1,980 research outputs found
Selective Reagent Ion Mass Spectrometric Investigations of the Nitroanilines
This paper presents an investigation of proton and charge transfer reactions to 2-, 3- and 4-nitroanilines (C6H6N2O2) involving the reagent ions H3O+·(H2O)n (n=0, 1 and 2) and O2+, respectively, as a function of reduced electric field (60-240 Td), using Selective Reagent Ion-Time-of-Flight-Mass Spectrometry (SRI-ToF-MS). To aid in the interpretation of the H3O+·(H2O)n experimental data, the proton affinities and gas-phase basicities for the three nitroaniline isomers have been determined using density functional theory. These calculations show that proton transfer from both the H3O+ and H3O+·H2O reagent ions to the nitroanilines will be exoergic and hence efficient, with the reactions proceeding at the collisional rate. For proton transfer from H3O+ to the NO2 sites, the exoergicities are 171 kJ mol-1 (1.8 eV), 147 kJ mol-1 (1.5 eV) and 194 kJ mol-1 (2.0 eV) for 2-, 3- and 4-nitroanilines, respectively. Electron transfer from all three of the nitroanilines is also significantly exothermic by approximately 4 eV. Although a substantial transfer of energy occurs during the ion/molecule reactions, the processes are found to predominantly proceed via non-dissociative pathways over a large reduced electric field range. Only at relatively high reduced electric fields (>180 Td) is dissociative proton and charge transfer observed. Differences in fragment product ions and their intensities provide a means to distinguish the isomers, with proton transfer distinguishing 2-nitroaniline (2-NA) from 3- and 4-NA, and charge transfer distinguishing 4-NA from 2- and 3-NA, thereby providing a means to enhance selectivity using SRI-ToF-MS.(VLID)4826158Version of recor
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
Multi-band high resolution spectroscopy rules out the hot Jupiter BD+20 1790b - First data from the GIARPS Commissioning
Context. Stellar activity is currently challenging the detection of young
planets via the radial velocity (RV) technique. Aims. We attempt to
definitively discriminate the nature of the RV variations for the young active
K5 star BD+20 1790, for which visible (VIS) RV measurements show divergent
results on the existence of a substellar companion. Methods. We compare VIS
data with high precision RVs in the near infrared (NIR) range by using the
GIANO - B and IGRINS spectrographs. In addition, we present for the first time
simultaneous VIS-NIR observations obtained with GIARPS (GIANO - B and HARPS -
N) at Telescopio Nazionale Galileo (TNG). Orbital RVs are achromatic, so the RV
amplitude does not change at different wavelengths, while stellar activity
induces wavelength-dependent RV variations, which are significantly reduced in
the NIR range with respect to the VIS. Results. The NIR radial velocity
measurements from GIANO - B and IGRINS show an average amplitude of about one
quarter with respect to previously published VIS data, as expected when the RV
jitter is due to stellar activity. Coeval multi-band photometry surprisingly
shows larger amplitudes in the NIR range, explainable with a mixture of cool
and hot spots in the same active region. Conclusions. In this work, the claimed
massive planet around BD+20 1790 is ruled out by our data. We exploited the
crucial role of multi- wavelength spectroscopy when observing young active
stars: thanks to facilities like GIARPS that provide simultaneous observations,
this method can reach its maximum potential.Comment: 12 pages, 7 figure
Uso y prescripción de cannabis medicinal por reumatólogos en Argentina
El uso y prescripción del cannabis y sus derivados en Reumatología está aún en discusión. La ley de cannabis fue sancionada hace casi 3 años, aunque la reglamentación recién está comenzando. El objetivo de este estudio fue conocer la forma en que el reumatólogo se posiciona frente al uso de cannabis en el marco de su práctica médica.
