COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 2427

                                    Konkoly Observatory
                                    Budapest
                                    2 November 1983

                                    HU ISSN 0374 - 0676



       PHOTOELECTRIC HalphaN AND HalphaW OBSERVATIONS OF R CMa *


  The eclipsing binary system R CMa (BD - 16d 1898) was observed in 8 nights
from February 18 to March 2, 1983 using a photoelectric photometer mounted on
the 51 cm Cassegrain reflector of Biruni Observatory. The photoelectric 
photometer is equipped with an unrefrigerated RCA 4509 multiplier photocell and
a Leeds and Northrup Speedomax was used to record the amplified signal from
the photomultiplier. The observations were made using Stromgren HalphaN and HalphaW
filters possessing characteristics indicated in Table I. The observing 
sequence was the usual pattern of sky - comparison - variable (3 times) - 
comparison - sky, with each observation lasting about 50 seconds.

Table I.      Filter characteristics

Filter        Lambda(max)(A)   FWHM(A)  Max
designation                            Transmission
---------------------------------------------------
H alpha W         6583         238         47%
H alpha N         6569          38         57%
---------------------------------------------------

  BD - 15d 1734 was used as the comparison star and BD - 15d 1732 was observed 
once a night as the check star. The effects of differential atmospheric
extinction were removed using the extinction coefficients derived from the
comparison star observations. The differential corrections were, however,
small due to the angular proximity of the variable and comparison stars. Light
curves are plotted in Figure 1 where the phases were computed according to the
following ephemeris (Koch, 1960):

            Min I = HJD 2422030.638 + 1.1359386d E

but a correction of 0.0211d was added to the epoch to bring the recent primary
minimum to the 0.0 phase. H alpha N - H alpha W index was also computed but no 
significant phase-dependent variation greater than the observational scatter
was observed.
  According to Guinan (1977 and 1983) R CMa is an old, high velocity, semi-
detached eclipsing binary with mass loss and exchange whose period undergoes
changes (an abrupt change in period was observed around 1914) and exhibits

* Contribution No. 10, Biruni Observatory

asymmetry in the light curve. All these suggest that the system should be
observed and studied more.


                            [FIGURE 1]

 Figure 1. The HalphaN and HalphaW light curves of R CMa as a function of
                          orbital phase


   We are presently analysing the observed light curves using Kopal's method 
for partial eclipses (Edalati, 1978). The characteristic parameters of
the light curve are given as follows:


     
     Min I (observed)  = 2445391.2364 ;   O-C = 0.0211d
     Amplitudes:

     Min I (H alpha W) = 0.545m,    Min II (H alpha W) = 0.120m
     Min I (H alpha N) = 0.570m,    Min II (H alpha N) = 0.115m

     Mean values of Delta alpha(V-C) index:

phase interval          Delta alpha(V-C)
----------------------------------------
0.97- 0.03   (Min I)    -0.08 +- 0.01
0.10- 0.40   (Max I)    -0.08 +- 0.02 
0.47- 0.53   (Min II)   -0.07 +- 0.02
0.60- 0.90   (Max II)   -0.09 +- 0.03
----------------------------------------


M.T. EDALATI and B. KHALESSE      N. RIAZI
Physics Department                Biruni Observatory
School of Sciences                Shiraz University
Mashad University                 Shiraz, Iran
Mashad, Iran





References:

Edalati, M.T. 1978, Astrophys. Space Sci., 58, 3. [BIBCODE 1978Ap&SS..58....3E ]
Guinan, E.F. 1977, A.J., 82, 51. [BIBCODE 1977AJ.....82...51G ]
Guinan, E.F. 1983, A.J., 88, 126. [BIBCODE 1983AJ.....88..126G ]
Koch, R.H. 1960, A.J., 65, 326. [BIBCODE 1960AJ.....65..326K ]