INTERMEDIATE-RESOLUTION SPECTROPOLARIMETRY OF A SMALL SAMPLE OF QUASARS

We present spectropolarimetric observations of a sample of three quasa rs selected because of their very different broad-band polarization pr operties. All of the objects in the sample show frequency-dependent po larization degree (FDP), and two of them also show frequency-dependent polarization position angle (FDPA). We have not detected polarization in the spectral emission lines in any object of the sample, although the possibility exists that the iron blends in CTA 102 may be polarize d. Our observations show important differences between the three objec ts. While 3C 273 has been previously discussed in terms of a multiple synchrotron source model, a conclusion supported by our results, this seems not to be the case for 3C 345. We examine a number of processes capable of generating the observed FDP and FDPA of this object. A comb ination of a nonthermal source and scattering from dust or gas in the local interstellar medium can explain our observations, although some restrictions must be imposed to avoid polarization of the spectral emi ssion lines. The quasar CTA 102 shows a very complex wavelength-depend ent polarization, which may be related to the iron blends in the spect rum. We also present a statistical test developed by us to examine the possible polarization of the lines.