Context. The nearby ultra-compact multiplanetary system YZ Ceti consists of at least three planets, and a fourth tentative signal. The orbital period of each planet is the subject of discussion in ...the literature due to strong aliasing in the radial velocity data. The stellar activity of this M dwarf also hampers significantly the derivation of the planetary parameters. Aims. With an additional 229 radial velocity measurements obtained since the discovery publication, we reanalyze the YZ Ceti system and resolve the alias issues. Methods. We use model comparison in the framework of Bayesian statistics and periodogram simulations based on a method by Dawson and Fabrycky to resolve the aliases. We discuss additional signals in the RV data, and derive the planetary parameters by simultaneously modeling the stellar activity with a Gaussian process regression model. To constrain the planetary parameters further we apply a stability analysis on our ensemble of Keplerian fits. Results. We find no evidence for a fourth possible companion. We resolve the aliases: the three planets orbit the star with periods of 2.02 d, 3.06 d, and 4.66 d. We also investigate an effect of the stellar rotational signal on the derivation of the planetary parameters, in particular the eccentricity of the innermost planet. Using photometry we determine the stellar rotational period to be close to 68 d and we also detect this signal in the residuals of a three-planet fit to the RV data and the spectral activity indicators. From our stability analysis we derive a lower limit on the inclination of the system with the assumption of coplanar orbits which is imin = 0.9 deg. From the absence of a transit event with TESS, we derive an upper limit of the inclination of imax = 87.43 deg. Conclusions. YZ Ceti is a prime example of a system where strong aliasing hindered the determination of the orbital periods of exoplanets. Additionally, stellar activity influences the derivation of planetary parameters and modeling them correctly is important for the reliable estimation of the orbital parameters in this specific compact system. Stability considerations then allow additional constraints to be placed on the planetary parameters.
Surveys have shown that super-Earth and Neptune-mass exoplanets are more frequent than gas giants around low-mass stars, as predicted by the core accretion theory of planet formation. We report the ...discovery of a giant planet around the very-low-mass star GJ 3512, as determined by optical and near-infrared radial-velocity observations. The planet has a minimum mass of 0.46 Jupiter masses, very high for such a small host star, and an eccentric 204-day orbit. Dynamical models show that the high eccentricity is most likely due to planet-planet interactions. We use simulations to demonstrate that the GJ 3512 planetary system challenges generally accepted formation theories, and that it puts constraints on the planet accretion and migration rates. Disk instabilities may be more efficient in forming planets than previously thought.
Spectroscopy of transiting exoplanets can be used to investigate their atmospheric properties
and habitability. Combining radial velocity (RV) and transit data provides additional information
on ...exoplanet physical properties. We detect a transiting rocky planet with an orbital period
of 1.467 days around the nearby red dwarf star Gliese 486. The planet Gliese 486 b is
2.81 Earth masses and 1.31 Earth radii, with uncertainties of 5%, as determined from RV data
and photometric light curves. The host star is at a distance of ~8.1 parsecs, has a J-band magnitude of ~7.2, and is observable from both hemispheres of Earth. On the basis of these properties and the planet’s short orbital period and high equilibrium temperature, we show that this terrestrial planet is suitable for emission and transit spectroscopy.
The high-resolution, dual channel, visible and near-infrared spectrograph CARMENES offers exciting opportunities for stellar and exoplanetary research on M dwarfs. In this work we address the ...challenge of reaching the highest radial velocity precision possible with a complex, actively cooled, cryogenic instrument, such as the near-infrared channel. We describe the performance of the instrument and the work flow used to derive precise Doppler measurements from the spectra. The capability of both CARMENES channels to detect small exoplanets is demonstrated with the example of the nearby M5.0 V star CD Cet (GJ 1057), around which we announce a super-Earth (4.0 ± 0.4
M
⊕
) companion on a 2.29 d orbit.
