COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3541 Konkoly Observatory Budapest 13 November 1990 HU ISSN 0374 - 0676 1990 Optical Elliptical Polarimetry and Centimeter Flux Observations of the Very Active Solar-type Star HD 129333 A. Elliptical Polarimetry The infant solar-type star HD 129333 has received considerable attention recently because it exhibits the highest level of chromospheric activity known for single G -type stars. An extensive account of this star has been given by Dorren and Guinan (1990). Because of the extreme activity of HD 129333, it was placed on the Flower and Cook Observatory (University of Pennsylvania) elliptical polarimetry observing program in 1988. A complete description of the polarimeter and observational technique is presented in Elias (1990) and Elias and Dorren (1990). A summary of the results from the 1988 and 1989 seasons (Elias and Dorren 1990) follows. Most of the observations were performed in blue light, although a few were performed in green light. The normalised Stokes parameters q, u, and v were all variable. The average linear polarization p[overline]_L(pL = square root(q*q + u*u)) was 0.12%+/-0.02% and did not deviate significantly from this value. Most of the circular polarization (v) measures were not statistically significant, but there were two highly significant measures close to -1%. After periodogram analysis, the linear polarization parameters q and u and the position angle Theta = 0.5*tanE-1*u/q exhibited periods close to 14 days; 13.95 days was deemed to be the best value. A plot of Theta versus phase is shown in Figure 1. Elias and Dorren (1990) have concluded that this 14-day variation is intrinsic to the star and not produced by the environment or the instrument. Differential saturation due to the Zeeman effect (Leroy 1962) is not considered likely as the mechanism for this variation because 1) the rotational period of the star is about 2.7 days (Dorren and Guinan 1990) and 2) the amount of linear polarization is an order-of magnitude larger than predicted and observed for this effect by Leroy and LeBorgne (1989). A better mechanism for the observed linear polarization is scattering (Thomson, Rayleigh, or Mie) from a circumstellar envelope, with the 14-day period possibly resulting from the orbital motion of an unseen companion. Additional HD 129333 elliptical polarimetry was obtained during the 1990 season; the results are listed in Table 1. The blue Theta measures (180 deg have been added or subtracted when necessary) have been incorporated into the Figure 1 phase plot. Although it is not possible to confirm the existence of the 14-day period observed during the 1989 season, the data from the 1990 season are not inconsistent with the ephemeris HJD 2447628.802 + 13.95E from Elias and Dorren (19D0). Further observations are necessary in order to investigate the possible binary nature of this star. Linear polarization spectra were obtained on HJD 2447930, 2448043, and 2448105 (see Table 1). Within errors, it appears that the spectra are flat, implying Thomson scattering, although Rayleigh and Mie scattering cannot be ruled out. It is possible, however, to rule out magnetic effects because the ultraviolet linear polarisation is not significantly larger than the blue linear polarization. B. Centimeter Flux Observations The cm observations of HD 129333 were performed using the NRAO (*1) Very Large Array (VLA) in the A/B hybrid configuration on 1990 June 27. The observations were performed at 20, 6, 3.6 and 2 cm, each with two pairs of intermediate frequency stages (IFs; these included both right- and left- handed circular polarisation). The IF bandwidths were 50 MHz except for the 20 cm IFs which had a bandwidth of 25 MHz. The primary calibrator was 3C286, and the secondary calibrators (B1950.0) were 1437+624 (20 cm) and 1435+638 (6, 3.6, and 2 cm). The visibilities were edited and calibrated at the VLA Array Operations Center (AOC) using natural weighting to maximize signal-to-noise. HD 129333 was not detected at any wavelength. The 3Sigma upper limits to the specific flux are as follows (1 Jy =10^-26 W m^-2 Hz^-1): 20 cm, 183 mJy; 6 cm, 81 mJy; 3.6 cm, 57 mJy; and 2 cm, 243 mJy. These values correspond to a specific luminosity of order 10^14 erg s^-1 Hz^-1 at a distance of 30 pc. These results are surprising because comparison with other chromospherically-active stars suggested estimates of the specific fluxes between 0.1 and 1.0 mJy. --------------------- *1 The National Astronomy Observatory is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation. Table 1 HD 129555 Elliptical Polarimetry -1990 Filter HJD PL Theta v (%) (deg) (%) Red 2447950.907 0.06(0.05) 156(14) -0.01(0.06) 2448043.674 0.05(0.05) 4(24) -0.01(0.06) 2448105.679 0.01(0.06) 21(90) +0.03(0.08) Green 2447930.884 0.10(0.04) 22(12) +0.10(0.09) 2448043.651 0.05(0.09) 119(49) -0.01(0.02) 2448105.657 0.09(0.03) 79(11) -0.12(0.08) Blue 2447930.862 0.08(0.08) 155(28) -0.09(0.11) 2447940.760 0.10(0.06) 76(17) +0.14(0.09) 2447948.707 0.09(0.05) 8(14) -0.14(0.09) 2447949.763 0.16(0.08) 19(14) +0.15(0.09) 2448043.593 0.11(0.08) 179(15) +0.19(0.13) 2448105.634 0.06(0.06) 38(31) +0.03(0.10) Ultraviolet 2447930.840 0.13(0.15) 49(31) +0.15(0.18) 2447949.794 0.24(0.15) 174(19) +0.02(0.29) 2448043.627 0.06(0.18) 94(82) -0.14(0.32) 2448105.611 0.13(0.14) 153(32) +0.03(0.17) -------------------------------------------------------- Note: Parenthesized quantities are 1 sigma errors. [FIGURE 1] Figure 1 The filled-in circles are from the 1988 to 1989 season and the open circles are from the 1990 season. The values from the 1990 season may differ by +- 180deg from Table 1. Dr. Nicholas M. Elias II United States Naval Observatory 34th St. and Massachusetts Ave., NW Code AD5, Building 52 Washington, DC 20392-5100 Dr. J. David Dorren Department of Astronomy and Astrophysics David Rittenhouse Laboratory, E1 University of Pennsylvania Philadelphia, PA 19104-6394 References: Dorren, J. D. and Guinan, E.F. 1990, to be published in Ap. J. Elias, N.M. 1990, Ph.D. thesis, University of Pennsylvania. [BIBCODE 1990PhDT.........2E ] Elias, N.M. and Dorren, J.D., 1990, A. J., 100, 818. [BIBCODE 1990AJ....100..818E ] Leroy, J-L. 1962, Annales d'Astrophys., 25, 127. [BIBCODE 1962AnAp...25..127L ] Leroy, J-L. and LeBorgne, J.F. 1989, Astron. Astrophys., 223, 336. [BIBCODE 1989A&A...223..336L ]