98 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
A wide planetary-mass companion to a young low-mass brown dwarf in Ophiuchus
We present the discovery of a planetary-mass companion to CFHTWIR-Oph 98, a low-mass brown dwarf member of the young Ophiuchus star-forming region, with a wide 200 au separation (1farcs46). The companion was identified using Hubble Space Telescope images, and confirmed to share common proper motion with the primary using archival and new ground-based observations. Based on the very low probability of the components being unrelated Ophiuchus members, we conclude that Oph 98 AB forms a binary system. From our multiband photometry, we constrain the primary to be an M9–L1 dwarf, and the faint companion to have an L2–L6 spectral type. For a median age of 3 Myr for Ophiuchus, fits of evolutionary models to measured luminosities yield masses of 15.4 ± 0.8 MJup for Oph 98 A and 7.8 ± 0.8 MJup for Oph 98 B, with respective effective temperatures of 2320 ± 40 K and 1800 ± 40 K. For possible system ages of 1–7 Myr, masses could range from 9.6–18.4 MJup for the primary, and from 4.1–11.6 MJup for the secondary. The low component masses and very large separation make this binary the lowest binding energy system imaged to date, indicating that the outcome of low-mass star formation can result in such extreme, weakly bound systems. With such a young age, Oph 98 AB extends the growing population of young free-floating planetary-mass objects, offering a new benchmark to refine formation theories at the lowest masses
A new white dwarf companion to the star GJ 3346
We present the discovery of a white dwarf companion at 3.6" from GJ3346, a
nearby (42 mas) K star observed with SPHERE@VLT as part of an open
time survey for faint companions to objects with significant proper motion
discrepancies () between Gaia DR1 and Tycho-2. Syrius-like systems
like GJ3346AB, which include a main sequence star and a white dwarf, can be
difficult to detect because of the intrinsic faintness of the latter. They
have, however, been found to be common contaminants for direct imaging
searches. White dwarfs have in fact similar brightness to sub-stellar
companions in the infrared, while being much brighter in the visible bands like
those used by Gaia. Combining our observations with Gaia DR2 and with several
additional archival data sets, we were able to fully constrain the physical
properties of GJ3346B, such as its effective temperature
(1110500 K) as well as the cooling age of the system (64858
Myrs). This allowed us to better understand the system history and to partially
explains the discrepancies previously noted in the age indicators for this
objects. Although further investigation is still needed, it seems that GJ3346,
which was previously classified as young, is in fact most likely to be older
than 4 Gyrs. Finally, given that the mass (0.580.01)} and
separation (85 au) of GJ3346B are compatible with the observed ,
this discovery represents a further confirmation of the potential of this kind
of dynamical signatures as selection methods for direct imaging surveys
targeting faint, sub-stellar companions.Comment: 10 pages, 7 figure
VIBES: VIsual Binary Exoplanet survey with SPHERE Upper limits on wide S-planet and S-BD frequencies, triple system discovery, and astrometric confirmation of 20 stellar binaries and three triple systems
Recent surveys indicate that planets in binary systems are more abundant than
previously thought, which is in agreement with theoretical work on disc
dynamics and planet formation in binaries. In order to measure the abundance
and physical characteristics of wide-orbit giant exoplanets in binary systems,
we have designed the 'VIsual Binary Exoplanet survey with Sphere' (VIBES) to
search for planets in visual binaries. It uses the SPHERE instrument at VLT to
search for planets in 23 visual binary and four visual triple systems with ages
of <145 Myr and distances of <150 pc. We used the IRDIS dual-band imager on
SPHERE to acquire high-contrast images of the sample targets. For each binary,
the two components were observed at the same time with a coronagraph masking
only the primary star. For the triple star, the tight components were treated
as a single star for data reduction. This enabled us to effectively search for
companions around 50 individual stars in binaries and four binaries in triples.
