335 research outputs found
SUBARU Near-Infrared Multi-Color Images of Class II Young Stellar Object, RNO91
We conducted sub-arcsecond near-infrared imaging observations of RNO91 with
CIAO mounted on the SUBARU 8.2 m telescope. We present our JHK band data along
with optical images, which when considered together reveal a complex
circumstellar structure. We examined the colors of associated nebula and
compared the geometry of the outflow/disk system suggested by our data with
that already proposed on the basis of previous studies. Our K-band image shows
bright circumstellar nebulosity detected within 2"(300AU) around the central
source while it is less conspicuous at shorter wavelengths such as J and
optical. P.A. and size of this red color nebulosity in our H-K color image
agree with those of the previously detected polarization disk. These data
agreement indicate that this bright circumstellar nebulosity region which
follows the reddening law might be attributed to a disk-like structure. At J
and optical wavelengths, several blue knot-like structures are detected around
and beyond the bright circumstellar nebulosity. We suggest that these knotty
reflection nebulae may represent disintegrating fragments of an infalling
envelope. The three-color composite image has an appearance of arc-shaped
nebulosity extending to the north and to the east through the central source.
On the other end of this arc-shaped structure, the nebula appears to become
more extended (2."3 long) to the southwest. We interpret these structures as
roots of bipolar cavities opening to the northeast and southwest. The complex
distribution of reflection nebulosity seen around RNO91 appears to confirm the
interpretation of this source as an object dispersing its molecular envelope
while transitioning from protostar to T Tauri star.Comment: 18 pages, 6 figures, Accepted by Publications of the Astronomical
Society of Japa
Near-Infrared Coronagraphic Observations of the T Tauri Binary System UY Aur
We present a near-infrared image of UY Aur, a 0.9" separated binary system,
using the Coronagraphic Imager with Adaptive Optics on the Subaru Telescope.
Thanks to adaptive optics, the spatial resolution of our image was ~0.1" in the
full width at half maximum of the point spread function, the highest achieved.
By comparison with previous measurements, we estimated that the orbital period
is ~1640 yrs and the total mass of the binary is ~1.73 solar mass. The observed
H-band magnitude of the secondary varies by as much as 1.3 mag within a decade,
while that of the primary is rather stable. This inconstancy may arise from
photospheric variability caused by an uneven accretion rate or from the
rotation of the secondary. We detected a half-ring shaped circumbinary disk
around the binary with a bright southwest part but a barely detectable
northeast portion. The brightness ratio is ~57. Its inner radius and
inclination are about 520 AU and 42, respectively. The disk is not uniform but
has remarkable features, including a clumpy structure along the disk,
circumstellar material inside the inner cavity, and an extended armlike
structure. The circumstellar material inside the cavity probably corresponds to
a clump or material accreting from the disk onto the binary. The armlike
structure is a part of the disk, created by the accretion from the outer region
of the disk or encounters with other stellar systems.Comment: 16 pages, 6 figures; accepted for publication in A
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
Microstructure dependence of fatigue crack propagation behavior in wrought magnesium alloy
This paper deals with the fatigue crack propagation behavior of rolled AZ31B magnesium alloy (grain size: approximately 40 ?m). Fatigue crack propagation tests were performed on single edge notched tension specimens at a stress ratio of R = 0.1 and a frequency of 10 Hz at room temperature. Loading axes were parallel to the rolling direction; fatigue cracks propagated parallel to the transverse direction (L-T specimen), parallel to the short transverse direction (L-S specimen). Loading axis was perpendicular to the rolling direction; fatigue cracks propagated parallel to the transverse direction (S-T specimen). The crack growth rate (da/dN) of the L-S specimen was several times lower than that of the L-T specimen in the examined stress intensity factor range (?K). Fracture surfaces of the L-T and L-S specimens showed many steps parallel and perpendicular, respectively, to the macroscopic crack growth direction. The da/dN of the S-T specimen was higher than that of the L-T and L-S specimens in the examined ?K. The fracture surface was covered by quasi-cleavage facets independent of macroscopic crack growth direction, and the fracture surface roughness at low ?K was larger than that at high ?K
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
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
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