The research team will conduct extensive follow-up observations and analysis of several thousands of transiting planet candidates that are identified by the HATNet North and South telescope facilities. By using telescopes in both the northern and southern hemispheres, the researchers will be able to provide increased spatial and temporal coverage, which will aid in establishing the orbits of relatively long-period exoplaents.

Transiting planets are those whose orbits cause them to pass in front of, and behind, the host star, which provides unique opportunities for characterization through subsequent photometric and spectroscopic observations. The project is expected to have broader impacts by significantly increasing the number of transiting exoplanets available to the community, and will involve students with special attention to under-represented groups in astronomy.

Project Report

During the past two decades there has been an extraordinary growth in our understanding of planets around stars other than the Sun, with some 1500 so-called exoplanets having been validated to date. For most of these planets only a limited amount of information is available: the average separation of the planet from its star, and either the mass of the planet, or its radius, but typically not both. The planets having both mass and radius measurements are special because knowing both quantities tells us about the composition and structure of the planet. This gives us a much clearer idea of what the planet is "like" as opposed to simply knowing that there is a planet around a particular star. The only exoplanets for which it is possible to get both pieces of information are planets with orbits that periodically carry them in front of their host stars as viewed from Earth. Planets with these special orbital geometries are known as transiting planets. As a practical matter, to be able to measure the mass of the planet it is also necessary for the host star to be relatively bright. This NSF grant was used to discover and characterize transiting planets around bright stars, and to measure their masses and radii, among other properties. The planets that we discovered were first identified as candidates by the HATNet and HATSouth networks of small robotic ground-based telescopes (11 cm and 18 cm diameters; smaller than some amateur telescopes). We carried out follow-up observations of hundreds these candidate planets using much larger ground-based telescopes (from 1 m up to 10 m diameters) which allowed us to reject most of the candidates as false positives, and to confirm 21 new transiting planets. We measured both masses and radii for all of these planets. The planets represent a broad class of objects, from planets smaller than Saturn to some that are several times the mass of Jupiter. They range from compact planets which likely have very massive solid cores, to some of the most inflated planets known (e.g., one enormous planet, called HAT-P-40b, has a radius that is 1.7 times that of Jupiter, but has only 0.6 times the mass). These inflated planets continue to defy theoretical models for understanding planetary structures. The planets are found around a broad class of stars, from the smallest stars known to host planets (HATS-6b orbits a star with a mass that is 0.6 times that of the Sun) to some of the largest stars known to host planets (HAT-P-49b orbits a star that is more than 1.5 times the mass of the Sun). Because they orbit bright stars, it is possible to measure a number of additional properties of the planets, such as their atmospheric compositions (what are the planets made out of?) and the alignments of the orbital planes with respect to their stars (are they well-aligned like the solar system?). Such studies in the long term provide a possible avenue for finding life on other planets, but getting to this point requires incremental progress in our ability to find planets, to measure the properties, and to model them. Our project is a part of this incremental progress. All of the information we gather on exoplanets feeds into our understanding of how planetary systems in general form and evolve in time, which in turn gives us insights into how our own solar system formed.

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