We derived upper limits of 13.7\% for the frequency of sub-stellar
companions around primaries in visual binaries, 26.5\% for the fraction of
sub-stellar companions around secondaries in visual binaries, and an occurrence
rate of 9.0\% for giant planets and brown dwarfs around either component of
visual binaries. We have combined our observations with literature measurements
to astrometrically confirm, for the first time, that 20 binaries and two triple
systems, which were previously known, are indeed physically bound. Finally, we
discovered a third component of the binary HD~121336. The upper limits we
derived are compatible with planet formation through the core accretion and the
gravitational instability processes in binaries. These limits are also in line
with limits found for single star and circumbinary planet search surveys.Comment: Accepted for publication in Astronomy & Astrophysics on 18.09.2020 21
pages, 11 figure
A high binary fraction for the most massive close-in giant planets and brown dwarf desert members
Stellar multiplicity is believed to influence planetary formation and
evolution, although the precise nature and extent of this role remain
ambiguous. We present a study aimed at testing the role of stellar multiplicity
in the formation and/or evolution of the most massive, close-in planetary and
substellar companions. Using direct imaging observations, as well as the Gaia
DR2 catalogue, we searched for wide binary companions to 38 stars hosting
massive giant planets or brown dwarfs (M > 7 MJup) on orbits shorter than ~1
AU. We report the discovery of a new component in the WASP-14 system, and
present an independent confirmation of a comoving companion to WASP-18. From a
robust Bayesian statistical analysis, we derived a binary fraction of
79.0+13.2-14.7% between 20-10,000 AU for our sample, twice as high as for field
stars with a 3-{\sigma} significance. This binary frequency was found to be
larger than for lower-mass planets on similar orbits, and we observed a
marginally higher binary rate for inner companions with periods shorter than 10
days. These results demonstrate that stellar companions greatly influence the
formation and/or evolution of these systems, suggesting that the role played by
binary companions becomes more important for higher-mass planets, and that this
trend may be enhanced for systems with tighter orbits. Our analysis also
revealed a peak in binary separation at 250 AU, highlighting a shortfall of
close binaries among our sample. This indicates that the mechanisms affecting
planet and brown dwarf formation or evolution in binaries must operate from
wide separations, although we found that the Kozai-Lidov mechanism is unlikely
to be the dominant underlying process. We conclude that binarity plays a
crucial role in the existence of very massive short-period giant planets and
brown dwarf desert inhabitants, which are almost exclusively observed in
multiple systems.Comment: Accepted for publication in MNRAS. 30 pages, 20 figures. Updated to
include proof correction
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
An optimized survey strategy for the ERIS/NIX imager: searching for young giant exoplanets and very low mass brown dwarfs using the K-peak custom photometric filter
Stars and planetary system
A Near-infrared Variability Survey of Young Planetary-mass Objects
We present a photometric variability survey of young planetary-mass objects
using the New Technology Telescope in the Js and Ks bands. Surface gravity
plays an important role in the atmospheric structure of brown dwarfs, as young
low gravity L dwarfs have a higher variability rate than field L dwarfs. In
this study, we extend variability studies to young T-type planetary-mass
objects and investigate the effects of surface gravity on the variability of L
and T dwarfs across a large sample. We conduct continuous monitoring for 18
objects with spectral types from L5 to T8 and detect four new variables and two
variable candidates. Combining with previous variability surveys of field and
young L and T objects, we find that young objects tend to be more variable than
field objects within peak-to-peak variability amplitude ranges of 0.5-10 per
cent and period ranges of 1.5-20 hr. For the first time, we constrain the
variability rate of young T dwarfs to be 56 per cent compared to 25 per cent
for field T dwarfs. Both field and young samples have higher variability rates
at the L/T transition than outside the L/T transition. The differences in the
variability rates between field and young samples are about 1 sigma and
therefore larger sample sizes are needed to confirm and refine the results.
Besides the L/T transition, young L dwarfs with strong variability tend to
assemble in a narrow spectral type range of L6-L7.5. This work supports the
critical role of surface gravity on the atmospheric structure from L to T
spectral types.Comment: Accepted for publication in MNRAS, 21 pages of main text including 6
tables and 17 figure
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