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Register a new userThe CARMENES search for exoplanets around M dwarfs. Two terrestrial planets orbiting G 264-012 and one terrestrial planet orbiting Gl 393
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We report the discovery of two planetary systems, namely G 264-012, an M4.0 dwarf with two terrestrial planets ($M_{rm b}sin{i} = 2.50^{+0.29}_{-0.30}$ M$_{oplus}$ and $M_{rm c}sin{i} = 3.75^{+0.48}_{-0.47}$ M$_{oplus}$), and Gl 393, a bright M2.0 dwarf with one terrestrial planet ($M_{rm b}sin{i} = 1.71 pm 0.24$ M$_{oplus}$). Although both stars were proposed to belong to young stellar kinematic groups, we estimate their ages to be older than about 700 Ma. The two planets around G 264-012 were discovered using only radial-velocity (RV) data from the CARMENES exoplanet survey, with estimated orbital periods of $2.30$ d and $8.05$ d, respectively. Photometric monitoring and analysis of activity indicators reveal a third signal present in the RV measurements, at about 100 d, caused by stellar rotation. The planet Gl 393 b was discovered in the RV data from the HARPS, CARMENES, and HIRES instruments. Its identification was only possible after modelling, with a Gaussian process (GP), the variability produced by the magnetic activity of the star. For the earliest observations, this variability produced a forest of peaks in the periodogram of the RVs at around the 34 d rotation period determined from {em Kepler} data, which disappeared in the latest epochs. After correcting for them with this GP model, a significant signal showed at a period of $7.03$ d. No significant signals in any of our spectral activity indicators or contemporaneous photometry were found at any of the planetary periods. Given the orbital and stellar properties, the equilibrium temperatures of the three planets are all higher than that for Earth. Current planet formation theories suggest that these two systems represent a common type of architecture. This is consistent with formation following the core accretion paradigm.
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We report on radial velocity time series for two M0.0V stars, GJ338B and GJ338A, using the CARMENES spectrograph, complemented by ground-telescope photometry from Las Cumbres and Sierra Nevada observatories. We aim to explore the presence of small planets in tight orbits using the spectroscopic radial velocity technique. We obtained 159 and 70 radial velocity measurements of GJ338B and A, respectively, with the CARMENES visible channel. We also compiled additional relative radial velocity measurements from the literature and a collection of astrometric data that cover 200 a of observations to solve for the binary orbit. We found dynamical masses of 0.64$pm$0.07M$_odot$ for GJ338B and 0.69$pm$0.07M$_odot$ for GJ338A. The CARMENES radial velocity periodograms show significant peaks at 16.61$pm$0.04 d (GJ338B) and 16.3$^{+3.5}_{-1.3}$ d (GJ338A), which have counterparts at the same frequencies in CARMENES activity indicators and photometric light curves. We attribute these to stellar rotation. GJ338B shows two additional, significant signals at 8.27$pm$0.01 and 24.45$pm$0.02 d, with no obvious counterparts in the stellar activity indices. The former is likely the first harmonic of the stars rotation, while we ascribe the latter to the existence of a super-Earth planet with a minimum mass of 10.27$^{+1.47}_{-1.38}$$M_{oplus}$ orbiting GJ338B. GJ338B b lies inside the inner boundary of the habitable zone around its parent star. It is one of the least massive planets ever found around any member of stellar binaries. The masses, spectral types, brightnesses, and even the rotational periods are very similar for both stars, which are likely coeval and formed from the same molecular cloud, yet they differ in the architecture of their planetary systems.
Context. Teegardens Star is the brightest and one of the nearest ultra-cool dwarfs in the solar neighbourhood. For its late spectral type (M7.0V), the star shows relatively little activity and is a prime target for near-infrared radial velocity surveys such as CARMENES. Aims. As part of the CARMENES search for exoplanets around M dwarfs, we obtained more than 200 radial-velocity measurements of Teegardens Star and analysed them for planetary signals. Methods. We find periodic variability in the radial velocities of Teegardens Star. We also studied photometric measurements to rule out stellar brightness variations mimicking planetary signals. Results. We find evidence for two planet candidates, each with $1.1M_oplus$ minimum mass, orbiting at periods of 4.91 and 11.4 d, respectively. No evidence for planetary transits could be found in archival and follow-up photometry. Small photometric variability is suggestive of slow rotation and old age. Conclusions. The two planets are among the lowest-mass planets discovered so far, and they are the first Earth-mass planets around an ultra-cool dwarf for which the masses have been determined using radial velocities.
