Associate Professor Warrick Lawson Associate Professor, Deputy Head of School BSc, MSc, PhD Cant. School of Physical, Environmental and Mathematical Sciences UNSW @ ADFA Canberra   ACT   2600 AUSTRALIA Phone: +61 2 626 88810 Fax: +61 2 6268 8786 Email: w.lawson@adfa.edu.au Location: PEMS Nth, Room 330

Astronomy and Astrophysics Research Group

Current Research

Before planets – the mineralogy and chemistry of pre-planetary disks
Dr Chris Wright & Assoc. Prof. Warrick Lawson

Measuring the rotation periods of young low-mass stars
Assoc. Prof. Warrick Lawson with Dr Lisa Crause & Dr Yvonne Unruh

Lawson has several observing projects in place to complement other ground-based and spacespaced studies of nearby young stars. In particular he is interested in measuring the rotation periods of young low-mass stars and relating the results to disk properties and other population studies. In the eta Cha cluster, diskless binary stars are the fastest rotators; this can be related to the absence of ‘disk locking’ in these objects allowing them to rotate faster due to angular momentum conservation. Several stars in the TW Hya association of young stars were found to have fast periods of less than 1 day and large light amplitudes, making them suitable for Doppler imaging techniques to reconstruct their surface starspot distribution. This work is ongoing and several interesting astrophysical questions can be addressed by this work including when, for stars of different mass, a star begins to build up a radiative core which has a considerable affect on the early evolution of the object. This work is being conducted with colleagues in South Africa and the UK.

Star formation
Dr Robert Smith, Assoc. Prof. Warrick Lawson & Dr Chris Wright

The earliest stages of star formation, young stellar objects (YSO’s) are characterized by a protostellar core, surrounded by an envelope which feeds the core, most likely via an accretion disk. This stage is often accompanied by large scale energetic outflows of matter from the core/disk. The envelope is normally so dense that only infrared or radio observations are able to penetrate it sufficiently to investigate the core. We are currently studying one such YSO, GGD30, by means of optical spectroscopy and imaging, infrared spectroscopy and imaging and radio interferometric and single dish observations.

Utilizing NASA’s Spitzer Space Telescope
Assoc. Prof. Warrick Lawson with Dr Jerome Bouwman & Prof. Eric Feigelson

Lawson is a Chief Investigator or co-Investigator on a number of projects utilizing NASA’s Spitzer Space Telescope. Most of these projects involve observing protoplanetary disks surrounding stars in some of the nearest young stellar groups to Earth. Two of these groups were co-discovered at UNSW@ADFA. Spitzer allows high-sensitivity study of the disks to detection limits unavailable from the ground. Merged withground-based observations of the disk-bearing stars, a number of programmes are in place to relate disk properties to stellar properties such as mass, age, binarity and star formation environment. First results from a Spitzer study of the eta Cha cluster shows that the presence of proto-planetary disks is related to whether stars are single (in which case disks are common) or binary (in which case disks are rare). A characteristic disk lifetime for single stars is estimated at ~ 9 million years, while it is only ~ 4 million years for binary stars. Similar studies are being extended to other clusters to better clarify the disk lifetime estimate. Other influences might be the presence of hot stars, whose winds and UV radiation might impact the evolution of disks around low-mass stars. Other projects are addressing this issue. This work is being conducted with colleagues in Germany, the USA and the Netherlands.

Recent Achievements

• Lawson is a co-investigator of successful proposals in 2006 and 2007 to use to NASA’s Spitzer Space Telescope. The proposals are to investigate the influence of hot stars on the formation and evolution of protoplanetary disks (CI: Bouwman, Max Planck Institute for Astronomy, Heidelberg, Germany), and a joint Spitzer Space Telescope/Chandra X-ray Observatory study of star formation in the Carina Giant Molecular Cloud (CI: Townsley, Pennsylvania State University, State College, USA.
• Along with colleagues in Europe and the USA, Lawson completed a study of Spitzer Space Telescope observations of stars in the eta Chamaeleontis star cluster, which was co-discovered at UNSW@ADFAin 1998. The Spitzer study shows that the presence of protoplanetary disks in the cluster is related to whether stars are single (in which case disks are common) or binary (in which case disks are rare). A characteristic disk lifetime for single stars is estimated at ~ 9 million years, while for binary stars the lifetime is ~ 4 million years. The former timescale is consistent with core accretion models of planet formation; the latter may be too short. The results were published by Bouwman et al. 2006, Astrophysical Journal, 653, L57-60.
• Results of dynamical modeling of the eta Cha star cluster were published by Moraux, Lawson & Clarke (2007, Astronomy & Astrophysics, 473, 163–170). The cluster appears unusual compared to other young clusters of stars in having remained in a relatively compact configuration for ~ 10 million years while appearing to have lost most of its low mass objects. N-body modeling showed that a very dense initial state can reproduce the observed configuration in ~ 5% of realisations. Further modeling will investigate the impact of binary systems and residual gas in the young cluster, while observational programs will attempt to locate cluster members that may have escaped the cluster core region.

