COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2014 Konkoly Observatory Budapest 1981 September 7 HU ISSN 0374-0676 PERIOD VARIABILITY AND NEW EPHEMERIS OF RU LEPORIS The eclipsing variable star RU Lep (CoD -24d3651, CPD -24d 1206, discovery No. 637.1935) was pointed out by Hoffmeister (1935) as a variable star with Algol-type light curve. The first ephemeris based on visual estimates of brightness was published by Kaho (1938). The epoch of his ephemeris is further considered as zero epoch. Kaho gave the ranges of the eclipse D = 7.7, d = 2.4 h. Later he (Kaho 1950) published revised ephemeris based on photographic observations. One of the authors (ZK) included RU Lep in the list of potentially interesting systems and on 7/8 Jan. 1978 the star was measured photoelectrically with the photometer P7 (Burnet, Rufener 1979) attached to the 40cm Swiss reflector at ESO La Silla, Chile. All measurements were made in the Geneva seven-colour photometric system. The eclipse was not sufficiently covered by observations as it occurred earlier than expected according to the ephemeris. In addition the descending branch of the minimum was influenced by a slight instability in atmospheric transparency and thus the accuracy of the time of minimum is lower than would be under normal conditions. Photometric quality of the night did not satisfy criteria for the normal photometry in the Geneva system but the observations were made differentially and thus the accuracy is reasonable. Standard stars were observed both at the beginning and at the end of the night. The star HD 41490 (CoD -25d2811) served as comparison star. The measurements were done in the sequence CVCVC.....CVC, C for comparison, V for variable. Both comparison and variable stars were observed again on 15/16 Jan. 1978, a night of normal photometry when RU Lep was outside the minimum phase (0.81). In this way the measurements were tied-in to the Geneva standard photometric system. For details of reduction methods see Rufener (1964), for the properties of the Geneva photometric system see Golay (1980). The new ephemeris based on measurements in filter V of the Geneva system, which is in fact the same as V in the UBV system (Rufener, Maeder 1973), is given in Table I, together with Kaho's two ephemerides. The period of the new ephemeris is calculated from the epoch 3352 (this paper) and from Kaho's epoch 1064 thus representing the mean period between 1947 and 1978. If we use the epoch 0 and 3352 we obtain for the period the value 4.459608. Using this value for P the minimum at epoch 1064 should have occurred at 33313.086 or 24 minutes earlier. Table I E T min P Ref. ------------------------------------------------------- 0 28568.063 + 4.45907 E 1937 Kaho v 1064 33313.103 + 4.45963 E 1947 Kaho p 3352 43516.670 + 4.459601E 1978 Kviz pe ------------------------------------------------------- [FIGURE 1] We may assume that the period was increasing after 1937 and is now decreasing. Even if we take the error of the time of minimum as 0.004 day the cyclic behaviour of the length of the period remains. Further photoelectric timing of the minimum and a careful search for secondary minimum is thus very desirable. Individual V magnitudes vs. heliocentric Julian day are graphically represented in Fig. 1. This graph shows clearly the discrepancy with Kaho's conclusion about the flat bottom of the minimum. Kaho's original observations were not available to the authors and thus it is difficult to assess the reason for this discrepancy. It may be the low accuracy of the earlier visual and photographic estimates or the real change of the shape of the light curve. The measured magnitudes with heliocentric Julian days are given in Table II. Table III gives the time of minimum for individual filters of the Geneva system calculated according to the Kwee and Van Woerden (1956) version of the Hertzsprung method. The mean errors are given in the last row under the respective digit. Table II HJD U B1 B B2 V V1 G ---------------------------------------------------------------------------- 1 43516.6014 12.457 12.041 11.145 12.618 11.766 12.505 12.840 2 43516.6302 12.753 12.429 11.431 12.915 12.009 12.809 13.130 3 43516.6442 12.775 12.467 11.495 12.963 12.081 12.805 13.311 4 43516.6571 12.934 12.511 11.591 12.983 12.099 12.896 13.181 5 43515.6720 12.941 12.508 11.576 13.003 12.121 12.838 13.181 6 43516.6948 12.906 12.471 11.522 12.910 12.057 12.787 13.158 7 43516.7172 12.736 12.252 11.335 12.734 11.945 12.647 13.025 8 43516.7394 12.501 12.037 11.131 12.578 11.793 12.522 12.876 9 43516.7615 12.400 11.847 10.957 12.408 11.647 12.355 12.742 10 43516.7841 12.245 11.639 10.746 12.211 11.479 12.204 12.587 11 43516.8234 12.006 11.329 10.449 11.948 11.231 11.943 12.382 ---------------------------------------------------------------------------- Table III --------------------------------------------- U B1 B B2 V V1 G --------------------------------------------- .674 .667 .669 .665 .670 .669 668 2 1 1 2 1 3 4 --------------------------------------------- The change of colour indices and multicolour indices (d,Delta,g,X,Y,Z) during the eclipse is quite remarkable. According to the preliminary results and on the assumption that the eclipse is not far from the totality the components should be close to AV and FIII. As the minimum is not total, the interpretation of colour changes based on one minimum only is not possible and a full light curve is necessary for the solution of the system. We wish to acknowledge the assistance of Dr. M. Burnet during the observations. One of us (Z.K.) thanks the director of Geneva Observatory for supporting the stay at La Silla. Z. KVIZ, F. RUFENER Observatoire de Geneve CH-1290 Sauverny References: Burnet, M., Rufener, F. 1979, Astron. Astrophys. 74, 54. [BIBCODE 1979A&A....74...54B ] Golay, M. 1980, Vistas in Astronomy 24, 141. [BIBCODE 1980VA.....24..141G ] Hoffmeister, C. 1935, Astron. Nachr. 258, 39. [BIBCODE 1936AN....258...39H ] Kaho, S. 1938, Tokyo Astron. Bull. No. 284. Kaho, S. 1950, Tokyo Astron. Bull., II. Ser. No. 30. Kwee, K., van Woerden, H. 1956, BAN 12, 327. [BIBCODE 1956BAN....12..327K ] Rufener, F. 1964, Publ. Obs. Geneve, serie A, 66. Rufener, F., Maeder, A. 1973, in Symp. IAU No. 54: Problems of Calibration of Absolute Magnitudes and Temperatures of Stars. B. Hauck and B. Westerlund /ed/ p. 298, Reidel Publ. Co. [BIBCODE 1973IAUS...54..298R ]