425 research outputs found
Acaulon fontiquerianum Casas et Sérgio (Musci, Pottiaceae) nouveau pour la bryoflore du Portugal, de France et de Corse
Découverte au Portugal (Cabo Espichel), dans le sud-est de la France (Bouches-du RhBne: Crau, Var: environs de Pierrefeu) et en Corse méridionale (Bocca di Curali), d'Acaulon fontiquerianurn Casas et Sérgio récemment décrit d'Espagne. Aprbs un rappel des caracteres morphologiques et anatomiques tres particuliers de cet Acaulon, les spores de spécimens récoltés au Portugal et dans la Crau son illustrées (microscopie électronique 21 balayage). L'écologie d'Acaulon fontiquerianum dans les 5 nouvelles stations est précisée (substrat, végétation, bryophytes associées).Discovery in Portugal (Cabo Espichel), south-eastern France (Bouches-du-RhBne: Crau, Var: vicinity of Pierrefeu) and Corsica (Bocca di Curali) of Acaulon fontiquerianurn Casas et Sérgio, recently described from Spain. After a recapitulation of the very particular morphological and anatomical features of Acaulon fontiquerianum, the spores of specimens collected in Portugal and Crau are illustrated using S.E.M. The ecology of the moss in the 5 new stations is stated (substrate, vegetation, associated bryophytes)
PASTIS: Bayesian extrasolar planet validation II. Constraining exoplanet blend scenarios using spectroscopic diagnoses
The statistical validation of transiting exoplanets proved to be an efficient
technique to secure the nature of small exoplanet signals which cannot be
established by purely spectroscopic means. However, the spectroscopic diagnoses
are providing us with useful constraints on the presence of blended stellar
contaminants. In this paper, we present how a contaminating star affects the
measurements of the various spectroscopic diagnoses as function of the
parameters of the target and contaminating stars using the model implemented
into the PASTIS planet-validation software. We find particular cases for which
a blend might produce a large radial velocity signal but no bisector variation.
It might also produce a bisector variation anti-correlated with the radial
velocity one, as in the case of stellar spots. In those cases, the full width
half maximum variation provides complementary constraints. These results can be
used to constrain blend scenarios for transiting planet candidates or radial
velocity planets. We review all the spectroscopic diagnoses reported in the
literature so far, especially the ones to monitor the line asymmetry. We
estimate their uncertainty and compare their sensitivity to blends. Based on
that, we recommend the use of BiGauss which is the most sensitive diagnosis to
monitor line-profile asymmetry. In this paper, we also investigate the
sensitivity of the radial velocities to constrain blend scenarios and develop a
formalism to estimate the level of dilution of a blended signal. Finally, we
apply our blend model to re-analyse the spectroscopic diagnoses of HD16702, an
unresolved face-on binary which exhibits bisector variations.Comment: Accepted for publication in MNRA
Magnetic activity and hot Jupiters of young Suns : the weak-line T Tauri stars V819 Tau and V830 Tau
SGG acknowledges support from the Science & Technology Facilities Council (STFC) via an Ernest Rutherford Fellowship [ST/J003255/1]. SHPA acknowledges financial support from CNPq, CAPES and Fapemig. AAV acknowledges support from the Swiss National Science Foundation (SNSF) via the allocation of an Ambizione Followship. Date of Acceptance: 06/08/2015We report results of a spectropolarimetric and photometric monitoring of the weak-line T Tauri stars (wTTSs) V819 Tau and V830 Tau within the MaTYSSE (Magnetic Topologies of Young Stars and the Survival of close-ingiant Exoplanets) programme, involving the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope. At ≃3 Myr, both stars dissipated their discs recently and are interesting objects for probing star and planet formation. Profile distortions and Zeeman signatures are detected in the unpolarized and circularly polarized lines, whose rotational modulation we modelled using tomographic imaging, yielding brightness and magnetic maps for both stars. We find that the large-scale magnetic fields of V819 Tau and V830 Tau are mostly poloidal and can be approximated at large radii by 350-400 G dipoles tilted at≃30° to the rotation axis. They are significantly weaker than the field of GQ Lup, an accreting classical T Tauri star (cTTS) with similar mass and age which can be used to compare the magnetic properties of wTTSs and cTTSs. The reconstructed brightness maps of both stars include cool spots and warm plages. Surface differential rotation is small, typically ≃4.4 times smaller than on the Sun, in agreement with previous results on wTTSs. Using our Doppler images to model the activity jitter and filter it out from the radial velocity(RV) curves, we obtain RV residuals with dispersions of 0.033 and 0.104km s-1 for V819 Tau and V830 Tau, respectively. RV residuals suggest that a hot Jupiter may be orbiting V830 Tau, though additional data are needed to confirm this preliminary result. We find no evidence for close-in giant planet around V819 Tau.Publisher PDFPeer reviewe
