84 research outputs found
The RoPES project with HARPS and HARPS-N. I. A system of super-Earths orbiting the moderately active K-dwarf HD 176986
We report the discovery of a system of two super-Earths orbiting the
moderately active K-dwarf HD 176986. This work is part of the RoPES RV program
of G- and K-type stars, which combines radial velocities (RVs) from the HARPS
and HARPS-N spectrographs to search for short-period terrestrial planets. HD
176986 b and c are super-Earth planets with masses of 5.74 and 9.18
M, orbital periods of 6.49 and 16.82 days, and distances of 0.063
and 0.119 AU in orbits that are consistent with circular. The host star is a
K2.5 dwarf, and despite its modest level of chromospheric activity (log(R'hk) =
- 4.90 +- 0.04), it shows a complex activity pattern. Along with the discovery
of the planets, we study the magnetic cycle and rotation of the star. HD 176986
proves to be suitable for testing the available RV analysis technique and
further our understanding of stellar activity.Comment: 21 pages, 24 figures, 7 table
CONTRIBUCIÓN AL ESTUDIO DE LOS BRIÓFITOS EPÍFITOS DE JUNIPERUS PHOElVlCEA L. EN LA ISLA DEL HIERRO (l. CANARIAS). I
A study of the bryophytic epiphytes of Juniperus phoenicea L present on the island of Hierro has been carried out. As a result of this investigation, a total of 23 taxa have been catalogued, of which, 5 represent new records for the island. Stations situated on the highest ground and the midmontane zone orientated S-SW, were selected, the former being richer in both flora and covering of bryophytes.En esta comunicación se aborda el estudio de los briófitos epífitos de Juniperus phoenicea L. en el Hierro y se cataloga un total de 23 táxones de los que 5 se citan por primera vez para esta isla. Se han elegido estaciones de cumbre y de piso montano seco en orientación S-SW, las primeras más ricas en flora y cobertura briofítica
HADES RV Programme with HARPS-N at TNG. VII. Rotation and activity of M-Dwarfs from time-series high-resolution spectroscopy of chromospheric indicators
We aim to investigate the presence of signatures of magnetic cycles and
rotation on a sample of 71 early M-dwarfs from the HADES RV programme using
high-resolution time-series spectroscopy of the Ca II H & K and Halpha
chromospheric activity indicators, the radial velocity series, the parameters
of the cross correlation function and the V-band photometry. We used mainly
HARPS-N spectra, acquired over four years, and add HARPS spectra from the
public ESO database and ASAS photometry light-curves as support data, extending
the baseline of the observations of some stars up to 12 years. We provide
log(R'hk) measurements for all the stars in the sample, cycle length
measurements for 13 stars, rotation periods for 33 stars and we are able to
measure the semi-amplitude of the radial velocity signal induced by rotation in
16 stars. We complement our work with previous results and confirm and refine
the previously reported relationships between the mean level of chromospheric
emission, measured by the log(R'hk), with the rotation period, and with the
measured semi-amplitude of the activity induced radial velocity signal for
early M-dwarfs. We searched for a possible relation between the measured
rotation periods and the lengths of the magnetic cycle, finding a weak
correlation between both quantities. Using previous v sin i measurements we
estimated the inclinations of the star's poles to the line of sight for all the
stars in the sample, and estimate the range of masses of the planets GJ 3998 b
and c (2.5 - 4.9 Mearth and 6.3 - 12.5 Mearth), GJ 625 b (2.82 Mearth), GJ 3942
b (7.1 - 10.0 Mearth) and GJ 15A b (3.1 - 3.3 Mearth), assuming their orbits
are coplanar with the stellar rotation.Comment: 19 pages, 16 figures, 10 table
HADES RV Programme with HARPS-N at TNG VI. GJ 3942 b behind dominant activity signals
Short- to mid-term magnetic phenomena on the stellar surface of M-type stars
cannot only resemble the effects of planets in radial velocity data, but also
may hide them. We analyze 145 spectroscopic HARPS-N observations of GJ 3942
taken over the past five years and additional photometry to disentangle stellar
activity effects from genuine Doppler signals as a result of the orbital motion
of the star around the common barycenter with its planet. To achieve this, we
use the common methods of pre-whitening, and treat the correlated red noise by
a first-order moving average term and by Gaussian-process regression following
an MCMC analysis. We identify the rotational period of the star at 16.3 days
and discover a new super-Earth, GJ 3942 b, with an orbital period of 6.9 days
and a minimum mass of 7.1 Me. An additional signal in the periodogram of the
residuals is present but we cannot claim it to be related to a second planet
with sufficient significance at this point. If confirmed, such planet candidate
would have a minimum mass of 6.3 Me and a period of 10.4 days, which might
indicate a 3:2 mean-motion resonance with the inner planet
The acid crater lake of Taal Volcano, Philippines: hydrogeochemical and hydroacoustic data related to the 2010–11 volcanic unrest
