276 research outputs found
Annular substructures in the transition disks around LkCa 15 and J1610
We present high resolution millimeter continuum ALMA observations of the
disks around the T Tauri stars LkCa 15 and J1610. These disks host
dust-depleted inner regions, possibly carved by massive planets, and are of
prime interest to study the imprints of planet-disk interactions. While at
moderate angular resolution they appear as a broad ring surrounding a cavity,
the continuum emission resolves into multiple rings at a resolution of
~6040 mas (~7.5 au for LkCa 15, ~6 au for J1610) and ~Jy
beam rms at 1.3 mm. In addition to a broad extended component, LkCa 15
and J1610 host 3 and 2 narrow rings, respectively, with two bright rings in
LkCa 15 being radially resolved. The rings look marginally optically thick,
with peak optical depths of ~0.5 (neglecting scattering), in agreement with
high angular resolution observations of full disks. We perform hydrodynamical
simulations with an embedded, sub-Jovian-mass planet and show that the observed
multi-ringed substructure can be qualitatively explained as the outcome of the
planet-disk interaction. We note however that the choice of the disk cooling
timescale alone can significantly impact the resulting gas and dust
distributions around the planet, leading to different numbers of rings and gaps
and different spacings between them. We propose that the massive outer disk
regions of transition disks are favorable places for planetesimals and possibly
second generation planet formation of objects with a lower mass than the
planets carving the inner cavity (typically few ), and that the
annular substructures observed in LkCa 15 and J1610 may be indicative of
planetary core formation within dust-rich pressure traps. Current observations
are compatible with other mechanisms being at the origin of the observed
substructures, in particular with narrow rings generated at the edge of the CO
and N snowlines.Comment: 17 pages, accepted for publication in Astronomy & Astrophysic
Orbits and Masses in the T Tauri System
We investigate the binary star T Tauri South, presenting the orbital
parameters of the two components and their individual masses. We combined
astrometric positions from the literature with previously unpublished VLT
observations. Model fits yield the orbital elements of T Tau Sa and Sb. We use
T Tau N as an astrometric reference to derive an estimate for the mass ratio of
Sa and Sb. Although most of the orbital parameters are not well constrained, it
is unlikely that T Tau Sb is on a highly elliptical orbit or escaping from the
system. The total mass of T Tau S is rather well constrained to 3.0 +0.15/-0.24
M_sun. The mass ratio Sb:Sa is about 0.4, corresponding to individual masses of
M_Sa = 2.1+/-0.2 M_sun and M_Sb = 0.8+/-0.1 M_sun. This confirms that the
infrared companion in the T Tauri system is a pair of young stars obscured by
circumstellar material.Comment: 10 pages, 11 figures, accepted by Astronomy and Astrophysic
TLSim: A software for Electrical Public Transportation Systems
The Laboratory of Electrical Machines of the Swiss Federal Institute of Technology (Lausanne) has developed a software (TLSim) for the simulation of electrical urban transportation systems. This program can simulate the behaviour of the power supply network (current and voltage level at any point of the topology) comprising uni- and bi- directionnal sub-stations. In the network the vehicules (trolleybus) may run along any defined path through different electrical supply sectors. Several models of trolleybus are available, one of these allowing for the injection of current back in the supply network. The operating schedule of the buses as well as the geographical data of the network are provided by the user. This program is a perfect tool for system planning as ascertained by its use by a Swiss transportation operator. A comparison of simulation and measurements on a real network has been performed with satisfactory results. This software evolved from a specific study to a flexible program still being extended with new developments. The latest of such developments being the study of the influence of capacitors in helping the system to keep voltages over a specified level mainly by supplying the surge current during the acceleration of the trolleybuses
Subaru Imaging of Asymmetric Features in a Transitional Disk in Upper Scorpius
We report high-resolution (0.07 arcsec) near-infrared polarized intensity
images of the circumstellar disk around the star 2MASS J16042165-2130284
obtained with HiCIAO mounted on the Subaru 8.2 m telescope. We present our
-band data, which clearly exhibits a resolved, face-on disk with a large
inner hole for the first time at infrared wavelengths. We detect the
centrosymmetric polarization pattern in the circumstellar material as has been
observed in other disks. Elliptical fitting gives the semimajor axis, semiminor
axis, and position angle (P.A.) of the disk as 63 AU, 62 AU, and -14
, respectively. The disk is asymmetric, with one dip located at P.A.s
of . Our observed disk size agrees well with a previous study
of dust and CO emission at submillimeter wavelength with Submillimeter Array.
Hence, the near-infrared light is interpreted as scattered light reflected from
the inner edge of the disk. Our observations also detect an elongated arc (50
AU) extending over the disk inner hole. It emanates at the inner edge of the
western side of the disk, extending inward first, then curving to the
northeast. We discuss the possibility that the inner hole, the dip, and the arc
that we have observed may be related to the existence of unseen bodies within
the disk.Comment: 21 pages, 3 figures, published 2012 November 7 by ApJL, typo
correcte
Discovery of Small-Scale Spiral Structures in the Disk of SAO 206462 (HD 135344B): Implications for the Physical State of the Disk from Spiral Density Wave Theory
We present high-resolution, H-band, imaging observations, collected with
Subaru/HiCIAO, of the scattered light from the transitional disk around SAO
206462 (HD 135344B). Although previous sub-mm imagery suggested the existence
of the dust-depleted cavity at r~46AU, our observations reveal the presence of
scattered light components as close as 0.2" (~28AU) from the star. Moreover, we
have discovered two small-scale spiral structures lying within 0.5" (~70AU). We
present models for the spiral structures using the spiral density wave theory,
and derive a disk aspect ratio of h~0.1, which is consistent with previous
sub-mm observations. This model can potentially give estimates of the
temperature and rotation profiles of the disk based on dynamical processes,
independently from sub-mm observations. It also predicts the evolution of the
spiral structures, which can be observable on timescales of 10-20 years,
providing conclusive tests of the model. While we cannot uniquely identify the
origin of these spirals, planets embedded in the disk may be capable of
exciting the observed morphology. Assuming that this is the case, we can make
predictions on the locations and, possibly, the masses of the unseen planets.
