Orbital structure of the GJ876 extrasolar planetary system based on the latest Keck and HARPS radial velocity data
- 138 Downloads
We use full available array of radial velocity data, including recently published HARPS and Keck observatory sets, to characterize the orbital configuration of the planetary system orbiting GJ876. First, we propose and describe in detail a fast method to fit perturbed orbital configuration, based on the integration of the sensitivity equations inferred by the equations of the original N-body problem. Further, we find that it is unsatisfactory to treat the available radial velocity data for GJ876 in the traditional white noise model, because the actual noise appears autocorrelated (and demonstrates non-white frequency spectrum). The time scale of this correlation is about a few days, and the contribution of the correlated noise is about 2 m/s (i.e., similar to the level of internal errors in the Keck data). We propose a variation of the maximum-likelihood algorithm to estimate the orbital configuration of the system, taking into account the red noise effects. We show, in particular, that the non-zero orbital eccentricity of the innermost planet d, obtained in previous studies, is likely a result of misinterpreted red noise in the data. In addition to offsets in some orbital parameters, the red noise also makes the fit uncertainties systematically underestimated (while they are treated in the traditional white noise model). Also, we show that the orbital eccentricity of the outermost planet is actually ill-determined, although bounded by ~0.2. Finally, we investigate possible orbital non-coplanarity of the system, and limit the mutual inclination between the planets b and c orbits by 5°–15°, depending on the angular position of the mutual orbital nodes.
KeywordsExtrasolar planets Radial velocity Red noise Mean-motion resonance GJ876
- Baluev R.V.: Several problems of exoplanetary orbits determination from radial velocity observations. In: Sun, Y.-S., Ferraz-Mello, S., Zhou, J.-L. (eds) Exoplanets: Detection, Formation and Dynamics (IAU Symp. 249), IAU Proc., 3. Suzhou, October 2007, pp. 101–110. Cambridge University Press, Cambridge (2008)Google Scholar
- Benedict G.F., McArthur B.E., Forveille T., Delfosse X., Nelan E., Butler R.P., Spiesman W., Marcy G., Goldman B., Perrier C., Jefferys W.H., Mayor M.: A mass for the extrasolar planet Gliese 876b determined from Hubble space telescope fine guidance sensor 3 astrometry and high-precision radial velocities. Astrophys. J. 581, L115–L118 (2002)ADSCrossRefGoogle Scholar
- Correia A.C.M., Couetdic J., Laskar J., Bonfils X., Mayor M., Bertaux J.-L., Bouchy F., Delfosse X., Forveille T., Lovis C., Pepe F., Perrier C., Queloz D., Udry S.: The HARPS search for southern extra-solar planets XIX. Characterization and dynamics of the GJ 876 planetary system. Astron. Astrophys. 511, A21 (2010)ADSCrossRefGoogle Scholar
- Duboshin, G.N. (ed.): Handbook of Celestial Mechanics and Astrodynamics (in Russian). Science, Moscow (1976)Google Scholar