Observations of infrared sources associated with on 1 and G 110.25+0.01.

The detection of three infrared sources, measured at the wavelength of 2.25 microns by a 77 K SbIn photometer, is reported. Cooled diaphragms yielded sky apertures from 6.3 to 25.2 arcsec and a 64 arcsec beam separation was adopted. IRS 1 is coincident with the radio continuum and maser sources of ON 1; IRS 2 is coincident with the CO peak; and IRS 3 is located about 1.8 arcmin south-east of the CO peak. The sizes of the three infrared sources at the wavelength of 2.25 microns, and the 1.27-3.95 micron energy distribution of IRS 3 are presented. The infrared sources IRS 1 and 2 are very faint, and they both have comparable fluxes, but the spectral slope of IRS 1 is significantly redder than the one observed for IRS 2. A model for IRS 1 and IRS 2 could be emission from dust clouds, powered by embedded sources, while IRS 3 could be a reddened cool giant star, possibly connected with the CO cloud. During the exploration of the S 156 region at 2.25 microns, an infrared source (G 110.25 plus 0.01, IRS 1) was detected, which is very close to the secondary peak observed by Blair et al. (1975).