The Birth of Stars in Serpens Click here for an image without labels.

Serpens is a busy star-forming region and a popular target for astronomers studying the birth of stars. The above "colour" image was constructed from 3 separate mosaics taken with a molecular hydrogen filter, an ionised iron filter and a broad-band J filter. Molecular hydrogen (H₂) is abundant throughout the galaxy, though it is only detected if heated to thousands of degrees. This occurs in shocks in jets, and we can see two examples of "protostellar jets" in this image (labelled molecular hydrogen jets). Iron is also excited in jets, although only if the gas is heated to even higher temperatures -- tens-of-thousands of degrees! Thus, the absence of iron emission from the jets observed in Serpens immediately tells us something about the physics of these flows; they must be low-excitation jets made up of molecules rather than atoms and ions. The image of the HH 1 jet shown elsewhere in the UKIRT gallery gives a nice example of a jet that radiates in H₂ and iron emission.

Close-up images of the two molecular hydrogen jets

Apart from molecular jets, we also see some of the deeply embedded young stars in this region - though we don't see all of them. The very youngest stars are obscurred from view even at UKIRT's near-infrared wavelengths. To study these targets we must observe at very long "mid-infrared" or "submillimetre" wavelengths. A star that is not hidden in the cloud, a foreground star for example, would appear white in this "three-colour" image (there is an example on the left of the image); an embedded young star, on the other hand, would appear reddish, since light at shorter wavelengths is absorbed by the gas and dust in the region.

The source labelled "Deeply Embedded Outburst Source" is one of the more interesting young stars in this region. A few years ago it was observed to become 50-times brighter than it is today. This "flaring" occurred over a period of only a year or so. The event is probably associated with bursts of accretion which feed the surrounding gas and dust onto the forming young star. This Deeply Embedded Outburst Source is probably the infrared counterpart of "FU Orionis" outburst sources, which are observed at optical wavelengths.

Data obtained during UFTI engineering - May 2001 (CJD) - and reduced on-line with ORAC.