3,521 research outputs found
Deep search for companions to probable young brown dwarfs
We have obtained high contrast images of four nearby, faint, and very low
mass objects 2MASSJ04351455-1414468, SDSSJ044337.61+000205.1,
2MASSJ06085283-2753583 and 2MASSJ06524851-5741376 (here after 2MASS0435-14,
SDSS0443+00, 2MASS0608-27 and 2MASS0652-57), identified in the field as
probable isolated young brown dwarfs. Our goal was to search for binary
companions down to the planetary mass regime. We used the NAOS-CONICA adaptive
optics instrument (NACO) and its unique capability to sense the wavefront in
the near-infrared to acquire sharp images of the four systems in Ks, with a
field of view of 28"*28". Additional J and L' imaging and follow-up
observations at a second epoch were obtained for 2MASS0652-57. With a typical
contrast DKs= 4.0-7.0 mag, our observations are sensitive down to the planetary
mass regime considering a minimum age of 10 to 120 Myr for these systems. No
additional point sources are detected in the environment of 2MASS0435-14,
SDSS0443+00 and 2MASS0608-27 between 0.1-12" (i.e about 2 to 250 AU at 20 pc).
2MASS0652-57 is resolved as a \sim230 mas binary. Follow-up observations reject
a background contaminate, resolve the orbital motion of the pair, and confirm
with high confidence that the system is physically bound. The J, Ks and L'
photometry suggest a q\sim0.7-0.8 mass ratio binary with a probable semi-major
axis of 5-6 AU. Among the four systems, 2MASS0652-57 is probably the less
constrained in terms of age determination. Further analysis would be necessary
to confirm its youth. It would then be interesting to determine its orbital and
physical properties to derive the system's dynamical mass and to test
evolutionary model predictions.Comment: Research note, 5 pages, 2 tables and 3 figures, accepted to A&
Main steps for the fabrication of IPHI RFQ
The RFQ of the project IPHI is a 8 meter long, high power, very precise
tolerances (0.01 mm on 1 meter long for example) device to accelerate protons.
This RFQ is similar to the RFQ of the LEDA project. So, we realize a thermal
and mechanical studies followed by different tests for machining and brazing
copper. We describe in this paper those different steps and the way we proceed
to supply the fabrication itself by an independent company.Comment: 3 pages, 4 figure
beta Pic b position relative to the Debris Disk
Context. We detected in 2009 a giant, close-by planet orbiting {\beta} Pic, a
young star surrounded with a disk, extensively studied for more than 20 years.
We showed that if located on an inclined orbit, the planet could explain
several peculiarities of {\beta} Pictoris system. However, the available data
did not permit to measure the inclination of {\beta} Pic b with respect to the
disk, and in particular to establish in which component of the disk - the main,
extended disk or the inner inclined component/disk-, the planet was located.
