COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3698 Konkoly Observatory Budapest 2 March 1992 HU ISSN 0374 - 0676 The Eclipsinig Binary TX UMa - a Period Change Again Abstract. On the basis of the published visual times of minima and our UBV photometric observations of the eclipsing binary TX UMa, another change of its period is presented. The new photometric ephemeris was computed. 1. Introduction Recently we have been involved in the detailed analysis of the spectroscopic observational material of the eclipsing binary TX UMa obtained at the D.A.O. in 1969-70 and at the Ondrejov Observatory in 1972-80, (Hric et al., 1990; Grygar et al., 1991; Komzik et al., submitted to the Astrophys. Space Sci.). The spectroscopic detection of the interacting processes in this system showed the need for a further photoelectric monitoring. The photoelectric observations in the UBV system were taken at the Skalnate Pleso and Stara Lesna Observatories of the Astronomical Institute of the Slovak Academy of Sciences with the identical 60 cm Cassegrain reflecting telescopes equipped with single-channel pulse-counting photometers and photomultipliers. Observed data were recorded and processed using PC IBM-compatible computers. 2. Observations and Conclusions The first observed minimum (JD 2 448 303) shows the (O-C) value approximately +2 hours (computed using the photometric ephemeris by Oh and Chen, 1984). The last investigation of TX UMa's (O-C) diagram was carried out by the above mentioned authors. The new times of minima (visual, taken from the literature including Cracow database, as well as our photoelectric) can be found in Table I. These new data together with those published by Oh and Chen were used to construct the new (O-C) diagram shown in Fig. 1. The times of our photoelectric minima were determined using parabola fitting method, separately for each colour, and their errors were estimated TABLE I. Observed times of primary minima of TX UMa JDhel Error Epoch Type Observer Source Note +2440000 (days) 6122.372 -807. VI Hollis, A. Isles, J. 6171.395 -791. VI Duncan, H. Isles, J. * 6566.535 -662. VI Cluyse, L. Isles, J. * 6872.887 -562. VI Vystavel, R. Silhan, J. 6908.505 -552. VI Csipes, J. Silhan, J. * 6803.5208 -552. VI Renz, W. BAV Rundbr.37 7151.6452 -471. VI Renz, W. BAV Rundbr.37 7531.503 -347. VI Renz, W. Hubscher, J. et al 7565.200 -336,. VI Enskonatus, P. MVS 12, Nr.2 7626.477 -316. VI Enskonatus. P. MVS 12, Nr.3 * 7966.996 -205. VI Pietz, J. Hubscher, J. et al. 8303.46340 0.00005 -95. PE U Gliviak, M., this paper Komzik, R. 8303.46341 0.00008 -95. PE B Gliviak, M., this paper Komzik, R. 8303.46352 0.00007 -95. PE V Gliviak, this paper Komzik, R. 8306.5254 0.0002 -94. PE U Hric, L., this paper Komzik, R. 8306.5258 0.0002 -94. PE B Hric, L. this paper Komzik, R. 8306.52515 0.00012 -94. PE V Hric, L., this paper Komzik, R. 8306.5272 0.0004 -94. PE U Gliviak, M., this paper _ Kandra, M. 8306.527 0.001 -94. PE B Gliviak, M., this paper Kandra, M. 8306.5277 0.0003 -94. PE V Gliviak, M., this paper Kandra, M. 8444.373 -49. VI Dedoch, A. private comm. 8594.4786 0.0003 0. PE U Hric, L., this paper Komzik, R. 8594.4792 0.0002 0. PE B Hric, L., this paper Komzik, R. 8584.4792 0.0003 0. PE V Hric, L., this paper Komzik, R. Notes to Table I. VI - visual, PE - photoelectric, U - filter U, B - filter B, V - filter V, * - omitted [FIGURE 1] Fig. 1. (O-C) diagram for the times of primary minima of TX UMa, based on the ephemeris by Oh and Chen (1984): Min_hel = 2444998.1475 + 3.0632382d x E considering Kwee and Van Woerden (1956) method. The shapes of minima do not exhibit significant deviations from the symmetry. We were lucky enough to gain two simultaneous observations of TX UMa minimum (JD 2 448 306) one at the Skalnate Pleso Observatory and the other at the Stara Lesna Observatory. These two sets of data lead to a difference in the time of minimum determination which can not be explained by the data inaccuracy. We see the reason of this difference in the deterioration of the observational conditions at the Skalnate Pleso Observatory, and a subsequent sudden change of the extinction, which caused the drop of the observed brightness (in all colours) at the ascending branch of the eclipse, resulting in the time of minimum delay. This effect can be of more general relevance and we intend to study it in the future in more detail. The new photometric ephemeris of the system TX UMa was derived by means of the least-squares method using the data from the Table I. Four times of minima were omitted due to their great inherent inaccuracy (marked in the last column of the Table I.) The resulting photometric ephemeris is: Min. I - JD_hel 2 448 594.47957 + 3.0633292dxE +-0.00008 +-0.0000008 Finally we can summarize our results and their interpretation: 1. Between JD 2 445 111 and JD 2 446 122 a new period change of the TX UMa system, occurred, the fourth one in this century; 2. The new value of the period is 3.0633292 +-8 x 10^-7 days. This period is longer than that found by Oh and Chen; the difference is 0.0000910d; 3. The reason for the period change of TX UMa is the mass transfer from the less massive cooler secondary component F 6 IV to the hot component B 5 V. If the masses of the components M_1= 6.1 M_sun (hot one) and M_2 = 1.8 M_sun (cooler one) (Grygar et al., 1991) are assumed the new value of Delta P/ P = 0.000029706 yields to the value of the transferred matter delta M= 2.53 x 10^-5 M_sun. It is interesting to notice an increase of the value delta P/ P during last ninety years. Acknowledgements The authors wish to thank Mr. Milan Gliviak and Mr. Miroslav Kandra for their observational work at the Skalnate Pleso Observatory. Our thanks are also due to Mgr. Jindrich Silhan and to prof. J. M. Kreiner for their help with the search for archival data. Ladislav HRIC Richard KOMZIK Astronomical Institute Slovak Academy of Sciences 059 60 Tatranska Lomnica CZECH and SLOVAK FEDERAL REPUBLIC References Dedoch, A.: 1991 private comm. Grygar, J., Hric, L., Komzik, R., Sima, Z.: 1991, Astrophys. Space Sci. 185, 189-193. [BIBCODE 1991Ap&SS.185..189G ] Hric, L., Komzik, R., Grygar, J.: 1990, Astrophys. Space Sci. 169, 241-243. [BIBCODE 1990Ap&SS.169..241H ] Hubscher, J., Lichtenknecker, D., Wunder, E.: 1989, BAV Mitt. 52, Hubscher, J., Lichtenknecker, D., Wunder, E.: 1990, BAV Mitt. 56. Isles, J.: 1989, BAAVSS Circ. 68, 30. Komzik, R., Hric, L., Grygar, J.; submitted to Astrophys. Space Sci. [BIBCODE 1992Ap&SS.198..149K ] Kwee, K. K., Van Woerden, H.: 1956, BAN 12, No. 464, 327. [BIBCODE 1956BAN....12..327K ] MVS: 1989, 12, Nr. 2, 17. MVS: 1990, 12, Nr. 3, 51. Oh, K. D., Chen, K. Y.: 1984, Astron, J. 89, No. 1, 126. [BIBCODE 1984AJ.....89..126O ] Renz, W.: 1988, BAV Rundbrief 37, No. 1, 12. [BIBCODE 1988BAVRu..37...12R ] Silhan, J.: 1991, private comm.