532 research outputs found
Distinguishing between optical coherent states with imperfect detection
Several proposed techniques for distinguishing between optical coherent
states are analyzed under a physically realistic model of photodetection.
Quantum error probabilities are derived for the Kennedy receiver, the Dolinar
receiver and the unitary rotation scheme proposed by Sasaki and Hirota for
sub-unity detector efficiency. Monte carlo simulations are performed to assess
the effects of detector dark counts, dead time, signal processing bandwidth and
phase noise in the communication channel. The feedback strategy employed by the
Dolinar receiver is found to achieve the Helstrom bound for sub-unity detection
efficiency and to provide robustness to these other detector imperfections
making it more attractive for laboratory implementation than previously
believed
High-Resolution Infrared Imaging of Herschel 36 SE: A Showcase for the Influence of Massive Stars in Cluster Environments
We present high-resolution infrared imaging of the massive star-forming region around the O-star Herschel 36. Special emphasis is given to a compact infrared source at 0".25 southeast of the star. The infrared source, hereafter Her 36 SE, is extended in the broad-band images, but features spatially unresolved Br gamma line emission. The line-emission source coincides in position with the previous HST detections in H alpha and the 2 cm radio continuum emission detected by VLA interferometry. We propose that the infrared source Her 36 SE harbors an early B-type star, deeply embedded in a dusty cloud. The fan shape of the cloud with Herschel 36 at its apex, though, manifests direct and ongoing destructive influence of the O7V star on Her 36 SE
Kinematics of Ionized Gas at 0.01 AU of TW Hya
We report two-dimensional spectroastrometry of Br gamma emission of TW Hya to
study the kinematics of the ionized gas in the star-disk interface region. The
spectroastrometry with the integral field spectrograph SINFONI at the Very
Large Telescope is sensitive to the positional offset of the line emission down
to the physical scale of the stellar diameter (~0.01 AU). The centroid of Br
gamma emission is displaced to the north with respect to the central star at
the blue side of the emission line, and to the south at the red side. The major
axis of the centroid motion is P.A.= -20 degrees, which is nearly equal to the
major axis of the protoplanetary disk projected on the sky, previously reported
by CO sub millimeter spectroscopy (P.A.= -27 degrees) The line-of-sight motion
of the Br gamma emission, in which the northern side of the disk is approaching
toward us, is also consistent with the direction of the disk rotation known
from the CO observation. The agreement implies that the kinematics of Br gamma
emission is accounted for by the ionized gas in the inner edge of the disk. A
simple modeling of the astrometry, however, indicates that the accretion inflow
similarly well reproduces the centroid displacements of Br gamma, but only if
the position angles of the centroid motion and the projected disk ellipse is a
chance coincidence. No clear evidence of disk wind is found.Comment: A few corrections in the text and a figur
A new quadruple gravitational lens from the Hyper Suprime-Cam Survey: the puzzle of HSC~J115252+004733
We report the serendipitous discovery of a quadruply lensed source at , HSC~J115252+004733, from the Hyper Suprime-Cam (HSC) Survey. The
source is lensed by an early-type galaxy at and a satellite
galaxy. Here, we investigate the properties of the source by studying its size
and luminosity from the imaging and the luminosity and velocity width of the
Ly- line from the spectrum. Our analyses suggest that the source is
most probably a low-luminosity active galactic nucleus (LLAGN) but the
possibility of it being a compact bright galaxy (e.g., a Lyman- emitter
or Lyman Break Galaxy) cannot be excluded. The brighter pair of lensed images
appears point-like except in the HSC -band (with a seeing ). The
extended emission in the -band image could be due to the host galaxy
underneath the AGN, or alternatively, due to a highly compact lensed galaxy
(without AGN) which appears point-like in all bands except in -band. We also
find that the flux ratio of the brighter pair of images is different in the
Ks-band compared to optical wavelengths. Phenomena such as differential
extinction and intrinsic variability cannot explain this chromatic variation.
While microlensing from stars in the foreground galaxy is less likely to be the
cause, it cannot be ruled out completely. If the galaxy hosts an AGN, then this
represents the highest redshift quadruply imaged AGN known to date, enabling
study of a distant LLAGN. Discovery of this unusually compact and faint source
demonstrates the potential of the HSC survey.Comment: 9 pages, 7 figures, 3 Tables, MNRAS accepted, text reduce
Sumo Puff: Tidal Debris or Disturbed Ultra-Diffuse Galaxy?