Understanding stellar activity-induced radial velocity jitter using simultaneous K2 photometry and HARPS RV measurements
One of the best ways to improve our understanding of the stellar
activity-induced signal in radial velocity (RV) measurements is through
simultaneous high-precision photometric and RV observations. This is of prime
importance to mitigate the RV signal induced by stellar activity and therefore
unveil the presence of low-mass exoplanets. The K2 Campaign 7 and 8
field-of-views were located in the southern hemisphere, and provided a unique
opportunity to gather unprecedented simultaneous high precision photometric
observation with K2 and high-precision RV measurements with the HARPS
spectrograph to study the relationship between photometric variability and RV
jitter. We observed nine stars with different levels of activity; from quiet to
very active. We probe the presence of any meaningful relation between measured
RV jitter and the simultaneous photometric variation, and also other activity
indicators (e.g. BIS, FWHM, , and F8), by evaluating the strength
and significance of the correlation between RVs and each indicator. We found
that for the case of very active stars, strong and significant correlations
exist between almost all the observables and measured RVs; however, for lower
activity levels the correlations become random. Except for the F8 which its
strong correlation with RV jitter persists over a wide range of stellar
activity level, and thus our result suggests that F8 might be a powerful proxy
for activity induced RV jitter. Moreover, we examine the capability of two
state-of-the-art modeling techniques, namely the FF' method and SOAP2.0, in
accurately predicting the RV jitter amplitude using the simultaneous
photometric observation. We found that for the very active stars both
techniques can reasonably well predict the amplitude of the RV jitter, however,
at lower activity levels the FF' method underpredicts the RV jitter amplitude.Comment: 13 pages, 7 figures, 2 tables, accepted for publication in A&
World-leading science with SPIRou - the nIR spectropolarimeter / high-precision velocimeter for CFHT
SPIRou is a near-infrared (nIR) spectropolarimeter / velocimeter proposed as
a new-generation instrument for CFHT. SPIRou aims in particular at becoming
world-leader on two forefront science topics, (i) the quest for habitable
Earth-like planets around very- low-mass stars, and (ii) the study of low-mass
star and planet formation in the presence of magnetic fields. In addition to
these two main goals, SPIRou will be able to tackle many key programs, from
weather patterns on brown dwarf to solar-system planet atmospheres, to dynamo
processes in fully-convective bodies and planet habitability. The science
programs that SPIRou proposes to tackle are forefront (identified as first
priorities by most research agencies worldwide), ambitious (competitive and
complementary with science programs carried out on much larger facilities, such
as ALMA and JWST) and timely (ideally phased with complementary space missions
like TESS and CHEOPS).
SPIRou is designed to carry out its science mission with maximum efficiency
and optimum precision. More specifically, SPIRou will be able to cover a very
wide single-shot nIR spectral domain (0.98-2.35 \mu m) at a resolving power of
73.5K, providing unpolarized and polarized spectra of low-mass stars with a
~15% average throughput and a radial velocity (RV) precision of 1 m/s.Comment: 12 pages, 5 figures, conference proceedings of the French Society of
Astronomy and Astrophysics meeting 201
The spin-orbit angle of the transiting hot jupiter CoRoT-1b
We measure the angle between the planetary orbit and the stellar rotation
axis in the transiting planetary system CoRoT-1, with new HIRES/Keck and
FORS/VLT high-accuracy photometry. The data indicate a highly tilted system,
with a projected spin-orbit angle lambda = 77 +- 11 degrees. Systematic
uncertainties in the radial velocity data could cause the actual errors to be
larger by an unknown amount, and this result needs to be confirmed with further
high-accuracy spectroscopic transit measurements.
Spin-orbit alignment has now been measured in a dozen extra-solar planetary
systems, and several show strong misalignment. The first three misaligned
planets were all much more massive than Jupiter and followed eccentric orbits.
