An upper limit on anomalous dust emission at 31 GHz in the diffuse cloud [LPH96] 201.663+1.643

Abstract

[ LPH96] 201.663 + 1.643, a diffuse H II region, has been reported to be a candidate for emission from rapidly spinning dust grains. We present Cosmic Background Imager (CBI) observations at 26 - 36 GHz that show no evidence for significant anomalous emission. The spectral index within the CBI band, and between CBI and Effelsberg data at 1.4 and 2.7 GHz, is consistent with optically thin free-free emission. The best-fitting temperature spectral index from 2.7 to 31 GHz, beta = - 2.06 +/- 0.03, is close to the theoretical value, beta = - 2.12 for T-e = 9100 K. We place an upper limit of 24% ( 2 sigma) for excess emission at 31 GHz as seen in a 6' FWHM beam. Draine & Lazarian spinning-dust models, with typical grain properties, are not a good fit to the spectrum of LPH96 when both Green Bank and CBI data are included. No polarized emission is detected in the CBI data, with an upper limit of 2% on the polarization fraction.