COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 2452

                                          Konkoly Observatory
                                          Budapest
                                          27 December 1983

                                          HU ISSN 0374-0676




 ACTIVE AND INACTIVE STATES OF THE X- RAY BINARY 4U 2129+47 = V 1727 CYGNI



  From a letter of W. Pietsch, Institut fur extraterrestrische Physik of
Max-Planck-Institut fur Physik und Astrophysik, Garching/Munchen, we learned
that V 1727 Cyg was observed in a low state in September and October 1983 in
the optical and x-ray regions - see also the announcement of Pietsch et al.
in IAU Circ. 3887. Although the object's brightness is rather close to the
plate limit even of our best astrographic exposures (two 40 cm four-lens
cameras) I tried to look for further inactive phases, with the following 
results: V 1727 Cyg is strongly variable between 16.8m and 18.1m (B) on 75 plates
taken in 1963, 1967, 1969, 1970, and (scattered) 1972 to 1979, the last 
definitely bright observation (16.7m) being of 1979 Oct. 11. Figure 1 shows the


                             [FIGURE 1]


estimates, folded by means of the elements

     Min. (hel.) = 244 4403.743+0.2182579d (+ 0.0000008d)*E

given by McClintock et al. (Astrophys.J. 258, 245, 1982).

  In contrast to that behaviour the star was obviously in inactive faint


states on 39 plates of 1938 to 1943 and 1983. After the active time described
above the first exposure showing the object faint (>17.8m), when it should
have been around 17.0m according to the elements, is of 1983 Sep. 7. Figure 2


                              [FIGURE 2]


displays the observations of 1938 to 1943. The arrows indicate "fainter than"
observations, period as before, zero point arbitrary.
 Unfortunately, 7 plates of 1980, 1982 and August 1983 do not definitely
contradict either of the two possibilities.
 One should note that the light curve of Figure 1 is strongly flattened
because of the occasionally rather long exposure times (up to 1/3 P). The
asymmetric trend, which has been described by previous authors, is however
well seen. The large scatter is also due to the faintness of the star.
 The comparison stars used in this investigation can be located on the
finding charts of Thorstensen et al. (Astrophys.J. 233, L 57, 1979) as follows;
the positions are relative to the variable in millimetres, and the adopted
B magnitudes are given in parentheses:

     a 3.5 sf (16.5m), b 14.8 n, 4.5 f (17.5m), c 4.3 p (17.9m).





                  W. WENZEL
            Sternwarte Sonneberg
            Zentralinstitut fur Astrophysik
            der Akademie der Wissenschaften
            der DDR