COMMISSIONS 27 AND 42 OF THE IAU 
               INFORMATION BULLETIN ON VARIABLE STARS 
                            Number 3759 
 
                                          Konkoly Observatory 
                                          Budapest 
                                          24 August 1992 

                                          HU ISSN 0374 - 0676 
 
 
 
 A NEWLY DISCOVERED ECLIPSING VARIABLE IN THE SW URSAE MAJORIS FIELD 
 
 A new eclipsing variable star has been discovered by the authors in 
the field of the dwarf nova SW UMa during an observational program to 
collect data on superhump phenomena. Details of the instrumentation 
and filters may be found in (DeYoung, Schmidt, and Gritz 1991). The I 
band filter was used for 1199 images, the R band filter was used for 
66 images, and a V filter was used for 67 images. Observations were 
taken on eleven nights from Julian Date 2448705.53823 (March 24, 1992 
UT) through 2448762.61821 (May 20, 1992 UT). 
 
 The DAOPHOT photometry package, (Stetson 1987), was used in 
synthetic aperture mode, giving magnitudes of all of the brightest 
stars in the CCD field. The new star was discovered on the first 
night by intercomparing all of the stars in the CCD field of view. A 
search of the General Catalogue of Variable Stars (1985), The New 
Catalogue of Suspected Variable Stars (1982), and the various 
Information Bulletin on Variable Stars issues published since 1980 
revealed no object corresponding with the new variable. The method 
of Kwee and van Woerden (1956) was used to determine the heliocentric 
times of well observed minima (see Table 1). Using the three 
well-observed times of primary minima in a linear least squares fit 
gives the following preliminary ephemeris: 
 
              JD Hel. Min. I = 2448706.7253  +  0.358162 * E         (1) 
                                   +/-.0006   +/-.000007 
 
 The following data were found in the Space Telescope Guide Star 
Catalog (CD ROM Version 1 issued on 1 June 1989) on the new eclipsing 
variable. 
 
      Right Ascension (2000.0)   Declination (2000.0)   m_v 
            08h36m27.2s              +53d34'40"         12.4 
 
 
 The general shape of the light curve indicates a borderline 
semi-detached/contact type binary system. Preliminary fits to the 
light curve using the GDDSYN software (Hendry and Mochnacki 1992), and 
the May 1992 revision of the Wilson-Devinney method (Wilson and 
Devinney 1979) and (Wilson 1979, 1990, 1992) indicate an inclination 
of 56.5 degrees. The observed instrumental amplitude of primary 
minimum is 0.2 in the instrumental V, while 0.15 is indicated for the 
secondary minimum. Figure 1 shows the instrumental differential 
I-band magnitudes versus phase computed using Equation 1, Figure 2 is 
an I-band image finder chart for the new variable. Table 1 gives the 
times of both primary and secondary minima observed during this study 
reduced to Equation 1. 
 
 In the instrumental I band evidence for variation from cycle to cycle 
is indicated on the maximum occurring at phase 0.75. Secondary 
minimum is slightly skewed to approximately phase 0.513, or 0.0046 
days late, and is caused by the shape changes in the obviously 
variable light following maximum. The amplitude in the instrumental I 
band is 0.18 magnitude for primary and 0.14 magnitude for the 
secondary minimum. 
 
 
 
          TABLE 1. Times of primary and secondary minima 
                             MEAN ERROR       O-C       O-C 
    CYCLE         HJD          (DAYS)       (CYCLES)   (DAYS) 
    -0.5      2448706.5403   +/-0.0006      -0.0165   -0.0059 
     0.0      2448706.7259   +/-0.0005      +0.0017   +0.0006 
    11.0      2448710.6645   +/-0.0005      -0.0017   -0.0006 
    19.5      2448713.7062   +/-0.0009      -0.0092   -0.0033 
   156.0      2448762.5986   +/-0.0011      +0.0000   +0.0000 


                              [FIGURE 1]

          Figure 1. The instrumental I band light curve.

                              [FIGURE 2]

                Figure 2. An I band finder chart.

 
 
                 James A. DeYoung and 
                 Richard E. Schmidt 
                 U.S. Naval Observatory 
                 3450 Massachusetts Avenue NW 
                 Washington DC 20392-5420 USA 
 
 
References: 
 
DeYoung, J. A., Schmidt, R. E., and Gritz, L. I., 1991. 
  Information Bulletin on Variable Stars, No. 3578. 
 
Hendry, P. D. and Mochnacki, S. W. 1992. Astrophys. Journ., 388, 603.  [BIBCODE 1992ApJ...388..603H ]
 
Kholopov, P. N. (ed.) 1982. New Catalogue of Suspected Variable 
  Stars, Nauka, Moscow.  [BIBCODE 1982ncss.book.....K ]
 
Kholopov, P. N., (ed.), 1985. General Catalogue of Variable Stars, 
  4th ed., Nauka, Moscow. 
 
Kwee, K. K. and van Woerden, H., 1956. Bull. Astron. Netherlands, 
  12, 327.  [BIBCODE 1956BAN....12..327K ]
 
Space Telescope Science Institute, 1989. Guide Star Catalog (CD ROM, 
  Ver. 1), Baltimore. 
 
Stetson, P. B., 1987. Publ. Astron. Soc. Pacific, 99, 191.  [BIBCODE 1987PASP...99..191S ]
 
Wilson, R. E. 1979. Astrophys. Journ., 234, 1054.  [BIBCODE 1979ApJ...234.1054W ]
 
Wilson, R. E. 1990. Astrophys. Journ., 356, 613.  [BIBCODE 1990ApJ...356..613W ]
 
Wilson, R. E. 1992. in New Frontiers in Interacting Binary Star 
  Research, ed. K. C. Leung (Astron. Soc. of the Pacific Conf. 
  Series, in press).  [BIBCODE 1993ASPC...38...91W ]
 
Wilson, R. E. and Devinney, E. J. 1971, Astrophys. Journ., 166, 605.  [BIBCODE 1971ApJ...166..605W ]