Bright Trans-Neptunian Objects in the Southern Sky

Abstract

We complete the census of bright distant trans-Neptunian worlds through surveying the Southern Hemisphere sky, particularly the unexplored high-latitude regions that would contain trans-Neptunian objects (TNOs) that have experienced severe scattering.

In this thesis, we developed an archival TNO survey of 6,275 square degrees of sky south of the ecliptic that have more than thirty nights of observation over five years, to a limiting magnitude of 19.0 in clear. We generated our survey through an innovative analysis of the archive of more than half a million images taken between 2 March 2004 and 23 October 2009 by the Siding Spring Survey. This survey for near-Earth asteroids uses the 0.5 m Uppsala telescope at Siding Spring Observatory. Our survey took advantage of their dense temporal coverage to resample their cadence of observation into a survey for slow-moving objects. From twenty billion astronomical sources on the Uppsala images, we extracted thirteen million transient sources, computed a subset of the trillion possible Solar System orbits that these points of light could form, and produced only a few hundred potential candidate orbital arcs. This computational processing required a hundred thousand hours of CPU time.

Our survey adds to the last two decades of work into understanding the cold, distant outer regions of our Solar System that lie beyond Neptune’s orbit. These regions contain varied populations of small objects. As the remnant planetesimals of the protoplanetary disk, they offer insight into the early history and evolution of the Solar System. The brightest reflect enough photons to allow spectroscopy, indicating the composition of the topmost few millimetres of the volatile ices that form the mantles of these worlds. The sixteen hundred TNOs known have been discovered through sky surveys with optical telescopes; most extensive surveys have previously focussed on the Northern Hemisphere sky.

We detected no new objects in the southern sky. We defined the exact phase space of orbital parameters that was well sampled by the Uppsala TNO survey by developing a survey simulator. Examining our survey’s observation of the objects from a well-characterized synthetic population, we found we had a 90% detection efficiency of the Kuiper belt and scattered disk; seeing no objects with an absolute magnitude between our range of sensitivity of -2.5 to 3.5 limited the bright end of the TNO population distribution.

We unsuccessfully attempted to characterize two of the known distant objects. Pluto’s largest moon, Charon, is suspected to have cryovolcanism-related ammonia on its surface; we observed in the L-band with Gemini North’s GNIRS spectrograph to improve the detection, but received too little telescope time to detect Charon. In contrast, little is known about the newly discovered high-inclination Centaur-like object 2012 DR30: we obtained a light-curve with the Faulkes South 2m, but found only that this object was unvarying in brightness at better than the 5% level. Show more