86 research outputs found
The Y dwarf population with HST : unlocking the secrets of our coolest neighbours – I. Overview and first astrometric results
In this paper, we present our project that aims at determining accurate distances and proper motions for the Y brown dwarf population using the Hubble Space Telescope. We validate the program with our first results, using a single new epoch of observations of the Y0pec dwarf WISE J163940.83−684738.6. These new data allowed us to refine its proper motion and improve the accuracy of its parallax by a factor of three compared to previous determinations, now constrained to ϖ = 211.11 ± 0.56 mas. This newly derived absolute parallax corresponds to a distance of 4.737 ± 0.013 pc, an exquisite and unprecedented precision for faint ultracool Y dwarfs
HST astrometry of the closest Brown Dwarfs -- II. Improved parameters and constraints on a third body
Located at less than 2pc away, Luhman16AB (WISE.J104915.57-531906.1) is the
closest pair of brown dwarfs and third closest `stellar' system to Earth. An
exoplanet candidate in the Luhman16 binary system was reported in 2017 based on
a weak astrometric signature in the analysis of 12 HST epochs. An additional
epoch collected in 2018 and re-analysis of the data with more advanced methods
further increased the significance level of the candidate, consistent with a
Neptune-mass exoplanet orbiting one of the Luhman16 brown dwarf components. We
report the joint analysis of these previous data together with two new
astrometric HST epochs we obtained to confirm or disprove this astrometric
signature. Our new analysis rules out presence of a planet orbiting one
component of the Luhman16AB system for masses M > 1.5 M_Nep (Neptune masses)
and periods between 400 and 5000 days. However, the presence of third bodies
with masses M < 3 M_Nep and periods between 2 and 400 days (~1.1yrs) can not be
excluded. Our measurements make significant improvements to the
characterization of this sub-stellar binary, including its mass-ratio
0.8305+/-0.0006, individual component masses 35.4+/-0.2 M_Jup and 29.4+/-0.2
M_Jup (Jupiter masses), and parallax distance 1.9960pc +/- 50AU. Comparison of
the masses and luminosities of Luhman16AB to several evolutionary models shows
persistent discrepancies in the ages of the two components, but strengthens the
case that this system is a member of the 510+/-95 Myr Oceanus Moving Group.Comment: 17 pages, 8+A1 figures. Accepted for publication on Astronomische
Nachrichten on 10th January 2024 available
https://onlinelibrary.wiley.com/doi/10.1002/asna.20230158 on-line
supplementary material and animations
https://web.oapd.inaf.it/bedin/files/PAPERs_eMATERIALs/Luh16AB_II
Chemical stabilization of dentin extracellular matrix detected by FEISEM and EDS
Dentin collagen degradation represents an important limit to the stability of the resin-dentin interface in conservative dentistry. In vitro application of 1-ethyl-3-(3- dimethylaminopropyl)-carbodiimide hydrochloride (EDC), an imide-based zerolength cross-linking agent, showed [1] the capability to inactivate the endogenous dentin matrix metalloproteinases and to increase the mechanical properties of the organic dentin extracellular matrix. In the present study, a correlative high resolution SEM (FEISEM) with an Energy Dispersive Spectroscopy (EDS) analysis was performed to characterize the fine structure and the chemical modifications of EDCstabilized human dentin, after compressive mechanical stress (Chewing Simulation - CS). Demineralized human dentin disks were assigned to four groups: (1) artificial saliva at 37°C for 30 days; (2) pre-treatment with 0.5M EDC for 60 s, then as in Group 1; (3) CS challenge for 30 days; (4) 0.5M EDC as in Group 2 and CS challenge as in Group 3. The FEISEM analysis revealed that the EDC-pretreatment made the collagen fibrillar network more compact, in comparison to controls and this effect was particularly evident on the surface of not stressed samples. Along with the increased compactness of the collagen complex, the EDS analysis showed a significant semi-quantitative increase of sulfur. The presence of chlorine in EDC treated samples was also detectable. The increase of sulfur, not present in EDC composition, suggests a possible implication of sulfate glycosaminoglycans containing proteoglycans during the extracellular matrix stabilization, as also suggested by the concurrent increase of the amorphous matrix. The presence of chlorine in EDC treated samples induces to conclude that the activity of the cross-linking agent is stable even after the experimental time intervals
Shadows and spirals in the protoplanetary disk HD 100453
Understanding the diversity of planets requires to study the morphology and
the physical conditions in the protoplanetary disks in which they form. We
observed and spatially resolved the disk around the ~10 Myr old protoplanetary
disk HD 100453 in polarized scattered light with SPHERE/VLT at optical and
near-infrared wavelengths, reaching an angular resolution of ~0.02", and an
inner working angle of ~0.09". We detect polarized scattered light up to ~0.42"
(~48 au) and detect a cavity, a rim with azimuthal brightness variations at an
inclination of 38 degrees, two shadows and two symmetric spiral arms. The