LHS 1140 is a nearby mid-M dwarf known to host a temperate rocky super-Earth (LHS 1140 b) on a 24.737-day orbit. Based on photometric observations by MEarth and Spitzer as well as Doppler spectroscopy from HARPS, we report the discovery of an additional transiting rocky companion (LHS 1140 c) with a mass of $1.81pm0.39~{rm M_{Earth}}$ and a radius of $1.282pm0.024~{rm R_{Earth}}$ on a tighter, 3.77795-day orbit. We also obtain more precise estimates of the mass and radius of LHS 1140 b to be $6.98pm0.89~{rm M_{Earth}}$ and $1.727pm0.032~{rm R_{Earth}}$. The mean densities of planets b and c are $7.5pm1.0~rm{g/cm^3}$ and $4.7pm1.1~rm{g/cm^3}$, respectively, both consistent with the Earths ratio of iron to magnesium silicate. The orbital eccentricities of LHS 1140 b and c are consistent with circular orbits and constrained to be below 0.06 and 0.31, respectively, with 90% confidence. Because the orbits of the two planets are co-planar and because we know from previous analyses of Kepler data that compact systems of small planets orbiting M dwarfs are commonplace, a search for more transiting planets in the LHS 1140 system could be fruitful. LHS 1140 c is one of the few known nearby terrestrial planets whose atmosphere could be studied with the upcoming James Webb Space Telescope.
We report the detection of a Neptune-mass exoplanet around the M4.0 dwarf GJ 4276 (G 232-070) based on radial velocity (RV) observations obtained with the CARMENES spectrograph. The RV variations of GJ 4276 are best explained by the presence of a planetary companion that has a minimum mass of $m_{rm b}sin i approx 16, M_oplus$ on a $P_{rm b}=13.35$ day orbit. The analysis of the activity indicators and spectral diagnostics exclude stellar induced RV perturbations and prove the planetary interpretation of the RV signal. We show that a circular single-planet solution can be excluded by means of a likelihood ratio test. Instead, we find that the RV variations can be explained either by an eccentric orbit or interpreted as a pair of planets on circular orbits near a period ratio of 2:1. Although the eccentric single-planet solution is slightly preferred, our statistical analysis indicates that none of these two scenarios can be rejected with high confidence using the RV time series obtained so far. Based on the eccentric interpretation, we find that GJ 4276 b is the most eccentric ($e_{rm b} = 0.37$) exoplanet around an M dwarf with such a short orbital period known today.
This paper aims to derive a map of relative planet occurrence rates that can provide constraints on the overall distribution of terrestrial planets around FGK stars. Based on the planet candidates in the Kepler DR25 data release, I first generate a continuous density map of planet distribution using a Gaussian kernel model and correct the geometric factor that the discovery space of a transit event decreases along with the increase of planetary orbital distance. Then I fit two exponential decay functions of detection efficiency along with the increase of planetary orbital distance and the decrease of planetary radius. Finally, the density map of planet distribution is compensated for the fitted exponential decay functions of detection efficiency to obtain a relative occurrence rate distribution of terrestrial planets. The result shows two regions with planet abundance: one corresponds to planets with radii between 0.5 and 1.5 R_Earth within 0.2 AU, the other corresponds to planets with radii between 1.5 and 3 R_Earth beyond 0.5 AU. It also confirms the features that may be caused by atmospheric evaporation: there is a vacancy of planets of sizes between 2.0 and 4.0 R_Earth inside of ~ 0.5 AU, and a valley with relatively low occurrence rates between 0.2 and 0.5 AU for planets with radii between 1.5 and 3.0 R_Earth.
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