AAVSO: Photoelectric Photometry Newsletter Volume 19, No. 2

Margarita Marinova and I have just completed an analysis of AAVSO and Hipparcos photometry of this star, to be published in the JAAVSO later this year. Most of the recent AAVSO photometry of this star comes from Mr. R.W. Jones, in South Africa. This M4III red giant has a period of 78 days, some irregularity and possibly some long-term variability - all typical of pulsating red giants. The Hipparcos photometry, however, tells a slightly different story: there are variations on a much shorter time scale - hours or days. One explanation is that the red giant has a close blue companion, perhaps even like a symbiotic star. This possibility is supported by the fact that the colors of AG Cet are unusually blue. The investigation continues .....

RU Cam

Percy and Hale have recently published a paper on the interesting behaviour of this star (1998 PASP 110, 1428-30). The abstract is as follows: "We have studied the period change in the peculiar Population II Cepheid RU Cam, which abruptly decreased in amplitude in 1965-66. The (O-C) diagram prior to 1965-66 can best be explained as the superposition of small, random, cycle-to-cycle changes in period, plus a constant linear decrease whose timescale (31,000 years) is consistent with evolutionary predictions. The (O-C) diagram after 1965-66 can best be explained as the superposition of much larger random, cycle-to-cycle changes (which mask the evolutionary changes), plus wavelike changes in (O-C) on a timescale of 10-20 periods. These - and the variations in the amplitude of the star that occur on the same timescale - may be due to multiperiodicity."

The variations in the amplitude, mentioned in the last sentence, were determined from the AAVSO photoelectric photometry of this star.

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