Ph.D.

Towards a complete census of young stars in the Solar neighbourhood with SkyMapper

Until a decade ago, the vast majority of known young stars were located near dark molecular clouds, or in giant star formation complexes such as Orion. The only coeval, comoving groups of stars in the solar neighbourhood were the Hyades and Ursa Majoris Moving Groups. Although nearby both are hundreds of millions of years old. Recently however, samples of young stars near the Sun have dramatically increased with the discoveries of several new comoving, young associations: the TW Hydrae Association, the Tucana-Horologium Association, the Beta Pictoris Moving Group, the AB Doradus Moving Group and the compact Eta Chamaeleontis cluster, among others. All are <50 Myr old and lie at distances <100 pc from the Sun.



New associations in the deep Southern sky around the Scorpius-Centaurus OB association. Approxmiate distances and ages to the assocations are given in yellow, as well as proper motion vectors.

These new associations make them ideal laboratories for testing theories of planet formation and evolution. Observations of our Solar System and nearby extrasolar systems suggest that giant gas planets form on timescales <10 Myr and terrestrial planets in <30 Myr. At 10-50 Myr, the ages of stellar associations are intermediate between pre-main sequence stars, typically seen embedded in or close to their natal molecular clouds, and classical moving groups such as the Hyades, where planet formation has ceased and any protoplanetary disks have dissipated. The disks and planets around such young stars are prime targets for high resolution direct imaging and spectroscopic studies on the next generation of ground and space-based planetary science instruments.

However, finding these associations is an observational challenge. Because they are sparsely populated and spread over vast areas of sky there is usually no clustering where an overdensity of stars can be seen over the stellar background. Furthermore, most associations lie deep in the Southern sky, while most telescopes and astronomers are in the Northern hemisphere. This bias towards Southern declinations is most likely due to recent episodes of star formation in the nearby Scorpius-Centaurus OB association, which dispersed the associations across the Southern sky. The Sco-Cen complex is the nearest site of massive star formation, and is comprised of three distinct subgroups: Upper Scorpius (US), Upper Centaurus Lupus (UCL) and Lower Centaurus Crux (LCC), each with different ages, distances and kinematics (see Figure above).

To complement existing samples of young, nearby stars, we will use the SkyMap- per telescope to search for young, late-type stars in the Solar neighbourhood, particularly in the sky around the Scorpius Centaurus OB association. The large size of ScoCen on the sky and its deep Southern declination means it has not been well-studied as other, more Northern sites of massive star formation such as Orion. Given the number of B- and A-type stars in ScoCen, any sensible Initial Mass Function (IMF) means there are probably thousands of late-type stars awaiting discovery.

We will address the following outstanding questions:

SkyMapper's large field-of-view, excellent optics, filter set and Southern vantage point make it an ideal facility for such a task.




The SkyMapper enclosure at Siding Springs Observatory in Northern New South Wales. SkyMapper is a 1.3m wide-field (5.7 sq deg) survey telescope which will survey the entire Southern sky in five bands at five epochs.