[Paper Review] Elodie metallicity-biased search for transiting Hot Jupiters IV. Intermediate period planets orbiting the stars HD43691 and HD132406

R. da Silva, S. Udry+22 more|arXiv (Cornell University)|Jul 6, 2007

Stellar, planetary, and galactic studies16 citations

TL;DR

This paper reports the discovery of two intermediate-period exoplanets—HD 43691 b (2.5 M_Jup, P = 40 days, e = 0.14) and HD 132406 b (5.6 M_Jup, P = 974 days, e = 0.34)—via a metallicity-biased radial velocity survey using ELODIE and SOPHIE spectrographs at the Haute-Provence Observatory. The study confirms the effectiveness of targeting metal-rich stars to accelerate hot Jupiter detection, with improved orbital solutions from SOPHIE data replacing ELODIE.

ABSTRACT

We report here the discovery of two planet candidates as a result of our planet-search programme biased in favour of high-metallicity stars, using the ELODIE spectrograph at the Observatoire de Haute Provence. One of them has a minimum mass m_2\sin{i} = 2.5 M_Jup and is orbiting the metal-rich star HD43691 with period P = 40 days and eccentricity e = 0.14. The other planet has a minimum mass m_2\sin{i} = 5.6 M_Jup and orbits the slightly metal-rich star HD132406 with period P = 974 days and eccentricity e = 0.34. Both stars were followed up with additional observations using the new SOPHIE spectrograph that replaces the ELODIE instrument, allowing an improved orbital solution for the systems.

Motivation & Objective

• To accelerate the detection of transiting hot Jupiters by targeting metal-rich stars, which show a higher frequency of giant planet occurrence.
• To improve orbital solutions for planet candidates using high-precision radial velocity measurements from the new SOPHIE spectrograph, replacing the older ELODIE instrument.
• To validate the metallicity bias strategy in exoplanet surveys by identifying new planetary systems with measurable orbital parameters.
• To assess the completeness and expected yield of the survey by estimating the number of giant planets expected in different metallicity bins.

Proposed method

• A metallicity-biased radial velocity survey was conducted on 1,061 solar-type stars, prioritizing those with [Fe/H] ≥ 0.1 dex.
• Radial velocities were measured using the ELODIE spectrograph at the 193-cm telescope at Haute-Provence Observatory.
• The SOPHIE spectrograph was used for follow-up observations to improve orbital solution precision and reduce measurement scatter.
• Keplerian orbital fits were applied to radial velocity data to derive orbital elements, including period, eccentricity, and minimum planetary mass (m₂ sin i).
• Stellar parameters such as mass, age, and metallicity were derived using stellar evolution models and literature values (e.g., from Santos et al. 2004).
• Bisector span and chromospheric activity indicators (e.g., Ca II H&K lines) were analyzed to rule out stellar activity as a source of radial velocity variations.

Experimental results

Research questions

• RQ1 Does targeting metal-rich stars significantly increase the detection rate of intermediate-period giant planets?
• RQ2 Can the SOPHIE spectrograph improve the precision and reliability of orbital solutions compared to ELODIE for planet candidates?
• RQ3 What is the expected yield of giant planets in different metallicity bins based on statistical models of planet frequency?
• RQ4 Are the radial velocity variations in HD 43691 and HD 132406 consistent with planetary signals or stellar activity?
• RQ5 How do the orbital parameters of the newly discovered planets compare with those of known hot Jupiters?

Key findings

• A planet with a minimum mass of 2.5 M_Jup orbits HD 43691 every 40 days with an eccentricity of 0.14, and the star has a metallicity of [Fe/H] = 0.14 dex.
• A more massive planet of 5.6 M_Jup orbits HD 132406 with a period of 974 days and eccentricity 0.34, and the star has [Fe/H] = 0.15 dex.
• The radial velocity data from SOPHIE significantly improved the orbital solution, reducing the weighted RMS to 7.5 m s⁻¹ for the combined ELODIE and SOPHIE dataset.
• No correlation was found between bisector span and radial velocity for either star, indicating that the signals are unlikely due to stellar activity.
• The survey has so far discovered six planets, including four hot Jupiters (P < 10 days) and two intermediate-period planets, with 45% of the expected hot Jupiters already detected among metal-rich stars.
• The statistical yield model predicts a total of 36 giant planets in the sample, with about 9 expected to be hot Jupiters, and the team has already detected nearly half of this expected number.