340 research outputs found
A super-Earth orbiting the nearby M-dwarf GJ 536
We report the discovery of a super-Earth orbiting the star GJ 536 based on
the analysis of the radial-velocity time series from the HARPS and HARPS-N
spectrographs. GJ 536 b is a planet with a minimum mass M sin of 5.36 +-
0.69 Me with an orbital period of 8.7076 +- 0.0025 days at a distance of
0.066610(13) AU, and an orbit that is consistent with circular. The host star
is the moderately quiet M1 V star GJ 536, located at 10 pc from the Sun. We
find the presence of a second signal at 43 days that we relate to stellar
rotation after analysing the time series of Ca II H&K and H alpha spectroscopic
indicators and photometric data from the ASAS archive. We find no evidence
linking the short period signal to any activity proxy. We also tentatively
derived a stellar magnetic cycle of less than 3 years.Comment: 14 pages, 14 figures, 5 tables, Accepted in A&
The HADES RV Programme with HARPS-N at TNG XI. GJ 685 b: a warm super-Earth around an active M dwarf
Small rocky planets seem to be very abundant around low-mass M-type stars.
Their actual planetary population is however not yet precisely understood.
Currently several surveys aim to expand the statistics with intensive detection
campaigns, both photometric and spectroscopic. We analyse 106 spectroscopic
HARPS-N observations of the active M0-type star GJ 685 taken over the past five
years. We combine these data with photometric measurements from different
observatories to accurately model the stellar rotation and disentangle its
signals from genuine Doppler planetary signals in the RV data. We run an MCMC
analysis on the RV and activity indexes time series to model the planetary and
stellar signals present in the data, applying Gaussian Process regression
technique to deal with the stellar activity signals. We identify three periodic
signals in the RV time series, with periods of 9, 24, and 18 d. Combining the
analyses of the photometry of the star with the activity indexes derived from
the HARPS-N spectra, we identify the 18 d and 9 d signals as activity-related,
corresponding to the stellar rotation period and its first harmonic
respectively. The 24 d signals shows no relations with any activity proxy, so
we identify it as a genuine planetary signal. We find the best-fit model
describing the Doppler signal of the newly-found planet, GJ 685\,b,
corresponding to an orbital period d and a
minimum mass M. We also study a
sample of 70 RV-detected M-dwarf planets, and present new statistical evidence
of a difference in mass distribution between the populations of single- and
multi-planet systems, which can shed new light on the formation mechanisms of
low-mass planets around late-type stars.Comment: 18 pages, 13 figures, accepted for publication in A&
The Ability of Significant Tidal Stress to Initiate Plate Tectonics
Plate tectonics is a geophysical process currently unique to Earth, has an
important role in regulating the Earth's climate, and may be better understood
by identifying rocky planets outside our solar system with tectonic activity.
The key criterion for whether or not plate tectonics may occur on a terrestrial
planet is if the stress on a planet's lithosphere from mantle convection may
overcome the lithosphere's yield stress. Although many rocky exoplanets closely
orbiting their host stars have been detected, all studies to date of plate
tectonics on exoplanets have neglected tidal stresses in the planet's
lithosphere. Modeling a rocky exoplanet as a constant density, homogeneous,
incompressible sphere, we show the tidal stress from the host star acting on
close-in planets may become comparable to the stress on the lithosphere from
mantle convection. We also show that tidal stresses from planet-planet
interactions are unlikely to be significant for plate tectonics, but may be
strong enough to trigger Earthquakes. Our work may imply planets orbiting close
to their host stars are more likely to experience plate tectonics, with
implications for exoplanetary geophysics and habitability. We produce a list of
detected rocky exoplanets under the most intense stresses. Atmospheric and
topographic observations may confirm our predictions in the near future.
Investigations of planets with significant tidal stress can not only lead to
observable parameters linked to the presence of active plate tectonics, but may
also be used as a tool to test theories on the main driving force behind
tectonic activity.Comment: 34 pages, 3 figures, 3 Tables, accepted to Icaru
Detection Limits and Planet Occurrence Rate in the CARMENES Sample
Màster Oficial d'Astrofísica, Física de Partícules i Cosmologia, Facultat de Física, Universitat de Barcelona, Curs: 2019-2020, Tutors: Juan Carlos Morales, Carme JordiThe CARMENES survey is monitoring more than 300 M-dwarf stars looking for exoplanets. Besides planet discoveries, the data it produces can also be used to estimate the statistics of planets around late-type stars. In this work, we aim at estimating the detection limits of the CARMENES survey, and the occurrence rate of Jupiter- and Neptune-like planets around M-dwarf stars. For this purpose, we use a sample with 324 stars for which values for the radial velocity as a function of time have been measured. We remove the signals produced by planets or intrinsic stellar variability to analyse the instrumental noise. In this noise we look for the minimum planetary mass that could be discovered, obtaining a lower detection limit. With this result we estimate the occurrence rate of M-dwarf planets at different minimum mass and orbital period ranges. For Jupiter- and Neptune-like planets we obtained an occurrence rate of ~ 1%
Chemo-kinematic ages of eccentric-planet-hosting M dwarf stars
M dwarf stars are exciting targets for exoplanet investigations; however,
their fundamental stellar properties are difficult to measure. Perhaps the most
challenging property to measure is stellar age. Once on the main sequence, M
dwarfs change imperceptibly in their temperature and luminosity, necessitating
novel statistical techniques for estimating their ages. In this paper, we infer
ages for known eccentric-planet-hosting M dwarfs using a combination of
kinematics and -element-enrichment, both shown to correlate with age
for Sun-like FGK stars. We calibrate our method on FGK stars in a Bayesian
context. To measure -enrichment, we use publicly-available spectra from
the CARMENES exoplanet survey and a recently developed [Ti/Fe] calibration
utilizing individual Ti I and Fe I absorption lines in band. Tidal effects
are expected to circularize the orbits of short-period planets on short
timescales; however, we find a number of mildly eccentric, close-in planets
orbiting old (8 Gyr) stars. For these systems, we use our ages to
constrain the tidal dissipation parameter of the planets, . For
two mini-Neptune planets, GJ 176b and GJ 536b, we find they have
values more similar to the ice giants than the terrestrial planets in our Solar
System. For GJ 436b, we estimate an age of Gyr and
constrain the to be , in good agreement with constraints
from its inferred tidal heating. We find that GJ 876d has likely undergone
significant orbital evolution over its Gyr lifetime,
potentially influenced by its three outer companions which orbit in a Laplace
resonance.Comment: accepted for publication in Ap
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