scholarly journals The CARMENES search for exoplanets around M dwarfs

2020 ◽  
Vol 643 ◽  
pp. A112
Author(s):  
S. Stock ◽  
E. Nagel ◽  
J. Kemmer ◽  
V. M. Passegger ◽  
S. Reffert ◽  
...  
Keyword(s):  
Gaussian Process Regression ◽  
Stellar Rotation ◽  
M Dwarfs ◽  
Stellar Activity ◽  
Rotation Periods ◽  
Photometric Observations ◽  
Orbital Periods ◽  
Stellar Properties ◽  
Core Accretion ◽  
Common Architecture

We announce the discovery of two planets orbiting the M dwarfs GJ 251 (0.360 ± 0.015M⊙) and HD 238090 (0.578 ± 0.021M⊙) based on CARMENES radial velocity (RV) data. In addition, we independently confirm with CARMENES data the existence of Lalande 21185 b, a planet that has recently been discovered with the SOPHIE spectrograph. All three planets belong to the class of warm or temperate super-Earths and share similar properties. The orbital periods are 14.24 d, 13.67 d, and 12.95 d and the minimum masses are 4.0 ± 0.4 M⊕, 6.9 ± 0.9 M⊕, and 2.7 ± 0.3 M⊕ for GJ 251 b, HD 238090 b, and Lalande 21185 b, respectively. Based on the orbital and stellar properties, we estimate equilibrium temperatures of 351.0 ± 1.4 K for GJ 251 b, 469.6 ± 2.6 K for HD 238090 b, and 370.1 ± 6.8 K for Lalande 21185 b. For the latter we resolve the daily aliases that were present in the SOPHIE data and that hindered an unambiguous determination of the orbital period. We find no significant signals in any of our spectral activity indicators at the planetary periods. The RV observations were accompanied by contemporaneous photometric observations. We derive stellar rotation periods of 122.1 ± 2.2 d and 96.7 ± 3.7 d for GJ 251 and HD 238090, respectively. The RV data of all three stars exhibit significant signals at the rotational period or its first harmonic. For GJ 251 and Lalande 21185, we also find long-period signals around 600 d, and 2900 d, respectively, which we tentatively attribute to long-term magnetic cycles. We apply a Bayesian approach to carefully model the Keplerian signals simultaneously with the stellar activity using Gaussian process regression models and extensively search for additional significant planetary signals hidden behind the stellar activity. Current planet formation theories suggest that the three systems represent a common architecture, consistent with formation following the core accretion paradigm.

scholarly journals The CARMENES search for exoplanets around M dwarfs

2019 ◽  
Vol 627 ◽  
pp. A116 ◽  
Author(s):  
S. Lalitha ◽  
D. Baroch ◽  
J. C. Morales ◽  
V. M. Passegger ◽  
F. F. Bauer ◽  
...  
Keyword(s):  
Near Infrared ◽  
Correlated Noise ◽  
Stellar Rotation ◽  
M Dwarfs ◽  
Stellar Activity ◽  
Orbital Parameters ◽  
Rotation Periods ◽  
Planetary Mass ◽  
Low Mass ◽  
Orbital Periods

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.

scholarly journals The CARMENES search for exoplanets around M dwarfs

2020 ◽  
Vol 636 ◽  
pp. A119 ◽  
Author(s):  
S. Stock ◽  
J. Kemmer ◽  
S. Reffert ◽  
T. Trifonov ◽  
A. Kaminski ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Radial Velocity ◽  
Model Comparison ◽  
Gaussian Process Regression ◽  
System Stability ◽  
M Dwarfs ◽  
Stellar Activity ◽  
Orbital Parameters ◽  
Orbital Periods

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.

scholarly journals Tidal effects on stellar activity

2016 ◽  
Vol 12 (S328) ◽  
pp. 308-314
Author(s):  
K. Poppenhaeger
Keyword(s):  
Orbital Period ◽  
Binary Systems ◽  
Semimajor Axis ◽  
Rotation Period ◽  
Magnetic Activity ◽  
Stellar Rotation ◽  
Stellar Activity ◽  
Tidal Interaction ◽  
Hot Jupiters ◽  
Orbital Periods