Dynamical histories of planetary systems, as well as the atmospheric evolution of highly irradiated planets, can be studied by characterizing the ultra-short-period planet population, which the TESS ...mission is particularly well suited to discover. Here, we report on the follow-up of a transit signal detected in the TESS sector 19 photometric time series of the M3.0 V star TOI-1685 (2MASS J04342248+4302148). We confirm the planetary nature of the transit signal, which has a period of
P
b
= 0.6691403
−0.0000021
+0.0000023
d, using precise radial velocity measurements taken with the CARMENES spectrograph. From the joint photometry and radial velocity analysis, we estimate the following parameters for TOI-1685 b: a mass of
M
b
= 3.78
−0.63
+0.63
M
⊕
, a radius of
R
b
= 1.70
−0.07
+0.07
R
⊕
, which together result in a bulk density of
ρ
b
= 4.21
−0.82
+0.95
g cm
−3
, and an equilibrium temperature of
T
eq
= 1069
−16
+16
K. TOI-1685 b is the least dense ultra-short-period planet around an M dwarf known to date. TOI-1685 b is also one of the hottest transiting super-Earth planets with accurate dynamical mass measurements, which makes it a particularly attractive target for thermal emission spectroscopy. Additionally, we report with moderate evidence an additional non-transiting planet candidate in the system, TOI-1685 c, which has an orbital period of
P
c
= 9.02
−0.12
+0.10
d.
We report the confirmation of a transiting planet around the bright weakly active M0.5 V star TOI-1235 (TYC 4384–1735–1, V ≈ 11.5 mag), whose transit signal was detected in the photometric time ...series of sectors 14, 20, and 21 of the TESS space mission. We confirm the planetary nature of the transit signal, which has a period of 3.44 d, by using precise RV measurements with the CARMENES, HARPS-N, and iSHELL spectrographs, supplemented by high-resolution imaging and ground-based photometry. A comparison of the properties derived for TOI-1235 b with theoretical models reveals that the planet has a rocky composition, with a bulk density slightly higher than that of Earth. In particular, we measure a mass of M(p) = 5.9 ± 0.6 Mꚛ and a radius of R(p) = 1.69 ± 0.08 Rꚛ, which together result in a density of ρp = 6.7(− 1.1,+ 1.3) g/cu. cm. When compared with other well-characterized exoplanetary systems, the particular combination of planetary radius and mass places our discovery in the radius gap, which is a transition region between rocky planets and planets with significant atmospheric envelopes. A few examples of planets occupying the radius gap are known to date. While the exact location of the radius gap for M dwarfs is still a matter of debate, our results constrain it to be located at around 1.7 Rꚛ or larger at the insolation levels received by TOI-1235 b (~60 Sꚛ). This makes it an extremely interesting object for further studies of planet formation and atmospheric evolution.
We announce the discovery of two planetary companions orbiting around the low-mass stars Ross 1020 (GJ 3779, M4.0V) and LP 819-052 (GJ 1265, M4.5V). The discovery is based on the analysis of CARMENES ...radial velocity (RV) observations in the visual channel as part of its survey for exoplanets around M dwarfs. In the case of GJ 1265, CARMENES observations were complemented with publicly available Doppler measurements from HARPS. The datasets reveal two planetary companions, one for each star, that share very similar properties: minimum masses of 8.0 ± 0.5
M
⊕
and 7.4 ± 0.5
M
⊕
in low-eccentricity orbits with periods of 3.023 ± 0.001 d and 3.651 ± 0.001 d for GJ 3779 b and GJ 1265 b, respectively. The periodic signals around 3 d found in the RV data have no counterpart in any spectral activity indicator. Furthermore, we collected available photometric data for the two host stars, which confirm that the additional Doppler variations found at periods of approximately 95 d can be attributed to the rotation of the stars. The addition of these planets to a mass-period diagram of known planets around M dwarfs suggests a bimodal distribution with a lack of short-period low-mass planets in the range of 2–5
M
⊕
. It also indicates that super-Earths (>5
M
⊕
) currently detected by RV and transit techniques around M stars are usually found in systems dominated by a single planet.
Context.
The nearby ultra-compact multiplanetary system YZ Ceti consists of at least three planets, and a fourth tentative signal. The orbital period of each planet is the subject of discussion in ...the literature due to strong aliasing in the radial velocity data. The stellar activity of this M dwarf also hampers significantly the derivation of the planetary parameters.
Aims.
With an additional 229 radial velocity measurements obtained since the discovery publication, we reanalyze the YZ Ceti system and resolve the alias issues.
Methods.
