The continuum radiation of Quasars (QSO) and the line radiation of
SiO masers is polarized, in single dish and interferometer
observations from a few percent to 10
for QSO's, and
up to
70 - 80
for the individual components of SiO
masers. VLBI observations are normally made at Left Hand-Circular
Polarization (LCP =
) in order to eliminate amplitude
modulations of a polarized source due to hour angle variations.
For polarization observations, measurements are made at LCP and
RCP (right hand-circular,
) polarization. The Stokes
parameters I,Q,U,V, describing the polarization, and the complex
correlations
,
,
,
are
related by
= I + V;
= I - V;
= Q +
iU; and
= Q - iU ([Kemball et al. 1995]). cm
Table 3.5 summarizes the possibility of VLBI
polarization observations (status 2000) at 86GHz. The BIMA (Hat
Creek) interferometer can be phased and split into 3 antennas LCP
and 3 antennas RCP; this will eventually also be possible with the
PdB interferometer. cm Polarization
observations at 86GHz of QSO's are so far without convincing
success, mainly because of their low degree of polarization; VLBI
polarization observations at 86GHz of SiO masers are in
progress.
Telescope | Polarization | Bandwidth |
(number of channels, 4MHz) | ||
Effelsberg | 14 LCP | 122 MHz LCP |
Onsala | 14 LCP | 122 MHz LCP |
+ Pico Veleta | 7 LCP / 7 RCP | 56 MHz LCP / 56 MHz RCP |
+ Haystack | 7 LCP / 7 RCP | 56 MHz LCP / 56 MHz RCP |
Amherst | 14 LCP | 122 MHz LCP |
+ Pietown | 4 LCP / 4 RCP | 28 MHz LCP / 28 MHz RCP |
+ BIMA | 7 LCP / 7 RCP | 56 MHz LCP / 56 MHz RCP |