Jump to: navigation, search

While long anticipated in both science and science fiction, the existence of a circumbinary planet orbiting a pair of normal stars was not definitively established until the discovery of Kepler-16 b, announced by the Kepler Team last September. Yet many questions remained about the nature of circumbinary planets: What kinds of orbits, masses, radii, temperatures, etc., could they have? What kinds of binary stars can host planets? And most of all, was Kepler-16 just a fluke? To address these questions we needed more cases of circumbinary planet systems, and we initially searched for non-transiting planets: transits require an extremely favorable orientation in the sky and are thus expected to be rare. Non-transiting planets do not require a fortuitous configuration and should be roughly 10x more common. By carefully measuring the eclipse times of the binary stars, we have discovered that a sizable number of systems possess significant eclipse timing variations, indicating the presence of (at least) a third body that is perturbing the binary orbit. The amplitude and period of the timing variations allow us to constrain the mass of the unseen third body: a small amplitude and a short period implies a nearby, low-mass object, perhaps substellar. While the goal was to find non-transiting planets, this search quickly revealed two more transiting circumbinary planets, Kepler-34 and Kepler-35. With three systems, we can now compare their characteristics and estimate how common such objects are in the galaxy. In this talk I will briefly showcase some highlights of the Kepler Mission, then discuss the search method, discovery, and characteristics of the three Kepler transiting circumbinary planets, and conclude with some interesting trends we have seen.

Isolated rotating neutron stars are gradually spinning down to lower frequencies because of the emission of magnetic dipole radiation and a wind of electron-positron pairs. This spin-down compresses the matter inside of such neutron stars monotonically to higher densities, leading to changes in the global properties and the hadronic core compositions of such objects. In particular, spin-down may drive rotation-driven phase transitions in the cores of rotating neutron stars, which is the key topic of this talk. First, the structure and stability of rotating neutron stars will be discussed. This is followed by an overview of the different types of phase transitions that may be triggered by stellar spin-down. Finally, astrophysical signatures by means of which such phase transitions may register themselves observationally will be discussed.