The CARMENES search for exoplanets around M dwarfs

Abstract

Although M dwarfs are known for high levels of stellar activity, they are ideal targets for the search of low-mass exoplanets with the radial velocity (RV) method. We report the discovery of a planetary-mass companion around LSPM J2116+0234 (M3.0 V) and confirm the existence of a planet orbiting GJ 686 (BD+18 3421; M1.0 V). The discovery of the planet around LSPM J2116+0234 is based on CARMENES RV observations in the visual and near-infrared channels. We confirm the planet orbiting around GJ 686 by analyzing the RV data spanning over two decades of observationsfrom CARMENES VIS, HARPS-N, HARPS, and HIRES. We find planetary signals at 14.44 and 15.53 d in the RV data for LSPM J2116+0234 and GJ 686, respectively. Additionally, the RV, photometric time series, and various spectroscopic indicators show hints of variations of 42 d for LSPM J2116+0234 and 37 d for GJ 686, which we attribute to the stellar rotation periods. The orbital parameters of the planets are modeled with Keplerian fits together with correlated noise from the stellar activity. A mini-Neptune with a minimum mass of 11.8 M⊕ orbits LSPM J2116+0234 producing a RV semi-amplitude of 6.19 m s−1, while a super-Earth of mass 6.6 M⊕ orbits GJ 686 and produces a RV semi-amplitude of 3.0 m s−1. Both LSPM J2116+0234 and GJ 686 have planetary companions populating the regime of exoplanets with masses lower than 15 M⊕ and orbital periods <20 d.

A Collage of Small Planets from the Lick–Carnegie Exoplanet Survey: Exploring the Super-Earth and Sub-Neptune Mass Regime*

“…Full set of Bayes Factor Periodograms for GL 686. The red line denotes the 15d planet signal originally identified in Affer et al (2019) and Lalitha et al (2019) and confirmed again in this work. The gold lines show the ∼40 day and ∼2,000 day signals that we identify as the star's rotational and magnetic activity cycles, respectively.…”

“…We also confirmed the orbital parameters of two previously published low-mass planets. First, we derived an updated orbital solution for the planet orbiting the M1.0V star GJ 686 reported by Affer et al (2019) and Lalitha et al (2019) using an additional 134 new RV APF measurements and 18 new PFS measurements. And second we updated the orbital solution of the planet orbiting the M3.0V star HD 180617 detailed in Kaminski et al (2018), adding 126 new APF measurements to the combined data set.…”

“…(Table 1) 7 . The star was recently reported to host an m sin i = 7.1 ± 0.9 M ⊕ planet on a 15.53 day orbit by (Affer et al 2019), and the signal was subsequently confirmed by Lalitha et al (2019) (m sin i = 6.24 +0.58 −0.59 M ⊕ ). Here we present an updated orbital analysis of the system that includes additional data taken with the APF and PFS, and present an updated minimum mass with 7% uncertainty.…”

The CARMENES search for exoplanets around M dwarfs

“…distinguish between planetary and activity-related signals in RV time series. These projects include both M-dwarf data taken under the CARMENES survey program (Kaminski et al 2018;Luque et al 2018;Reiners et al 2018b;Lalitha et al 2019;Nagel et al 2019b;Perger et al 2019;Schöfer et al 2019) as well as open time observations of other cool stars (Luque et al 2019;Pallé et al 2019). We observe that the indicators in different stars display notable differences depending on the spectral type and activity level of the stars.…”

Discovery of a hot, transiting, Earth-sized planet and a second temperate, non-transiting planet around the M4 dwarf GJ 3473 (TOI-488)

“…At a distance of 8.66 +0.13 −0.13 × 10 −2 au from the host star, GJ 3473 c receives 1.98 +0.17 −0.15 times the stellar flux compared to Earth, which places it outside the inner boundary of the optimistic habitable zone, 1.49 S ⊕ > S > 0.22 S ⊕ , as defined by Kopparapu et al (2014). The planet therefore is a temperate super-Earth or mini-Neptune such as GJ 887 c (Jeffers et al 2020), GJ 686 b (Lalitha et al 2019;Affer et al 2019), GJ 685 (Pinamonti et al 2019) or GJ 581 c (Udry et al 2007) (see Fig. 11).…”