2 33 Tau

Winzer (1974) mistakenly thought that 33 Tau (= HD 24769 = HR 1221) was a magnetic CP star and found a period of 1.48 days. Instead (Morris 1985) it is a close binary star, an ellipsoidal variable. The photometric variations show two maxima and minima each orbital revolution with the two minima coinciding with the time of conjunction. Hube (1981) derived the orbital elements from radial velocity measurements and gave as the ephemerides for the phase of the velocity maximum = HJD 2430000.626 + ($2.975272\ \pm\ 0.000004$) E. Gulliver et al. (1985) obtained UBV photometry and modeled the system.

Forty-three and 38 sets of Strömgren observations were obtained during the 1995-96 and 1996-97 observing seasons, respectively. An examination of the y photometry using the Scargle periodogram suggests a frequency of 0.3305 per day (a period of 3.0266 days) or its alias of 0.6695 per day. A periodogram analysis of the V data of Gulliver et al. (1985) to our surprise also gave the same results. But that of the radial velocities confirms Hube's period. The 3.0266 day period results in a light curve with a single maximum and a single minimum and a radial velocity curve which is not easily interpreted.

Figure 1 shows our FCAPT data plotted with Hube's ephemeris. Our light curves look like those of Gulliver et al. We include their V values in our y plot after we renormalized them to our comparison star. We did not adjust the initial epoch as for three of the four light curves it is satisfactory. The light curves show differences between the first and second halves of the period. The amplitudes are about 0.07 mag in u, 0.06 mag in v, 0.05 mag in b, and 0.06 mag in y which compare with Gulliver et al.'s 0.07 mag in U, 0.055 mag in B, and 0.05 mag in V. Additional uvby values near the extrema are needed to refine these values. That our y values fall on top on their adjusted V values using Hube's period indicates that his period error estimate should be reduced by a factor of 4.

  

Figure 1: Photometry of 33 Tau plotted according to the phase of the radial velocity maximum from Hube's ephemeris: HJD 2430000.626 + ($2.975272\ \pm\ 0.000004$) E. The closed squares are FCAPT values from this paper and the crosses in the y panel are the V data of Gulliver et al. transformed to the FCAPT system