Studies of the water chemistry of Taal crater lake and echo-sounding surveys have provided new insights into its chemical and physical dynamics. During the volcano-seismic unrest of April 2010–June 2011, the waters of Taal crater lake showed changes in chemical composition and increases in CO2 emissions associated with the seismic unrest. The chemical and isotopic data show that the lake water has contributions from both seawater and meteoric water and receives injections of deep hydrothermal water and gases during periods of intense volcano-seismic unrest. These inflationary periods may lead to faulting of the impermeable cap rock that usually seals the deeper Taal hydrothermal reservoir in response to degassing and convective movements in the underlying Taal magma chamber.Instituto Volcanológico de Canarias, EspañaEnvironmental Research Division, Instituto Tecnológico y de Energías Renovables, EspañaAgencia Insular de Energía de Tenerife, EspañaÁrea de Geología Marina, Instituto Geológico y Minero de España, EspañaInstitute of Agriculture and Environment, Massey University, AustraliaPhilippine Institute of Volcanology and Seismology, FilipinasGeochemical Research Center, The University of Tokyo, JapónEarth & Environmental Sciences, Wesleyan University, Estados UnidosPeer reviewe
HADES RV Programme with HARPS-N at TNG XII. The abundance signature of M dwarf stars with planets
Most of our current knowledge on planet formation is still based on the
analysis of main-sequence, solar-type stars. Conversely, detailed chemical
studies of large samples of M-dwarf planet hosts are still missing. We develop
for the first time a methodology to determine stellar abundances of elements
others than iron for M dwarf stars from high-resolution, optical spectra. Our
methodology is based on the use of principal component analysis and sparse
Bayesian's methods. We made use of a set of M dwarfs orbiting around an FGK
primary with known abundances to train our methods. We applied our methods to
derive stellar metalliticies and abundances of a large sample of M dwarfs
observed within the framework of current radial velocity surveys. We then used
a sample of nearby FGK stars to cross-validate our technique by comparing the
derived abundance trends in the M dwarf sample with those found on the FGK
stars. The metallicity distribution of the different subsamples shows that M
dwarfs hosting giant planets show a planet-metallicity correlation as well as a
correlation with the stellar mass. M dwarfs hosting low-mass planets do not
seem to follow the planet-metallicity correlation. We also found that the
frequency of low-mass planets does not depend on the mass of the stellar host.
These results seem in agreement with previous works. However, we note that for
giant planet hosts our metallicities predict a weaker planet metallicity
correlation but a stronger mass-dependency than photometric values. We show,
for the first time, that there seems to be no differences in the abundance
distribution of elements different from iron between M dwarfs with and without
known planets. Our data shows that low-mass stars with planets follow the same
metallicity, mass, and abundance trends than their FGK counterparts.Comment: Accepted for publication by Astronomy & Astrophysic
HADES RV Programme with HARPS-N at TNG XIII. A sub-Neptune around the M dwarf GJ 720 A
Context. The high number of super-Earth and Earth-like planets in the
habitable zone (HZ) detected around M-dwarf stars in the last years has
revealed these stellar objects to be the key for planetary radial velocity (RV)
searches. Aims. Using the HARPS-N spectrograph within The HArps-n red Dwarf
Exoplanet Survey (HADES) we reach the precision needed to detect small planets
with a few Earth masses using the RV technique. Methods. We obtained 138
HARPS-N RV measurements between 2013 May and 2020 September of GJ 720 A,
classified as an M0.5V star located at a distance of 15.56 pc. To characterize
the stellar variability and to discern the periodic variation due to the
Keplerian signals from those related to stellar activity, the HARPS-N
spectroscopic activity indicators and the simultaneous photometric observations
were analyzed. The combined analysis of HARPS-N RVs and activity indicators let
us to address the nature of the periodic signals. The final model and the
orbital planetary parameters were obtained by fitting simultaneously the
stellar variability and the Keplerian signal using a Gaussian process
regression and following a Bayesian criterion. Results. The HARPS-N RV periodic
signals around 40 d and 100 d have counterparts at the same frequencies in
HARPS-N activity indicators and photometric light curves. Then we attribute
these periodicities to stellar activity the former period being likely
associated with the stellar rotation. GJ 720 A shows the most significant
signal at 19.4660.005 d with no counterparts in any stellar activity
indices. We hence ascribe this RV signal, having a semiamplitude of
4.720.27 m/s , to the presence of a sub-Neptune mass planet. The planet GJ
720 Ab has a minimum mass of 13.640.79 M, it is in circular
orbit at 0.1190.002 AU from its parent star, and lies inside the inner
boundary of the HZ around its parent star
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