COMMISSION 27 AND 42 OF THE IAU
                    INFORMATION BULLETIN ON VARIABLE STARS
                               Number 3819

                                                         Konkoly Observatory
                                                         Budapest
                                                         18 December 1992

                                                         HU ISSN 0374 - 0676



                   A NEW EPHEMERIS FOR TX URSAE MAIORIS


   From a preliminary analysis of observed primary minima, Plavec (1960) has
determined U=~50 years for the assumed apsidal period. In fact, TX UMa is the
only semi-detached binary system in which apsidal motion could still be
postulated, as it was emphasized by Semeniuk (1968).
   Moreover, the new primary minima, observed after Plavec's (1960) paper was
published, show that a new study of the corresponding orbital period may be
undertaken. In order to do so, we have used Plavec's table of primary minima,
which was completed with observed minima obtained subsequently. Then we have
constructed the O-C diagram where the O-C differences refer to the linear
formula:

     Min. hel. =J.D. 2416426.783 + 3.0633175d x E_1.

   As it is shown in Figure I, the run of the normal residuals clearly puts in
evidence the fact that the corresponding diagram could not be caused only by
apsidal motion. It was impossible for Plavec to reach this conclusion in 1960
because the time interval covered by observed minima was too short.


                              [FIGURE 1]


   Anyhow, TX UMa could have an apsidal motion superimposed on the light-time
effect or strong period variations due to the mass exchange. This is why this
binary system needs new observed minima, especially some secondary minima in
order to remove the contribution of the apsidal motion effect.
   For the near future the following ephemeris can be used for the prediction
of the primary minima:

     Min. hel. = J.D. 2441766.427 + 3.0632455d x E_2.



                                        IOAN TODORAN
                                        RODICA ROMAN
                                        Observatorul Astronomic
                                        Strada Ciresilor no. 19
                                        3400 Cluj-Napoca
                                        Romania



References:

Plavec, M., 1960, Bull. Astr. Inst. Czechoslovakia 11, 148. [BIBCODE 1960BAICz..11..148P ]
Semeniuk, I., 1968, Acta Astronomica 18, 1. [BIBCODE 1968AcA....18....1S ]