COMMISSION 27 OF THE I. A. U.
              INFORMATION BULLETIN ON VARIABLE STARS
                           Number 2286

                                                         Konkoly Observatory
                                                         Budapest
                                                         1983 March 1

                                                         HU ISSN 0374-0676



           IS BF ARAE DWARF NOVA OF SU UMa TYPE? *



 Little is known about the dwarf nova BF Ara. Since the variability of
this star was discovered by Shapley and Swope (1934) no further observations
have been published. Its photometric maximum brightness is quoted as 13.6mag
by Kukarkin et al. (1969). On ESO Schmidt-plates it appears as a star of
roughly 17.5mag. A chart based upon the observations to be described in this
note is given by Vogt and Bateson (1982).
 Photometric observations of BF Ara in the UBV colour system have been
carried out on 15 September 1979 at the 1-m-telescope of the European
Southern Observatory with the one-channel photometer (for details of the
observations and reductions, see Bruch, 1982). A light curve of BF Ara has
been measured for about 120m with a time resolution of about 80s. It is 


                            [FIGURE 1]

            Fig. 1: Light- and colour curves of BF Ara


* Based on observations collected at the European Southern Observatory




reproduced in Figure 1. The mean values of brightness and colours are:

                 V = 14.24 +/- 0.09
               B-V =  0.01 +/- 0.05
               U-B = -0.72 +/- 0.04

  BF Ara was obviously observed in outburst. Most dwarf novae do not show
strong variations in this phase. However, the light curve of BF Ara exhibits
an outstanding hump with an amplitude of about 0.25mag. Such a feature is well
known from the light curves of SU UMa - stars in superoutburst (Vogt, 1980).
The amplitudes of these so-called superhumps range between 0.15mag and 0.35mag. The
appear with a period a few percent longer than the orbital period of the
systems.
  The striking similarity between the hump in the light curve of BF Ara
and the superhumps of the SU UMa - stars suggest a classification of BF Ara
as SU UMa - star. This is supported by the good agreement of the colours of
BF Ara with the mean colours of SU UMa - stars during superoutburst, after
reasonable corrections for the interstellar reddening have been applied (see
Tables 31 and 47 of Bruch, 1982).
  If BF Ara is really a member of the SU UMa - subgroup of dwarf novae a
lower limit of about 2h for the orbital period can be estimated from the
light curve. This is long for the period of a SU UMa - star, but it is not
an extreme value. YZ Cnc (Vogt, 1980) and TU Men (Stolz and Schoembs, 1981)
have even longer periods. Thus, also from this point of view BF Ara fits
well among the SU UMa - stars.
  A spectrum of BF Ara was taken on 16 September 1979, the night after the
photometric observations, at the 1.5-m-telescope of ESO, equipped with a
Boller and Chivens Cassegrain spectrograph and an EMI image tube. Like almost
all outburst spectra of dwarf novae, it shows a strong blue continuum with
superimposed broad and shallow absorption lines of hydrogen.
  The classification of BF Ara as SU UMa - star might be premature in view
of the scarce observations. Nevertheless it appears worthwhile to keep an eye
on this star.




                  A. BRUCH


                  Astronomisches Institut
                  Domagkstrasse 75
                  D-4400 Munster
                  Fed. Rep. Germany




References:


Bruch, A.; 1982: "Kataklysmische Veranderliche in Beobachtung, Statistik
          und Analyse", Ph.D. thesis, Munster* [BIBCODE 1982PhDT.......145B ]
Kukarkin, B.V.; Kholopov, P.N.; Efremov, Yu.N.; Kukarkina, N.P.; 
         Medvedeva, G.I.; Perova, N.B.; Fedorovich, V.P.; Frolov, M.S.; 1969:
         General Catalogue of Variable Stars, Moscow [BIBCODE 1969gcvs.book.....K ]
Shapley, H.; Swope, H.H.; 1934: Harvard Annals 80, No. 5
Stolz, B.; Schoembs, R.; 1981: Inf. Bull. Var. Stars 2029
Vogt, N.; 1980: Astron. Astrophys. 88, 66 [BIBCODE 1980A&A....88...66V ]
Vogt, N.; Bateson, F.M.; 1982: Astron. Astrophys. Suppl. 48, 382 [BIBCODE 1982A&AS...48..383V ]




* copies are available from the author on request