COMMISSIONS 27 AND 42 OF THE IAU 
           INFORMATION BULLETIN ON VARIABLE STARS 
                        Number 3741 
 
                                               Konkoly Observatory 
                                               Budapest 
                                               29 June 1992 
 
                                               HU ISSN 0374 - 0676 
 
  
 
     THE LIGHT CURVE OF THE Ap VARIABLE HD 153947=V974 Sco ^* 
 
 
  The variability of HD 153947=NGC 6281-9=V974 Sco was pointed out by North et 
al. (1988); Feinstein & Forte (1974) did not support its membership to NGC 6281, while 
Bolton & Herbst (1976) and North et al. (1988) considered it an open question. The 
latter authors also reported a photometric period of 2.662+/-0.003 d; from their Fig.1 a 
time of maximum light at HJD 2446966.96+/-0.05 can be derived. 
  In April and May 1992 we observed the delta Scuti star V922 Sco, located near NGC 
6281, with the ESO 50-cm telescope and we decided to include V974 Sco in the 
observing cycle. On each night, 5-8 measurements were collected and grouped into the 11 
normal points listed in the table. The V standard magnitudes were calculated assuming 
V=7.444 for the comparison star HD 153426, as obtained from the observation of 
some nearby standard stars. V974 Sco has a faint companion star, located about 18 
arcsec further east and not previously reported: we measured a difference of 3.8 mag in 
V-light. 
 
  The period search was performed using a least-squares method and we were able 
to confirm the photometric period reported by North et al. (1988). The figure shows 
the normal points with the interpolating light curve, calculated by including also the 
first harmonic 2f. The V light amplitude is 0.06 mag, in good agreement with the 
0.07 mag amplitude reported by North et al. (1988). The derived time of maximum 
is HJD 2448740.72+/-0.03; the elapsed cycles from North et al.'s maximum should be 
666, giving a period of 2.6633+/-0.0001 d, but 665 or 667 cycles are also possible. The 
standard deviation of the fit is 0.0055 mag: this value is 2-3 times greater than the 
expected one. This discrepancy can be due to the contaminating light from the close 
companion, only a few arcseconds outside the diaphragm field, or to a slight variability 
of HD 153426=NSV 08104. 
 
* Based on observations collected at European Southern Observatory, La Silla, Chile 
 
                      Table I 
 
                Hel. J.D.      V 
               2448732.88    8.759 
                  8734.73    8.797 
                  8735.89    8.796 
                  8736.87    8.826 
                  8743.83    8.780 
                  8743.91    8.789 
                  8745.82    8.779 
                  8745.91    8.762 
                  8746.80    8.804 
                  8746.87    8.805 
                  8746.91    8.807 


                                   [FIGURE 1]


 
                           E. PORETTI 
                           Osservatorio Astronomico di Brera 
                           Via E. Bianchi, 46 
                           22055 Merate - Italy 
 
References: 
Bolton C.T., Herbst W., 1976, Astron. J. 81, 339  [BIBCODE 1976AJ.....81..339B ]
Feinstein A., Forte J.C., 1974, Pub. Astron. Soc. Pacific 274, 284  [BIBCODE 1974PASP...86..284F ]
North P., Jasniewicz G., Waelkens Ch., 1988, Inf. Bull. Var. Stars n. 3199