Photometry of the nearby irregular galaxy, NGC 6822

irregular galaxy;Local Group;NGC 6822

Kayser, Susan Elizabeth ; Arp, Halton C. (advisor)

University:California Institute of Technology

Department:Physics, Mathematics and Astronomy

关键词: irregular galaxy;    Local Group;    NGC 6822;   

Others  :  https://thesis.library.caltech.edu/3708/1/Kayser_se_1966.pdf

美国|英语

来源: Caltech THESIS

【 摘 要 】

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.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 [...].