5 HR 6718

Winzer (1974) found that HR 6718 (= HD 164429 = V771 Her) was a relatively low amplitude photometric variable with its largest amplitude of 0.03 mag in U. The variation in B is less than 0.01 mag and is smaller than the V amplitude. His period of 0.51747 days was confirmed by Catalano et al. (1979). Burke & Barr (1981) obtained additional UBV photometry, found slightly larger amplitudes, and essentially the same period of variability. For such a short period variable, its v sin i value of 85 km s^-1 (Abt & Morrell 1995) suggests it is seen very close to pole-on which in part explains its low degree of variability. Bohlender et al. (1993) made a measurement of its magnetic field: 640 $\pm$ 480 G.

Seventy-seven sets of uvby differential values were obtained with the FCAPT, 11 in 1995-96, 35 in 1996-97, and 31 in 1997-98. A periodogram analysis of the u data showed that the period was close to either a half-day or a day. When we used Winzer's (1974) and Burke & Barr's (1981) U data rezeroed to be as consistent as possible with our data we had increase the period slightly and make a slight adjustment to Winzer's zero epoch. Hence

HJD(u$_{\max}$) = 2441450.808 $\pm$ 0.005 + (0.51899 $\pm$ 0.00004) E.

The uvby photometry plotted with this period (Fig. 4) shows that u is definitely variable with an amplitude of 0.045 mag. Further v, b, and y are probably variable with amplitudes of order 0.015 mag, 0.01 mag, and 0.01 mag, respectively. In addition these light curves are probably shifted in phase by 0.1 with respect to u which indicates a complicated surface distribution of abundances.

  

Figure 4: Photometry of HR 6718 plotted using the ephemeris HJD(u$_{\max}$) = 2441450.808 + 0.51899 E. The FCAPT uvby values are shown as + signs while Winzer's and Burke & Barr's U values as rezeroed to the u scale are closed diamonds and closed circles, respectively