Astrophysics, abstract
astro-ph/0502404
From: Genya Takeda [view email]
Date (v1): Mon, 21 Feb 2005 10:36:24 GMT (55kb)
Date (revised v2): Thu, 9 Jun 2005 22:53:11 GMT (56kb)

High Orbital Eccentricities of Extrasolar Planets Induced by the Kozai Mechanism

Authors: G. Takeda, F.A. Rasio (Northwestern University)
Comments: 24 pages, 6 figures, ApJ, in press, minor changes to reflect the accepted version

One of the most remarkable properties of extrasolar planets is their high orbital eccentricities. Observations have shown that at least 20% of these planets, including some with particularly high eccentricities, are orbiting a component of a wide binary star system. The presence of a distant binary companion can cause significant secular perturbations to the orbit of a planet. In particular, at high relative inclinations, a planet can undergo a large-amplitude eccentricity oscillation. This so-called "Kozai mechanism" is effective at a very long range, and its amplitude is purely dependent on the relative orbital inclination. In this paper, we address the following simple question: assuming that every host star with a detected giant planet also has a (possibly unseen, e.g., substellar) distant companion, with reasonable distributions of orbital parameters and masses, how well could secular perturbations reproduce the observed eccentricity distribution of planets? Our calculations show that the Kozai mechanism consistently produces an excess of planets with very high (e >0.6) and very low (e < 0.1) eccentricities. The paucity of near-circular orbits in the observed sample cannot be explained solely by the Kozai mechanism, because, even with high enough inclinations, the Kozai mechanism often fails to produce significant eccentricity perturbations when there are other competing sources of orbital perturbations on secular timescales, such as general relativity. On the other hand, the Kozai mechanism can produce many highly eccentric orbits. Indeed the overproduction of high eccentricities observed in our models could be combined with plausible circularizing mechanisms (e.g., friction from residual gas) to create more intermediate eccentricities (e=0.1-0.6).

http://arxiv.org/abs/astro-ph/0502404

Astrophysics, abstract
astro-ph/0504162
From: Joshua Pepper [view email]
Date (v1): Wed, 6 Apr 2005 20:01:46 GMT (99kb)
Date (revised v2): Fri, 10 Jun 2005 19:08:09 GMT (99kb)

Searching for Transiting Planets in Stellar Systems

Authors: J. Pepper (1), B. S. Gaudi (2) ((1) The Ohio State University, (2) Harvard-Smithsonian Center for Astrophysics)
Comments: 24 pages, 10 figures. Minor changes. Accepted to ApJ, to appear in the September 20, 2005 issue
Journal-ref: Astrophys.J. 631 (2005)

We analyze the properties of searches devoted to finding planetary transits by observing simple stellar systems, such as globular clusters, open clusters, and the Galactic bulge. We develop the analytic tools necessary to predict the number of planets that a survey will detect as a function of the parameters of the system, the observational setup, site properties, and planet properties. We find that the detection probability is generally maximized for I-band observations. The signal-to-noise ratio of a planetary transit is weakly dependent on the mass of the primary for sources with flux above the sky background, and falls very sharply for sources below sky. Therefore the number of detectable planets is roughly proportional to the number of stars with fluxes above sky (and not necessarily the number of sources with photometric error less a given threshold). In order to maximize the number of detections, experiments should be tailored such that stars near sky are above the detection threshold. Once this requirement is met, the number of detected planets is relatively weakly dependent on the detection threshold, diameter of the telescope, exposure time, seeing, age of the system, and planet radius. The number of detected planets is a strongly decreasing function of the distance to the system, implying that the nearest, richest clusters may prove to be optimal targets.

http://arxiv.org/abs/astro-ph/0504162