COMMISSIONS 27 AND 42 OF THE IAU 
             INFORMATION BULLETIN ON VARIABLE STARS 
                          Number 3731 
 
                                         Konkoly Observatory 
                                         Budapest 
                                         27 May 1992 
 
                                         HU ISSN 0374 - 0676 
 
 
 
                        W DELPHINI 
               REQUEST FOR NEW OBSERVATIONS 
 
 
 
 As it is known, W Delphini is a semi-detached close binary system. 
It has been frequently observed and an unpublished list of primary 
minima was prepared by D. Lichtenknecker and F. Agerer. That is why 
a new study of the orbital period may be undertaken. 
 
 Years ago, Plavec (1960) considered that period variation of W 
Delphini could be caused by the apsidal motion. Then, this star was 
included among the semi-detached binary systems with "observed" 
apsidal motion. 
 
 From the actual list of primary minima, we have drawn the diagram of 
O-C residuals based on the linear formula: 
 
           Min. Hel. = JD 2418048.6187 + 4.8060633d x E. 
 
 An inspection of O-C differences (see Figure 1) makes it evident 
that, if the corresponding curve is a periodic one, its period must 
be U>90 years; while in Plavec's paper, U approx. 51 years has been given 
for apsidal period. 


                             [FIGURE 1]

 
 As we can see in Figure 1, in order to determine an accurate value 
for the long period U, new series of primary minima are necessary. In 
addition, in order to accept or to reject the hypothesis of the 
apsidal motion, very accurate photometric observations of the 
secondary minima are necessary. Anyhow, in our days, there are many 
observers who could contribute to the study of the semi-detached 
system W Delphini. 
 
 
 
 
F. AGERER 
Dorfstrasse 19 
D-W-8311 Zweikirchen 
Germany 
 
I. TODORAN 
Astronomical Observatory 
3400 Cluj-Napoca 
Romania 
 
Reference: 
 
Plavec, M.: 1960, Bull. Astr. Inst. Czech. 11, 148.  [BIBCODE 1960BAICz..11..148P ]