The photometric variability of EU Delphini

EU Del (HR 7886, HD 196610, M6 III) is a small-amplitude red variable with a catalog period and visual amplitude of 59.7 day and 1.1 mag, respectively. New photoelectric V observations of EU Del are reported, obtained each season from 1983 to 1988 as part of the AAVSO photoelectric photometry program. Times and magnitudes of maximum and minimum light, determined from these and earlier observations are given. Power spectra and (O-C) diagrams are used to determine a period of 62.832 days, which is remarkably stable over two decades, even though the amplitude is highly variable. The variability in amplitude does not appear to be due to a secondary period. There are, however, long-term variations in mean visual magnitude, with a range of 0.3 mag and a period of about 240 (or 600) d. The range of these observations is from 5.59 to 6.45 in V, giving a total range of 0.86 mag.