AbstractThe architecture of many exoplanetary systems is different from the solar system, with exoplanets being in close orbits around their host stars and having orbital periods of only a few days. We can expect interactions between the star and the exoplanet for such systems that are similar to the tidal interactions observed in close stellar binary systems. For the exoplanet, tidal interaction can lead to circularization of its orbit and the synchronization of its rotational and orbital period. For the host star, it has long been speculated if significant angular momentum transfer can take place between the planetary orbit and the stellar rotation. In the case of the Earth-Moon system, such tidal interaction has led to an increasing distance between Earth and Moon. For stars with Hot Jupiters, where the orbital period of the exoplanet is typically shorter than the stellar rotation period, one expects a decreasing semimajor axis for the planet and enhanced stellar rotation, leading to increased stellar activity. Also excess turbulence in the stellar convective zone due to rising and subsiding tidal bulges may change the magnetic activity we observe for the host star. I will review recent observational results on stellar activity and tidal interaction in the presence of close-in exoplanets, and discuss the effects of enhanced stellar activity on the exoplanets in such systems.

scholarly journals The CARMENES search for exoplanets around M dwarfs

2019 ◽  
Vol 623 ◽  
pp. A24 ◽  
Author(s):  
B. Fuhrmeister ◽  
S. Czesla ◽  
J. H. M. M. Schmitt ◽  
E. N. Johnson ◽  
P. Schöfer ◽  
...  
Keyword(s):  
Gaussian Process ◽  
Near Infrared ◽  
Rotation Period ◽  
Gaussian Process Regression ◽  
Process Models ◽  
M Dwarfs ◽  
String Length ◽  
Phase Dispersion ◽  
Rotation Periods ◽  
Gaussian Process Models

We use spectra from CARMENES, the Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs, to search for periods in chromospheric indices in 16 M0–M2 dwarfs. We measure spectral indices in the Hα, the Ca II infrared triplet (IRT), and the Na I D lines to study which of these indices are best-suited to finding rotation periods in these stars. Moreover, we test a number of different period-search algorithms, namely the string length method, the phase dispersion minimisation, the generalized Lomb–Scargle periodogram, and the Gaussian process regression with quasi-periodic kernel. We find periods in four stars using Hα and in five stars using the Ca II IRT, two of which have not been found before. Our results show that both Hα and the Ca II IRT lines are well suited for period searches, with the Ca II IRT index performing slightly better than Hα. Unfortunately, the Na I D lines are strongly affected by telluric airglow, and we could not find any rotation period using this index. Further, different definitions of the line indices have no major impact on the results. Comparing the different search methods, the string length method and the phase dispersion minimisation perform worst, while Gaussian process models produce the smallest numbers of false positives and non-detections.

scholarly journals Simulated mass measurements of the young planet K2-33b

2020 ◽  
Vol 493 (1) ◽  
pp. L92-L97 ◽  
Author(s):  
Baptiste Klein ◽  
J-F Donati
Keyword(s):  
Near Infrared ◽  
Gaussian White Noise ◽  
Gaussian Process Regression ◽  
Stellar Rotation ◽  
Mass Measurements ◽  
Radial Magnetic Field ◽  
Stellar Activity ◽  
Central Wavelength ◽  
Bright Surface ◽  
Good Coverage

ABSTRACT In this paper, we carry out simulations of radial velocity (RV) measurements of the mass of the 8–11 Myr Neptune-sized planet K2-33b using high-precision near-infrared velocimeters like SPIRou at the Canada–France–Hawaii Telescope. We generate an RV curve containing a planet signature and a realistic stellar activity signal, computed for a central wavelength of 1.8 µm and statistically compatible with the light curve obtained with K2. The modelled activity signal includes the effect of time-evolving dark and bright surface features hosting a 2 kG radial magnetic field, resulting in an RV signal of semi-amplitude ∼30 m s−1. Assuming a 3-month visibility window, we build RV time series including Gaussian white noise from which we retrieve the planet mass while filtering the stellar activity signal using Gaussian process regression. We find that 35/50 visits spread over three consecutive bright-time runs on K2-33 allow one to reliably detect planet RV signatures of, respectively, 10 and 5 m s−1 at precisions &gt;3σ. We also show that 30 visits may end up being insufficient in some cases to provide a good coverage of the stellar rotation cycle, with the result that the planet signature can go undetected or the mass estimation be plagued by large errors.

scholarly journals Occurrence rates of planets orbiting M Stars: applying ABC to Kepler DR25, Gaia DR2, and 2MASS data

2020 ◽  
Vol 498 (2) ◽  
pp. 2249-2262 ◽  
Author(s):  
Danley C Hsu ◽  
Eric B Ford ◽  
Ryan Terrien
Keyword(s):  
Small Sample ◽  
Occurrence Rate ◽  
Early Type ◽  
M Dwarfs ◽  
Orbital Periods ◽  
M Stars ◽  
Stellar Properties ◽  
Approximate Bayesian ◽  
M Dwarf ◽  
Gaia Dr2

