COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS NUMBER 495 Konkoly Observatory Budapest 1970 December 9 THE OPTICAL POLARIZATION OF NOVA Del 1967 From Aug. 2., 1967 to Nov. 20, 1967 the optical polarization of Nova Delphini 1967 has been observed. The observations have been carried out with the Zeiss refractor 65/1055 cm of Belgrade Astronomical Observatory. The photoelectric polarimeter (Oskanjan et al., 1969) without filters and slightly modified has been used. The observed degree or polarization in percents, P, and the position angle of the plane of vibration, Theta, of the Nova are shown in Table I and in Figure 1. The lowest curve in the same Figure represents the amount of polarization of the comparison star BD +19deg4484, All individual measurements have been obtained by one-minute integration of the observed polarimetric signal. Table I Date JD 24397 p% Theta deg 1967 VIII. 2 705.500 1.13 20 5 708.504 1.60 49 8 711.560 1.49 28 10 713.438 1.45 25 IX. 4 738.307 1.04 24 8 740.299 1.03 34 24 758.357 0.92 29 28 760.378 1.17 20 30 764.356 0.89 24 X. 8 770.258 1.10 10 12 778.322 1.97 31 20 784.281 1.51 36 22 788.396 1.83 31 24 788.340 1.85 40 28 790.319 1.66 24 XI. 2 797.219 2.81 32 14 809.252 1.93 29 18 813.219 1.18 11 20 815.250 1.50 27 [FIGURE 1] The r. m. s. error of a single measurement in the case of the comparison star amounts to +/-0.34%. Taking into account the brightness difference between Nova and the 6th magnitude comparison star, we can ascribe the same value as an upper limit of the error to the observations of the Nova. On the other hand, the r. m. s. error of one-minute single measurements of the position angle of the plane of vibration of a 1% polarized 8th magnitude standard star amounts to +13deg. A similar scatter about the mean value of 0m = 28deg in the case of the Nova can also be noticed, The degree of polarization of the Nova from Aug. 2 to Oct. 6; was lower than 1.5%, and from Oct. 6 to Nov. 14, was higher than 1.5% with an increase to 2.8% on Nov. 2. It was noticed that seven from nine values of P higher than the average appeared simultaneously with the 0 values higher than the average. However, the correlation coefficient amounting to +0.42 does not confirm any linear correlation between P and Theta. Nevertheless the observed time variation of polarization is in accordance with H. D. Morrison and W. Liller's (1968) measurements and seems to be real. The observed plane of vibration of the electrical vector is parallel to the galactic equator what could suggest the interstellar origin of the observed polarization, or at least, a considerable interstellar component in it. But Hutchings' (1969) statement that the Nova is closer than 400 pc agrees well with Zellner's (1969) conclusion, based on the observed untypical wavelength dependence of P, that the Nova's polarization can not be of interstellar origin. Furthermore, according to the rather scarce polarimetric observation of the field stars (available data only for HD 196035 and HD 196775, Hall 1958) the interstellar contribution to the observed polarization is probably not higher than PM = 0.4% in the direction Theta = 7deg. As more definite conclusion on the interstellar polarization is impossible without some more data on the closer field stars and a more certain estimation of the distance of Nova, at this stage one should take the observed polarization as mainly intrinsic. JELISAVETA ARSENIJEVIC and KUBICELO ALEXSANDAR Astronomical Observatory in Belgrade References Hall J. S., 1958, Publ. of the U. S. Naval Obs., second series, 17 VI [BIBCODE 1958PUSNO..17....1H ] Hutchings J. B., 1969, Mass loss from Stars, Ed. M. Hack, (Proc. of the Second Trieste Coll. on Astroph.) [BIBCODE 1969ASSL...13..290H ] Morrison N. D. and Liller W., 1968, A. J. vol. 73, No 5, p. II, Oskanjan V,, Kubicela A. and Arsenijevic J., 1969, Bull. Astr. Obs. Beograd, 27, 1. [BIBCODE 1969BOBeo..27....1O ] Zellner B., 1969, Mass Loss from Stars, Ed. M. Hack, (Proc. of the Second Trieste Coll. on Astroph.) [BIBCODE 1969ASSL...13..300Z ]