COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3439 Konkoly Observatory Budapest 6 March 1990 HU ISSN 0374 - 0676 POLARIMETRY OF R CORONAE BOREALIS TYPE STARS AND RELATED OBJECTS During the 1988-89 period polarimetric observations of some R Coronae Borealis type stars (RCB), several hydrogen-deficient carbon stars (HdC) and related objects were obtained with the 60-cm reflectors of Soviet- Bolivian Observatory Santa Ana (Tarija, Bolivia) and Middle Asia Expedition of the Main Astronomical Observatory of the Academy of Sciences of Ukrainian (Mount Maidanak, Uz.SSR) using a spectrophotopolarimeter (Bugaenko and Guralchuk, 1985) and standard UBVR filters. The observations are given in Table I. From left to right the data tabulated are: star name, the epoch of observations in Julian date, the colour-excess E(B-V), percentage polarization P and position angle theta and their standard errors in the bands U,B,V,R and integral light (Int.) respectively. UBVR photometric observations were also obtained for several stars. The results are given in Table II. The typical photometric errors are about 0.01 m in V, 0.02 mag in (B-V), 0.03 mag in (U-B) and 0.02 mag in (V-R). All the stars were at the maximum brightness or near it. A detailed analysis of the results of polarimetric observations of RCB and related stars show absence of the intrinsic polarization at the maximum light and when weakening of brightness is about 2 mag. Thus, the polarization has interstellar origin. From here we evaluated the colour-excesses of these stars (Allen, 1977). They are comparable to values found by Rosenbush (1982) for some stars using intrinsic colours (in Table I values E(B-V) in the brackets are from Rosenbush (1982)). Following Rosenbush (1982) we added and defined more precisely the position of the studied stars on the Hertzsprung-Russell diagram (Rosenbush, 1986). UW Cen should be attributed to group I of stars (UV Cas, V CrA, R CrB, RY Sgr, SU Tau and members of LMC); AE Cir belongs to group II (S Aps, U Aqr, WX CrA, RT Nor, SV Sge, GU Sgr, RS Tel). However, according to Kilkenny (1989), AE Cir should be excluded from the list of R CrB stars. Y Mus has to be displaced in the region of extreme helium stars, near MV Sgr. Table I Name JD E(B-V) U. B V R Int. 2440000+ P% P% P% P% P% RCB-type S Aps 7568.8 0.10 - - 0.9+/-0.2 - - (<.13) 64+/-6 7600.7 - - .9+/-.3 - - 67+/-9 U Aqr 7834.1 .06 - - .5+/-.2 - - 158+/-8 UV Cas 7832.4 .4 - - 3.5+/-.2 - - (.66) 56+/-1 7833.2 - - 3.7+/-.2 - - 58+/-1 UW Cen 7507.8 .14 - - - - 1.2+/.4 56+/10 DY Cen 7568.8 .15 - - - - 1.3+/.8 57+/6 AE Cir 7623.8 .07 - - - - .6+/.4 49+/18 V482 Cyg 555.5 .31* - - 2.8+/-.1 36+/-1 V CrA 7411.6 .04 - - .3+/-.4 - - (.05) 162+/-12 7600.8 - - .5+/-.2 - - 172+/-11 WX CrA 7600.8 .11 - - 1.0+/-.2 - - (.05) 164+/-6 Y Mus 7647.6 .21 - - 2.4+/-.1 - - 85+/-2 RT Nor 7600.8 .14 - - 1.2+/-.2 - - (.02) 36+/-5 RY Sgr 7348.5- .06 .50+/.28 .54+/.07 .47+/-.07 .42+/.12 - -7438.5 (.06) 176+/16 180+/4 179+/-4 174+/8 MV Sgr 7623.9 .15 - - 1.3+/1.1 172+/8 CW-type RU Cam 7205.2 .05 - .24+/.12 .42+/.07 .35+/.08 - 69+/14 72+/5 73+/6 V553 Cen 7614.8 .02 - - .1+/.2 - 168+/94 EB-type nu Sgr 7624.9 .10 .60+/.10 .90+/.18 .82+/.06 .85+/.06 - 173+/5 174+/2 167+/2 174+/2 HD137613 7644.6 .08 - 64+/.10 .80+/.10 .39+/.10 - 78+/4 62+/4 76+/7 Unique V348 Sgr 7624.8 .24 - - - - 2.2+/.3 149+/4 rho Cas 7834.2 .16 1.51+./14 1.26+/.06 1.36+/.02 1.32+/.06 - 62+/3 57+/2 53+/1 51+/1 * - Observations were obtained together with N.N. Kiselev at the 1-m telescope of the Institute of Astrophysics of the Academy of Sciences of Tadzhik SSR. Table II Name JD V B-V U-B V-R 2447000+ U Aqr 839.3 11.04 .96 - RY Sgr 351.7 6.50 .75 .21 .55 371.6 6.19 .47 -.17 .42 372.7 6.18 .51 -.14 .42 380.7 6.44 .70 .13 .63 640.8 6.13 ·51 -.03 - 647.9 6.27 .66 .07 - SV Sge 839.3 11.93 2.20 - 1.88 HD 182040 372.7 6.94 1.05 .49 .83 A.E. ROSENBUSH and V.K. ROSENBUSH Main Astronomical Observatory 252127 Kiev, Ukranian SSR References: Allen, C.W.: 1977, Astrophysical Quantities, Moscow, "Mir", 446 p. [BIBCODE 1977asqu.book.....A ] Bugaenko, O.I. and Guralchuk, A.L.: 1985, in Photometric and Polarimetric Investigations of the Celestial Bodies (ed. Morozhenko A.V.), Kiev, "Naukova Dumka", p. 160. [BIBCODE 1985ppic.conf..160B ] Kilkenny, D.: 1989, Observatory, 109, 88. [BIBCODE 1989Obs...109...88K ] Rosenbush, A.E.: 1982, Astrometry and Astrophysics, 47, 17. [BIBCODE 1982AAfz...47...17R ] Rosenbush, A.E.: 1986, Kinematics Phys. Celest. Bodies, 2, 6, 83. [BIBCODE 1986KFNT....2...83R ]