17 May 1971
Record Number:CaltechETD:etd-05132008-145722
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-05132008-145722
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:1781
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:16 May 2008
Last Modified:26 Dec 2012 02:41

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