Astronomers are getting a better look at a region rich with newborn stars, the RCW 108 cloud deep in the Southern Milky Way, using the new SOFI instrument on ESO's 3.58-meter New Technology Telescope at the La Silla Observatory in Chile. The most recent images, released by ESO last week, offer some of the widest and deepest infrared views ever obtained of a stellar nursery. This area of the sky, located some 4,000 light-years away from the sun in the constellation Ara, is named RCW 108 after the last initials of astronomers A. W. Rodgers, C. T. Campbell and J. B. Whiteoak, who included it in a catalogue they published in 1960. It is a dark, molecular cloud now being destroyed by the ultraviolet radiation from neighboring stars in the NGC 6193 cluster.
The new pictures of RCW 108, taken in February 2000, are based on roughly 600 separate exposures with SOFI. Comparing the infrared images (above) with earlier visible-wavelength versions (left) reveals some interesting differences. The bright nebula IRAS16362-4845, in the center of the infrared image, for instance, appears much more prominent because it is deeply embedded in the cloud, and so dust particles heavily obscure it in visible wavelengths. It is because most young stars are still swaddled in the parental dust and gas from which they have formed that they are better seen in infrared wavelengths. Dust not only dims the light they give off but also reddens that light. This effect shows up in the SOFI images in that stars within the cloud seem redder than those outside it. The few stars that seem to be in the cloud and blue are actually in front of it. In general, the redder a star in the cloud appears, the more deeply embedded in RCW 108 it is.