340 research outputs found
On the Mass Function, Multiplicity, and Origins of Wide-Orbit Giant Planets
A major outstanding question regarding the formation of planetary systems is
whether wide-orbit giant planets form differently than close-in giant planets.
We aim to establish constraints on two key parameters that are relevant for
understanding the formation of wide-orbit planets: 1) the relative mass
function and 2) the fraction of systems hosting multiple companions. In this
study, we focus on systems with directly imaged substellar companions, and the
detection limits on lower-mass bodies within these systems. First, we uniformly
derive the mass probability distributions of known companions. We then combine
the information contained within the detections and detection limits into a
survival analysis statistical framework to estimate the underlying mass
function of the parent distribution. Finally, we calculate the probability that
each system may host multiple substellar companions. We find that 1) the
companion mass distribution is rising steeply toward smaller masses, with a
functional form of , and consequently, 2) many of
these systems likely host additional undetected sub-stellar companions.
Combined, these results strongly support the notion that wide-orbit giant
planets are formed predominantly via core accretion, similar to the better
studied close-in giant planets. Finally, given the steep rise in the relative
mass function with decreasing mass, these results suggest that future deep
observations should unveil a greater number of directly imaged planets.Comment: 19 pages, 10 figures, accepted to Ap
Hubble Space Telescope astrometry of the closest brown dwarf binary system -- I. Overview and improved orbit
Located at ~2pc, the L7.5+T0.5 dwarfs system WISE J104915.57-531906.1
(Luhman16AB) is the third closest system known to Earth, making it a key
benchmark for detailed investigation of brown dwarf atmospheric properties,
thermal evolution, multiplicity, and planet-hosting frequency. In the first
study of this series -- based on a multi-cycle Hubble Space Telescope (HST)
program -- we provide an overview of the project and present improved estimates
of positions, proper motions, annual parallax, mass ratio, and the current best
assessment of the orbital parameters of the A-B pair. Our HST observations
encompass the apparent periastron of the binary at 220.5+/-0.2 mas at epoch
2016.402. Although our data seem to be inconsistent with recent ground-based
astrometric measurements, we also exclude the presence of third bodies down to
Neptune masses and periods longer than a year.Comment: 19 pages, 9 figures, 9 tables. Accepted for publication in MNRAS on
2017 May
The young stellar population of Lynds 1340. An infrared view
We present results of an infrared study of the molecular cloud Lynds 1340,
forming three groups of low and intermediate-mass stars. Our goals are to
identify and characterise the young stellar population of the cloud, study the
relationships between the properties of the cloud and the emergent stellar
groups, and integrate L1340 into the picture of the star-forming activity of
our Galactic environment. We selected candidate young stellar objects from the
Spitzer and WISE data bases using various published color criteria, and
classified them based on the slope of the spectral energy distribution. We
identified 170 Class II, 27 Flat SED, and Class 0/I sources. High angular
resolution near-infrared observations of the RNO 7 cluster, embedded in L1340,
revealed eight new young stars of near-infrared excess. The surface density
distribution of young stellar objects shows three groups, associated with the
three major molecular clumps of L1340, each consisting of less than 100
members, including both pre-main sequence stars and embedded protostars. New
Herbig--Haro objects were identified in the Spitzer images. Our results
demonstrate that L1340 is a prolific star-forming region of our Galactic
environment in which several specific properties of the intermediate-mass mode
of star formation can be studied in detail.Comment: 73 pages, 33 figures, 15 tables. Accepted for publication in ApJ
A Search for Companions to Brown Dwarfs in the Taurus and Chamaeleon Star Forming Regions
We present the results of a search for companions to young brown dwarfs in
the Taurus and Chamaeleon I star forming regions (1/2-3 Myr). We have used
