High Contrast Imaging: Exoplanet and Low Stellar Mass Populations
In this thesis I report the results of a re-analysis of archival Spitzer IRAC direct imaging sur- veys encompassing 121 nearby stars. While the small size of Spitzer provides a lower resolution than 8 m class AO-assisted ground-based telescopes, which have been used for constraining the frequency of 0.5 − 13 MJ planets at separations of 10 − 102 AU, its exquisite infrared sensitivity provides the ability to place unmatched constraints on the planetary populations at wider sepa- rations. Sophisticated high-contrast techniques are applied to the sample in order to remove the stellar point-spread function and to open up sensitivity to planetary mass companions down to 5′′ separations. This enables sensitivity to 0.5 − 13 MJ planets at physical separations on the order of 102 − 103 AU, allowing a parameter space to be probed that has not previously been systematically explored to any similar degree of sensitivity. Based on a colour and proper motion analysis, no planetary detections are recorded. Exploiting this enhanced survey sensitivity with Bayesian analysis, the population of 0.5 − 13 MJ planets at separations of 100 − 1000 AU is constrained with an upper frequency limit of 9% (at 95% confidence). I also report the results of a FEROS radial velocity survey of low-mass binaries, the majority of which are high probability young moving group (YMG) members. YMGs are prime targets for exoplanet imaging due to their youth (∼ 10 − 100 Myr), as any potential orbiting planet will be equivalently young and therefore luminous. Lucky imaging multiplicity surveys have recently identified hundreds of new YMG low-mass binaries, where a subsample of M-dwarf multiples have estimated orbital periods less than 50 years. Radial velocity measurements for 29 such targets are presented here, complementing the astrometric data. This will allow enhanced orbital determinations and precise dynamical masses to be derived in a shorter timeframe than possible with astrometric monitoring alone. Derived dynamical masses will enable binary systems to be isochronally dated to a good level of precision. This dating can then potentially be applied to the YMG of which they are members, for improved age constraints on the full population of stars. Improved YMG age constraints are critical for estimating the mass or initial entropy of imaged planets using mass-luminosity evolutionary models.
Networked Digital Library of Theses and Dissertations