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Astron. Astrophys. 357, 548-552 (2000)

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2. HD 36668

Borra (1981) obtained six magnetic measurements of HD 36668, a member of the Ori OB 1 association, and proposed three possible periods. North (1984) used 19 sets of Geneva photometry to find a period of 2.11211 days, which is close to one of Borra's values. The light curves show primary and secondary maxima which suggest that we are observing most of the stellar surface including both poles.

Fifteen, 46, and 54 sets of differential Strömgren photometry were obtained with the FCAPT during the 1995-96, 1996-97, and 1997-98 observing seasons, respectively (Table 2). Period analyses of the u values suggest a period one-half of that of North. But this was due to the presence of two maxima. Comparison with the B data of North showed a slight shift in phase and the need for a minor adjustment in the zero point of the ephemeris. The following ephemeris fits both sets of data

HJD(u max) = 2444988.375[FORMULA]0.003 + (2.11884[FORMULA]0.00004)E.

Fig. 1 shows the FCAPT values plotted with this period. The amplitudes for u , v , b , and y are 0.05, 0.035, 0.03, and 0.025 mag., respectively. The zero phase was set by bisecting the u primary maximum, which is also seen in the v , b , and y light curves. The secondary maximum is near phase 0.40 which may indicate an off-set dipole magnetic field. For v and b , the secondary maximum is suggestive and is not seen in y . These light curves and those of North show clear wavelength dependences. They may be indicative of a complex magnetic field and distribution of elements in the photosphere.

[FIGURE] Fig. 1. Differential FCAPT uvby photometry of HD 36668 (filled circles) plotted with the ephemeris HJD(u max) = 2444988.375 + 2.11884 E. Note that the secondary maximum in u is not seen as well in the other light curves.

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© European Southern Observatory (ESO) 2000

Online publication: June 5, 2000