Comparison between the observed planet position and the disk orientation
measured on previous imaging data was not an option because of potential biases
in the measurements. Aims. Our aim is to measure precisely the planet location
with respect to the dust disk using a single high resolution image, and
correcting for systematics or errors that degrades the precision of the disk
and planet relative position measurements. Methods. We gathered new NaCo data
at Ks band, with a set-up optimized to derive simultaneously the orientation(s)
of the disk(s) and that of the planet. Results. We show that the projected
position of {\beta} Pic b is above the midplane of the main disk. With the
current data and knowledge on the system, this implies that {\beta} Pic b
cannot be located in the main disk. The data rather suggest the planet being
located in the inclined component.Comment: 13 pages, 6 figures, to appear in Astronomy and Astrophysic
A survey of young, nearby, and dusty stars to understand the formation of wide-orbit giant planets
Direct imaging has confirmed the existence of substellar companions on wide
orbits. To understand the formation and evolution mechanisms of these
companions, the full population properties must be characterized. We aim at
detecting giant planet and/or brown dwarf companions around young, nearby, and
dusty stars. Our goal is also to provide statistics on the population of giant
planets at wide-orbits and discuss planet formation models. We report a deep
survey of 59 stars, members of young stellar associations. The observations
were conducted with VLT/NaCo at L'-band (3.8 micron). We used angular
differential imaging to reach optimal detection performance. A statistical
analysis of about 60 % of the young and southern A-F stars closer than 65 pc
allows us to derive the fraction of giant planets on wide orbits. We use
gravitational instability models and planet population synthesis models
following the core-accretion scenario to discuss the occurrence of these
companions. We resolve and characterize new visual binaries and do not detect
any new substellar companion. The survey's median detection performance reaches
contrasts of 10 mag at 0.5as and 11.5 mag at 1as. We find the occurrence of
planets to be between 10.8-24.8 % at 68 % confidence level assuming a uniform
distribution of planets in the interval 1-13 Mj and 1-1000 AU. Considering the
predictions of formation models, we set important constraints on the occurrence
of massive planets and brown dwarf companions that would have formed by GI. We
show that this mechanism favors the formation of rather massive clump (Mclump >
30 Mj) at wide (a > 40 AU) orbits which might evolve dynamically and/or
fragment. For the population of close-in giant planets that would have formed
by CA, our survey marginally explore physical separations (<20 AU) and cannot
constrain this population
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
Discovery of a Low-Mass Companion to the F7V star HD 984
We report the discovery of a low-mass companion to the nearby (d = 47 pc) F7V
star HD 984. The companion is detected 0.19" away from its host star in the L'
band with the Apodizing Phase Plate on NaCo/VLT and was recovered by L'-band
non-coronagraphic imaging data taken a few days later. We confirm the companion
is co-moving with the star with SINFONI integral field spectrograph H+K data.
We present the first published data obtained with SINFONI in pupil-tracking
mode. HD 984 has been argued to be a kinematic member of the 30 Myr-old Columba
group, and its HR diagram position is not altogether inconsistent with being a
ZAMS star of this age. By consolidating different age indicators, including
isochronal age, coronal X-ray emission, and stellar rotation, we independently
estimate a main sequence age of 11585 Myr (95% CL) which does not rely on
this kinematic association. The mass of directly imaged companions are usually
inferred from theoretical evolutionary tracks, which are highly dependent on
the age of the star. Based on the age extrema, we demonstrate that with our
photometric data alone, the companion's mass is highly uncertain: between 33
and 96 M (0.03-0.09 M) using the COND evolutionary
models. We compare the companion's SINFONI spectrum with field dwarf spectra to
break this degeneracy. Based on the slope and shape of the spectrum in the
H-band, we conclude that the companion is an M dwarf. The age of the
system is not further constrained by the companion, as M dwarfs are poorly fit
on low-mass evolutionary tracks. This discovery emphasizes the importance of
obtaining a spectrum to spectral type companions around F-stars.Comment: Accepted for publication in MNRAS, 10 pages, 5 figure
Confirmation of the planet around HD 95086 by direct imaging
VLT/NaCo angular differential imaging at L' (3.8 microns) revealed a probable
giant planet comoving with the young and early-type HD 95086 also known to
harbor an extended debris disk. The discovery was based on the proper motion
analysis of two datasets spanning 15 months. However, the second dataset
suffered from bad atmospheric conditions, which limited the significance of the
redetection at the 3 sigma level. In this Letter, we report new VLT/NaCo
observations of HD 95086 obtained on 2013 June 26-27 at L' to recover the
planet candidate. We unambiguously redetect the companion HD 95086 b with
multiple independent pipelines at a signal-to-noise ratio greater than or equal
to 5. Combined with previously reported measurements, our astrometry decisively
shows that the planet is comoving with HD 95086 and inconsistent with a
background object. With a revised mass of 5 pm 2 Jupiter masses, estimated from
its L' photometry and "hot-start" models at 17 pm 4 Myr, HD 95086 b becomes a
new benchmark for further physical and orbital characterization of young giant
planets.Comment: accepted for publication to AP
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
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