Published online by Cambridge University Press: 25 May 2016
We are presently carrying out a northern hemisphere survey of the Galactic Hα emission. Our instrument, the Virginia Tech Spectral Line Imaging Camera (SLIC) utilizes a fast objective lens (f/1.2) with a cryogenically-cooled TK 512×512 CCD. A filter wheel in front of the lens allows us to select interference filters, including a narrowband Hα filter and a broader bandpass continuum filter in a line free part of the spectrum. The fast optics in combination with the low noise CCD result in sub-Rayleigh sensitivity at confusion limited levels. (1 Rayleigh = 106/4π photons cm–2 s–1 sr–1.) This corresponds to an emission measure sensitivity of ≈ 1 pc cm–6. Parameters of our system are given in Table 1.