Bioastronomy 2002: Life Among the Stars IA U Symposium, Vol. 213, 2004 R.P.Norris and F.H.Stootman (eds.) Polarimetric & Spectropolarimetric Properties of FG K Type Stars and Extrasolar Systems S. Ortolani t, F. Tamburini t & A. Bianchini! t Universitd di Padova, Dipartimento di Astronomia, Vicolo dell'Osservatorio 2, 1-35122 Padova, Italy. emails:bianchini@pd.astro.it.ortolani@pd.astro.it t Institute oj Cosmology and Gravitation, Univ. oj Portsmouth, P02 lEG, Portsmouth, UK email: Jabrizio.tamburini@port.ac.uk 1. Introduction The study of extra solar planets represents a new exciting frontier for modern astronomy. Most of the results on extrasolar systems are obtained with Doppler surveys. Here we suggest a different approach aimed to study the polarimetric properties of the residual interplanetary dust. Dust can produce observable effects such as infrared emission excess (Beckwith & Sargent 1996; Spangler et al. 2001) and partial polarization of the star light via scattering (Mauron & Dole 1998; Yudin 2000), like in (3 Pictoris (Voshchinnikov & KriigeI1999). Some polarization could also be produced by a giant planet in a close orbit around the star (Saeger et al. 2000), but the resulting effect is too weak to be responsible for the polarizations actually observed. 2. Polarization properties The polarization data are taken from the Heiles catalogue (Heiles 2000) by se- lecting stars within a distance of 70 pc, that roughly corresponds to the largest distance amongst the observed extrasolar planet systems so far observed. The main characteristics of the extra-solar planetary systems within our sample are given in the Planet Encyclopedia (Schneider 2002). The errors in the polar- ization measurements are those reported in Heiles catalogue, typically around 0.03%. We have compared the polarization distribution of extrasolar systems to that of a selected sample of stars without planets 1. The two distributions shown in Fig. 1 are different, as confirmed by the Kolmogorov-Smirnov test with 99% confidence level. Single stars show a maximum between p = 0.01 - 0.02, while stars with planets show a well defined maximum around 0 and a rather steeper decline towards higher polarization degrees. lSince we do not observe extrasolar systems with p > 0.09, we have taken this value as an upper limit also for the sample of single stars. 69 use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S007418090019299X Downloaded from https://www.cambridge.org/core. IP address: 107.174.32.29, on 14 Jun 2019 at 01:34:27, subject to the Cambridge Core terms of