323 research outputs found
Excellent daytime seeing at Dome Fuji on the Antarctic plateau
Context. Dome Fuji, the second highest region on the Antarctic plateau, is
expected to have some of the best astronomical seeing on Earth. However, site
testing at Dome Fuji is still in its very early stages.
Aims. To investigate the astronomical seeing in the free atmosphere above
Dome Fuji, and to determine the height of the surface boundary layer.
Methods. A Differential Image Motion Monitor was used to measure the seeing
in the visible (472 nm) at a height of 11 m above the snow surface at Dome Fuji
during the austral summer of 2012/2013.
Results. Seeing below 0.2'' has been observed. The seeing often has a local
minimum of ~0.3'' near 18 h local time. Some periods of excellent seeing, 0.3''
or smaller, were also observed, sometimes extending for several hours at local
midnight. The median seeing is higher, at 0.52''---this large value is believed
to be caused by periods when the telescope was within the turbulent boundary
layer.
Conclusions. The diurnal variation of the daytime seeing at Dome Fuji is
similar to that reported for Dome C, and the height of the surface boundary
layer is consistent with previous simulations for Dome Fuji. The free
atmosphere seeing is ~0.2'', and the height of the surface boundary layer can
be as low as ~11 m.Comment: 4 pages, 6 figures, Submitted to Astronomy & Astrophysics (letter
Efficient injection from large telescopes into single-mode fibres: Enabling the era of ultra-precision astronomy
Photonic technologies offer numerous advantages for astronomical instruments
such as spectrographs and interferometers owing to their small footprints and
diverse range of functionalities. Operating at the diffraction-limit, it is
notoriously difficult to efficiently couple such devices directly with large
telescopes. We demonstrate that with careful control of both the non-ideal
pupil geometry of a telescope and residual wavefront errors, efficient coupling
with single-mode devices can indeed be realised. A fibre injection was built
within the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument.
Light was coupled into a single-mode fibre operating in the near-IR (J-H bands)
which was downstream of the extreme adaptive optics system and the pupil
apodising optics. A coupling efficiency of 86% of the theoretical maximum limit
was achieved at 1550 nm for a diffraction-limited beam in the laboratory, and
was linearly correlated with Strehl ratio. The coupling efficiency was constant
to within <30% in the range 1250-1600 nm. Preliminary on-sky data with a Strehl
ratio of 60% in the H-band produced a coupling efficiency into a single-mode
fibre of ~50%, consistent with expectations. The coupling was >40% for 84% of
the time and >50% for 41% of the time. The laboratory results allow us to
forecast that extreme adaptive optics levels of correction (Strehl ratio >90%
in H-band) would allow coupling of >67% (of the order of coupling to multimode
fibres currently). For Strehl ratios <20%, few-port photonic lanterns become a
superior choice but the signal-to-noise must be considered. These results
illustrate a clear path to efficient on-sky coupling into a single-mode fibre,
which could be used to realise modal-noise-free radial velocity machines,
very-long-baseline optical/near-IR interferometers and/or simply exploit
photonic technologies in future instrument design.Comment: 15 pages, 16 figures, 1 table, published in A&
H Emission Nebulosity Associated with KH 15D
An H emission filament is found in close proximity to the unique object
KH 15D using the adaptive optics system of the Subaru Telescope. The morphology
of the filament, the presence of spectroscopic outflow signatures observed by
Hamilton et al., and the detection of extended H emission from KH 15D by
Deming, Charbonneau, & Harrington suggest that this filament arises from
shocked H in an outflow. The filament extends about 15" to the north of KH
15D.Comment: 11 pages, 3 figures, 1 table. Astrophysical Journal Letters, in pres
Near-Infrared Adaptive Optics Spectroscopy of Binary Brown Dwarf HD 130948B and C
We present near-infrared spectroscopy of low-mass companions in a nearby
triple system HD 130948 (Gliese 564, HR 5534). Adaptive optics on the Subaru
Telescope allowed spectroscopy of the individual components of the 0".13 binary
system. Based on a direct comparison with a series of template spectra, we
determined the spectral types of HD 130948B and C to be L4 +- 1. If we take the
young age of the primary star into account (0.3-0.8 Gyr), HD 130948B and C most
likely are a binary brown dwarf system.Comment: 6 pages, 3 figures, accepted for publication in ApJ Letter
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
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