The new period determination of the $\delta$ Scuti star HR 5437

Liu Zong-Li, Jiang Shi-Yang, Zhou Ai-Ying, Liu Yan-Ying, Li Zhi-Ping
Beijing Astronomical Observatory, Chinese Academy of Sciences, 100012 Beijing, China

The photoelectric observations of HR 5437 were carried out between 1986 and 1988 at the Piszkéstetö Station of Konkoly Observatory of Hungary and the Xinglong Station of Beijing Observatory of China. Using the data obtained at the Xinglong Station in 1988 Jiang and Li (1988) discovered HR 5437 to be a $\delta$ Scuti variable star. They did not derive frequencies. From the 1988 data set obtained at the Piszkésteto Station and the Xinglong Station, Paparó et al. (1990) determined two frequencies. The first frequency is 8.437 cd^-1, the second is 12.362 cd^-1. Joining the 1988 data set and the data obtained at the Piszkéstetö Station in 1986-1987, Paparó et al. (1990) gave two other frequencies. The first is 8.5367 cd^-1, the second is 11.3759 cd^-1. Paparó et al. pointed out that due to the poor quality of the data distribution and the complex structure of the spectral window the precise values of frequencies were not found. Li and Jiang (1992) obtained only one frequency of 11.38993 cd^-1 from their data obtained in 1989. However, comparing with the results given by Paparó et al. (1990), Li and Jiang (1992) thought that the frequency of 8.5367 cd^-1 given by Paparó et al. (1990) was the fundamental frequency, the frequency of 11.38993 cd^-1 was the first overtone frequency. The situation is quite confused.

Figure 13: The light curves of HR 5437 obtained during 1997-1998. The ordinate is the v magnitude difference (HR 5437 - SAO 16408) normalized to zero. The abscissa is the time (+HJD 2450000). The fit of the two-frequency solution given in Table 12 is shown as a solid curve.

Figure 14: Power spectra of the 1997-1998 data of HR 5437. The ordinate is the Power (mag²). The abscissa is frequency (cd^-1).

In order to obtain the correct pulsation frequencies of HR 5437 and study its character we observed this star from 8 to 17 April 1997, and from 6 to 8 March 1998 using the 85 cm telescope at the Xinglong Station of Beijing Astronomical Observatory. The 4-channel photometer (Michel and Chevreton 1991) with Strömgren v filter was used. The star SAO 16408 was used as comparison, and SAO 16394 was used as check star. The three stars and sky background were observed simultaneously. The integration time was one minute. No evidence for any variability of SAO 16408 was found. Seven tracks of data were obtained for HR 5437 from 1997 to 1998 covering a period of 334 days. The light curves are shown in Fig. 13, where the ordinate is the v magnitude difference normalized to zero. The abscissa is the time (+HJD 2450000). Period analysis were made using the Hao's program (1991), the program PERIOD (Breger 1990), and PERIOD96 (Sperl 1996). After careful calculation of power spectra we obtained two frequencies. The computed two-frequency solution of the data is given in Table 12.

Table 10: The pulsation frequency solution of HR 5437.

Frequency	Amplitude	Phase	Standard error of fit
(cd-1)	(mag)		mag
11.3545	0.0071	0.052	0.002
5.9966	0.0030	0.65

The power spectra of the data are shown in Fig. 14 together with the spectral window. The frequency with strongest power in the second panel is the frequency of 11.3545 cd^-1. The frequency with strongest power in the third panel is the frequency of 5.9966 cd^-1. Due to the high signal to noise ratio of the power spectra the 11.3545 cd^-1 has the far highest peak . The two frequencies can fit the variable light curves very well. The fit of the two-frequency solution derived is shown as a solid curve (see Fig. 13). This work was supported by a research grant from National Natural Science Fund of China (NSFC). The authors would like to express their thanks.

References
Breger M., 1990, Comm. Asteroseismology 20, Austrian Acad. Sciences, Vienna Hao Jin-Xin, 1991, Pub. of the Beijing Astron. Observatory 18, 35 Jiang Shi-Yang, Li Zhi-Ping, 1998, Astronomical Circular, 22 Li Zhi-Ping, Jiang Shi-Yang, 1992, A&AS, 93, 87 Michel E., Chevreton M., 1991, ASPCS, 11, 332 Paparó M., Jiang Shi-Yang, Li Zhi-Ping, Kollath Z., 1990, IBVS, No. 3451 Sperl M., 1996, Delta Scuti Star Newsletter, 10, 5