2,797 research outputs found
An accurate distance to 2M1207Ab
In April 2004 the first image was obtained of a planetary mass companion (now
known as 2M1207 b) in orbit around a self-luminous object different from our
own Sun (the young brown dwarf 2MASSW J1207334-393254, hereafter 2M1207 A).
2M1207 b probably formed via fragmentation and gravitational collapse, offering
proof that such a mechanism can form bodies in the planetary mass regime.
However, the predicted mass, luminosity, and radius of 2M1207 b depend on its
age, distance, and other observables such as effective temperature. To refine
our knowledge of the physical properties of 2M1207 b and its nature, we
obtained an accurate determination of the distance to the 2M1207 A and b system
by measurements of its trigonometric parallax at the milliarcsec level. With
the ESO NTT/SUSI2 telescope, in 2006 we began a campaign of photometric and
astrometric observations to measure the trigonometric parallax of 2M1207 A. An
accurate distance ( pc) to 2M1207A was measured. From distance and
proper motions we derived spatial velocities fully compatible with TWA
membership. With this new distance estimate, we discuss three scenarios
regarding the nature of 2M1207 b: (1) a cool ( K) companion of mass
M, (2) a warmer ( K) and heavier (
M) companion occulted by an edge-on circum-secondary disk or (3) a
hot protoplanet collision afterglow.Comment: 5 pages, 3 figures, accepted for publication as letter in A&A,
6/11/200
Deep infrared imaging of close companions to austral A- and F-type stars
The search for substellar companions around stars with different masses along
the main sequence is critical to understand the different processes leading to
the formation of low-mass stars, brown dwarfs, and planets. In particular, the
existence of a large population of low-mass stars and brown dwarfs physically
bound to early-type main-sequence stars could imply that the massive planets
recently imaged at wide separations (10-100 AU) around A-type stars are
disc-born objects in the low-mass tail of the binary distribution. Our aim is
to characterize the environment of early-type main-sequence stars by detecting
brown dwarf or low-mass star companions between 10 and 500 AU. High contrast
and high angular resolution near-infrared images of a sample of 38 southern A-
and F-type stars have been obtained between 2005 and 2009 with the instruments
VLT/NaCo and CFHT/PUEO. Multi-epoch observations were performed to discriminate
comoving companions from background contaminants. About 41 companion candidates
were imaged around 23 stars. Follow-up observations for 83% of these stars
allowed us to identify a large number of background contaminants. We report the
detection of 7 low-mass stars with masses between 0.1 and 0.8 Msun in 6
multiple systems: the discovery of a M2 companion around the A5V star HD14943
and the detection of the B component of the F4V star HD41742 quadruple system;
we resolve the known companion of the F6.5V star HD49095 as a short-period
binary system composed by 2 M/L dwarfs. We also resolve the companions to the
astrometric binaries iot Crt (F6.5V) and 26 Oph (F3V), and identify a M3/M4
companion to the F4V star omi Gru, associated with a X-ray source. The global
multiplicity fraction measured in our sample of A and F stars is >16%. A
parallel velocimetric survey of our stars let us conclude that the imaged
companions can impact on the observed radial velocity measurements.Comment: 21 pages, 12 figures, 7 tables. Accepted for publication in Astronomy
and Astrophysics. The full version of the preprint including the appendices
(24 pages of figures), can be retrieved at
http://www-laog.obs.ujf-grenoble.fr/~dehrenre/articles/afsurvey
Near-infrared integral-field spectra of the planet/brown dwarf companion AB Pic b
Chauvin et al. 2005 imaged a co-moving companion at ~260 AU from the young
star AB Pic A. Evolutionary models predictions based on J H K photometry of AB
Pic b suggested a mass of ~13 - 14 MJup, placing the object at the
deuterium-burning boundary. We used the adaptive-optics-fed integral field
spectrograph SINFONI to obtain high quality medium-resolution spectra of AB Pic
b (R = 1500-2000) over the 1.1 - 2.5 microns range. Our analysis relies on the
comparison of our spectra to young standard templates and to the latest
libraries of synthetic spectra developed by the Lyon's Group. AB Pic b is
confirmed to be a young early-L dwarf companion. We derive a spectral type
L0-L1 and find several features indicative of intermediate gravity atmosphere.
