The Galactic Census of High and Medium-mass Protostars (CHaMP)
What is CHaMP?
The beginning stages of the formation of stars are still somewhat of a mystery, especially for stars which are much more massive than our Sun, or for large
clusters of stars. How do such large stars assemble themselves, individually and in clusters? A simple theory would predict massive clusters could not be
as tightly packed as we see, other theories predict they should form faster or slower than they do. Do massive stars drive off their nascent gas in the same way as
low-mass stars? Do they have similar, or any, solar systems? The mysteries of massive star formation are important since these stars, while few in number,
are a major part of the engine driving the Galactic ecology.
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 Ibaraki University
& Yasuo Fukui's Nanten group at Nagoya University, Jonathan Tan at the University of Florida, and Paola Caselli at Leeds University, we will be able for the
first time to build a reliable picture of the typical evolution of these rare but powerful objects.
CHaMP starts with a large area (20°×6°) of the southern Milky Way in Carina and Vela. The Nanten telescope has made
complete, but low-resolution, maps of this area in a number of molecular spectral lines, which trace the cold dense gas where stars are forming in our
Galaxy. The carbon monoxide molecule in particular is a useful tracer: see Figures 1 & 2.
Fig. 1: Widespread emission from Giant Molecular Clouds in the Milky Way, as traced by the CO molecule and mapped
by the Nanten telescope. This is where the interstellar gas can get cold enough to allow gravity to collapse parts of the clouds into young stars.
Fig. 2: Similar map to Fig. 1, but now of emission from the much rarer C18O molecule. We only see this species
in the densest parts of GMCs, where the gas is coldest and gravity is strongest. This is where new protostars actually form.
The Mopra dish near Coonabarabran (part of the Australia Telescope) is now mapping these cold, massive clouds at much higher resolution, and
simultaneously in a number of molecular spectral lines. Looking at different molecules lets us understand the physical processes that
dominate the star formation activity we see: see Figures 3 & 4. Most significantly, since we are surveying a large number of clouds in the
whole area in a uniform way, we will be able to look at the population of protostars, and derive lifetimes and other physical parameters that
would not otherwise be possible.
Fig. 3
Fig. 4
We are also using other telescopes around the world to complete this "big picture" view of massive star formation. With Stuart Ryder & Andrew
Hopkins at the Anglo-Australian Observatory, we are imaging the young stellar clusters and the hot gas they produce, that are the end product of
gravitational collapse in the molecular clouds. In Chile using the Atacama Submillimetre Telescope Experiment (ASTE), with Philippe Andre at Saclay
Observatory using the ArTeMiS camera on APEX, and using the Herschel Space Observatory, we will look at the temperature evolution of the cold
gas as gravity compresses and heats the clumps that will become protostars.
More Information
For more information contact Peter Barnes