Physical Properties of Spicules from Simultaneous Spectro-Polarimetric Observations of He I and Ca II Lines

Abstract

We present full Stokes observations from SPINOR in the \ion{Ca}{2} infrared triplet and the \ion{He}{1} multiplet at 1083 nm from which some properties of spicules have been derived. There are important advantages in multi-line observations, particularly from different elements. We find that the orientation of the plane of polarization is very different for the Ca and He lines, which provides the first direct model-independent evidence for magnetic fields in spicules. Our data shows that the Ca and He lines have almost identical widths. Since the Ca atom is 10 times heavier than He, we are able to conclude that most of the broadening is non-thermal ($\simeq$16 km s$^{-1}$) and to set an upper limit of 13 kK to the spicular temperatures. The bisectors of the lines span a velocity range of over 15 km s$^{-1}$ for the He line and 30 km s$^{-1}$ for the Ca ones. The vertical gradient of line-of-sight velocities is also very different for both elements. We obtain 2.8 km s$^{-1}$ Mm$^{-1}$ from He versus 6.4 km s$^{-1}$ Mm$^{-1}$ from Ca. These properties, and others from similar observations, should be taken into account in future physical models of spicules.