COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2406

                                      Konkoly Observatory
                                      Budapest
                                      30 September 1983

                                      HU ISSN 0374-0676



            PHOTOELECTRIC OBSERVATIONS OF 20 CVn *



  In spite of many reports (Danziger and Dickens 1967, Breger 1969, Leung
1970, Shaw 1976, and others) on the possible Delta Scuti-type light variations,
20 CVn is listed in the Finding List (Wood et al. 1980) as an interacting
binary whose orbital period is very short, P = 0.135d or 0.176d. In addition
to this the Finding List gives auxiliary informations such as small light
variation of 0.03m possibly due to the elliptical nature of the system.
  Our attention to 20 CVn was paid to clarify the nature of the light variations
of this star, the amount of light variations, and the period of light
variation of this star. Using the 60-cm reflector of the Yonsei University
Observatory, differential magnitudes in the two colours, B and V, were made
with the observations of 19 CVn as the comparison star. Atmospheric extinction
coefficients were derived from the comparison star measurements for each
night and the differential corrections for the variable star were made.
  Out of 10 nights attempted only 4 nights turned out to be useful to cover
enough for one full period. The results are given in Table I and the light
curves are shown in Figure 1. As are clear in the figure the small light


             Table I

  Periods and amplitudes of 20 CVn.
-------------------------------------
JD Hel. Filter   Period   Amplitude
-------------------------------------
2445070   v        0.12d     0.03m
          v        0.12      0.03
2445084
          b        0.12      0.04
          v        0.13      0.02
2445378
          b        0.14      0.03
          v        0.13      0.04
2445399
          b        0.13      0.04
------------------------------------

*Yonsei University Observatory Contribution No. 13.


                              [FIGURE 1]

        Figure 1   Yellow and blue light curves of 20 CVn


variations with periodicities are indeed present but the shape of light curves
are subject to change night to night. Furthermore, the estimates of the periods,
0.12d - 0.14d, and the amplitudes, 0.02m - 0.04m, of light curves listed in the
table suggest that the light variation cannot be originated by the close
binary nature.





            Y.W. CHUN, Y.S. LEE, and I.-S. NHA
         Yonsei University Observatory, Seoul, Korea





References:

Breger, M. 1969, Astron. J. 74, 166 [BIBCODE 1969AJ.....74..166B ]
Danziger, I.J. and  Dickens, R.J. 1967, Astrophys. J. 149, 55 [BIBCODE 1967ApJ...149...55D ]
Leung, K.-C. 1970, Astron. J. 75, 643 [BIBCODE 1970AJ.....75..643L ]
Shaw, J.S. 1976, Astron. J. 81, 661 [BIBCODE 1976AJ.....81..661S ]
Wood, F.B., Oliver, J.P., Florkowski, D.R., and Koch, R.H. 1980, Publ. Univ. 
   Florida, Vol. 1. [BIBCODE 1996yCat.6044....0W ]