COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2023

                                  Konkoly Observatory
                                  Budapest
                                  1981 October 5

                                  HU ISSN 0374-0676




 AN ULTRAVIOLET PHOTOELECTRIC LIGHTCURVE OF THE ECLIPSING
                  BINARY BB Peg



  The W UMa type eclipsing binary BB Peg (Spectral Type F8)
has a period of 8h41m. Photoelectric lightcurves in three 
colors (U, B and V) were performed by Cerruti Sola and Scaltriti 
during Summer 1978, mainly at Catania Astrophysical Observatory; 
the details concerning the employed equipment and the
observational routine can be found elsewhere (Cerruti Sola and
Scaltriti 1980). In that paper a study of the period and 
approximate geometric elements were derived, using the B and V
lightcurves only. A refined analysis was made subsequently by
Cerruti Sola et al. (1981) applying the Wilson-Devinney 
computer code; an unusual high degree of overcontact was obtained,
  In this note we present the ultraviolet lightcurve of BB Peg.
Due to the faintness of the star, the ratio signal to noise
was very small, even with the largest gain in photoelectric
equipment; moreover, the scatter in a single deflection was
higher than usual. The resulting lightcurve was rather noisy;
this is the reason why we have not used it in our previous
papers. However, it seems advisable to us to publish our 
observing results in U filter for a direct comparison with B
and V runs.
  The scatter in a single Delta m measurement may be estimated
about +-0.02 mag; therefore we have formed normal points with
steps of 0.02 in phase (except few cases). The average
number of single Delta m's forming a normal point is about 6 for
phases relative to primary minimum and to first maximum,
whereas poorer coverage of secondary minimum and of maximum
around phase 0.75 reduces that number to half its value.

  The U lightcurve we have obtained is shown in Figure 1
(where the Delta m_U 's (var.-comp) are plotted against phases 
calculated with the ephemeris given by Cerruti Sola and 

                          [FIGURE 1]

 Figure 1. Ultraviolet lightcurve of BB Peg (normal points
           are plotted).

Scaltriti (1980)). The maxima have practically the same level,
whereas the second maximum is less luminous (by few hundredths
of magnitude) than the first one in B and V lightcurves; the
level difference between the minima appears to be about 0.1
mag, larger than that found in B and V filters. Also the total
luminosity range grows from V (~0.68 mag) to U (~0.75 mag).
  From the U runs it was possible to derive epochs of 
primary and secondary minima, bisecting chords at different light
levels in a free-hand drawing through the observed single
Delta m's; we have obtained: Min_I(Hel.) = 2443750.594 and Min_II(Hel.)=
2443754.389, in very good agreement with the times found from
B and V runs. The estimated errors of those minima amount to
+-0.002d for both.





    M. CERRUTI SOLA (*) and F. SCALTRITI

    Osservatorio Astronomico di Torino
    I-10025 Pino Torinese (Torino) - Italia





  (*) Now at the Astrophysical Observatory of Arcetri
      Firenze -  Italia





References:
Cerruti Sola, M., and Scaltriti, F.: 1980 Astron. Astroph.
       Suppl, 40, 85. [BIBCODE 1980A&AS...40...85C ]
Cerruti Sola, M., Milano, L., and Scaltriti, F.:
       1981, Astron. Astroph, (in press). [BIBCODE 1981A&A...101..273C ]