COMMISSIONS 27 AND 42 OF THE IAU 
           INFORMATION BULLETIN ON VARIABLE STARS 
                        Number 3740 
 
                                             Konkoly Observatory 
                                             Budapest 
                                             26 June 1992
 
                                             HU ISSN 0374 - 0676 
 
 
 
         PHOTOGRAPHIC PHOTOMETRY OF THE MIRA STAR S ORI 
 
 
The star S Ori is reported in the GCVS (Kholopov et al., 1985) as a Mira Ceti star with 
a period of 414.3 days, a spectral type of M6.5e - M9.5e and an amplitude 
of variation between V_max of 7.2m and V_min of 14.0m. 
  The current, photographic photometric values presented here were obtained from the 
plate collection of the INAOE at Tonantzintla, Mexico. Twenty-four plates taken with 
the Schmidt camera in the U filter of Johnson's system in a time span from 1971 to 1978 
were selected. 
  In order to obtain the variation of S Ori, a set of 16 standard stars from the catalogue 
of Andrews (1981) were considered. Table I lists the plates utilized, whereas Table II 
presents the standard stars. The apparent magnitudes of these stars cover the expected 
amplitude of variation of S Ori. 
  The image diameters of both the programme star and the standard stars were measured 
with the PDS microdensitometer of the INAOE. For the diameters determined in each 
plate, a least squares fit to a straight line was carried out. The mean percentual error of 
the measurements of the diameter of S Ori is of 0.032 +/- 0.018, which 
yields an accuracy of each point of less than 0.1 mag. 
  The final magnitude values of S Ori as well as the corresponding HJD are presented in 
Table III. Figure 1 shows the magnitude variation with phase determined with the period 
proposed by Kholopov et al. (1985). The amplitude of variations of S Ori found is 5.6 
mag within the limits 9.0 mag at maximum light and 14.4 mag as minimum. 


                                [FIGURE 1]

 Figure 1. Phase diagram of S Ori. The period utilized is that of Kholopov
 et al. (1985).
 
 
            Table 1. List of the utilized Plates 
 
Plate       Date           Obsever 
ST5330      DEC 15/16,71   E. Chavira 
ST5620      DEC 07/08,72   E. Chavira 
ST5652      DEC 28/29,72   E. Chavira 
ST5660      JAN 02/03,73   E. Chavira 
ST6028      JAN 20/21,74   E. Chavira 
ST6231      NOV 22/23,74   E. Chavira 
ST6354      MAR 07/08,75   E. Chavira 
ST6573      DEC 27/28,75   J. Campos 
ST6615      FEB 21/22,76   E. Chavira 
ST6655      MAR 04/05,76   E. Chavira 
ST6669      MAR 32/24,76   E. Chavira 
ST6921      DEC 21/22,76   J. Campos 
ST6929      JAN 08/09,77   E. Chavira 
ST6944      JAN 20/21,77   E. Chavira 
ST6958      FEB 14/15,77   E. Chavira 
ST6987      MAR 19/20,77   E. Chavira 
ST7064      NOV 16/17,77   E. Chavira 
ST7083      DEC 16/17,77   E. Chavira 
ST7114      JAN 14/15,78   E. Chavira 
ST7121      FEB 01/02,78   E. Chavira 
ST7141      FEB 11/12,78   E. Chavira 
ST7162      MAR 08/09,78   E. Chavira 
ST7275      Nov 02/03,78   E. Chavira 
 
 
                  Table 2. Standard Stars 
 
       No.                              PARENAGO 
No.   ANDREWS   U       B       V       or HD 
 
  1     92       --      8.88    8.82   HD36957 
  2    136       --      7.66    7.64   H036629 
  3    139       --     13.47   11.87   P1049 
  4    140      12.03   --      11.52   P1179 
  5    141      15.07   15.04   14.03   P1092 
  6    144      13.86   13.75   13.03   P1122 
  7    150       --      7.98    8.09   HD36842 
  8    165       --     14.95   13.80   P1143 
  9   9123      11.26   --      10.34   P1037 
 10   9128      13.64   12.47   11.12   P1036 
 11   7635      12.95   12.74   12.03   P1287 
 12   7598      14.05   13.46   12.59   P1304 
 13   6895      11.28   11.16   10.55   P1467 
 14   6933      13.97   13.51   12.73   P1523 
 15   6880      15.12   --      13.33   P1582 
 16   6252       6.88    7.44    7.56   HD36936 
 
 
         Table 3. Photographic Photometry of S Ori 
 
 
HJD-24000       U 
 
1301.8656      13.835 
1659.8427      14.190 
1680.8112      14.003 
1685.7843      14.150 
2068.8037      12.566 
2374.7996      11.207 
2479.6043      14.380 
2830.6423      12.916 
2842.6129      12.804 
2861.5784      12.890 
3134.7167       9.550 
3152.5626       9.884 
3164.5981      10.294 
3189.7034      10.375 
3222.5666      11.637 
3464.8674       9.408 
3494.8608       9.086 
3523.7515       9.838 
3541.7064      10.690 
3551.5723      10.616 
3576.5716      10.269 
3815.7545      12.497 
 
 
  We would like to acknowledge the assistance of R. Ramos at the microdensitometer, V. 
Soriano and A. Gomez at the computer and to Cosnet (319.91 grant) for funds provided 
for the maintenance of the plate collection. One of us, F. Valera, acknowledges support 
by Conacyt through scholarship grant 61245. This work was done as a class problem in 
a course on Observational Astronomy. 
 
 
  J.H. PENA ^1,2, F. VALERA ^1 and C. ESCAMILLA ^1 
 
1 Instituto Nacional de Astrofisica Optica y Electronica 
  Ap. Postal 51 y 216 
  C.P. 7200 Puebla, Mexico 
 
2 Instituto de Astronomia 
  Ap. Postal 70-264 
  C.P. 04510 D.F., Mexico 
 
References: 
 
Andrews, A.D.: 1981, A photometric Atlas of the Orion Nebula. Armagh Observatory.  [BIBCODE 1981paon.book.....A ]
Kholopov. P.N., Samus, N.N., Frolov, M.S., Goranskij, V.P., Gorynya, N.A., Kazarovets, 
 E.V, Kireeva, N.N., Kukarkina, N.P., Kurochkin; N.E, Medvedeva, G.I., Perova, N.B., 
 Rastorguev, A.S., Shugarov, S.Yu.: 1985, General Catalogue of Variable Stars. 
 Fourth Edition, Moscow.