238 research outputs found
The shadow knows: using shadows to investigate the structure of the pretransitional disk of HD 100453
We present GPI polarized intensity imagery of HD 100453 in Y-, J-, and K1
bands which reveals an inner gap ( au), an outer disk ( au) with
two prominent spiral arms, and two azimuthally-localized dark features also
present in SPHERE total intensity images (Wagner 2015). SED fitting further
suggests the radial gap extends to au. The narrow, wedge-like shape of the
dark features appears similar to predictions of shadows cast by a inner disk
which is misaligned with respect to the outer disk. Using the Monte Carlo
radiative transfer code HOCHUNCK3D (Whitney 2013), we construct a model of the
disk which allows us to determine its physical properties in more detail. From
the angular separation of the features we measure the difference in inclination
between the disks 45, and their major axes, PA = 140 east
of north for the outer disk and 100for the inner disk. We find an
outer disk inclination of from face-on in broad agreement
with the Wagner 2015 measurement of 34. SPHERE data in J- and H-bands
indicate a reddish disk which points to HD 100453 evolving into a young debris
disk
Differences in the gas and dust distribution in the transitional disk of a sun-like young star, PDS 70
We present ALMA 0.87 mm continuum, HCO+ J=4--3 emission line, and CO J=3--2
emission line data of the disk of material around the young, Sun-like star PDS
70. These data reveal the existence of a possible two component transitional
disk system with a radial dust gap of 0."2 +/- 0."05, an azimuthal gap in the
HCO+ J=4--3 moment zero map, as well as two bridge-like features in the gas
data. Interestingly these features in the gas disk have no analogue in the dust
disk making them of particular interest. We modeled the dust disk using the
Monte Carlo radiative transfer code HOCHUNK3D (Whitney et al. 2013) using a two
disk components. We find that there is a radial gap that extends from 15-60 au
in all grain sizes which differs from previous work
The SPHERE view of three interacting twin disc systems in polarized light
Dense stellar environments as hosts of ongoing star formation increase the probability of gravitational encounters among stellar systems during the early stages of evolution. Stellar interaction may occur through non-recurring, hyperbolic, or parabolic passages (a so-called 'fly-by'), through secular binary evolution, or through binary capture. In all three scenarios, the strong gravitational perturbation is expected to manifest itself in the disc structures around the individual stars. Here, we present near-infrared polarized light observations that were taken with the SPHERE/IRDIS instrument of three known interacting twin-disc systems: AS 205, EM∗ SR 24, and FU Orionis. The scattered light exposes spirals likely caused by the gravitational interaction. On a larger scale, we observe connecting filaments between the stars. We analyse their very complex polarized intensity and put particular attention to the presence of multiple light sources in these systems. The local angle of linear polarization indicates the source whose light dominates the scattering process from the bridging region between the two stars. Further, we show that the polarized intensity from scattering with multiple relevant light sources results from an incoherent summation of the individuals' contribution. This can produce nulls of polarized intensity in an image, as potentially observed in AS 205. We discuss the geometry and content of the systems by comparing the polarized light observations with other data at similar resolution, namely with ALMA continuum and gas emission. Collective observational data can constrain the systems' geometry and stellar trajectories, with the important potential to differentiate between dynamical scenarios of stellar interaction
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
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
phot1 inhibition of ABCB19 primes lateral auxin fluxes in the shoot apex required for phototropism
It is well accepted that lateral redistribution of the phytohormone auxin underlies the bending of plant organs towards light. In monocots, photoreception occurs at the shoot tip above the region of differential growth. Despite more than a century of research, it is still unresolved how light regulates auxin distribution and where this occurs in dicots. Here, we establish a system in Arabidopsis thaliana to study hypocotyl phototropism in the absence of developmental events associated with seedling photomorphogenesis. We show that auxin redistribution to the epidermal sites of action occurs at and above the hypocotyl apex, not at the elongation zone. Within this region, we identify the auxin efflux transporter ATP-BINDING CASSETTE B19 (ABCB19) as a substrate target for the photoreceptor kinase PHOTOTROPIN 1 (phot1). Heterologous expression and physiological analyses indicate that phosphorylation of ABCB19 by phot1 inhibits its efflux activity, thereby increasing auxin levels in and above the hypocotyl apex to halt vertical growth and prime lateral fluxes that are subsequently channeled to the elongation zone by PIN-FORMED 3 (PIN3). Together, these results provide new insights into the roles of ABCB19 and PIN3 in establishing phototropic curvatures and demonstrate that the proximity of light perception and differential phototropic growth is conserved in angiosperm
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
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
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