Doubleblind test program for astrometric planet detection with Gaia
Abstract
Aims: The scope of this paper is twofold. First, it describes the simulation scenarios and the results of a largescale, doubleblind test campaign carried out to estimate the potential of Gaia for detecting and measuring planetary systems. The identified capabilities are then put in context by highlighting the unique contribution that the Gaia exoplanet discoveries will be able to bring to the science of extrasolar planets in the next decade.
Methods: We use detailed simulations of the Gaia observations of synthetic planetary systems and develop and utilize independent software codes in doubleblind mode to analyze the data, including statistical tools for planet detection and different algorithms for single and multiple Keplerian orbit fitting that use no a priori knowledge of the true orbital parameters of the systems.
Results: 1) Planets with astrometric signatures α≃ 3 times the assumed singlemeasurement error σ_ψ and period P≤ 5 yr can be detected reliably and consistently, with a very small number of false positives. 2) At twice the detection limit, uncertainties in orbital parameters and masses are typically 1520%. 3) Over 70% of twoplanet systems with wellseparated periods in the range 0.2≤ P≤ 9 yr, astrometric signaltonoise ratio 2≤α/σ_ψ≤ 50, and eccentricity e≤ 0.6 are correctly identified. 4) Favorable orbital configurations (both planets with P≤ 4 yr and α/σ_ψ≥ 10, redundancy over a factor of 2 in the number of observations) have orbital elements measured to better than 10% accuracy > 90% of the time, and the value of the mutual inclination angle i_rel determined with uncertainties ≤ 10°. 5) Finally, nominal uncertainties obtained from the fitting procedures are a good estimate of the actual errors in the orbit reconstruction. Extrapolating from the presentday statistical properties of the exoplanet sample, the results imply that a Gaia with σ_ψ = 8 μas, in its unbiased and complete magnitudelimited census of planetary systems, will discover and measure several thousands of giant planets out to 34 AUs from stars within 200 pc, and will characterize hundreds of multipleplanet systems, including meaningful coplanarity tests. Finally, we put Gaia's planet discovery potential into context, identifying several areas of planetarysystem science (statistical properties and correlations, comparisons with predictions from theoretical models of formation and evolution, interpretation of direct detections) in which Gaia can be expected, on the basis of our results, to have a relevant impact, when combined with data coming from other ongoing and future planet search programs.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 May 2008
 DOI:
 10.1051/00046361:20078997
 arXiv:
 arXiv:0802.0515
 Bibcode:
 2008A&A...482..699C
 Keywords:

 stars: planetary systems;
 astrometry;
 methods: data analysis;
 methods: numerical;
 methods: statistical;
 stars: statistics;
 Astrophysics
 EPrint:
 32 pages, 24 figures, 6 tables. Accepted for pubolication in A&