[Paper Review] CoRoT-10b: a giant planet in a 13.24 day eccentric orbit

A. S. Bonomo, A. Santerne+48 more|Oxford University Research Archive (ORA) (University of Oxford)|Jun 15, 2010

Stellar, planetary, and galactic studiesPhysics and Astronomy4 references54 citations

TL;DR

This paper reports the discovery of CoRoT-10b, a giant exoplanet with a highly eccentric orbit (e = 0.53 ± 0.04) and a 13.24-day orbital period, transiting a metal-rich K1V star. Using CoRoT photometry, HARPS radial velocities, and UVES spectroscopy, the study determines a planetary mass of 2.75 ± 0.16 M_Jup and radius of 0.97 ± 0.07 R_Jup, yielding a high bulk density of 3.70 ± 0.83 g cm⁻³, indicating a planet highly enriched in heavy elements, likely formed via giant collisions.

ABSTRACT

The space telescope CoRoT searches for transiting extrasolar planets by continuously monitoring the optical flux of thousands of stars in several fields of view. We report the discovery of CoRoT-10b, a giant planet on a highly eccentric orbit (e=0.53 +/- 0.04) revolving in 13.24 days around a faint (V=15.22) metal-rich K1V star. We use CoRoT photometry, radial velocity observations taken with the HARPS spectrograph, and UVES spectra of the parent star to derive the orbital, stellar and planetary parameters. We derive a radius of the planet of 0.97 +/- 0.07 R_Jup and a mass of 2.75 +/- 0.16 M_Jup. The bulk density, rho_pl=3.70 +/- 0.83 g/cm^3, is ~2.8 that of Jupiter. The core of CoRoT-10b could contain up to 240 M_Earth of heavy elements. Moving along its eccentric orbit, the planet experiences a 10.6-fold variation in insolation. Owing to the long circularisation time, tau_circ > 7 Gyr, a resonant perturber is not required to excite and maintain the high eccentricity of CoRoT-10b.

Motivation & Objective

• To characterize CoRoT-10b, a transiting exoplanet detected by the CoRoT space mission, with a highly eccentric orbit.
• To determine the planetary, stellar, and orbital parameters using multi-wavelength observational data.
• To investigate the origin of the planet's high eccentricity and its implications for planetary system formation.
• To assess the planet's internal composition and heavy element content based on its high bulk density.

Proposed method

• CoRoT space telescope provided continuous optical photometry to detect planetary transits.
• High-precision radial velocity measurements from the HARPS spectrograph were used to determine the planet's mass and orbital parameters.
• UVES spectroscopy of the host star enabled determination of stellar parameters such as effective temperature, metallicity, and radius.
• Stellar evolution models (CESAM) were combined with observed stellar parameters to constrain the age and mass of the host star.
• Planetary evolution models with varying core masses and solar-composition envelopes were used to interpret the planet's radius and density.
• Tidal circularization timescale was estimated using the tidal quality factor Q'p, assuming a range of values to assess orbital stability.

Experimental results

Research questions

• RQ1 What are the precise orbital, stellar, and planetary parameters of CoRoT-10b?
• RQ2 What is the origin of the planet's high orbital eccentricity (e = 0.53 ± 0.04), and is it maintained by resonant perturbations?
• RQ3 What is the internal composition of CoRoT-10b, and how much heavy element mass does it contain?
• RQ4 How does the planet's insolation vary across its eccentric orbit, and what are the atmospheric implications?
• RQ5 Is the long circularization timescale (τ_circ > 7 Gyr) sufficient to explain the current eccentricity without requiring a resonant companion?

Key findings

• CoRoT-10b has a mass of 2.75 ± 0.16 M_Jup and a radius of 0.97 ± 0.07 R_Jup, resulting in a bulk density of 3.70 ± 0.83 g cm⁻³, approximately 2.8 times that of Jupiter.
• The planet's high density implies a core containing up to 240 M⊕ of heavy elements, indicating a formation history likely involving giant collisions.
• The planet experiences a 10.6-fold variation in insolation as it moves from periastron to apastron due to its eccentric orbit.
• The tidal circularization timescale τ_circ is estimated at ∼7.4 Gyr for Q'p = 10⁵, indicating that the orbit is long-lived and does not require a resonant perturber to maintain its eccentricity.
• The high eccentricity is not driven by a nearby massive planet or Kozai oscillations, as the circularization timescale exceeds the age of the system.
• The planet is likely in pseudo-synchronous rotation with a rotation period of 4.25 ± 0.53 days, due to strong tidal interactions near periastron.