4 HD 192678

Leroy (1995) found the time variations of the Stokes parameters of HD 192678 (= V1372 Cyg = BD +53$^{\circ}$ 2368) could be described as

JD (magnetic maximum) = 2444890.17 + 6.4186 E.

Mathys & Lanz (1992) demonstrated that the determination of its period by Stepien (1968) of order 18 days was incorrect. Wade et al. (1996) presented a magnetic model consisting of an oblique rotating dipole with modified field line inclinations. The dipole has $\iota$ = 173$^{\circ}$ and $\beta$ = 120$^{\circ}$. Their ephemeris uses the same period, but a slightly different zero point. Essentially the surface magnetic field is strongest near phase 0.00 and weakest near phase 0.50.

We obtained 77 differential uvby observations of HD 192678, 45 during the 1995-96 and 32 during the 1996-97 observing season (Table 4). As our analyses revealed a period close to that of Leroy's, we adopted his ephemeris and found that it was adequate to describe our observations. To improve the period requires photometry for this star over a longer period of time. Figure 3 shows the uvby photometry as a function of phase. HD 192678 is brightest in u when the surface magnetic field strength is weakest. The amplitude in u is 0.017 mag and in b is about 0.010 mag while this star is essentially constant in v and y. The light curves for u and b are shifted by about 0.15 in phase with u reaching its maximum before b. This behavior is consistent with the need for a complex magnetic model such as that of Wade et al. (1996).

  

Figure 3: Photometry of HD 192678 plotted with the ephemeris of Leroy (1995) JD (magnetic maximum) = 2444890.17 + 6.4186 E. The FCAPT uvby values are indicated by + signs