We present a study of two spectral lines, Fe I 6173 Å and Ni I 6768 Å, that were candidates to be used in the Helioseismic and Magnetic Imager (HMI) for observing Doppler velocity and the vector magnetic field. The line profiles were studied using the Mt. Wilson Observatory, the Advanced Stokes Polarimeter and the Kitt Peak-McMath Pierce telescope

We propose a new approach to minimize the instrumental polarization (IP) of current polarimetric observations. It is shown how the instrumental polarization can be deduced and removed, by using lines with no intrinsic linear polarization. Notably, no specific understanding of the polarizing properties of our optical setup is required. For the

Recordings of the full Stokes vector of filaments in the Hα and He I D3 lines were obtained at the Gregory-Coudé telescope in Locarno with the polarimeter ZIMPOL. The aim was to perform preliminary studies to explore the presence of forward scattering polarization. The observations show linear polarization signatures, whose interpretation is still

A large set of high-precision, full-Stokes spectro-polarimetric observations of prominences in He I D3, Hα, and Hβ lines has been recorded with the ZIMPOL polarimeter at the Gregory-Coudé Telescope in Locarno. The observational technique allows us to obtain measurements free from seeing-induced spurious effects. The instrumental polarization is

The polarization spectrum of OJ287 was obtained during the 1993/94 observing campaign within the OJ-94 International Collaboration. Data were taken on December 17-18-19/1993, an on Januarty 11-12/1994. Between both periods of observations, OJ287 showed minor flare activity, where brightness raised from V=15.75 to V=15.25, and the polarization

Planetary nebula NGC6543 has a complex structure with a central hot bubble showing both point- and plane symmetry, and a large outer halo that is likely interacting with the local ISM. Between these two structures the HST has revealed a series of a least nine regularly spaced concentric circular rings that are faint and have low contrast. The