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\IBVShead{4497}{21 July 1997}

\centerline{\ft MULTIPERIODICITY OF THE $\delta$ SCUTI STAR BR CANCRI}

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BR Cancri (=HD\,73175=SAO\,97975, also known as KW 45 in Praesepe cluster) was
discovered as a $\delta$ Scuti star by Breger (1973) on the basis of 
several-hour-long observations. 
It pulsates with a period of 0.038$\pm$0.005 days. 
The author found no more data available in the literature. 
For checking its variability, observations covering a total of ten nights were 
secured between February 14 and March 30 1997. The observations were 
carried out by using a three-channel high-speed photometer P45-A attached to 
a 85cm reflector of Xinglong Station of Beijing Astronomical Observatory, 
China. The photometer is especially used in WET, the Whole Earth Telescope 
network (Nather et al., 1990). 
The comparison star ($RA=08^{\rm h}38^{\rm m}32\fs 17, 
Dec=19\degr 27'54\farcs 5,2000.0,10.2V$) used was chosen carefully. 
No variation was found in its brightness. 
Furthermore, the constancy of comparison star was independently inspected with 
another star ($RA=08^{\rm h}37^{\rm m}38\fs 10, Dec=19\degr 31'06\farcs$, 2000.0, 11.5V) in one night. The data were 
acquired as continuous 10s exposures through Johnson's V filter. The data were 
corrected for the sky background contribution and the atmospheric extinction. 
In order to analyze pulsational frequencies, all the measurements were binned 
into 120s integrations by taking 12-point averages and the times of 
measurements of BR Cnc were converted into HJD. This way 684 datapoints were obtained. The characteristics of the light curve of BR Cnc 
is shown schematically in Figure 1 according to the high-time-resolution 
photoelectric photometry. The brightness variation appears to be multi-periodic.

After the application of consecutive prewhitening procedure and frequency 
analysis, at least 3 frequencies were resolved through a standard Fourier 
program Period (Breger 1990). Figure 2 displays the preliminary power spectra 
of three apparently exhibited\break

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Figure 1. One of the typical high-time-resolution V light curves of  
BR~Cnc observed on February 16 1997. Exposure time of each point is 
10s 
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Figure 2. The spectral window (in top panel) and power spectra of three 
suggested frequencies of BR Cnc. The fundamental frequency 26.0023 c/d is 
displayed in the second panel; the third and fourth panels correspond to 
10.4776 and 10.8994 c/d respectively. Note that different ordinates were used: 
for the DATA-00P ($f_{1}$), ordinate goes up to 1.45$\times$10$^{-5}$ mag from the
origin; for DATA-01P ($f_{2}$), ordinate goes from 0 to 6.0$\times$10$^{-6}$; 
for DATA-02P ($f_{3}$), the  peak value is just 3.2$\times$10$^{-6}$ power of mag; the bottom panel shows the power of the residuals of the fitting with 
3 frequencies above. Abscissa in cycles/day
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\noindent  frequencies: $f_{1}$=26.0023, $f_{2}$=10.4776 
and $f_{3}$=10.8994 cycles/day with a standard error of 0.007. The peaks 
at frequencies $f_{2}$ and $f_{3}$ could be influenced by a 1 c/d aliasing 
which can be seen from the spectral window. In view of the relatively short coverage the pulsational nature of this low amplitude $\delta$ Sct star deserves further investigation. 
 
I would like to thank Dr. Li Zhiping for valuable suggestion which greatly inspired me in the analysis of the  observational data. This research was granted by the  National Science Foundation of China.

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\beginauthors  
\authorsrightcol
Aiying ZHOU
Beijing Astronomical Observatory
Chinese Academy of Sciences
Beijing 100080, P.R.China
Internet: aiying@bao01.bao.ac.cn
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\references

Breger, M. 1973, {\it A\&A}, {\bf 22}, 247

Breger, M., 1990, {\it Comm. Asteroseismology} {\bf 20}, 1, Vienna: 
Austrian Academy of Sciences

Nather, R. E., Winget, D. E., Clemens, J. C., Hansen, C. J., Hine, B. P., 
1990, {\it ApJ}, {\bf 361}, 309

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