ABSTRACT We present robust planet occurrence rates for Kepler planet candidates around M stars for planet radii Rp = 0.5–4 R⊕ and orbital periods P = 0.5–256 d using the approximate Bayesian computation technique. This work incorporates the final Kepler DR25 planet candidate catalogue and data products and augments them with updated stellar properties using Gaia DR2 and 2MASS point source catalogue. We apply a set of selection criteria to select a sample of 1746 Kepler M dwarf targets that host 89 associated planet candidates. These early-type M dwarfs and late K dwarfs were selected from cross-referenced targets using several photometric quality flags from Gaia DR2 and colour–magnitude cuts using 2MASS magnitudes. We estimate a habitable zone occurrence rate of $f_{\textrm {M,HZ}} = 0.33^{+0.10}_{-0.12}$ for planets with 0.75–1.5 R⊕ size. We caution that occurrence rate estimates for Kepler M stars are sensitive to the choice of prior due to the small sample of target stars and planet candidates. For example, we find an occurrence rate of $4.2^{+0.6}_{-0.6}$ or $8.4^{+1.2}_{-1.1}$ planets per M dwarf (integrating over Rp = 0.5–4 R⊕ and P = 0.5–256 d) for our two choices of prior. These occurrence rates are greater than those for FGK dwarf target when compared at the same range of orbital periods, but similar to occurrence rates when computed as a function of equivalent stellar insolation. Combining our result with recent studies of exoplanet architectures indicates that most, and potentially all, early-type M dwarfs harbour planetary systems.

scholarly journals Quantization of Planetary Systems and its Dependency on Stellar Rotation

2011 ◽  
Vol 28 (3) ◽  
pp. 177-201 ◽  
Author(s):  
Jean-Paul A. Zoghbi
Keyword(s):  
Gravitational Instability ◽  
Rotation Period ◽  
Planetary Systems ◽  
Stellar Rotation ◽  
Tidal Dissipation ◽  
Half Integer ◽  
Pure Chance ◽  
Rotation Periods ◽  
Planetary Orbits ◽  
Orbital Periods

AbstractWith the discovery of now more than 500 exoplanets, we present a statistical analysis of the planetary orbital periods and their relationship to the rotation periods of their parent stars. We test whether the structural variables of planetary orbits, i.e. planetary angular momentum and orbital period, are ‘quantized’ in integer or half-integer multiples of the parent star's rotation period. The Solar System is first shown to exhibit quantized planetary orbits that correlate with the Sun's rotation period. The analysis is then expanded over 443 exoplanets to statistically validate this quantization and its association with stellar rotation. The results imply that the exoplanetary orbital periods are highly correlated with the parent star's rotation periods and follow a discrete half-integer relationship with orbital ranks n = 0.5, 1.0, 1.5, 2.0, 2.5, etc. The probability of obtaining these results by pure chance is p < 0.024. We discuss various mechanisms that could justify this planetary quantization, such as the hybrid gravitational instability models of planet formation, along with possible physical mechanisms such as the inner disc's magnetospheric truncation, tidal dissipation, and resonance trapping. In conclusion, we statistically demonstrate that a quantized orbital structure should emerge from the formation processes of planetary systems and that this orbital quantization is highly dependent on the parent star's rotation period.

scholarly journals Magnetic fields in M dwarfs from the CARMENES survey

2019 ◽  
Vol 626 ◽  
pp. A86 ◽  
Author(s):  
D. Shulyak ◽  
A. Reiners ◽  
E. Nagel ◽  
L. Tal-Or ◽  
J. A. Caballero ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Near Infrared ◽  
Magnetic Energy ◽  
Spectral Lines ◽  
High Spectral Resolution ◽  
Stellar Rotation ◽  
M Dwarfs ◽  
Dynamo Action ◽  
Rotation Periods ◽  
Consistent Picture

Context. M dwarfs are known to generate the strongest magnetic fields among main-sequence stars with convective envelopes, but we are still lacking a consistent picture of the link between the magnetic fields and underlying dynamo mechanisms, rotation, and activity. Aims. In this work we aim to measure magnetic fields from the high-resolution near-infrared spectra taken with the CARMENES radial-velocity planet survey in a sample of 29 active M dwarfs and compare our results against stellar parameters. Methods. We used the state-of-the-art radiative transfer code to measure total magnetic flux densities from the Zeeman broadening of spectral lines and filling factors. Results. We detect strong kG magnetic fields in all our targets. In 16 stars the magnetic fields were measured for the first time. Our measurements are consistent with the magnetic field saturation in stars with rotation periods P < 4 d. The analysis of the magnetic filling factors reveal two different patterns of either very smooth distribution or a more patchy one, which can be connected to the dynamo state of the stars and/or stellar mass. Conclusions. Our measurements extend the list of M dwarfs with strong surface magnetic fields. They also allow us to better constrain the interplay between the magnetic energy, stellar rotation, and underlying dynamo action. The high spectral resolution and observations at near-infrared wavelengths are the beneficial capabilities of the CARMENES instrument that allow us to address important questions about the stellar magnetism.

