COMMISSION 27 OF THE I. A. U.
                  INFORMATION BULLETIN ON VARIABLE STARS
                              Number 3568

                                                        Konkoly Observatory
                                                        Budapest
                                                        1 March 1991

                                                        HU ISSN 0374 - 0676


                Nature of the variability of VV Scl

   HD 7676 is an Ap star, the spectral type of which is A5 SrCrEu (Renson et
al. 1991). Its light variability found by Cousins and Stoy (1962) has been
studied by Strohmeier (1985), who derived a period of 2.47962d days, with a
double-wave variation curve considered to be due to eclipses. Accordingly HD
7676 received the variable-star name VV Scl.
  But we believe that it is unduly classified as an eclipsing variable.
   With a period as large as 2.48 days, an A5 eclipsing star would most
probably be of the Algol type. But the figure on the fifth page of
Strohmeier's paper shows that the maxima of VV Scl are not flat at all, and
that the variation is smooth and continuous, the minima being not deep. The
latter are only somewhat sharper than the maxima.
   The error of the measurements is not quoted, but from the dispersion of the
points it can be inferred that it is relatively large. It is even not quite
sure that the variation is double-waved; it may be that the real period is only
1.24 day instead of 2.48. According to Strohmeier's figure, the B values at
the primary and the secondary minima are perhaps 8.73 and about 8.70
respectively, while at the maxima they are about 8.58 and 8.59. Thus the
difference between the minima is not larger than the difference between the
maxima, and it remains within the limits of the errors.
   Even if the double wave is real, it remains most probable that the
variations of VV Scl are of the alpha CVn type and not due to eclipses, since
many Ap stars exhibit double-wave variations.
   The main argument against the hypothesis of an eclipsing or an ellipsoidal
variable lies in the fact that V does not vary similarly to B. According to
the table in Strohmeier's paper, V remains almost constant within the limits of
error. The mean value is 8.39, and the extreme values in that table are 8.35
and 8.43. Such differences for the behaviour in various colours are typical of
Ap-star variations.
   If VV Scl were an eclipsing variable, the observed variation should be
considered as being small, implying very partial eclipses. On the contrary the
range in B is very large if the variation is only of the alpha CVn type. The
difference between the values quoted above for the higher maximum and the
lower minimum in B is 0.17. This range is among the largest known for Ap
stars. Thus it would be very interesting to have accurate measurements of
this star in the Stromgren system for instance. Moreover it is to be hoped
that they will enable to confirm that the variations do not originate from
eclipses. Such measures are now already planned at the European Southern
Observatory (ESO).


                                            P. RENSON

                                      Institut d'Astrophysique
                                         Université de Liege
                                         Avenue de Cointe, 5
                                        B-4000 Liege (Belgium)



References:

Cousins, A.W.J., Stoy, R.B., 1962, Roy. Obs. Bull. 64 [BIBCODE 1962smer.book.....C ]
Renson, P., Gerbaldi, M., Catalano, F.A., 1991, Astron. Astrophys. Suppl.,
        in press [BIBCODE 1991A&AS...89..429R ]
Strohmeier, W., 1965, Inform. Bull. Var. Stars 89