This project will examine results from direct-imaging surveys of exoplanets (planets orbiting other stars), and produce a distribution of planets from a star that expands out to 1000 astronomical units from the parent star, where an astronomical unit is approximately the average distance between the Sun and Earth. New direct-imaging observations will be obtained, and data will also be used from archival sources, as well as orbital measurements of planets detected by other means, such as microlensing, radial velocity and transit techniques. When feasible, follow-up spectroscopy will be performed of newly detected planets. The modeling efforts will focus on whether there is a continuous distribution of planets, or instead, any significant breaks are evident. The team will also search for variations of planetary distance populations as a function of stellar mass, age and iron content. The outcomes from these studies are intended to provide strong tests of standard models of core-accretion planet formation. As part of the process of identifying new planets from direct-imaging, and ruling out background objects, the project is also expected to reveal new high proper motion galactic halo stars. This project will provide publicly-available software tools useful to the exoplanet and stellar stronomy community. The PI will supervise and mentor undergraduate students, two doctoral students, and a postdoctoral researcher.

Project Report

This project examined results from the largest direct-imaging survey of exoplanets (planets orbiting other stars) ever attempted (the Gemini NICI Science Campaign: Principal Scientist : M. Liu; Deputy Scientist L. Close). We successfully completed very deep imaging around over 200 nearby young stars looking for the very faint thermal light (up to a million times fainter than that of the host star) to publish produce a distribution of planets from a star that expands out to 1000 astronomical units from the parent star (where an astronomical unit (AU) is approximately the average distance between the Sun and Earth). These new direct-imaging observations were published and archival sources were published as well. We discovered four brand new very low mass companions (PZ Tel B (36+-6 jupiters mass at 16.4+-1.0 AU, Biller et al. 2010), CD -35 2722B (31+-8 Jupiters, at 67+-4 AU, Wahhaj et al. 2011), HD 12894B (0.46+-0.08 Solar masses at 15.7+-1.0 AU), and BD+07 1919C (0.20+-0.03 MSun, 12.5+-1.4 AU) Nielsen et al. 2013). In each of these cases follow-up spectroscopy and modeling was done and masses and temperatures determined. Modeling efforts allowed us to place better constraints on the population of faint companions (like exo-planets). For example we found that an analysis of the achieved H band ADI and ASDI contrasts, using power-law models of planet distributions and hot-start evolutionary models, we restrict the frequency of 1--20 jupiter mass companions at semi-major axes from 10--150 AU to <18% at a 95.4% confidence level using DUSTY models and to <6% at a 95.4% using COND models (Nielsen et al. 2013). In other words, we conclude that it is quite rare to have very wide massive planets. However, we know these wide massive planets do exist --but they are just very rare. This grant helped support several undergraduate students, three doctoral students, and three postdoctorial researchers. All of the these scientists are still continuing to explore the exciting field of extra-solar planets --so this project had a successful broader impact by training a strong group of young scientists.

National Science Foundation (NSF)
Division of Astronomical Sciences (AST)
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Maria Womack
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University of Arizona
United States
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