Observational biases in determining extrasolar planet eccentricities in single-planet systems

Nadia L. Zakamska, Margaret Pan, Eric B. Ford

Research output: Contribution to journalArticle

60 Citations (Scopus)

Abstract

We investigate potential biases in the measurements of exoplanet orbital parameters obtained from radial velocity observations for single-planet systems. We create a mock catalogue of radial velocity data, choosing input planet masses, periods and observing patterns from actual radial velocity surveys and varying input eccentricities. We apply Markov chain Monte Carlo simulations and compare the resulting orbital parameters to the input values. We find that a combination of the effective signal-to-noise ratio of the data, the maximal gap in phase coverage, and the total number of periods covered by observations is a good predictor of the quality of derived orbit parameters. As eccentricity is positive definite, we find that eccentricities of planets on nearly circular orbits are preferentially overestimated, with typical bias of one to two times the median eccentricity uncertainty in a survey (e.g. 0.04 in the Butler et al. catalogue).When performing population analysis, we recommend using the mode of the marginalized posterior eccentricity distribution to minimize potential biases. While the Butler et al. catalogue reports eccentricities below 0.05 for just 17 per cent of single-planet systems, we estimate that the true fraction of e ≤ 0.05 orbits is about f0.05 = 38 ± 9 per cent. For planets with P > 10 d, we find f0.05 = 28 ± 8 per cent versus 10 per cent from Butler et al. These planets either never acquired a large eccentricity or were circularized following any significant eccentricity excitation.

Original languageEnglish (US)
Pages (from-to)1895-1910
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Volume410
Issue number3
DOIs
StatePublished - Jan 1 2011

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extrasolar planets
eccentricity
planets
planet
radial velocity
catalogs
orbits
orbitals
Markov chains
circular orbits
Markov chain
signal-to-noise ratio
signal to noise ratios
estimates
predictions
excitation
simulation
parameter

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

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title = "Observational biases in determining extrasolar planet eccentricities in single-planet systems",
abstract = "We investigate potential biases in the measurements of exoplanet orbital parameters obtained from radial velocity observations for single-planet systems. We create a mock catalogue of radial velocity data, choosing input planet masses, periods and observing patterns from actual radial velocity surveys and varying input eccentricities. We apply Markov chain Monte Carlo simulations and compare the resulting orbital parameters to the input values. We find that a combination of the effective signal-to-noise ratio of the data, the maximal gap in phase coverage, and the total number of periods covered by observations is a good predictor of the quality of derived orbit parameters. As eccentricity is positive definite, we find that eccentricities of planets on nearly circular orbits are preferentially overestimated, with typical bias of one to two times the median eccentricity uncertainty in a survey (e.g. 0.04 in the Butler et al. catalogue).When performing population analysis, we recommend using the mode of the marginalized posterior eccentricity distribution to minimize potential biases. While the Butler et al. catalogue reports eccentricities below 0.05 for just 17 per cent of single-planet systems, we estimate that the true fraction of e ≤ 0.05 orbits is about f0.05 = 38 ± 9 per cent. For planets with P > 10 d, we find f0.05 = 28 ± 8 per cent versus 10 per cent from Butler et al. These planets either never acquired a large eccentricity or were circularized following any significant eccentricity excitation.",
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Observational biases in determining extrasolar planet eccentricities in single-planet systems. / Zakamska, Nadia L.; Pan, Margaret; Ford, Eric B.

In: Monthly Notices of the Royal Astronomical Society, Vol. 410, No. 3, 01.01.2011, p. 1895-1910.

Research output: Contribution to journalArticle

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