Research Collaborators

PhD Opportunities and Scholarships

MPhil, MSc and PhD topics studies of the stellar populations of some of the nearest star forming regions to Earth are available. These studies will make use of Australian groundbased optical, infrared and radio facilities, and archival space-based data from satellites such as NASA’s Spitzer Space Telescope.

There is an opportunity for a student to become involved, at the PhD or MSc level, in the study of the young stellar object GGD30. The project would build on the discovery of a Herbig-Haro (HH) Object associated with this source and involve new optical, infrared and radio observations combined with existing observations. HH objects trace the shocks that form when collimated outflows collide with either (i) previously ejected lower-velocity material or (ii) the undisturbed ambient medium. There is the real possibility that what we are seeing at the moment is only a portion of a large scale outflow. At the very least it is one part of an active star formation region with at least one and possibly more Herbig-Haro Objects nearby.

Contact: Assoc. Prof. Warrick Lawson
Email: w.lawson@adfa.edu.au

Assoc. Prof. Warrick Lawson with PEMS dish, UNSW@ADFA.

Recent Publications

Journal - refereed

2008

Getman, K. V., Feigelson, E. D., Lawson, W. A., Broos, P. S. & Garmire, G. P., 2008, The stellar population and origin of the mysterious high-latitude star forming cloud CG 12, Astrophysical Journal, 673(1), 331-353.

Skelly, M. B., Unruh, Y. C., Collier Cameron, A., Barnes, J. R., Donati, J.-F., Lawson, W. A., Carter, B. D., 2008, Doppler images and chromospheric variability of TWA 6, Monthly Notices of the Royal Astronomical Society, 385(2), 708-715.

2007

Crause, L. A., Lawson, W. A. & Henden, A., 2007, Pulsation-decline relationships in R Coronae Borealis stars, Monthly Notices of the Royal Astronomical Society, 375(1), 301-306.

Moraux, E., Lawson, W. A. & Clarke, C. L., 2007, eta Chamaeleontis: Abnormal initial mass function or dynamical evolution?, Astronomy & Astrophysics, 473(1), 163-170.

Smith, R. G., Lawson, W. A. & Wright, C. M., 2007, A Herbig-Haro object associated with GGD30 and its exciting source, Monthly Notices of the Royal Astronomical Society, 375(1), 257-260.

2006

Bouwman, J., Lawson, W. A., Dominik, C., Feigelson, E. D., Henning, T., Tielens, A. G. & Waters, L. B., 2006, Binarity as a key factor in protoplanetary disk evolution: SPITZER disk census of the eta Camaeleontis cluster, The Astrophysical Journal, 653(1), L57-L60.

Feigelson, E. D., Lawson, W. A., Stark, M., Townsley, L. & Garmire, G. P., 2006, 51 Eridani and GJ 3305: A 10-15 Myr old binary star system at 30 Parsecs, Astronomical Journal, 131(3), 1730-1739.

Lyo, A. R., Song, I., Lawson, W. A., Bessell, M. S. & Zuckerman, B., 2006, A deep photometric survey of the eta Chamaeleontis cluster down to the brown dwarf - planet boundary, Monthly Notices of the Royal Astronomical Society, 368(3), 1451-1455.

Recent Grants

External Grants

W.A. Lawson, Australian Academy of Science Academic Exchange Program, 2008: $6,700.
W. A. Lawson, Australia France Cooperation Fund in Astronomy, ARC Linkage, 2006: $1,800, 2007: $1,800.

UNSW Grants

W. A. Lawson, Angular momentum and planet-forming disk evolution in young stars: The epsilon Cha group, Special Research Grants, 2008: $7,420.
W. A. Lawson, What stellar properties most influence planet formation, Faculty Research Grants, 2007: $12,000.
W. A. Lawson, Unraveling nearby star clusters with the Spitzer Space Telescope, UNSW@ADFA Faculty Research Grant, 2006: $15,760.
W. A. Lawson, Rotation periods of stars in the beta Pic moving group, UNSW@ADFA Special Research Grant, 2006: $1,086.

Service

• Chair of Scientific Organising Committee, member of Local Organising Committee, Annual Scientific Meeting of the Astronomical Society of Australia held in July 2006 at UNSW@ADFA.