POLARIZATION VARIABILITY AMONG WOLF-RAYET STARS .7. THE SINGLE STARS WR-14, WR-25, AND WR-69

We have monitored over an interval of 1 month the linear polarization in visible light of three single Wolf-Rayet stars, WR 14 (WC6), WR 25 (WN7), and WR 69 (WC9). As for other early-type WC stars, WR 14 is not significantly variable (at the sigma approximately 0.03% level) during this set of observations; however, its mean polarization level is significantly different from its value in 1987. The two other stars do vary (sigma approximately 0.06%) as expected for late-type W-R stars of either sequence. The high value of P(max)/E(B-V) greater-than-or-equal-to 11 for WR 25 suggests an extremely high efficiency of grain alignment in the line of sight to the star. The wavelength dependency of the polarization angle, as well as long-term variability in the U band, suggest some intrinsic polarization component as well for this star.