COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2836 Konkoly Observatory Budapest 19 December 1985 HU ISSN 0374 - 0676 A FURTHER UPDATE ON THE PERIOD OF V566 OPHIUCHI V566 Ophiuchi (BD+ 5d3547, HD 163 611) is an A-type W Ursae Majoris system with a period that remained essentially constant at 0.40964091 day from 1952 to 1966 (Binnendijk, 1959; Bookmyer, 1969). Beginning about Julian Date 2440000 (1968) the O-C values begin to show a steep positive trend indicating an increase in period (Maddox and Bookmyer, 1981, hereafter MB). Since that time observations suggest that the period may be continuing to change at a slow rate. Table I shows the results of solutions for the period using data from different Julian date ranges. Column six in this table lists the period increase (in seconds) relative to the pre-1968 period published by Bookmyer (1969). The general trend of values in Table I suggests a small, continuous period change since 1968. However, attempts to fit a quadratic in E to the times of minimum (Dawson and Narayanaswamy, 1977; MB; Kennedy, 1984) have generated only very small second-order terms. Also, Dawson and Narayanaswamy (1977), fitting all data from 1952 to 1975, concluded that two linear fits, one to observations made before 1968 and one to observations made after 1968, were better than a single quadratic fit to the entire data set. Table II lists nine newly published times of minima for: V566 Oph. Six of these were obtained with the 40 centimeter Boller and Chivens reflector at the Joseph R. Grundy Observatory of Franklin and Marshall College using a thermoelectrically cooled 1P21 tube and DC electronics. The observation on J.D. 2445928 was made with the same telescope using a thermoelectrically cooled RCA C31034A-02 photomultiplier tube and pulse counting electronics. The observations on Julian dates 2445925 and 2445943 were made with the 40 centimeter Boller and Chivens reflector at The Mount Laguna Observatory of San Diego State University using a dry ice cooled 1P21 tube and a charge integration photometer. The differential accuracy of these observations was better than 0.01 magnitude. In all cases, the observations were made through V filters close to the UBV system. Photometry was taken differentially against BD+ 4d3558. No corrections for differential extinction were made as the comparison star lies within Table I Previous Solutions Year Source Data Range Epoch Period dP(sec) Rem. 1959 Bi 2434179-2436010 2435245.5440 0.40964101 0.009 1969 Bo 2442579-2442590 2436744.4200 0.40964091 0.000 1976 Bm 2440047-2442877 2441835.8617 0.40964387 0.26 1976 Bm 2440047-2442203 2441835.8618 0.40964399 0.26 1977 DN 2440000-2442590 2440418.4931 0.40964431 0.29 1978 Sc 2441119-2442987 2441835.8617 0.409645 0.35 1981 MB 2442600-2443677 2443281.5034 0.40964660 0.49 1981 MB 2440000-2443677 2441863.7179 0.40964506 * 1981 MB 2440000-2443677 2441863.7188 0.40964504 0.36 1984 Ke 2440400-2445197 2441119.8016 0.40964579 0.42 :% 1985 SD 2440000-2445943 2440047.3478 0.40964600 0.44 1985 SD 2440000-2445943 2440047.3542 0.40964392 Bi=Binnendijk 1959, Bm=Bookmyer 1976, Bo=Bookmyer 1969, DN=Dawson, Narayanaswamy 1977, Ke=Kennedy 1984, MB=Maddox and Bookmyer 1981, Sc=Scarfe and Barlow 1978, SD=Seeds and Dawson (present paper). * Quadratic term: 5.6x1010 ** Quadratic term:"negligible" *** Quadratic term: 1.3x10^-10 Table II Photoelectric Epochs of Minimum Light, V566 Oph JD Hel. Min O-C Source JD Hel. Min O-C Source 2443662.4770 I +0.0032 PG 2445144.5759 I +0.0029 SD 4406.8073 I +0.0067 Sc 5169.9749 I +0.0038 Ke 4448.7922 II +0.0029 Sc 5170.9988 II +0.0036 Ke 4750.4901 I -0.0035 MS 5172.6355 II +0.0017 SD 4751.5162 II -0.0015 MS 5175.7085 I +0.0024 SD 4780.8122 I +0.0047 Sc 5183.4926 I +0.0032 Po 4781.8357 II +0.0042 Sc 5196.6001 I +0.0020 SD 4795.3461 II -0.0037 Ni 5197.0117 I +0.0040 Ke 4796.3698 I -0.0041 Ni 5207.6598 I +0.0013 SD 4797.3946 II -0.0034 Ni 5512.8463 I +0.0015 Sc 4798.4191 I -0.0030 Ni 5513.8700 II +0.0011 Sc 4799.4434 II -0.0029 Ni 5554.6307 .I +0.0020 SD 4825.2510 II -0.0030 MS 5925.7694 I +0.0014 SD 4826.2739 I -0.0042 MS 5928.6376 I +0.0021 SD 4827.2992 