204 research outputs found
Soil salinity related to physical soil characteristics and irrigation management in four Mediterranean irrigation districts
25 Pag., 6 Tabl., 1 Fig. The definitive version is available at: http://www.sciencedirect.com/science/journal/03783774Irrigated agriculture is threatened by soil salinity in numerous arid and semiarid areas of the Mediterranean basin. The objective of this work was to quantify soil salinity through electromagnetic induction (EMI) techniques and relate it to the physical characteristics and irrigation management of four Mediterranean irrigation districts located in Morocco, Spain, Tunisia and Turkey. The volume and salinity of the main water inputs (irrigation and precipitation) and outputs (crop evapotranspiration and drainage) were measured or estimated in each district. Soil salinity (ECe) maps were obtained through electromagnetic induction surveys (ECa readings) and district-specific ECa–ECe calibrations. Gravimetric soil water content (WC) and soil saturation percentage (SP) were also measured in the soil calibration samples. The ECa–ECe calibration equations were highly significant (P 0.1) with WC, and was only significantly correlated (P Morocco (2.2 dS m−1) > Spain (1.4 dS m−1) > Turkey (0.45 dS m−1). Soil salinity was mainly affected by irrigation water salinity and irrigation efficiency. Drainage water salinity at the exit of each district was mostly affected by soil salinity and irrigation efficiency, with values very high in Tunisia (9.0 dS m−1), high in Spain (4.6 dS m−1), moderate in Morocco (estimated at 2.6 dS m−1), and low in Turkey (1.4 dS m−1). Salt loads in drainage waters, calculated from their salinity (ECdw) and volume (Q), were highest in Tunisia (very high Q and very high ECdw), intermediate in Turkey (extremely high Q and low ECdw) and lowest in Spain (very low Q and high ECdw) (there were no Q data for Morocco). Reduction of these high drainage volumes through sound irrigation management would be the most efficient way to control the off-site salt-pollution caused by these Mediterranean irrigation districts.This study was supported by the European Commission research project INCO-CT-2005-015031.Peer reviewe
The CARMENES search for exoplanets around M dwarfs: Radial-velocity variations of active stars in visual-channel spectra
Previous simulations predicted the activity-induced radial-velocity (RV)
variations of M dwarfs to range from cm/s to km/s, depending on
various stellar and activity parameters. We investigate the observed relations
between RVs, stellar activity, and stellar parameters of M dwarfs by analyzing
CARMENES high-resolution visual-channel spectra (m), which were
taken within the CARMENES RV planet survey during its first months of
operation. During this time, of the CARMENES-sample stars were observed
at least five times. From each spectrum we derived a relative RV and a measure
of chromospheric H emission. In addition, we estimated the chromatic
index (CRX) of each spectrum, which is a measure of the RV wavelength
dependence. Despite having a median number of only measurements per star,
we show that the RV variations of the stars with RV scatter of m/s and a
projected rotation velocity km/s are caused mainly by activity.
We name these stars `active RV-loud stars' and find their occurrence to
increase with spectral type: from for early-type M dwarfs
(MV) through for mid-type M dwarfs (MV) to
for late-type M dwarfs (MV). Their RV-scatter amplitude is
found to be correlated mainly with . For about half of the stars, we
also find a linear RVCRX anticorrelation, which indicates that their
activity-induced RV scatter is lower at longer wavelengths. For most of them we
can exclude a linear correlation between RV and H emission. Our results
are in agreement with simulated activity-induced RV variations in M dwarfs. The
RV variations of most active RV-loud M dwarfs are likely to be caused by dark
spots on their surfaces, which move in and out of view as the stars rotate.Comment: A&A accepte
The CARMENES search for exoplanets around M dwarfs: Nine new double-line spectroscopic binary stars
Context. The CARMENES spectrograph is surveying ~300 M dwarf stars in search
for exoplanets. Among the target stars, spectroscopic binary systems have been
discovered, which can be used to measure fundamental properties of stars. Aims.
