AAVSO: American Association of Variable Star Observers

Sine Waves in the Light Curves of RS Cancri (Abstract)

Volume 30 number 1 (2002)

Raymond R. Thompson


(Abstract only) The light curve of a semiregular variable star is often erratic, sometimes showing considerable variability and other times showing virtually none. This behavior may be due to the interaction of multiple periods. During the past three decades, the light curve of the SRc variable RS Cancri has appeared to be sinusoidal on at least two, and possibly more, occasions. Photoelectric (V) data on RS Cnc obtained since 1983 by the author or other observers as part of the AAVSO Photoelectric Photometry Committee’s observing program (Landis 1997) were examined for sinusoidal behavior. Also examined were visual observations of RS Cnc from the AAVSO International Database for 1961– 1982 (Mattei 1997). The interval December 1993–May 1994 was seen in the author’s photoelectric data to be somewhat sinusoidal (Figure 1), as was the 1989–1990 interval in the AAVSO’s photoelectric photometry archive (Figure 2). A third sinusoidal interval, less clearly defined, was seen in the AAVSO visual 1982–1983 data (Figure 3) and reinforced by photoelectric data from one observer, while an additional possible interval was seen in the visual data for 1969 (Figure 4). Figure 1. The author’s photoelectric light curve of RS Cnc from December 12, 1993, to May 28, 1994. The shape is an almost perfect sinusoid, although it is not quite complete. Figure 2. Light curve of RS Cnc from AAVSO archival photoelectric data. Observations run from November 19, 1989, to June 12, 1990. The curve defines a period of 143 days. Figure 3. AAVSO visual observations from August 1982 to June 1983 show a closer approach to a sinusoid with scatter nearer 0.4 magnitude. The shape of the curve was partially confirmed by 8 observations from a single PEP observer (see text). Figure 4. AAVSO visual observations of RS Cnc from January to July 1969. The scatter occupies almost a whole magnitude, but a sinusoid can be drawn through the middle. Its validity, however, is doubtful.