We present observations of Galactic { H } \alpha emission along two declination bands where the South Pole cosmic microwave background experiment reports temperature fluctuations .
The high spectral resolution of our Fabry–Perot system allows us to separate the Galactic signal from the much larger local sources of { H } \alpha emission , such as the Earth ’ s geocorona .
For the two bands ( at \delta = -62 °and -63 ° ) , we find a total mean emission of \sim 1 R with variations of \sim 0.3 R. The variations are within the estimated uncertainty of our total intensity determinations .
For an ionized gas at T \sim 10 ^ { 4 } K , this corresponds to a maximum free–free brightness temperature of less than 10 \mu K at 30 GHz ( K–band ) .
Thus , unless there is a hot gas component with T \sim 10 ^ { 6 } K , our results imply that there is essentially no free–free contamination of the SP91 ( Schuster et al .
1993 ) and SP94 ( Gunderson et al .
1995 ) data sets .