spiral arms originate near the location of the shadows, close to the semi major
axis. We detect a faint spiral-like feature in the SW that can be interpreted
as the scattering surface of the bottom side of the disk, if the disk is
tidally truncated by the M-dwarf companion currently seen at a projected
distance of ~119 au. We construct a radiative transfer model that accounts for
the main characteristics of the features with an inner and outer disk
misaligned by ~72 degrees. The azimuthal brightness variations along the rim
are well reproduced with the scattering phase function of the model. While
spirals can be triggered by the tidal interaction with the companion, the close
proximity of the spirals to the shadows suggests that the shadows could also
play a role. The change in stellar illumination along the rim, induces an
azimuthal variation of the scale height that can contribute to the brightness
variations. Dark regions in polarized images of transition disks are now
detected in a handful of disks and often interpreted as shadows due to a
misaligned inner disk. The origin of such a misalignment in HD 100453, and of
the spirals, is unclear, and might be due to a yet-undetected massive companion
inside the cavity, and on an inclined orbit.Comment: A&A, accepte
Post conjunction detection of Pictoris b with VLT/SPHERE
With an orbital distance comparable to that of Saturn in the solar system,
\bpic b is the closest (semi-major axis \,9\,au) exoplanet that has
been imaged to orbit a star. Thus it offers unique opportunities for detailed
studies of its orbital, physical, and atmospheric properties, and of
disk-planet interactions. With the exception of the discovery observations in
2003 with NaCo at the Very Large Telescope (VLT), all following astrometric
measurements relative to \bpic have been obtained in the southwestern part of
the orbit, which severely limits the determination of the planet's orbital
parameters. We aimed at further constraining \bpic b orbital properties using
more data, and, in particular, data taken in the northeastern part of the
orbit.
We used SPHERE at the VLT to precisely monitor the orbital motion of beta
\bpic b since first light of the instrument in 2014. We were able to monitor
the planet until November 2016, when its angular separation became too small
(125 mas, i.e., 1.6\,au) and prevented further detection. We redetected \bpic b
on the northeast side of the disk at a separation of 139\,mas and a PA of
30 in September 2018. The planetary orbit is now well constrained.
With a semi-major axis (sma) of au (1 ), it
definitely excludes previously reported possible long orbital periods, and
excludes \bpic b as the origin of photometric variations that took place in
1981. We also refine the eccentricity and inclination of the planet. From an
instrumental point of view, these data demonstrate that it is possible to
detect, if they exist, young massive Jupiters that orbit at less than 2 au from
a star that is 20 pc away.Comment: accepted by A&
Transferência de tecnologia em práticas promotoras de rendimento de grãos de milho em instituições de ensino agrotécnico do Rio Grande do Sul e Santa catarina, safra 2004/2005.
bitstream/CNPT-2010/40665/1/p-do47.pd
The SPHERE infrared survey for exoplanets (SHINE). III. The demographics of young giant exoplanets below 300 au with SPHERE
The SHINE project is a 500-star survey performed with SPHERE on the VLT for
the purpose of directly detecting new substellar companions and understanding
their formation and early evolution. Here we present an initial statistical
analysis for a subsample of 150 stars that are representative of the full SHINE
sample. Our goal is to constrain the frequency of substellar companions with
masses between 1 and 75 MJup and semimajor axes between 5 and 300 au. We adopt
detection limits as a function of angular separation from the survey data for
all stars converted into mass and projected orbital separation using the
BEX-COND-hot evolutionary tracks and known distance to each system. Based on
the results obtained for each star and on the 13 detections in the sample, we
use a MCMC tool to compare our observations to two different types of models.
The first is a parametric model based on observational constraints, and the
second type are numerical models that combine advanced core accretion and
gravitational instability planet population synthesis. Using the parametric
model, we show that the frequencies of systems with at least one substellar
companion are , , and
for BA, FGK, and M stars, respectively. We also
demonstrate that a planet-like formation pathway probably dominates the mass
range from 1-75 MJup for companions around BA stars, while for M dwarfs, brown
dwarf binaries dominate detections. In contrast, a combination of binary
star-like and planet-like formation is required to best fit the observations
for FGK stars. Using our population model and restricting our sample to FGK
stars, we derive a frequency of , consistent with
predictions from the parametric model. More generally, the frequency values
that we derive are in excellent agreement with values obtained in previous
studies.Comment: 24 pages, 14 figures, 3 tables. Accepted for publication in A&
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