Using spectroscopic observations, we determine the orbital and physical
properties of nine new double-line spectroscopic binary systems by analysing
their radial velocity curves. Methods. We use two-dimensional cross-correlation
techniques to derive the radial velocities of the targets, which are then
employed to determine the orbital properties. Photometric data from the
literature are also analysed to search for possible eclipses and to measure
stellar variability, which can yield rotation periods. Results. Out of the 342
stars selected for the CARMENES survey, 9 have been found to be double-line
spectroscopic binaries, with periods ranging from 1.13 to ~8000 days and orbits
with eccentricities up to 0.54. We provide empirical orbital properties and
minimum masses for the sample of spectroscopic binaries. Absolute masses are
also estimated from mass-luminosity calibrations, ranging between ~0.1 and ~0.6
Msol . Conclusions. These new binary systems increase the number of double-line
M dwarf binary systems with known orbital parameters by 15%, and they have
lower mass ratios on average.Comment: Accepted for publication in A&A. 17 pages, 4 figure
The Hot Neptune WASP-166 b with ESPRESSO II: Confirmation of atmospheric sodium
The hot Neptune desert, a distinct lack of highly irradiated planets in the
size range of Neptune, remains one of the most intriguing results of exoplanet
population studies. A deeper understanding of the atmosphere of exoplanets
sitting at the edge or even within the Neptune desert will allow us to better
understand if planetary formation or evolution processes are at the origin of
the desert. A detection of sodium in WASP-166b was presented previously with
tentative line broadening at the 3.4 sigma with the HARPS spectrograph. We
update this result with two transits observed with the ESPRESSO spectrograph,
confirming the detection in each night and the broadened character of the line.
This result marks the first confirmed resolved sodium detection within the
Neptune desert. In this work, we additionally highlight the importance of
treating low-SNR spectral regions, particularly where absorption lines of
stellar sodium and planetary sodium overlap at mid-transit - an important
caveat for future observations of the system.Comment: Letter, re-submitted to MNRAS after minor referee report; comments
welcom
Effect of storage on total phenolics, antioxidant capacity, and physicochemical properties of blueberry (Vaccinium corymbosum L.) jam
This study investigated the effects of storage on the physicochemical and nutritional aspects ofblueberry jam. Jams were stored at either 4, 25, or 358C during a 56-day period. The pH was sig-nificantly reduced during storage (p<.05). Overall, results demonstrated the significant effect ofstorage temperature and time on the color degradation and on the texture of the samples studied(p<.05). The total antioxidant activity was significantly affected by temperature as the total anti-oxidant activity retention of samples stored at 48C was significantly higher to that of the samplesstored at either 25 or 358C after a 56-day storage period (p<.05). A strong positive correlationwas found between the total phenolic content and the antioxidant activity withR2ranging from0.617 to 0.716. Results obtained herein suggested that blueberry jams should be refrigerated tobetter retain their overall quality attributes and their antioxidant capacityinfo:eu-repo/semantics/acceptedVersio
Magnetic fields in M dwarfs from the CARMENES survey
M dwarfs are known to generate the strongest magnetic fields among
main-sequence stars with convective envelopes, but the link between the
magnetic fields and underlying dynamo mechanisms, rotation, and activity still
lacks a consistent picture. In this work we 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. We use the state-of-the-art radiative transfer code to
measure total magnetic flux densities from the Zeeman broadening of spectral
lines and filling factors. 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<4d. 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.
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.Comment: 13 pages of main text, 14 pages of online material, 2 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 HADES RV Programme with HARPS-N@TNG II. Data treatment and simulations
The distribution of exoplanets around low-mass stars is still not well
understood. Such stars, however, present an excellent opportunity of reaching
down to the rocky and habitable planet domains. The number of current
detections used for statistical purposes is still quite modest and different
surveys, using both photometry and precise radial velocities, are searching for
planets around M dwarfs. Our HARPS-N red dwarf exoplanet survey is aimed at the
detection of new planets around a sample of 78 selected stars, together with
the subsequent characterization of their activity properties. Here we
investigate the survey performance and strategy. From 2700 observed spectra, we
compare the radial velocity determinations of the HARPS-N DRS pipeline and the
HARPS-TERRA code, we calculate the mean activity jitter level, we evaluate the
planet detection expectations, and we address the general question of how to
define the strategy of spectroscopic surveys in order to be most efficient in
the detection of planets. We find that the HARPS-TERRA radial velocities show
less scatter and we calculate a mean activity jitter of 2.3 m/s for our sample.