We use model comparison in the framework of Bayesian statistics and periodogram simulations based on a method by Dawson and Fabrycky to resolve the aliases. We discuss additional signals in the RV data, and derive the planetary parameters by simultaneously modeling the stellar activity with a Gaussian process regression model. To constrain the planetary parameters further we apply a stability analysis on our ensemble of Keplerian fits.
Results.
We find no evidence for a fourth possible companion. We resolve the aliases: the three planets orbit the star with periods of 2.02 d, 3.06 d, and 4.66 d. We also investigate an effect of the stellar rotational signal on the derivation of the planetary parameters, in particular the eccentricity of the innermost planet. Using photometry we determine the stellar rotational period to be close to 68 d and we also detect this signal in the residuals of a three-planet fit to the RV data and the spectral activity indicators. From our stability analysis we derive a lower limit on the inclination of the system with the assumption of coplanar orbits which is
i
min
= 0.9 deg. From the absence of a transit event with TESS, we derive an upper limit of the inclination of
i
max
= 87.43 deg.
Conclusions.
YZ Ceti is a prime example of a system where strong aliasing hindered the determination of the orbital periods of exoplanets. Additionally, stellar activity influences the derivation of planetary parameters and modeling them correctly is important for the reliable estimation of the orbital parameters in this specific compact system. Stability considerations then allow additional constraints to be placed on the planetary parameters.
Context.
A challenge with radial-velocity (RV) data is disentangling the origin of signals either due to a planetary companion or to stellar activity. In fact, the existence of a planetary companion ...has been proposed, as well as contested, around the relatively bright, nearby M3.0 V star AD Leo at the same period as the stellar rotation of 2.23 days.
Aims.
We further investigate the nature of this signal. We introduce new CARMENES optical and near-IR RV data and an analysis in combination with archival data taken by HIRES and HARPS, along with more recent data from HARPS-N, GIANO-B, and HPF. Additionally, we address the confusion concerning the binarity of AD Leo.
Methods.
We consider possible correlations between the RVs and various stellar activity indicators accessible with CARMENES. We additionally applied models within a Bayesian framework to determine whether a Keplerian model, a red-noise quasi-periodic model using a Gaussian process, or a mixed model would explain the observed data best. We also exclusively focus on spectral lines potentially associated with stellar activity.
Results.
The CARMENES RV data agree with the previously reported periodicity of 2.23 days, correlate with some activity indicators, and exhibit chromaticity. However, when considering the entire RV data set, we find that a mixed model composed of a stable and a variable component performs best. Moreover, when recomputing the RVs using only spectral lines insensitive to activity, there appears to be some residual power at the period of interest. We therefore conclude that it is not possible to determinedly prove that there is no planet orbiting in synchronization with the stellar rotation given our data, current tools, machinery, and knowledge of how stellar activity affects RVs. We do rule out planets more massive than 27
M
⊕
(=0.084
M
Jup
). Likewise, we exclude any binary companion around AD Leo with M sin
i
greater than 3–6
M
Jup
on orbital periods <14 yr.
Context.
GJ 1148 is an M-dwarf star hosting a planetary system composed of two Saturn-mass planets in eccentric orbits with periods of 41.38 and 532.02 days.
Aims.
We reanalyze the orbital ...configuration and dynamics of the GJ 1148 multi-planetary system based on new precise radial velocity measurements taken with CARMENES.
Methods.
We combined new and archival precise Doppler measurements from CARMENES with those available from HIRES for GJ 1148 and modeled these data with a self-consistent dynamical model. We studied the orbital dynamics of the system using the secular theory and direct
N
-body integrations. The prospects of potentially habitable moons around GJ 1148 b were examined.
Results.
The refined dynamical analyses show that the GJ 1148 system is long-term stable in a large phase-space of orbital parameters with an orbital configuration suggesting apsidal alignment, but not in any particular high-order mean-motion resonant commensurability. GJ 1148 b orbits inside the optimistic habitable zone (HZ). We find only a narrow stability region around the planet where exomoons can exist. However, in this stable region exomoons exhibit quick orbital decay due to tidal interaction with the planet.
Conclusions.
The GJ 1148 planetary system is a very rare M-dwarf planetary system consisting of a pair of gas giants, the inner of which resides in the HZ. We conclude that habitable exomoons around GJ 1148 b are very unlikely to exist.
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