[Paper Review] ELODIE metallicity-biased search for transiting Hot Jupiters V. An intermediate-period Jovian planet orbiting HD45652

N. C. Santos, S. Udry+21 more|ArXiv.org|May 7, 2008

Stellar, planetary, and galactic studies35 references13 citations

TL;DR

This paper reports the discovery of HD 45652b, a 0.47 M⨢ Jovian planet in a 44-day, eccentric (e = 0.39) orbit around the metal-rich star HD 45652, detected via radial-velocity measurements from the ELODIE, CORALIE, and SOPHIE spectrographs. The planet, the seventh giant planet found in the ELODIE metallicity-biased survey, resides in the 'period valley' of exoplanet orbital distributions, offering insights into giant planet formation and migration in metal-rich systems.

ABSTRACT

We present the detection of a 0.47 Jupiter mass planet in a 44-day period eccentric trajectory (e=0.39) orbiting the metal-rich star HD45652. This planet, the seventh giant planet discovered in the context of the ELODIE metallicity-biased planet search program, is also confirmed using higher precision radial-velocities obtained with the CORALIE and SOPHIE spectrographs. The orbital period of HD45652b places it in the middle of the "gap" in the period distribution of extra-solar planets.

Motivation & Objective

• To detect transiting hot Jupiters using a metallicity-biased survey targeting metal-rich stars.
• To identify and characterize giant planets in intermediate orbital periods, particularly in the 'period valley' where few planets are observed.
• To confirm the planetary nature of radial-velocity signals using high-precision spectrographs (CORALIE and SOPHIE) and rule out stellar activity or instrumental effects.
• To investigate the implications of the planet's location in the period distribution for planet formation and migration models.
• To contribute to understanding the metallicity-planet mass correlation and its role in core-accretion planet formation.

Proposed method

• Radial-velocity measurements were obtained using the ELODIE, CORALIE, and SOPHIE spectrographs on 1.93-m and 1.2-m telescopes at OHP and La Silla-Paranal observatories.
• Stellar parameters and metallicity were derived from high-resolution (R = 50,000) CORALIE spectra with S/N ~ 100, using the method of Santos et al. (2004).
• Orbital solutions were fitted using Keplerian models to radial-velocity data, with uncertainties propagated via Monte Carlo simulations.
• Activity indicators such as bisector inverse slope (BIS) and CCF shape were analyzed to rule out stellar activity as the source of the signal.
• Residuals from the Keplerian fit were examined for additional signals, and long-term trends were checked using archival CORAVEL data.
• Stellar mass and age were estimated using evolutionary tracks from Schaerer et al. (1993), based on derived Teff, log g, and [Fe/H].

Experimental results

Research questions

• RQ1 Does the metallicity-biased survey strategy successfully detect intermediate-period giant planets?
• RQ2 Can a planetary signal with a 44-day period and eccentricity e = 0.39 be robustly confirmed using multi-instrument radial-velocity data?
• RQ3 Is the observed radial-velocity variation due to a planetary companion or stellar activity?
• RQ4 How does the orbital period of HD 45652b compare to the observed 'period valley' in exoplanet distributions?
• RQ5 What does the planet's location in the period distribution imply for planet formation and migration models?

Key findings

• HD 45652b is a 0.47 M⨢ planet with a 44-day orbital period and eccentricity e = 0.39, orbiting a metal-rich star with [Fe/H] = +0.29 dex.
• The planet was detected and confirmed using radial-velocity data from ELODIE, CORALIE, and SOPHIE spectrographs, with high-precision measurements from CORALIE and SOPHIE dominating the orbital solution.
• No significant correlation was found between radial velocity and bisector inverse slope (BIS), indicating the signal is not caused by stellar activity.
• The planet lies in the middle of the 'period valley' in the orbital period distribution, a region where few giant planets are observed.
• The system's characteristics—0.83 M⨢ star, 0.47 M⨢ planet, 44-day period—align with predictions from models suggesting shorter disk depletion timescales for lower-mass stars, which may explain the period gap.
• No evidence for a second planetary signal or long-term radial-velocity trend was found in the data, supporting the single-planet model.