COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS NUMBER 742 Konkoly Observatory Budapest 1972 November 27 POLARIMETRIC OBSERVATIONS OF R CORONAE BOREALIS Multicolour polarimetric observations of R CrB were carried out in April-June and August-September, 1971, and in June, 1972. In 1971 the star was in quiet state (maximum brightness), and during the 1972 period of our observations it was in minimum (at the stage of rise of the brightness, 3 months after the beginning of the active phase). Measurements have been made on the 70 cm reflector at the Main Astronomical Observatory of the Ukrainian Academy of Sciences and on the 122 cm reflector at the Crimean Astrophysical Observatory with the photoelectric polarimeter built at Kiev (Bugayenko et al. 1958). The method of observations and reduction is similar to that described by us earlier (Kolotilov, Orlov and Rodriguez, in press). The standard errors of the values p cos2Theta and p sin2Theta (p is the amount of polarization, and Theta is the position angle of the plane of vibration) are 0.02 - 0.06%. The filters used for observations during maximum brightness had the following band halfwidths: 300A for lambda3730 650A for lambda7650; 120-200A for other (interference) filters. During the minimum wide filters with halfwidths of 650-800A were used. The results are given in the Table. The value of polarization of R CrB at maximum brightness is in good agreement with the data by Serkowski and Kruszewski (1969) obtained in January- March, 1968 in the UBV system, as well as with the Behr`s catalogue (Behr 1959) where values of p and Theta are given for a wide spectral band, 3500-6000A. These values are also represented in the Table. There are no other polarimetric observations of R CrB in the phase of minimum brightness to be compared with. Comparison of polarization of R CrB at maximum with that of a neighbor star HD 141352 (Sp F2) at the distance of 21' from R CrB (0.18% and 0.16% respectively, according to our observations in integral light) seems to suggest this polarization to be of interstellar origin. The observed increase of polarization and change of position angle, as well as the character of wavelength dependence of polarization at minimum indicate the appearance of intrinsic polarization during the active phase of the star. --------------------------------------------------------- Date Phase lambda,A p,% Theta,degr. Remarks --------------------------------------------------------- Between 1956 maximum 4600 0.26 131 Behr, 1959 and 1958 Jan.-Mar.1968 " U 0.17-0.22 6;53 Serkowski, B 0.09-0.19 95-111 Kruszewski, V 0.10-0.24 108-110 1969 June 1971 maximum 4120 0.10 70cm refl. 4500 0.18 Kiev 5040 0.32 6220 0.30 7200 0.15 Aug.-Sept.1971 " 3730 0.11 70.8 122cm refl. 4120 0.16 78.1 Crimea 4500 0.18 89.9 5040 0.17 85,9 5440 0.18 91.4 5960 0.19 96.5 6220 0.22 85.5 6530 0.16 86.8 6880 0.30: 96.5 7650 0.18 89.3 June 5/6-10/11 rise of 3900 0.78 135.0 70cm refl. bright- 4900 0.45 132.6 Kiev 1972 ness 5900 0.41 144.4 (~8.7m- 7650 0.21 132.8 8.2m_vis) -------------------------------------------------------- Main Astronomical Observatory M.Ya. ORLOV of the Ukrainian Academy of Sciences M.H. RODRIGUEZ Goloseevo, Kiev 252127 USSR References: Behr, A., 1959, Veroff.Univ.Sternwarte Gottingen, No. 126. Bugayenko, L.A., Bugayenko, O.I., Krugov, V.D., Parusimov, V.G., 1968, Astrometrica y Astrofisica, 1, 193, Kiev, Naukova Dumka Press. Kolotilov, E.A., Orlov, M.Ya., Rodriguez, M.H., Astr.Zhurnal (in press). Serkowski, K., Kruszewski, A., 1969, Astrophys.J. 155, L15. [BIBCODE 1969ApJ...155L..15S ]