COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2086 Konkoly Observatory Budapest 1982 February 12 HU ISSN 0374-0676 PHOTOELECTRIC TIMES OF MINIMA OF ECLIPSING BINARIES The following times of minimum light have been determined from V- filter observation made during the 1981 observing season with the 40-cm f/18 Cassegrain reflector operated by the Department of Physics and Astronomy at the University of Montana. The observing procedure has been described previously (Margrave et al. 1978). As has been done previously, a least-squares parabolic fit to the observations was used to find each time in Table I, in which are listed the Heliocentric Julian Date (minus 2,440,000) for each minimum, its epoch number E, the O-C value, and N, the number of observations (each being the average of three 10-second integrations) used in the determination. As a check, the chord-bisection method was also used on the above eclipses, and the average difference between the results from the parabolic fit and the chord bisection methods was 0.0004d, which gives +-0.0002d as a reasonable estimate of the uncertainty in the final results. The ephemerides used to calculate the above O-C values are given in Table II. The residuals for RZ Cas continue to become more negative, extending a trend exhibited during the previous observing season (Margrave, 1981). The trend suggests that a period decrease of about 0.1 seconds occurred between October 1979 and August 1980. Table I. Heliocentric Times of Primary Minimum ----------------------------------------------------- Star Hel.JD-2,440,000 E O-C N ----------------------------------------------------- KO Aql 4785.8991 1012 +0.0030d 48 44 i Boo 4813.7845 20325 +0.0021 29 RZ Cas 4813.8884 12498 -0.0026 32 4855.7220 12533 -0.0026 27 TV Cas 4859.8426 1801 +0.0019 40 4879.7816 1812 +0.0024 55 TW Cas 4827.8954 1974 -0.0035 45 DO Cas 4859.8888 15969 -0.0014 37 XX Cep 4839.8022 1412 +0.0078 40 4860.8373 1421 +0.0071 23 SW Lac 4854.8834 22706 -0.1414 40 4856.8064 22712 -0.1427 27 4860.8188* 22724 -0.1394 25 4914.8574 22893 -0.1435 27 AT Peg 4826.7553 3856 +0.0055 47 ------------------------------------------------------ *Secondary minimum Table II. Ephemerides for Program Stars ------------------------------------------------------ Star Epoch (24...) Period Source ------------------------------------------------------ KO Aql 41,887.4724 2.864055d IBVS 1869 44 i Boo 39,370.4222 0.2678160 SAC 53 RZ Cas 29,875.6902 1.1952473 Herczeg and Friboes-Conde TV Cas 41,595.3582 1.8125944 IBVS 1869 TW Cas 42,008.3873 1.4283240 IBVS 1869 DO Cas 33,926.4573 0.6846661 SAC 53 XX Cep 41,539.4971 2.337321 SAC 53 SW Lac 37,572.5723 0.32072811 Bookmyer (1965) AT Peg 40,407.4370 1.14610886 IBVS 1930 -5.5772x10^-9E ------------------------------------------------------ The recent residuals for TV Cas exhibit a continuing positive trend, a result which has also been noted by deLandtsheer (1981), who has suggested that the period of TV Cas may have increased slightly relative to that given by Margrave (1980). In the case of SW Lac the residuals have continued to grow more negative but at a diminishing rate. This result would seem to support the suggestion by Faulkner and Bookmyer (1978) that the period of this system has increased. It is also possible that a continuous period decrease lasting ten years or so has been replaced by a phase of continuous period increase, but further observations are required to substantiate this hypothesis. THOMAS E. MARGRAVE Blue Mountain Observatory University of Montana Missoula, Montana 59812 USA References: Bookmyer, B. B. 1965, Astr. J., 70, 415. [BIBCODE 1965AJ.....70..415B ] Faulkner, D. R. and Bookmyer, B. B. 1978, IBVS No. 1503. Herczeg, T. and Friboes-Conde, H. 1974, Astr. and Ap., 30, 259. [BIBCODE 1974A&A....30..259H ] deLandtsheer, A. C. 1981, IBVS No. 1985. Margrave, T. E. et al. 1978, IBVS No. 1478. Margrave, T. E. 1980, IBVS No. 1869. Margrave, T. E. 1981, IBVS No. 1930. Rudnicki, K. 1982, Supplemento ad Annuario Cracoviense No. 53, Krakow.