Fig. 1: Spectra of HCO+ from four quadrants around one of our cores, showing profiles typical of gravitational infall. These correspond to a very high mass infall rate of ~10-2 Msun/yr.

We have made significant progress on 2 major projects in 2005, each aimed at systematically addressing some of the outstanding mysteries of star fomation. Using the Mopra dish of the Australia Telescope, CHaMP is collecting a large database of properties of medium- and high-mass star formation throughout the Milky Way by looking at different tracers of dense interstellar gas. In collaboration with Yoshi Yonekura at Osaka Prefecture University, and Yasuo Fukui and his NANTEN group at Nagoya University, for the first time we are building a reliable picture of the typical evolution of these rare but powerful engines of galactic ecology. Some of these results include the extreme rapidity of gravitational collapse in massive protostars, and a turbulent structure in the protostellar clouds which is apparently at odds with some current theory (see Fig. 1). Based on this, we have successfully obtained a further large amount of time at Mopra for the 2006 season using the newly upgraded systems. This will allow us to complete 1/3 of our ambitious project next season.

The second large survey is in collaboration with Tyler Bourke and Phil Myers of Harvard University and other members of the Spitzer Space Telescope Legacy Project “C2D - From Cores to Disks”. This project is similarly compiling detailed and uniform data on low-mass star forming clouds in our local Galactic neighbourhood. Again, Mopra will allow us to examine the chemical signatures in the cold molecular gas of protostellar evolution, revealing important clues to how Sun-like stars and their solar systems form. Last season, despite difficult weather, we obtained some tantalising results along these lines. For example, although the species N2H+ and CS are both excited under similar physical conditions (n ~ 105 H2 molecules/cm-3, T ~ 10 K), their very different distributions in maps of dense cores show that chemical evolution in the gas plays an important role, and that different species trace different regimes in the dense gas (see Fig. 2). This tends to confirm recent chemical models of such low-mass star formation. For 2006, we have also obtained a large amount of time to map ~40 of these cores in many species using Mopra’s pioneering spectrometer.

Fig. 2: Mopra intensity contours overlaid on Spitzer images for DC297. The Spitzer image is the 4.5 mm channel, where the emission that is not stellar is dominated by rotational H2, and so is tracing shocked outflow emission. Contours on the left panel are CS, on the right are N2H+. The 36” beam is shown for scale. CS seems to have an outflow and a core component. N2H+ is more compact and tracing the densest part of the core.

Peter Barnes