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Photometry of the nearby irregular galaxy, NGC 6822

Citation

Kayser, Susan Elizabeth (1966) Photometry of the nearby irregular galaxy, NGC 6822. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-09232002-112325

Abstract

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NGC 6822 is a member of the Local Group, type Im, coordinates [...]. The main body has a diameter of 3.6 c kpc and a mass (from radio rotation curves) of [...]. Mass-to-light ratio is 6.1 x c[superscript -1]. The color-magnitude diagram is plotted from measures on photographic plates calibrated by a photoelectric sequence. Photometry is complete to 19.5 (M[subscript v] = -5). Major features are bright blue supergiants, the brightest star having M [subscript v] = -9, and a sequence of very red supergiants one magnitude fainter than the blue, many of which show variations of over 1000 days. A significant number of stars lie in the Hertzsprung gap. Two-color photometry shows there is intervening reddening of [...]. A luminosity function is calculated.

Thirty-two variable stars are discussed, of which thirteen are Cepheids, two are red semi-regulars, one may be eclipsing, and the others are irregular. The period-luminosity relations for the Cepheids are < V > = 23.35 - 2. 97 log P and < B > = 23.91 - 2.61 log P. These lead to a true distance modulus (m-M) = 23.75 [plus or minus] 0.10. Secular changes in period are less than 0.001% in 40 years. The eleven variables with 1.6 < (B-V)[...] < 2. 1 have cycles 200-2500 days.

Comparisons with evolutionary models indicate that the stars observed have masses of 9 to 63 [...].

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:irregular galaxy; Local Group; NGC 6822
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Astronomy
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Arp, Halton C. (advisor)
  • Greenstein, Jesse L. (advisor)
Thesis Committee:
  • Unknown, Unknown
Defense Date:13 December 1965
Record Number:CaltechETD:etd-09232002-112325
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-09232002-112325
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3708
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:24 Sep 2002
Last Modified:26 Dec 2012 03:02

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