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Title:
GJ 581 update: Additional evidence for a Super-Earth in the habitable zone
Authors:
Vogt, S. S.; Butler, R. P.; Haghighipour, N.
Affiliation:
AA(UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064, USA), AB(Department of Terrestrial Magnetism, Carnegie Institute of Washington, Washington, DC 20015, USA), AC(Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii-Manoa, Honolulu, HI 96822, USA)
Publication:
Astronomische Nachrichten, Vol.333, Issue 7, p.561 (AN Homepage)
Publication Date:
08/2012
Origin:
AN
Keywords:
methods: numerical, planetary systems -stars: individual (GJ 581, HIP 74995), techniques: radial velocities
Abstract Copyright:
(c) 2012: WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI:
10.1002/asna.201211707
Bibliographic Code:
2012AN....333..561V

Abstract

We present an analysis of the significantly expanded HARPS 2011 radial velocity data set for GJ 581 that was presented by Forveille et al. (2011). Our analysis reaches substantially different conclusions regarding the evidence for a Super-Earth-mass planet in the star's Habitable Zone. We were able to reproduce their reported χν2 and RMS values only after removing some outliers from their models and refitting the trimmed down RV set. A suite of 4000 N-body simulations of their Keplerian model all resulted in unstable systems and revealed that their reported 3.6σ detection of e=0.32 for the eccentricity of GJ 581e is manifestly incompatible with the system's dynamical stability. Furthermore, their Keplerian model, when integrated only over the time baseline of the observations, significantly increases the χν2 and demonstrates the need for including non-Keplerian orbital precession when modeling this system. We find that a four-planet model with all of the planets on circular or nearly circular orbits provides both an excellent self-consistent fit to their RV data and also results in a very stable configuration. The periodogram of the residuals to a 4-planet all-circular-orbit model reveals significant peaks that suggest one or more additional planets in this system. We conclude that the present 240-point HARPS data set, when analyzed in its entirety, and modeled with fully self-consistent stable orbits, by and of itself does offer significant support for a fifth signal in the data with a period near 32 days. This signal has a false alarm probability of <4 % and is consistent with a planet of minimum mass 2.2 M_⊙, orbiting squarely in the star's habitable zone at 0.13 AU, where liquid water on planetary surfaces is a distinct possibility.
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