Photometry of the nearby irregular galaxy, NGC 6822

Creators: Kayser, Susan E.

Abstract

NGC 6822 is a dwarf irregular in the Local Group at α=19^h 42^m, δ= —14° 53'.1 (1950). The color-magnitude diagram is plotted from measures on photographic plates calibrated by a photoelectric sequence. Photometry is complete to V=19^h.5 (M_ν=—5). Major features are bright blue supergiants, the brightest star having M_ν=—9, and a sequence of very red supergiants only one-half magnitude fainter than the blue, many of which have light variations lasting over 1000 days. A significant number of stars lie in the Hertzsprung gap. Two-color photometry shows there is intervening reddening of 0^m.27. A luminosity function is calculated. Thirty-two variable stars are discussed, of which 13 are Cepheids, two are red semiregulars, one may be eclipsing, and the others are irregular. The 11 variables with 1^m.6< (B-V)_0<2^m.1 have cycles of 200-2500 days. The period-luminosity relations for the Cepheids are〈V〉= 23.35—2.97 log P and〈B〉= 23.80—2.61 log P. These lead to a true distance modulus (m—M) = 23^m.75±0^m.15. Secular changes in period are less than 0.001 % in 40 yr.

Additional Information

© 1967 American Astronomical Society. Provided by the NASA Astrophysics Data System. (Received 18 July 1966). This work is adapted from the thesis submitted to the California Institute of Technology, Department of Astronomy, in partial fulfillment of the requirements for the degree of Ph.D. Part of this work was performed under the auspices of the U.S. Atomic Energy Commission. It is a pleasure to thank Dr. Halton C. Arp for his assistance and guidance, and the staff of the Mount Wilson and Palomar Observatories for the facilities they placed at my disposal. This paper exists in complete form as Lawrence Radiation Laboratory report UCRL-14801-T, including a listing of the photographic plates used (Table 2), the colors and magnitudes (V> 19.5) of all nonvariable stars in the main body of the nebula (Table 3), finding charts for the stars in Table 3 (Plates II-VII), and a tabulation of the variable star magnitudes from each photographic plate (Table 10). Copies of the report are available from the author and from the laboratory.

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Published - 1967AJ_____72__134K.pdf

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