A comparison to synthetic spectra yields Teff = 2000+100-300 K and log(g) = 4
+- 0.5 dex. The determination of the derived atmospheric parameters of AB Pic b
is limited by a non-perfect match of current atmosphere spectra with our
near-infrared observations of AB Pic b. The current treatment of dust settling
and missing molecular opacity lines in the atmosphere models could be
responsible. By combining the observed photometry, the surface fluxes from
atmosphere models and the known distance of the system, we derive new mass,
luminosity and radius estimates of AB Pic b. They confirm independently the
evolutionary model predictions. We finally review the current methods used to
characterize planetary mass companions and discuss them in the perspective of
future planet deep imaging surveys.Comment: 8 pages, 8 figure
Direct exoplanet detection and characterization using the ANDROMEDA method: Performance on VLT/NaCo data
Context. The direct detection of exoplanets with high-contrast imaging
requires advanced data processing methods to disentangle potential planetary
signals from bright quasi-static speckles. Among them, angular differential
imaging (ADI) permits potential planetary signals with a known rotation rate to
be separated from instrumental speckles that are either statics or slowly
variable. The method presented in this paper, called ANDROMEDA for ANgular
Differential OptiMal Exoplanet Detection Algorithm is based on a maximum
likelihood approach to ADI and is used to estimate the position and the flux of
any point source present in the field of view. Aims. In order to optimize and
experimentally validate this previously proposed method, we applied ANDROMEDA
to real VLT/NaCo data. In addition to its pure detection capability, we
investigated the possibility of defining simple and efficient criteria for
automatic point source extraction able to support the processing of large
surveys. Methods. To assess the performance of the method, we applied ANDROMEDA
on VLT/NaCo data of TYC-8979-1683-1 which is surrounded by numerous bright
stars and on which we added synthetic planets of known position and flux in the
field. In order to accommodate the real data properties, it was necessary to
develop additional pre-processing and post-processing steps to the initially
proposed algorithm. We then investigated its skill in the challenging case of a
well-known target, Pictoris, whose companion is close to the detection
limit and we compared our results to those obtained by another method based on
principal component analysis (PCA). Results. Application on VLT/NaCo data
demonstrates the ability of ANDROMEDA to automatically detect and characterize
point sources present in the image field. We end up with a robust method
bringing consistent results with a sensitivity similar to the recently
published algorithms, with only two parameters to be fine tuned. Moreover, the
companion flux estimates are not biased by the algorithm parameters and do not
require a posteriori corrections. Conclusions. ANDROMEDA is an attractive
alternative to current standard image processing methods that can be readily
applied to on-sky data
New constraints on the formation and settling of dust in the atmospheres of young M and L dwarfs
We obtained medium-resolution near-infrared spectra of seven young M9.5-L3
dwarfs classified in the optical. We aim to confirm the low surface gravity of
the objects in the NIR. We also test whether atmospheric models correctly
represent the formation and the settling of dust clouds in the atmosphere of
young late-M and L dwarfs. We used ISAAC at VLT to obtain the spectra of the
targets. We compared them to those of mature and young BD, and young late-type
companions to nearby stars with known ages, in order to identify and study
gravity-sensitive features. We computed spectral indices weakly sensitive to
the surface gravity to derive near-infrared spectral types. Finally, we found
the best fit between each spectrum and synthetic spectra from the BT-Settl 2010
and 2013 models. Using the best fit, we derived the atmospheric parameters of
the objects and identify which spectral characteristics the models do not
reproduce. We confirmed that our objects are young BD and we found NIR spectral
types in agreement with the ones determined at optical wavelengths. The
spectrum of the L2-gamma dwarf 2MASSJ2322-6151 reproduces well the spectrum of
the planetary mass companion 1RXS J1609-2105b. BT-Settl models fit the spectra
and the 1-5 m SED of the L0-L3 dwarfs for temperatures between 1600-2000
K. But the models fail to reproduce the shape of the H band, and the NIR slope
of some of our targets. This fact, and the best fit solutions found with
super-solar metallicity are indicative of a lack of dust, in particular at high
altitude, in the cloud models. The modeling of the vertical mixing and of the
grain growth will be revised in the next version of the BT-Settl models. These
revisions may suppress the remaining non-reproducibilities.Comment: Accepted in A&A, February 6, 201
A probable giant planet imaged in the Beta Pictoris disk
Since the discovery of its dusty disk in 1984, Beta Pictoris has become the
prototype of young early-type planetary systems, and there are now various
indications that a massive Jovian planet is orbiting the star at ~ 10 AU.
