Pedersen & Thomsen (1977) first found the spectrum variability of 12 CMa (HR 2509, HD 49333), a He weak star which is slightly hotter than the Si stars. According to Levato et al. (1996) its v sin i = 60 km s-1. Bohlender et al. (1993) using their own magnetic measurements of this star and previous measurements of the strength of He I 4026 derived an ephemeris
JD(max ) = 2447311.565 + (2.180100.00020) E.
For both the 1997-98 and the 1999-2000 observing seasons 33 sets of uvby data were obtained. When the Scargle (1982) algorithm was used a period of 2.17969 days was indicated. However, the 2.18010 day period was found to give better agreement between the two years' worth of data especially for the primary minimum and so the above ephemeris was adopted.
Figure 4 shows the light curves. The light minima are centered near phase
0.25 which is He I line strength maximum and where the magnetic equator
crosses the line of sight. The other phase of
= 0 occurs at phase
0.75. The light curves are in phase with amplitudes of about 0.065 mag,
0.045 mag, 0.040 mag, and 0.035 mag for u, v, b, and
y, respectively. The primary minimum is definitely asymmetric.
|Figure 4: Differential FCAPT uvby photometry of 12 CMa using the ephemeris JD(max ) = 2447311.565 + 2.18010 E. Each filter is plotted using a different symbol|
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