COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1874

                                  Konkoly Observatory
                                  Budapest
                                  1980 December 3

                                  HU ISSN 0374-0676


      VARIABLE STAR IN THE GALACTIC CLUSTER NGC 7654


   During the course of photographic photometry in the vicinity
of the galactic cluster NGC 7654 = M 52 one of the standard
stars was detected to be variable. It is NGC 7654-26 in the list
of Hoag et al. (1961). The photographic plates (UBV system) were
taken in the years of 1971 to 1980 with the 60/90-cm Schmidt telescope 
of Jena University Observatory (Grossschwabhausen outstation). 
Results of iris-photometry of all the plates are collected
in Table I and extracts drawn in Fig. 1. In the Figure the arrows
at the ordinate scale indicate the magnitudes published by Hoag
et al. (1961). The variation in brightness amounts to at least
0.5 mag in the B and V colours, it remains uncertain in U. The


                       [FIGURE 1]


light changes observed are inconclusive as to the type of variability. 
The ranges of types under consideration is restricted,
however, by the spectral type (early A-type) of the star. Further
photometric observations are desirable.

  Table I
  Photographic observations of NGC 7654-26
(Results of photoelectric observations by Hoag et al. (1961):

  V = 15.44 mag. (B - V) = 0.72 mag. (U - B) = 0.60 mag.)
J.D.      B       J.D.      V       J.D.      U
244...    (mag)   244...    (mag)   244...    (mag)
1237.49   16.11   1249.39   15.61   1249.45   16.79
1240.58   16.25   1251.36   15.29   1251.44   17.00
1251.48   16.70   1253.39   15.89   1592.45   16.68
1594.40   16.44   1276.34  >15.5    1594.37   16.58
1594.41   16.53   1593.40   15.81   1595.46   16.47
2477.36   16.70   1593.47   15.79   1982.40   16.65:
2494.37  >16.0    1595.40   15.34   1989.36   16.50
2521.60   16.32   2433.34   16.02
3075.40   16.52   2436.35   15.51
3157.36   16.62   2439.31   15.29
3336.51   16.38   2652.51   15.72
3745.43   16.44   2654.58   15.45
3745.59   16.45   2765.42   15.16
4254.39   16.47   3075.43   15.76
4257.31   16.56   3336.49   16.00
4259.31   16.19   3336.56   15.65
4266.30   15.89

  From the colour indices given at the head of Table I a reddening 
E(B-V) = 0.7 mag and spectral type A2 follow. If we assume
A2V (M_V =1.6 mag) then the star is at a distance of 2.3 kpc. This
is in accordance with r = 2.1 kpc and E(B-V) = 0.51 ... 0.81 mag
as quoted by Schmidt (1962) for the cluster. Upon photometric
quantities Mermilliod (1976) also classifies the star as a cluster 
member. For the importance of this statement an independent
proof of cluster membership was attempted.
  From the luminosity function and the total number of cluster
stars both given by Taff (1974) the number of cluster members
within an 1-mag interval about M_B = 1.6 mag can be derived as
N_cl (M_B = 1.6) = 68. For the field stars application of the
Schwarzschild integral equation of the space density law gives
N_f(B=16) = 20 as the number of stars per magnitude within the 18
min of arc diameter cluster area. The star densities used in the


computations are from Allen (1973), interstellar extinction was
taken into account, and the cluster diameter is from Wallenquist
(1933). If the areal densities of stars derived this way are adjusted 
to the star counts made by Wallenquist (1933) at brighter
magnitudes the higher and probably more reliable number N_f(B=16)=
44 results. So the probability that a certain star at B = 16 mag
is a cluster member turns out to be between 0.61 and 0.77 with
the lower value being of higher weight. From this statement together 
with the photometric result and the position of the star
5.2 min of arc from the cluster centre it seems to be quite sure
that NGC 7654-26 is really a cluster member.
   I am indebted to Mr. D. Uhlig, former member of the technical 
staff of our observatory. He directed my attention to the star
and made the first photometric measurements.




                               W. PFAU
                            University Observatory
                            DDR-69 Jena


References:

Allen, C.W. 1973, Astrophysical Quantities, 3rd ed. (London:
    The Athlone Press).
Hoag, A.A., Johnson, H.L., Iriarte, B., Mitchell, R.I., Hallam,
    K.L., and Sharpless, S. 1961, Publ. U.S. Naval Obs., 2nd
    Ser., vol. 17, part 7. [BIBCODE 1961PUSNO..17....1H ]
Mermilliod, J.Cl. 1976, Astron. Astrophys. Suppl., 24, 159. [BIBCODE 1976A&AS...24..159M ]
Schmidt, K.H. 1962, Astron. Nachr., 287, 41. [BIBCODE 1963AN....287...41S ]
Taff, L.G. 1974, Astron. Journ., 79,1280. [BIBCODE 1974AJ.....79.1280T ]
Wallenquist, A. 1933, Ann. Bosscha, vol. 4, part 5.