scholarly journals HADES RV Programme with HARPS-N at TNG

2019 ◽  
Vol 624 ◽  
pp. A27 ◽  
Author(s):  
E. González-Álvarez ◽  
G. Micela ◽  
J. Maldonado ◽  
L. Affer ◽  
A. Maggio ◽  
...  
Keyword(s):  
Rotation Period ◽  
High Resolution Spectroscopy ◽  
Slow Rotation ◽  
Stellar Rotation ◽  
M Dwarfs ◽  
Dwarf Stars ◽  
Rotation Periods ◽  
Coronal Activity ◽  
Low Mass ◽  
M Dwarf Stars

Aims. We extend the relationship between X-ray luminosity (Lx) and rotation period (Prot) found for main-sequence FGK stars, and test whether it also holds for early M dwarfs, especially in the non-saturated regime (Lx ∝ Prot−2) which corresponds to slow rotators. Methods. We use the luminosity coronal activity indicator (Lx) of a sample of 78 early M dwarfs with masses in the range from 0.3 to 0.75 M⊙ from the HArps-N red Dwarf Exoplanet Survey (HADES) radial velocity (RV) programme collected from ROSAT and XMM-Newton. The determination of the rotation periods (Prot) was done by analysing time series of high-resolution spectroscopy of the Ca II H & K and Hα activity indicators. Our sample principally covers the slow rotation regime with rotation periods from 15 to 60 days. Results. Our work extends to the low mass regime the observed trend for more massive stars showing a continuous shift of the Lx∕Lbol versus Prot power law towards longer rotation period values, and includes a more accurate way to determine the value of the rotation period at which the saturation occurs (Psat) for M dwarf stars. Conclusions. We conclude that the relations between coronal activity and stellar rotation for FGK stars also hold for early M dwarfs in the non-saturated regime, indicating that the rotation period is sufficient to determine the ratio Lx∕Lbol.

scholarly journals Gliese 49: activity evolution and detection of a super-Earth

2019 ◽  
Vol 624 ◽  
pp. A123 ◽  
Author(s):  
M. Perger ◽  
G. Scandariato ◽  
I. Ribas ◽  
J. C. Morales ◽  
L. Affer ◽  
...  
Keyword(s):  
Likelihood Function ◽  
Major Axis ◽  
Equilibrium Temperature ◽  
Stellar Rotation ◽  
Semi Major Axis ◽  
Low Mass Stars ◽  
Stellar Activity ◽  
Doppler Signals ◽  
Low Mass ◽  
Orbital Periods

Context. Small planets around low-mass stars often show orbital periods in a range that corresponds to the temperate zones of their host stars which are therefore of prime interest for planet searches. Surface phenomena such as spots and faculae create periodic signals in radial velocities and in observational activity tracers in the same range, so they can mimic or hide true planetary signals. Aims. We aim to detect Doppler signals corresponding to planetary companions, determine their most probable orbital configurations, and understand the stellar activity and its impact on different datasets. Methods. We analyzed 22 yr of data of the M1.5 V-type star Gl 49 (BD+61 195) including HARPS-N and CARMENES spectrographs, complemented by APT2 and SNO photometry. Activity indices are calculated from the observed spectra, and all datasets are analyzed with periodograms and noise models. We investigated how the variation of stellar activity imprints on our datasets. We further tested the origin of the signals and investigate phase shifts between the different sets. To search for the best-fit model we maximize the likelihood function in a Markov chain Monte Carlo approach. Results. As a result of this study, we are able to detect the super-Earth Gl 49b with a minimum mass of 5.6 M⊕. It orbits its host star with a period of 13.85 d at a semi-major axis of 0.090 au and we calculate an equilibrium temperature of 350 K and a transit probability of 2.0%. The contribution from the spot-dominated host star to the different datasets is complex, and includes signals from the stellar rotation at 18.86 d, evolutionary timescales of activity phenomena at 40–80 d, and a long-term variation of at least four years.

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