Polarimetry of extrasolar Kuiper belt candidate stars

CHAVERO, C., GOMEZ, M., WHITNEY, B.A., SAFFE, C.

Rio de Janeiro, Brasil

Conferencia; IAU Symposium No 229: Asteroids, Comets and Meteors; 2005

Observatorio Nacional - Rio de Janeiro - Brasil

We present UBRVI polarimetry measurements for a group of 60 Vega-like candidate stars and complement these observations with V-band data taken from the literature for 87 additional objects. We find that roughly 50 of the analyzed sample has a polarization excess over the general interstellar value. In addition, the polarization of Vega-like candidate stars correlate with infrared color excesses, particularly at 60 and 100 micron. We caution, however, that poor IRAS data quality at longer wavelengths and background source confusion may affect this correlation. We analyze the wavelength dependence of the linear polarization of 17 of the observed objects with P_V greater than 0.2 (i.e., with polarization excess over the general interstellar value), and find that for at least 7 stars the measured polarization differs significantly from the Serkowski empirical interstellar law, suggesting an intrinsic (likely circumstellar) origin. Using a radiative transfer code, we reproduce the average level of polarization for the Vega-like objects, and estimate a lower limit to the total dust mass in the disks of about 1 x 10^-7 M_sun for these sources. We analyze the polarimetry distribution of Vega-like objects in relation to the Exoplanet host stars (i.e., stars associated with at least one likely planetary mass object). The corresponding polarimetry distributions are different within a high confidence level. Finally, we compare the metallicity distributions of the Vega-like, Exoplanet host and field main sequence stars, and find that Vega-like objects have metallicities quite similar (although not identical) to field main sequence stars and significantly different from the Exoplanet host group.