Appendix A: polarization computations
The polarization level P together with the position angle of the polarization vector are obtained through 3 measurements through linear polaroids, at 3 different angles : , and . From the 3 corresponding intensities , , and , we deduce the Stokes parameters I, U and Q, together with their uncertainty :
and we compute the degree of polarization P and the position angle and their uncertainty from:
Note that an equivalent form of these equations was first used by Redman et al. (1986). Also, the equations given here (including the errors) were derived by Asselin (1991) and used (but not given) by Asselin et al. (1996). We give them all here for completeness and future reference.
© European Southern Observatory (ESO) 1998
Online publication: September 30, 1998