The light curve of comet 1942g.

Abstract

Comet I942 (Whipple) showed more remarkable fluctuations in brightness than any comet heretofore studied. The light curve is based on 146 observations reduced to the author's "system f" which is the total brightness of the comet observed by him with a -21-inch finder. The author's observations are based on 708 estimates and are discussed in Contr butions from the Perk ns Observatory Xo. 19, 1943. Other observations used for the light curve are: Ashbrook ;1 Martinoff, Bakharev, Lange ;2 Miss Farnsworth and Miss Pillans (unpublished); and Van Biesbroeck (unpublished). The light curve from January 5 to July 3, 1943 shows a periodic variation in light with a period of about 30 days and the semi-amplitude diminishing from o.6 mag. in January to 0.2 mag. in June. Such a diminution of the amplitude was previously observed in Comets 1902 III and 1912 11.1 However, in the present case there was a rather sudden increase in brightness on about February 21. The comet then began decreasing in brightness but faster than before. The result is that it is impossible to represent the brightness of the comet by any one formula. Before February 10 and after April 15 the brightness can be expressed as follows: H= 6.6o 5logA $5logr periodicterm. Between these dates, however, the following formula represents the observed brightness: H = 4.00 Y 5logA Y ~logr Y periodicterm. In spite of the change in brightness by 1.40 mag. and the accelerated decrease in brightness, the length of the period of intrinsic variation and even the phase did not change at all. Sudden changes in the light curve have been found previously for Comets 1858 VI, 1862 III, and 1884 I. Comet 1942f is unique in the combination of a sudden change with a distinctly periodic variation preserved throughout its period of observation of half a year. It is also remarkable in the closeness of the times of the nearest approach to the earth, January 28, and perihelion passage, February 6, which places the theoretical maximum of brightness between these two dates, about a month before the actually observed maximum. There is also evidence of minor fluctuations in brightness of a semi- periodic character. I.fop. Astr. 51, 362, 1943. 2.Astr. Circ. Acad. Sci. U.S.S.R. Nos. 12 and `3, `943. 3.Contr. Perkins Obs. No. ifi, 1942. Perkins Observatory, Delaware, Ohio.