CoRoT-1, however, is a jovian-mass close-in planet on a circular orbit. If its
strong misalignment is confirmed, it would break this pattern. The high
occurence of misaligned systems for several types of planets and orbits favours
planet-planet scattering as a mechanism to bring gas giants on very close
orbits.Comment: to appear in in MNRAS letters [5 pages
The SOPHIE search for northern extrasolar planets VIII. A warm Neptune orbiting HD164595
High-precision radial velocity surveys explore the population of low-mass
exoplanets orbiting bright stars. This allows accurately deriving their orbital
parameters such as their occurrence rate and the statistical distribution of
their properties. Based on this, models of planetary formation and evolution
can be constrained. The SOPHIE spectrograph has been continuously improved in
past years, and thanks to an appropriate correction of systematic instrumental
drift, it is now reaching 2 m/s precision in radial velocity measurements on
all timescales. As part of a dedicated radial velocity survey devoted to search
for low-mass planets around a sample of 190 bright solar-type stars in the
northern hemisphere, we report the detection of a warm Neptune with a minimum
mass of 16.1 +- 2.7 Mearth orbiting the solar analog HD164595 in 40 +- 0.24
days . We also revised the parameters of the multiplanetary system around
HD190360. We discuss this new detection in the context of the upcoming space
mission CHEOPS, which is devoted to a transit search of bright stars harboring
known exoplanets.Comment: 11 pages, 9 figure
The deuterium-to-oxygen ratio in the interstellar medium
Because the ionization balances for HI, OI, and DI are locked together by
charge exchange, D/O is an important tracer for the value of the D/H ratio and
for potential spatial variations in the ratio. As the DI and OI column
densities are of similar orders of magnitude for a given sight line,
comparisons of the two values will generally be less subject to systematic
errors than comparisons of DI and HI, which differ by about five orders of
magnitude. Moreover, D/O is additionally sensitive to astration, because as
stars destroy deuterium, they should produce oxygen. We report here the results
of a survey of D/O in the interstellar medium performed with FUSE. We also
compare these results with those for D/N. Together with a few results from
previous missions, the sample totals 24 lines of sight. The distances range
from a few pc to ~2000 pc and log N(DI) from ~13 to ~16 (cm-2). The D/O ratio
is constant in the local interstellar medium out to distances of ~150 pc and
N(DI) ~ 1x10^15 cm-2, i.e. within the Local Bubble. In this region of the
interstellar space, we find D/O = (3.84+/-0.16)x10^-2 (1 sigma in the mean).
The homogeneity of the local D/O measurements shows that the spatial variations
in the local D/H and O/H must be extremely small, if any. A comparison of the
Local Bubble mean value with the few D/O measurements available for low
metallicity quasar sight lines shows that the D/O ratio decreases with cosmic
evolution, as expected. Beyond the Local Bubble we detected significant spatial
variations in the value of D/O. This likely implies a variation in D/H, as O/H
is known to not vary significantly over the distances covered in this study.
Our dataset suggests a present-epoch deuterium abundance below 1x10^-5, i.e.
lower than the value usually assumed, around 1.5x10^-5.Comment: 17 pages, 9 figures, 4 tables, accepted for publication in the
Astrophysical Journa
First Report of Rice yellow mottle virus in rice in Malawi
International audienceFirst report of Rice yellow mottle virus in rice in Malaw
The SOPHIE search for northern extrasolar planets VIII. Follow-up of ELODIE candidates: long-period brown-dwarf companions
Long-period brown dwarf companions detected in radial velocity surveys are
important targets for direct imaging and astrometry to calibrate the
mass-luminosity relation of substellar objects. Through a 20-year radial
velocity monitoring of solar-type stars that began with ELODIE and was extended
with SOPHIE spectrographs, giant exoplanets and brown dwarfs with orbital
periods longer than ten years are discovered. We report the detection of five
new potential brown dwarfs with minimum masses between 32 and 83 Jupiter mass
orbiting solar-type stars with periods longer than ten years. An upper mass
limit of these companions is provided using astrometric Hipparcos data,
high-angular resolution imaging made with PUEO, and a deep analysis of the
cross-correlation function of the main stellar spectra to search for blend
effects or faint secondary components. These objects double the number of known
brown dwarf companions with orbital periods longer than ten years and reinforce
the conclusion that the occurrence of such objects increases with orbital
separation. With a projected separation larger than 100 mas, all these brown
dwarf candidates are appropriate targets for high-contrast and high angular
resolution imaging.Comment: 17 pages, 9 figures, accepted in A&
- …