Doctoral work

AP Col - the closest pre-main sequence star to the Sun

Hot off the press! My collaborators Adric Riedel (Georgia State University), Carl Melis (University of California, San Diego) and I recently discovered that the M4.5 star AP Columbae is in fact the closest (8.4 pc, trigonometric) young star to the Sun, with an estimated age of ~40 Myr.



AP Columbae (Image credit: Adric Riedel, GSU/RECONS/SMARTS)

Precision ground-based parallax, photometry and spectroscopic measurements prove that AP Col—an X-ray-bright star prone to extreme flares and outbursts—is a member of the Argus Association, a loose grouping of coeval, co-moving pre-main sequence stars that may be associated with the open cluster IC 2391. We established a robust age for the star of 40 Myr on the basis of colour-magnitude diagram placement, kinematics, gravity-sensitive spectral lines and lithium measurements. This combination of proximity and youth means AP Col is a prime candidate for the direct imaging of orbiting giant gas planets with adaptive optics coronagraphic cameras on 8-m class telescopes.



Four giant planets orbiting around HR 8799, a member of the of 30 Myr Columba Association (C. Marois & Keck Observatory).

Several young stars near the Sun have already been observed to have systems of giant gas planets orbiting them, including Beta Pictoris and HR 8799, a 30 Myr-old member of the Columba Association (see above). The future detection of any Jupiter-mass planets around AP Col promises to reveal much about how planets form around low-mass stars.


Revealing the Chamaeleon — Young, low-mass stars surrounding Eta and Epsilon Chamaeleontis

When I'm not hunting down new members of Argus, my thesis work looks at another group of young stars near the Sun:

Until a decade ago, the vast majority of known young stars were located near dark molecular clouds, or in giant star formation complexes like the Orion Nebula or Taurus-Auriga. Recently however, samples of young stars near the Sun have been dramatically improved with the discovery of several young, sparse stellar associations right on our celestial doorstep. These associations, including among others the TW Hydrae Association, the Beta Pictoris Moving Group and the AB Doradus Moving Group, are all <50 Myr old and lie at distances <150 pc from the Sun.

The new associations make ideal laboratories for testing theories of planet formation and evolution. Observations of our Solar System and nearby stars suggest that giant gas planets form on timescales <10 Myr and terrestrial planets in <30 Myr. At 10—50 Myr, the ages of the new associations are intermediate between T Tauri 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 long since dissipated. Like AP Col and HR 8799, 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.

Two of the most intriguing young groups are the sparse open cluster Eta Chamaeleontis (Eta Cha) and the Epsilon Cha Association. Both are 5—10 Myr old and only 100 pc away, at opposite ends of the southern constellation of Chamaeleon.



Infrared Astronomical Satellite colour mosaic of the region surrounding Eta Cha

My thesis work examines low-mass stars in Eta and Epsilon Cha — their dynamical histories, disk and accretion properties, and indicators of youth. This has taken the form of several projects so far:

Stay tuned for more as I write it!