We report the discovery of a diffuse stellar cloud with an angular extent
, which we term "Sumo Puff", in data from the Hyper
Suprime-Cam Subaru Strategic Program (HSC-SSP). While we do not have a redshift
for this object, it is in close angular proximity to a post-merger galaxy at
redshift and is projected within a few virial radii (assuming
similar redshifts) of two other galaxies, which we use to
bracket a potential redshift range of . The object's light
distribution is flat, as characterized by a low Sersic index (). It
has a low central -band surface brightness of mag
arcsec, large effective radius of (
kpc at and kpc at ), and an elongated
morphology (). Its red color () is consistent with a
passively evolving stellar population and similar to the nearby post-merger
galaxy, and we may see tidal material connecting Sumo Puff with this galaxy. We
offer two possible interpretations for the nature of this object: (1) it is an
extreme, galaxy-size tidal feature associated with a recent merger event, or
(2) it is a foreground dwarf galaxy with properties consistent with a quenched,
disturbed ultra-diffuse galaxy. We present a qualitative comparison with
simulations that demonstrates the feasibility of forming a structure similar to
this object in a merger event. Follow-up spectroscopy and/or deeper imaging to
confirm the presence of the bridge of tidal material will be necessary to
reveal the true nature of this object.Comment: 10 pages, 5 figures, submitted to PASJ for the HSC-SSP special issu
Absorption Line Survey of H3+ toward the Galactic Center Sources I. GCS 3-2 and GC IRS3
We present high-resolution (R = 20000) spectroscopy of H3+ absorption toward
the luminous Galactic center sources GCS 3-2 and GC IRS 3. With the efficient
wavelength coverage afforded by Subaru IRCS, six absorption lines of H3+ have
been detected in each source from 3.5 to 4.0 um, three of which are new. In
particular the 3.543 um absorption line of the R(3, 3)^l transition arising
from the metastable (J, K) = (3, 3) state has been tentatively detected for the
first time in the interstellar medium, where previous observations of H3+ had
been limited to absorption lines from the lowest levels: (J, K) = (1, 0) of
ortho-H3+ and (1, 1) of para-H3+. The H3+ absorption toward the Galactic center
takes place in dense and diffuse clouds along the line of sight as well as the
molecular complex close to the Galactic nucleus. At least four kinematic
components are found in the H3+ absorption lines. We suggest identifications of
the velocity components with those of HI, CO, and H2CO previously reported from
radio and infrared observations. H3+ components with velocities that match
those of weak and sharp CO and H2CO lines are attributed to diffuse clouds. Our
observation has revealed a striking difference between the absorption profiles
of H3+ and CO, demonstrating that the spectroscopy of H3+ provides information
complementary to that obtained from CO spectroscopy. The tentative detection of
the R(3, 3)^l line and the non-detection of spectral lines from other J > 1
levels provide observational evidence for the metastability of the (3, 3)
level, which is theoretically expected. This suggests that other metastable J =
K levels with higher J may also be populated.Comment: 18 pages, 7 figures, To appear in Publications of the Astronomical
Society of Japan vol. 54 no.
All-electron GW calculation based on the LAPW method: application to wurtzite ZnO
We present a new, all-electron implementation of the GW approximation and
apply it to wurtzite ZnO. Eigenfunctions computed in the local-density
approximation (LDA) by the full-potential linearized augmented-plane-wave
(LAPW) or the linearized muffin-tin-orbital (LMTO) method supply the input for
generating the Green function G and the screened Coulomb interaction W. A mixed
basis is used for the expansion of W, consisting of plane waves in the
interstitial region and augmented-wavefunction products in the
augmentation-sphere regions. The frequency-dependence of the dielectric
function is computed within the random-phase approximation (RPA), without a
plasmon-pole approximation. The Zn 3d orbitals are treated as valence states
within the LDA; both core and valence states are included in the self-energy
calculation. The calculated bandgap is smaller than experiment by about 1eV, in
contrast to previously reported GW results. Self-energy corrections are
orbital-dependent, and push down the deep O 2s and Zn 3d levels by about 1eV
relative to the LDA. The d level shifts closer to experiment but the size of
shift is underestimated, suggesting that the RPA overscreens localized states.Comment: 10 pages, 3 figures, submitted to Phys. Rev.
The LAOG-Planet Imaging Surveys
With the development of high contrast imaging techniques and infrared
detectors, vast efforts have been devoted during the past decade to detect and
characterize lighter, cooler and closer companions to nearby stars, and
ultimately image new planetary systems. Complementary to other observing
techniques (radial velocity, transit, micro-lensing, pulsar-timing), this
approach has opened a new astrophysical window to study the physical properties
and the formation mechanisms of brown dwarfs and planets. I here will briefly
present the observing challenge, the different observing techniques, strategies
and samples of current exoplanet imaging searches that have been selected in
the context of the LAOG-Planet Imaging Surveys. I will finally describe the
most recent results that led to the discovery of giant planets probably formed
like the ones of our solar system, offering exciting and attractive
perspectives for the future generation of deep imaging instruments.Comment: 6 pages, 5 figures, Invited talk of "Exoplanets and disks: their
formation and diversity" conference, 9-12 March 200
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