WFPC2 on board HST to obtain F791W and F850LP images of 47 members of these
regions that have spectral types of M6-L0 (0.01-0.1 Msun). An additional
late-type member of Taurus, FU Tau (M7.25+M9.25), was also observed with
adaptive optics at Keck Observatory. We have applied PSF subtraction to the
primaries and have searched the resulting images for objects that have colors
and magnitudes that are indicative of young low-mass objects. Through this
process, we have identified promising candidate companions to 2MASS
J04414489+2301513 (rho=0.105"/15 AU), 2MASS J04221332+1934392 (rho=0.05"/7 AU),
and ISO 217 (rho=0.03"/5 AU). We reported the discovery of the first candidate
in a previous study, showing that it has a similar proper motion as the primary
through a comparison of astrometry measured with WFPC2 and Gemini adaptive
optics. We have collected an additional epoch of data with Gemini that further
supports that result. By combining our survey with previous high-resolution
imaging in Taurus, Chamaeleon, and Upper Sco (10 Myr), we measure binary
fractions of 14/93 = 0.15+0.05/-0.03 for M4-M6 (0.1-0.3 Msun) and 4/108 =
0.04+0.03/-0.01 for >M6 (10 AU. Given the youth
and low density of these three regions, the lower binary fraction at later
types is probably primordial rather than due to dynamical interactions among
association members. The widest low-mass binaries (>100 AU) also appear to be
more common in Taurus and Chamaeleon than in the field, which suggests that the
widest low-mass binaries are disrupted by dynamical interactions at >10 Myr, or
that field brown dwarfs have been born predominantly in denser clusters where
wide systems are disrupted or inhibited from forming.Comment: Astrophysical Journal, in pres
Evolution of Young Brown Dwarf Disks in the Mid-Infrared
We have imaged two bona-fide brown dwarfs with TReCS/GEMINI-S and find
mid-infrared excess emission that can be explained by optically thick dust disk
models. In the case of the young (2Myr) Cha H1 we measure
fluxes at 10.4m and 12.3m that are fully consistent with a standard
flared disk model and prominent silicate emission. For the 10Myr old
brown dwarf 2MASS1207-3932 located in the TW Hydrae association we find excess
emission at 8.7m and 10.4m with respect to its photosphere, and
confirm disk accretion as likely cause of its strong activity. Disks around
brown dwarfs likely last at least as long as their low-mass stellar
counterparts in the T-Tauri phase. Grain growth, dust settling, and evolution
of the geometry of brown dwarfs disks may appear on a timescale of 10Myr and
can be witnessed by observations in the mid-infrared.Comment: 6 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
An HST Imaging Survey of Low-Mass Stars in the Chamaeleon I Star Forming region
We present new HST/WFPC2 observations of 20 fields centered around T Tauri
stars in the Chamaeleon I star forming region. Images have been obtained in the
F631N ([OI]6300A), F656N (Ha) and F673N ([SII]6716A+6731A) narrow-band filters,
plus the Johnson V-band equivalent F547M filter. We detect 31 T Tauri stars
falling within our fields. We discuss the optical morphology of 10 sources
showing evidence of either binarity, circumstellar material, or mass loss. We
supplement our photometry with a compilation of optical, infrared and
sub-millimeter data from the literature, together with new sub-mm data for
three objects, to build the Spectral Energy Distributions (SED) of 19 single
sources. Using an SED model fitting tool, we self-consistently estimate a
number of stellar and disk parameters, while mass accretion rates are directly
derived from our Ha photometry. We find that bolometric luminosities derived
from dereddened optical data tend to be underestimated in systems with high
alpha(2-24} IR spectral index, suggesting that disks seen nearly edge-on may
occasionally be interpreted as low luminosity (and therefore more evolved)
sources. On the other hand, the same alpha(2-24) spectral index, a tracer of
the amount of dust in the warmer layers of the circumstellar disks, and the
mass accretion rate appear to decay with the isocronal stellar age, suggesting
that the observed age spread (~0.5-5 Myr) within the cluster is real. Our
sample contains a few outliers that may have dissipated their circumstellar
disks on shorter time-scale.Comment: to appear on Astronomical Journal, accepted April 16, 2012 (AJ-10740
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