For a general radial velocity survey with limited observing time, the number of
observations per star is key for the detection efficiency. In the case of an
early M-type target sample, we conclude that approximately 50 observations per
star with exposure times of 900 s and precisions of about 1 m/s maximizes the
number of planet detections
A Machine Learning approach for correcting radial velocities using physical observables
Precision radial velocity (RV) measurements continue to be a key tool to
detect and characterise extrasolar planets. While instrumental precision keeps
improving, stellar activity remains a barrier to obtain reliable measurements
below 1-2 m/s accuracy. Using simulations and real data, we investigate the
capabilities of a Deep Neural Network approach to produce activity free Doppler
measurements of stars. As case studies we use observations of two known stars
(Eps Eridani and AUMicroscopii), both with clear signals of activity induced RV
variability. Synthetic data using the starsim code are generated for the
observables (inputs) and the resulting RV signal (labels), and used to train a
Deep Neural Network algorithm. We identify an architecture consisting of
convolutional and fully connected layers that is adequate to the task. The
indices investigated are mean line-profile parameters (width, bisector,
contrast) and multi-band photometry. We demonstrate that the RV-independent
approach can drastically reduce spurious Doppler variability from known
physical effects such as spots, rotation and convective blueshift. We identify
the combinations of activity indices with most predictive power. When applied
to real observations, we observe a good match of the correction with the
observed variability, but we also find that the noise reduction is not as good
as in the simulations, probably due to the lack of detail in the simulated
physics. We demonstrate that a model-driven machine learning approach is
sufficient to clean Doppler signals from activity induced variability for well
known physical effects. There are dozens of known activity related observables
whose inversion power remains unexplored indicating that the use of additional
indicators, more complete models, and more observations with optimised sampling
strategies can lead to significant improvements in our detrending capabilities
Detection of He I \AA{} absorption on HD 189733 b with CARMENES high-resolution transmission spectroscopy
We present three transit observations of HD 189733 b obtained with the
high-resolution spectrograph CARMENES at Calar Alto. A strong absorption signal
is detected in the near-infrared He I triplet at 10830 \AA{} in all three
transits. During mid-transit, the mean absorption level is %
measured in a 10 km s range at a net blueshift of km
s (10829.84--10830.57 \AA{}). The absorption signal exhibits radial
velocities of km s and km s during
ingress and egress, respectively; measured in the planetary rest frame. We show
that stellar activity related pseudo-signals interfere with the planetary
atmospheric absorption signal. They could contribute as much as 80% of the
observed signal and might also affect the radial velocity signature, but
pseudo-signals are very unlikely to explain the entire signal. The observed
line ratio between the two unresolved and the third line of the He I triplet is
, which strongly deviates from the value expected for an optically
thin atmospheres. When interpreted in terms of absorption in the planetary
atmosphere, this favors a compact helium atmosphere with an extent of only 0.2
planetary radii and a substantial column density on the order of cm. The observed radial velocities can be understood either in
terms of atmospheric circulation with equatorial superrotation or as a sign of
an asymmetric atmospheric component of evaporating material. We detect no clear
signature of ongoing evaporation, like pre- or post-transit absorption, which
could indicate material beyond the planetary Roche lobe, or radial velocities
in excess of the escape velocity. These findings do not contradict planetary
evaporation, but only show that the detected helium absorption in HD 189733 b
does not trace the atmospheric layers that show pronounced escape signatures.Comment: 13 pages, 12 figures, accepted for publication in A&
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