However, no planets have been detected around this star so far. Our goal was to
investigate the close environment of Beta Pic, searching for planetary
companion(s). Deep adaptive-optics L'-band images of Beta Pic were recorded
using the NaCo instrument at the Very Large Telescope. A faint point-like
signal is detected at a projected distance of ~ 8 AU from the star, within the
North-East side of the dust disk. Various tests were made to rule out with a
good confidence level possible instrumental or atmospheric artifacts. The
probability of a foreground or background contaminant is extremely low, based
in addition on the analysis of previous deep Hubble Space Telescope images. The
object L'=11.2 apparent magnitude would indicate a typical temperature of ~1500
K and a mass of ~ 8 Jovian masses. If confirmed, it could explain the main
morphological and dynamical peculiarities of the Beta Pic system. The present
detection is unique among A-stars by the proximity of the resolved planet to
its parent star. Its closeness and location inside the Beta Pic disk suggest a
formation process by core accretion or disk instabilities rather than a
binary-like formation process.Comment: 5 pages, 3 figures, 1 table. A&A Letters, in pres
Use of dipicolinate-based complexes for producing ion-imprinted polystyrene resins for the extraction of yttrium-90 and heavy lanthanide cations
Highly selective separation of yttrium (and lanthanides) is of interest for the design of radiopharmaceuticals, and an efficient method based on the ion-imprinting concept is proposed here. The synthesis and structural, thermodynamic and photophysical characterization of complexes of trivalent yttrium and lanthanides with two new vinyl derivatives of dipicolinic acid, HL1 and L2, are described. The feasibility of using ion-imprinted resins for yttrium and lanthanide separation is demonstrated. The resins were obtained by copolymerization with styrene and divinylbenzene and subsequent acid treatment to remove the metal ion. High-resolution Eu luminescence experiments revealed that the geometry of the complexation sites is well preserved in the imprinted polymers. The ion-imprinted polymer based on HL1 proved to be particularly well adapted for yttrium extraction, having a sizeable capacity (8.9 +- 0.2 g/mg resin) and a fast rate of extraction (t1/2 = 1.7 min). In addition, lighter and heavier lanthanide ions are separated. Finally, the resin displays high selectivity for yttrium and lanthanide cations against alkali and alkaline earth metals. For instance, in a typical experiment, 10 mg of yttrium was extracted from 5 g of milk ash sample by 2 g of the resin. The good separation properties displayed by the resin based on HL1 open interesting perspectives for the production of highly pure 90Y and radiolanthanides for medical applications, and for trace analysis of these radiochemicals in food and in the environment
The 2008 outburst in the young stellar system ZCMa: I. Evidence of an enhanced bipolar wind on the AU-scale
Accretion is a fundamental process in star formation. Although the time
evolution of accretion remains a matter of debate, observations and modelling
studies suggest that episodic outbursts of strong accretion may dominate the
formation of the protostar. Observing young stellar objects during these
elevated accretion states is crucial to understanding the origin of unsteady
accretion. ZCMa is a pre-main-sequence binary system composed of an embedded
Herbig Be star, undergoing photometric outbursts, and a FU Orionis star. The
Herbig Be component recently underwent its largest optical photometric outburst
detected so far. We aim to constrain the origin of this outburst by studying
