COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                       Number 2890


                                        Konkoly Observatory
                                        Budapest
                                        30 April 1986

                                        HU ISSN 0374-0676



                 NONVARIABILITY OF SVS 1740


     SVS 1740 is listed as NSV 3633 in the New Catalogue of Suspected
Variable Stars (NCSVS; Moscow; 1982), Lange noted its variability while
observing TV Lyn, an RR Lyr star situated about 12' south of SVS 1740.
Lange and Mandel (1971) gave the finding chart, evaluated the period, which
is nearly half the period of TV Lyn, and classified SVS 1740 as a W UMa
variable. They obtained independently complete light curves and derived
the following ephemeris on the basis of 38 instants of minimum;

      Min I = hel.JD 2441059.347 + 0.121369d E

According to the NCSVS the depths of minima are nearly half a magnitude.
During the ensuing years five visual epochs of minimum have been published
in MVS 7, 149, 1976 and MVS 8, 25, 1977 with good O-C computed by
means of the above ephemeris.
     According to Eggen (1967) there exists a sharp six-hour cut-off
in the period distribution of W UMa systems. More recent data set the limit
at 0.221d with CC Com, but some doubt has been raised about the reality of
the cut-off, which could be an effect of observational selection (Mochnacki,
1983).
     It seemed therefore useful to obtain more precise light curves for
a system which looked to be situated beyond the actual cut-off. B and V
observations were performed by means of a two beam photoelectrlic photometer
applied to the one meter reflector of the Merate Observatory ( Broglia and
Conconi; 1985). SVS 1740 was measured simultaneously with BD +48deg1548
during runs as long as about half the supposed period. No variations
greater than a few millimagnitudes appear in the Delta m = m(BD)-m(SVS) and the colour
of SVS 1740 is much bluer than expected from the colour-period relation
for W UMa systems (Eggen, 1967). In particular we have the following results:





           Interval                            DeltaV   DeltaB

        JD 2446121.341 --.394                -0.102m   -0.132m
                                            +-    1   +-    1  m.e.

              6144.325 --.385                -0.101m   -0.138m
                                            +-    2   +-    1

After these observations were performed, Dr. M. Frolov (private communication)
made known to us that the discovery of Lange and Mandel has inspired three
precedent photoelectric investigations on the variability of SVS 1740. Mandel
(1972) and Kovalenko's (1973) found constant light. Moreover sixty unpublished
measurements obtained by G. Zhukov gave also constancy: V= 10.98,
B-V= +0.50, U-B= +0.01.

  What can be the reasons of so discordant results between visual and
photoelectric measures, is not clear, because a misidentification or a choice of
TV Lyn as comparison star seem to be unlikely. In any case SVS 1740 can
be ruled out from the list of Suspected Variables.






                             P. BROGLIA


                             P. CONCONI

                             Merate Observatory
                             I - 22055 Merate
                             Italy


References:
Broglia P., Conconi P.; 1985: Astron. Astrophys, 149, 15 [BIBCODE 1985A&A...149...15B ]
Eggen O.J.; 1967: Mem. R. astr. Soc. 70., 111, [BIBCODE 1967MmRAS..70..111E ]
Kovalenko V.M., Kovalenko O.N.; 1973: Astron. Circ. No. 768 [BIBCODE 1973ATsir.768....3K ]
Lange G., Mandel O.; 1971: Astron. Circ. No. 637 [BIBCODE 1971ATsir.637....7L ]
Mandel O.; 1972: Astron. Circ. No. 747.
Mochnacki S.W.; 1983: Interacting Binaries, ed. P.P. Eggleton
            and J.E. Pringle, p. 51. [BIBCODE 1985ib...proc...51M ]