A través de una encuesta realizada durante el Congreso Argentino de Reumatología 2019 se recabó la opinión de 314 médicos que respondieron preguntas acerca del uso, recomendaciones y posturas respecto a la indicación y uso de cannabinoides en su práctica diaria
Placental thrombosis in acute phase abortions during experimental Toxoplasma gondii infection in sheep
43 p.After oral administration of ewes during mid gestation with 2000 freshly prepared sporulated oocysts of T. gondii
isolate M4, abortions occurred between days 7 and 11 in 91.6% of pregnant and infected ewes. Afterwards, a
further infection was carried out at late gestation in another group of sheep with 500 sporulated oocysts. Abortions
happened again between days 9 and 11 post infection (pi) in 58.3% of the infected ewes. Classically, abortions in
natural and experimental ovine toxoplasmosis usually occur one month after infection. Few experimental studies
have reported the so-called acute phase abortions as early as 7 to 14 days after oral inoculation of oocysts, and
pyrexia was proposed to be responsible for abortion, although the underline mechanism was not elucidated. In the
present study, all placentas analysed from ewes suffering acute phase abortions showed infarcts and thrombosis in
the caruncullar villi of the placentomes and ischemic lesions (periventricular leukomalacia) in the brain of some
foetuses. The parasite was identified by PCR in samples from some placentomes of only one sheep, and no antigen
was detected by immunohistochemical labelling. These findings suggest that the vascular lesions found in the
placenta, and the consequent hypoxic damage to the foetus, could be associated to the occurrence of acute phase
abortions. Although the pathogenesis of these lesions remains to be determined, the infectious dose or virulence
of the isolate may play a role in their developmentS
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
The GAPS programme at TNG XXII. The GIARPS view of the extended helium atmosphere of HD189733 b accounting for stellar activity
Exoplanets orbiting very close to their host star are strongly irradiated.
This can lead the upper atmospheric layers to expand and evaporate into space.
The metastable helium (HeI) triplet at 1083.3nm has recently been shown to be a
powerful diagnostic to probe extended and escaping exoplanetary atmosphere. We
perform high-resolution transmission spectroscopy of the transiting hot Jupiter
HD189733b with the GIARPS (GIANO-B + HARPS-N) observing mode of the Telescopio
Nazionale Galileo, taking advantage of the simultaneous optical+near infrared
spectral coverage to detect HeI in the planet's extended atmosphere and to
gauge the impact of stellar magnetic activity on the planetary absorption
signal. Observations were performed during five transit events of HD189733b. By
comparison of the in- and out-of-transit GIANO-B observations we compute
high-resolution transmission spectra, on which we perform equivalent width
measurements and light-curves analyses to gauge the excess in-transit
absorption in the HeI triplet. We detect an absorption signal during all five
transits. The mean in-transit absorption depth amounts to 0.75+/-0.03%. We
detect night-to-night variations in the HeI absorption signal likely due to the
transit events occurring in presence of stellar surface inhomogeneities. We
evaluate the impact of stellar-activity pseudo-signals on the true planetary
absorption using a comparative analysis of the HeI and the H lines. We
interpret the time-series of the HeI absorption lines in the three nights not
affected by stellar contamination -exhibiting a mean in-transit absorption
depth of 0.77+/-0.04%- using a 3-d atmospheric code. Our simulations suggest
that the helium layers only fill part of the Roche lobe. Observations can be
explained with a thermosphere heated to 12000 K, expanding up to
1.2 planetary radii, and losing 1 g/s of metastable helium.Comment: 17 pages, 17 figures, accepted for publication in A&
Catalog for the ESPRESSO blind radial velocity exoplanet survey
One of the main scientific drivers for ESPRESSO,\'Echelle SPectrograph, is
the detection and characterization of Earth-class exoplanets. With this goal in
mind, the ESPRESSO Guaranteed Time Observations (GTO) Catalog identifies the
best target stars for a blind search for the radial velocity (RV) signals
caused by Earth-class exoplanets. Using the most complete stellar catalogs
available, we screened for the most suitable G, K, and M dwarf stars for the
detection of Earth-class exoplanets with ESPRESSO. For most of the stars, we
then gathered high-resolution spectra from new observations or from archival
data. We used these spectra to spectroscopically investigate the existence of
any stellar binaries, both bound or background stars. We derived the activity
level using chromospheric activity indexes using , as well as the
projected rotational velocity . For the cases where planet
companions are already known, we also looked at the possibility that additional
planets may exist in the host's habitable zone using dynamical arguments. We
estimated the spectroscopic contamination level, , activity,
stellar parameters and chemical abundances for 249 of the most promising
targets. Using these data, we selected 45 stars that match our criteria for
detectability of a planet like Earth. The stars presented and discussed in this
paper constitute the ESPRESSO GTO catalog for the RV blind search for
Earth-class planets. They can also be used for any other work requiring a
detailed spectroscopic characterization of stars in the solar neighborhood.Comment: Corrected a typo in references. Corrected typo in table B.
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
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
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