Detection of an Extended Near-Sun Neutral Helium Cloud from Ground-based Infrared Coronagraph Spectropolarimetry
Sensitive spectropolarimetric observations from the Haleakala SOLARC coronagraph and infrared imaging spectropolarimeter have detected an extended diffuse surface brightness flux at the 1083 nm wavelength of neutral helium (He I). This has the polarization signature of light scattered by an extended He I cloud in the vicinity of the Sun. The He I scattered surface brightness appears to be consistent with a previous eclipse measurement and satellite observations of the local interstellar medium (LISM) helium wind (LISW), obtained using observations of the He I UV resonance line at 58.4 nm. The sensitivity of the infrared coronagraphic method suggests that the LISW interaction with the local solar wind can have observable consequences that may yield a useful ground-based technique for studying the coronal and interplanetary plasma.