COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1853

                                    Konkoly Observatory
                                    Budapest
                                    1980 October 13

                                    HU ISSN 0374-0676


           A CEPHEID VARIABLE IN NGC 6067



    HD 144972 [CPD -54^o 7159) has been classified as of type F6 I
by Drilling (1968). The star is in the region of the cluster NGC
6067 discussed by Thackeray, Wesselink and Harding (1962, Plate 5)
but not observed by them. It is included in a current program of
intermediate band, H_beta and RI observations of southern supergiants
during which a variation of 0.3 mag was found in visual light.
The observations are shown in Figure 1, where filled circles represent 
means of two observations in different cycles. The observations
were obtained in the interval between 1 May and 7 September, 1980
with the 0.9 m reflector on Cerro Tololo. The preliminary light
elements are Max. = JD 2444361.875 + 3.770d. The path of the
variable in the (V, b-y) plane is shown in Figure 2 where the top
of the main sequence is shown schematically and two, known supergiants 
in the cluster (-53^o 7400p and -53^o 7400f) are labeled with
the types assigned by Thackeray et al. Both the median magnitude
and the spectral type are intermediate between the two cluster
supergiants, supporting cluster membership. The cluster velocity
is -43.4 km/sec from four stars observed by Thackeray et al. and
cluster membership for HD 144972 could be tested in this way.
   The cluster modulus, from the discussion by Thackeray et al.,
and a not entirely independent derivation by Engver (1966), is

                       [FIGURE 1]


near 11.5 mag. Adopting the mean reddening determined by Thackeray
et al., E(B-V) = 0.33 mag, (E(b-y) = 0.25 mag) the intrinsic
values of the median magnitude and color (read at phase 0.25) of
HD 144972 are V_o = 7.8 mag and (b-y)_o + 0.33 mag. The modulus of
11.5 gives M_V =-3.7 for the variable, which is about one magnitude
brighter than predicted by current period-luminosity relations.


                       [FIGURE 2]

The situation is reminiscent of that for Polaris, also a short
period (4 days) and small amplitude (0.1 mag) variable, for which
Mc Namara (1969) finds M_V =-3.7 mag from intermediate band and H_beta
observations of the common proper motion companion. It should be
noted that if both these cepheids are first overtone pulsators, the
fundamental periods would indicate luminosities near M_V =-3.7 mag
from the P-L relations.
    An alternate possibility is that the cluster modulus is about
one magnitude too large, a not unprecedented situation for very
young clusters fitted to a universal main sequence (see e.g. Eggen
1976). There is some preliminary indication that this may be the
case, in that single intermediate band and H_beta observations of three



early type cluster stars, with visual magnitude between 9.0 and
11.2, give a mean modulus of 10.6 +- 0.05 (sigma) mag and a mean reddening
of E(b-y) =0.29 +- 0.02 (sigma) mag. These values, if confirmed, will lead
to M_V=-3.0 mag for the median luminosity of the variable.





                           OLIN J. EGGEN
                 Cerro Tololo Inter-American Observatory*
                          La Serena, Chile

References:

Drilling, J.S. 1968, A.J. 73, 590. [BIBCODE 1968AJ.....73..590D ]
Eggen, O.J. 1976, Quart. Jour. R.A.S. 17, 472. [BIBCODE 1976QJRAS..17..472E ]
Engver, N. 1966, Arkiv f. Astr. 4, 53. [BIBCODE 1966ArA.....4...53E ]
McNamara, D.H. 1969, P.A.S.P. 81, 68. [BIBCODE 1969PASP...81...68M ]
Thackeray, A.D., Wesselink, A.T. and Harding, G.A. 1962, M.N.R.A.S.
   124, 445. [BIBCODE 1962MNRAS.124..445T ]

* Cerro Tololo Inter-American Observatory is supported by the
National Science Foundation under contract No. AST 78-27879.