the emission region of the HI Brackett gamma line, a powerful tracer of
accretion/ejection processes on the AU-scale in young stars. Using the
AMBER/VLTI instrument at spectral resolutions of 1500 and 12 000, we performed
spatially and spectrally resolved interferometric observations of the hot gas
emitting across the Brackett gamma emission line, during and after the
outburst. From the visibilities and differential phases, we derive
characteristic sizes for the Brackett gamma emission and spectro-astrometric
measurements across the line, with respect to the continuum. We find that the
line profile, the astrometric signal, and the visibilities are inconsistent
with the signature of either a Keplerian disk or infall of matter. They are,
instead, evidence of a bipolar wind, maybe partly seen through a disk hole
inside the dust sublimation radius. The disappearance of the Brackett gamma
emission line after the outburst suggests that the outburst is related to a
period of strong mass loss rather than a change of the extinction along the
line of sight. Based on these conclusions, we speculate that the origin of the
outburst is an event of enhanced mass accretion, similar to those occuring in
EX Ors and FU Ors.Comment: Accepted for publication in Astronomy and Astrophysics Letter
The near-infrared spectral energy distribution of {\beta} Pictoris b
A gas giant planet has previously been directly seen orbiting at 8-10 AU
within the debris disk of the ~12 Myr old star {\beta} Pictoris. The {\beta}
Pictoris system offers the rare opportunity to study the physical and
atmospheric properties of an exoplanet placed on a wide orbit and to establish
its formation scenario. We obtained J (1.265 {\mu}m), H (1.66 {\mu}m), and M'
(4.78 {\mu}m) band angular differential imaging of the system between 2011 and
2012. We detect the planetary companion in our four-epoch observations. We
estimate J = 14.0 +- 0.3, H = 13.5 +- 0.2, and M' = 11.0 +- 0.3 mag. Our new
astrometry consolidates previous semi-major axis (sma=8-10 AU) and excentricity
(e <= 0.15) estimates of the planet. These constraints, and those derived from
radial velocities of the star provides independent upper limits on the mass of
{\beta} Pictoris b of 12 and 15.5 MJup for semi-major axis of 9 and 10 AU. The
location of {\beta} Pictoris b in color-magnitude diagrams suggests it has
spectroscopic properties similar to L0-L4 dwarfs. This enables to derive
Log10(L/Lsun) = -3.87 +- 0.08 for the companion. The analysis with 7
PHOENIX-based atmospheric models reveals the planet has a dusty atmosphere with
Teff = 1700 +- 100 K and log g = 4.0+- 0.5. "Hot-start" evolutionary models
give a new mass of 10+3-2 MJup from Teff and 9+3-2 MJup from luminosity.
Predictions of "cold-start" models are inconsistent with independent
constraints on the planet mass. "Warm-start" models constrain the mass to M >=
6MJup and the initial entropies to values (Sinit >= 9.3Kb/baryon), intermediate
between those considered for cold/hot-start models, but likely closer to those
of hot-start models.Comment: 19 pages, accepted in Astronomy and Astrophysic
Planetary Science Virtual Observatory architecture
In the framework of the Europlanet-RI program, a prototype of Virtual
Observatory dedicated to Planetary Science was defined. Most of the activity
was dedicated to the elaboration of standards to retrieve and visualize data in
this field, and to provide light procedures to teams who wish to contribute
with on-line data services. The architecture of this VO system and selected
solutions are presented here, together with existing demonstrators
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