Hill & Blake (1996) discovered that the peculiar CP star HR 1094 (= HD 22316) possesses a fairly strong magnetic field whose effective longitudinal field varies between -2200 and 600 gauss with an ephemeris
HJD (magnetic maximum) = 2449007.589 0.130 + 2.9761 0.0014 E.
This star is one of the few CP stars with Co II lines in its spectrum and is also very Cl overabundant (Sadakane 1992).
Seven, 35, and 46 observations with HD 23383 as the comparison star and HD 23594 as the check star were obtained respectively in the 1995-96, 1996-97, and 1997-98 observing seasons. Another 12 observations were obtained in 1997-98 using HD 21447 as the comparison star and HD 20536 as the check star. Although Hipparcos photometry (Adelman et al. 1998) suggested that the use of the latter stars was preferable to the use of the former, the standard deviations of the means do not confirm this. Scargle periodograms of the larger set of HR 1094 observations suggests several possible periods of which only 2.9749 days is compatible with the magnetic field variations. As the light curves are very similar for this period and that of Hill & Blake, and as the latter period phases the light variations better relative to that of the magnetic field, I have adopted their ephemeris.
Figure 1 shows the photometry as a function of phase. HR 1094 is a low amplitude variable with the amplitudes of u and b being 0.015 mag, v being of order 0.007 mag, and y being 0.01 mag. For comparison the magnetic extrema occur at phases 0.0 and 0.5. The minimum of u is at phase 0.3 and its maximum at 0.8. The light curve for v is almost constant with a weak maximum near phase 0.5. The light curves for b and y are in phase with maxima near phase 0.5. Thus the photometry suggests that HR 1094 may have complex surface abundance patterns.
|Figure 1: FCAPT uvby photometry of HR 1094 plotted according to the Hill & Blake (1996) ephemeris: HJD (magnetic maximum) = 2449007.589 + 2.9761 E|
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