UBVR polarimetry of evolved carbon stars near the galactic equator.
LOPEZ J.M. and HIRIART D.
Abstract (from CDS):
We present polarimetry and photometry in the UBVR bands of nine low Galactic latitude carbon stars (| b II| ≤ 15°) over a period of one year: V384 Per, ST Cam, S Aur, CL Mon, HV Cas, Y Tau, TT Cyg, U Cyg, and V1426 Cyg. We have corrected the observed values for the effects of extinction and polarization by the interstellar medium to obtain the intrinsic polarization and photometry of the stars. All the observed objects present polarization in at least two bands. There is a statistical correlation between the temporal mean polarization <p> at each filter band and the IR color K -  with the redder stars tending to be more polarized. A related trend is found between polarization and mass-loss rate in gas. The degree of polarization increases with the mass-loss rate at around. We found two stars–TT Cyg and ST Cam–that increase polarization with decreasing mass-loss rate below this value. Multiple observations of TT Cyg, U Cyg, and V1426 Cyg during the campaign show no correlation between polarization and luminosity in any of the UBVR bands. Therefore, the distribution of the scatterers shall vary with time in a very irregular way.