Such planets may be detected by future multi-wavelengths observations.Comment: 8 pages, 5 figures, ApJL in press, typo correcte
Techniques for direct experimental evaluation of structure-transport relationships in disordered porous solids
Determining structure-transport relationships is critical to optimising the activity and selectivity performance of porous pellets acting as heterogeneous catalysts for diffusion-limited reactions. For amorphous porous systems determining the impact of particular aspects of the void space on mass transport often requires complex characterization and modelling steps to deconvolve the specific influence of the feature in question. These characterization and modelling steps often have limited accuracy and precision. It is the purpose of this work to present a case-study demonstrating the use of a more direct experimental evaluation of the impact of pore network features on mass transport. The case study evaluated the efficacy of the macropores of a bidisperse porous foam structure on improving mass transport over a purely mesoporous system. The method presented involved extending the novel integrated gas sorption and mercury porosimetry method to include uptake kinetics. Results for the new method were compared with those obtained by the alternative NMR cryodiffusometry technique, and found to lead to similar conclusions. It was found that the experimentally-determined degree of influence of the foam macropores was in line with expectations from a simple resistance model for a disconnected macropore network
Direct Imaging of a Cold Jovian Exoplanet in Orbit around the Sun-like Star GJ 504
Several exoplanets have recently been imaged at wide separations of >10 AU
from their parent stars. These span a limited range of ages (<50 Myr) and
atmospheric properties, with temperatures of 800--1800 K and very red colors (J
- H > 0.5 mag), implying thick cloud covers. Furthermore, substantial model
uncertainties exist at these young ages due to the unknown initial conditions
at formation, which can lead to an order of magnitude of uncertainty in the
modeled planet mass. Here, we report the direct imaging discovery of a Jovian
exoplanet around the Sun-like star GJ 504, detected as part of the SEEDS
survey. The system is older than all other known directly-imaged planets; as a
result, its estimated mass remains in the planetary regime independent of
uncertainties related to choices of initial conditions in the exoplanet
modeling. Using the most common exoplanet cooling model, and given the system
age of 160 [+350, -60] Myr, GJ 504 b has an estimated mass of 4 [+4.5, -1.0]
Jupiter masses, among the lowest of directly imaged planets. Its projected
separation of 43.5 AU exceeds the typical outer boundary of ~30 AU predicted
for the core accretion mechanism. GJ 504 b is also significantly cooler (510
[+30, -20] K) and has a bluer color (J-H = -0.23 mag) than previously imaged
exoplanets, suggesting a largely cloud-free atmosphere accessible to
spectroscopic characterization. Thus, it has the potential of providing novel
insights into the origins of giant planets, as well as their atmospheric
properties.Comment: 20 pages, 12 figures, Accepted for publication in ApJ. Minor updates
from the version
Orbital characterization of GJ1108A system, and comparison of dynamical mass with model-derived mass for resolved binaries
We report an orbital characterization of GJ1108Aab that is a low-mass binary
system in pre-main-sequence phase. Via the combination of astrometry using
adaptive optics and radial velocity measurements, an eccentric orbital solution
of =0.63 is obtained, which might be induced by the Kozai-Lidov mechanism
with a widely separated GJ1108B system. Combined with several observed
properties, we confirm the system is indeed young. Columba is the most probable
moving group, to which the GJ1108A system belongs, although its membership to
the group has not been established. If the age of Columba is assumed for
GJ1108A, the dynamical masses of both GJ1108Aa and GJ1108Ab ( and ) are more massive than what an
evolutionary model predicts based on the age and luminosities. We consider the
discrepancy in mass comparison can attribute to an age uncertainty; the system
is likely older than stars in Columba, and effects that are not implemented in
classical models such as accretion history and magnetic activity are not
preferred to explain the mass discrepancy. We also discuss the performance of
the evolutionary model by compiling similar low-mass objects in evolutionary
state based on the literature. Consequently, it is suggested that the current
model on average reproduces the mass of resolved low-mass binaries without any
significant offsets.Comment: Accepted in Ap
Direct Imaging of Fine Structures in Giant Planet Forming Regions of the Protoplanetary Disk around AB Aurigae
We report high-resolution 1.6 \micron polarized intensity () images of
the circumstellar disk around the Herbig Ae star AB Aur at a radial distance of
22 AU () up to 554 AU (3.85), which have been obtained by the
high-contrast instrument HiCIAO with the dual-beam polarimetry. We revealed
complicated and asymmetrical structures in the inner part (140 AU) of
the disk, while confirming the previously reported outer ( 200 AU)
spiral structure. We have imaged a double ring structure at 40 and
100 AU and a ring-like gap between the two. We found a significant
discrepancy of inclination angles between two rings, which may indicate that
the disk of AB Aur is warped. Furthermore, we found seven dips (the typical
size is 45 AU or less) within two rings as well as three prominent
peaks at 40 AU. The observed structures, including a bumpy double ring, a
ring-like gap, and a warped disk in the innermost regions, provide essential
information for understanding the formation mechanism of recently detected
wide-orbit ( 20 AU) planets.Comment: 12 pages, 3 figure
- …