COMMISSIONS 27 AND 42 OF THE IAU 
             INFORMATION BULLETIN ON VARIABLE STARS 
                         Number 3750 
 
                                       Konkoly Observatory 
                                       Budapest 
                                       21 July 1992 

                                       HU ISSN 0374 - 0676 
 
 
     DISCOVERY OF RAPID OSCILLATIONS IN THE Ap STAR HD 150562 
 
 
 The cool Ap star HD 150562 was monitored 4.67 hr on the night JD 
2448411 as part the Cape Rapidly Oscillating Ap Star Survey. 
Inspection of the real-time data display at the telescope indicated 
the presence of rapid oscillations with a period P = 10.75 min and 
amplitude A = 0.75 mmag (Fig. 1.). The observations were acquired 
using the St Andrews Photometer attached to the 1.0-m telescope at the 
Sutherland site of the South African Astronomical Observatory. 
 
 The data were acquired in continuous 10-s integrations through a 
Johnson B filter with occasional interruptions for sky background 
measurements. An autoguider was used to track an off-axis guide star 
thus minimizing the effect of light variations caused by tracking 
errors in the telescope. The data were corrected for 
coincidence-counting losses, sky background, extinction and some 
Long-term (P > 0.5 hr) trends caused by sky transparency variations. 
The data were then binned to 40-s integrations. The resulting 
instrumental magnitudes were not placed on the standard system. 


                           [FIGURE 1]
                           [FIGURE 2]

 
 To confirm the presence of rapid oscillations, we observed this star 
again on nights JD 2448427, 8462, 8465, 8723, 8783, 8786, 8790 and 
8792. In Figure 2 we show the amplitude spectra acquired on three 
good nights. The prominent peak is at nu_1 = 1.55 mHz. The solid line 
in Fig. 1 is a sinusoid of frequency nu_1 = 1.55 mHz, with 
least-squares-fitted amplitude and phase, which has been plotted to 
facilitate the reader's perception of the oscillations. 
 
 Inspection of all available amplitude spectra suggests that the 
oscillations in HD 150562 are amplitude modulated. To refine our 
determination of nu_1 and to search for additional frequencies, we 
Fourier analyzed the last four nights together. However, the daily 
aliases are too severe to accomplish either of these goals. The value 
of nu_1 is ambiguous by 1 cycle day^-1 in these data; we cannot 
distinguish between nu_1 = 1.5585 mHz and nu_1 = 1.5470 mHz. Further 
observations and a detailed frequency analysis of the rapid 
oscillations of HD 150562 will be presented in a future publication. 
 
 
PETER MARTINEZ & D. W. KURTZ 
Department of Astronomy 
University of Cape Town 
Rondebosch 7700 
South Africa 
PETER @ UCTVAX.UCT.AC.ZA