Observations of the infrared extinction of IRS 5 in W3 compared with the galactic center and the Becklin-Neugebauer object.

Abstract

Observations of the 8-13 spectrum of IRS Sin W3 are presented, indicating that it is a luminous object suffering a large extinction by an extended dust cloud. The cool source in W3, which has been observed at 100 , is probably associated with this obscuring cloud. When comparison is made with similar spectra of the Becklin-Neugebauer object in Orion and the galactic center, IRS 5 appears to be an extremely compact dust cloud optically thick at 10 and of high luminosity, probably containing a massive protostar. Evidence is also presented indicating that the 10- emission from the galactic center and the Becklin-Neugebauer object is thermal radiation from optically thin dust of the same composition as that obscuring all these sources. Subject headings: infrared sources - nebulae - pre-main-sequence stars