The HARPS search for southern extra-solar planets

Abstract

Context. M dwarfs have often been found to have super-Earth planets with short orbital periods. These stars are thus preferential targets in searches for rocky or ocean planets in the solar neighborhood. Aims. Our research group recently announced the discovery of one and two low-mass planets around the M1.5V stars Gl 433 and Gl 667C, respectively. We found these planets with the HARPS spectrograph on the ESO 3.6-m telescope at La Silla Observatory, from observations obtained during the guaranteed time observing program of that instrument. Methods. We obtained additional HARPS observations of those two stars, for a total of 67 and 179 radial velocity measurements for Gl 433 and Gl 667C, respectively, and present here an orbital analysis of these extended data sets and our main conclusions about both planetary systems. Results. One of the three planets, Gl 667Cc, has a mass of only M 2 sin i ∼ 4.25 M ⊕ and orbits in the central habitable zone of its host star. It receives only 10% less stellar energy from Gl 667C than the Earth receives from the Sun. However, planet evolution in the habitable zone can be very different if the host star is a M dwarf or a solar-like star, without necessarily questioning the presence of water. The two other planets, Gl 433b and Gl 667Cb, both have M 2 sin i of ∼5.5 M ⊕ and periods of ∼7 days. The radial velocity measurements of both stars contain longer timescale signals, which we fit with longer period Keplerians. For Gl 433, the signal probably originates in a magnetic cycle, while data of longer time span will be needed before conclusive results can be obtained for Gl 667C. The metallicity of Gl 433 is close to solar, while Gl 667C is metal poor with [Fe/H] ∼ −0.6. This reinforces the recent conclusion that the occurrence of super-Earth planets does not strongly correlate with the stellar metallicity.

Tidal Venuses: Triggering a Climate Catastrophe via Tidal Heating

“…Two or more planets orbit the 0.3 M Sun star Gl 667C Anglada-Escudé et al, 2012;Delfosse et al, 2012). Planets c and d appear to lie in the IHZ, while a third planet, b, lies interior.…”

“…At 0.23 AU, planet d is too far from the star to be subjected to strong tidal heating, at least if it is tidally locked. Anglada-Escudé et al (2012) and Delfosse et al (2012) proposed different solutions to the system with the former setting c's eccentricity to 0 but stating that it is only constrained to be < 0.27, while the latter assign its eccentricity to be 0.34 -0.1. The minimum mass estimates are almost identical at 4.25 M Earth (Anglada-Escudé et al, 2012) and 4.5 M Earth (Delfosse et al, 2012).…”

“…Anglada-Escudé et al (2012) and Delfosse et al (2012) proposed different solutions to the system with the former setting c's eccentricity to 0 but stating that it is only constrained to be < 0.27, while the latter assign its eccentricity to be 0.34 -0.1. The minimum mass estimates are almost identical at 4.25 M Earth (Anglada-Escudé et al, 2012) and 4.5 M Earth (Delfosse et al, 2012). Here, we use the Anglada- Escudé et al (2012) solution, but note that using data from (Delfosse et al, 2012) does not change our results.…”

“…Furthermore, these objects are the most abundant in the solar neighborhood. Planets with masses between 1 and 10 M Earth , ''super-Earths,'' have indeed been detected in the last few years around low-mass stars, such as Gl 581 d and Gl 667C c by radial velocity (Udry et al, 2007;Mayor et al, 2009;Vogt et al, 2010;Bonfils et al, 2011;Forveille et al, 2011;AngladaEscudé et al, 2012;Delfosse et al, 2012) and GJ 1214 b by transit (Charbonneau et al, 2009;Sada et al, 2010;Carter et al, 2011;Kundurthy et al, 2011). Several observational campaigns designed specifically to detect planets around low-mass stars are now underway (Nutzman and Charbonneau, 2008;Boss et al, 2009;Zechmeister et al, 2009;Bean et al, 2010;Rodler et al, 2011).…”

Up to four planets around the M dwarf GJ 163

“…This radial velocity (RV) method can be readily applied to M dwarfs that are the most populous stars in the Solar neighbourhood and are known to be hosts to several planetary systems, e.g. GJ 581 (Bonfils et al 2005;Udry et al 2007;Mayor et al 2009), GJ 667C Delfosse et al 2013;Bonfils et al 2013), GJ 676A (Forveille et al 2011;Anglada-Escudé & Tuomi 2012), and GJ 876 (Delfosse et al 1998;Marcy et al 1998Marcy et al , 2001Rivera et al 2005Rivera et al , 2010. Because of the several on-going highprecision RV surveys, this population of exoplanet systems with multiple planets can readily be expected to increase as the observational baselines extend and as the amount of high-precision data increases and enables the detections of signals with lower and lower amplitudes.…”