II -0.0030 MS 5943.7952 I +0.0028 SD Ke=Kennedy 1984 MS=Mahdy and Soliman 1982,Ni=Niarchos 1983, PG=Pohl et al.1981,Po=Pohl et al.1983,Sc=Scarfe et al.1984, SD=Seeds and Dawson (present paper), [FIGURE 1] Figure 1. Observed minus computed heliocentric times of minimum for V566 Oph versus Julian Date. The computed times of minimum are based upon the linear elements of Bookmyer (1969). Curve MB: quadratic solution of Maddox and Bookmyer (1981). Curve DN: linear solution of Dawson and Narayanaswamy (1977). Straight line and curve labeled SD: linear and quadratic solution based upon the present data. [FIGURE 2] Figure 2. O-C residuals for the authors' linear and quadratic fits to the data of Table II. The s.e. is +-0.0034 day for the linear fit and +-0.0029 day for the quadratic fit. 10 arc-minutes of the variable and is of nearly identical spectral type. Times of minimum were found using the tracing paper method or by bisection of times of equal brightness on declining and rising light. In addition to our new observations, Table II includes twenty-one recent times of minimum collected from the literature. All of these times are derived from photoelectric observations using V filters. The O-C values in the table were computed from the linear elements derived in this paper. The total data base for this analysis includes the times of minimum listed in Table II of this paper plus those since Julian Date 2440000 as listed in Table II of MB. Three minima in their tabulation (Julian Dates 2442225.4170, 2442230.3329, 2442621.3892) were not included in our analysis because they fell beyond three standard deviations from any reasonable solution. The omission of these three data points has little effect on the final solutions. We applied first and second order least squares solutions to the data described above. The results of these solutions are shown in Figure 1, which is a continuation of Figure 1 of MB, in which the (O-C)s of observations and solutions are calculated using the linear solution given by Bookmyer (1969). The curve labeled "MB" represents their second-order solution, and the straight line labeled "DN" represents the linear solution of Dawson and Narayanaswamy (1977). Our linear solution to these data yields the following ephemeris: J.D. Hel.Min. I = 2440047.3478 + 0.40964600d E +- 7 +- 9 The errors given are standard errors. The scatter of points about this solution is +-0.0034 day. Our linear solution is the straight line labeled "SD" in Figure 1. A quadratic solution to the same data produces the following ephemeris: J.D. Hel.Min. I = 2440047.3542 + 0.40964392d*E + 1.32x10^-10x E^2 +- 3 +- 9 +-11 The point scatter about this solution is +-0.0029 day. The quadratic solution is represented in Figure 1 by the curve labeled "SD". The linear and quadratic solutions are further compared in Figure 2. The quadratic solution is slightly better than the linear fit. This suggests that the period could be changing gradually by about 2.6x10^-10 day/cycle. These data do not permit a conclusive identification of this continuing period change, nor do they permit analysis by higher order solutions. All data in these analyses have been equally weighted (except for omitted points which have effective weights of zero); Without a detailed knowledge of the observers' methods of observation and reduction, further tests of significance do not seem warranted. Future observations of V 566 Oph are desirable to confirm a continuing change in the period and to detect additional sudden changes in period such as that which evidently occurred in 1968. This material is based upon work supported by the National Science Foundation under Grant No. PRM-8214360. MICHAEL A. SEEDS and DENNIS W. DAWSON* Department of Mathematics and Astronomy Franklin and Marshall College, P.O. Box 3003 Lancaster, Pennsylvania 17604-3003, U.S.A. References: Binnendijk, L., 1959, A.J., 64, 65. [BIBCODE 1959AJ.....64...65B ] Bookmyer, B.B., 1969, A.J., 74, 1197. 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Stars, No. 2545. * Now at San Diego State University, Department of Astronomy San Diego, CA 92182-0334