652 research outputs found
A Short Guide to Debris Disk Spectroscopy
Multi-wavelength spectroscopy can be used to constrain the dust and gas
properties in debris disks. Circumstellar dust absorbs and scatters incident
stellar light. The scattered light is sometimes resolved spatially at visual
and near-infrared wavelengths using high contrast imaging techniques that
suppress light from the central star. The thermal emission is inferred from
infrared through submillimeter excess emission that may be 1-2 orders of
magnitude brighter than the stellar photosphere alone. If the disk is not
spatially resolved, then the radial distribution of the dust can be inferred
from Spectral Energy Distribution (SED) modeling. If the grains are
sufficiently small and warm, then their composition can be determined from
mid-infrared spectroscopy. Otherwise, their composition may be determined from
reflectance and/or far-infrared spectroscopy. Atomic and molecular gas absorb
and resonantly scatter stellar light. Since the gas is believed to be
secondary, detailed analysis analysis of the gas distribution, kinematics, and
composition may also shed light on the dust composition and processing history.Comment: 6 pages, 2nd Subaru International Conference on Exoplanets and Disks:
Their Formation and Diversity, Keauhou - Hawaii, 9-12 March 200
Constraints on core-collapse supernova progenitors from explosion site integral field spectroscopy
Observationally, supernovae (SNe) are divided into subclasses pertaining to
their distinct characteristics. This diversity reflects the diversity in the
progenitor stars. It is not entirely clear how different evolutionary paths
leading massive stars to become a SN are governed by fundamental parameters
such as progenitor initial mass and metallicity. This paper places constraints
on progenitor initial mass and metallicity in distinct core-collapse SN
subclasses, through a study of the parent stellar populations at the explosion
sites. Integral field spectroscopy (IFS) of 83 nearby SN explosion sites with a
median distance of 18 Mpc has been collected and analysed, enabling detection
and spectral extraction of the parent stellar population of SN progenitors.
From the parent stellar population spectrum, the initial mass and metallicity
of the coeval progenitor are derived by means of comparison to simple stellar
population models and strong-line methods. Additionally, near-infrared IFS was
employed to characterise the star formation history at the explosion sites. No
significant metallicity differences are observed among distinct SN types. The
typical progenitor mass is found to be highest for SN Ic, followed by type Ib,
then types IIb and II. SN IIn is the least associated with young stellar
populations and thus massive progenitors. However, statistically significant
differences in progenitor initial mass are observed only when comparing SNe IIn
with other subclasses. Stripped-envelope SN progenitors with initial mass
estimate lower than 25~ are found; these are thought to be the result
of binary progenitors. Confirming previous studies, these results support the
notion that core-collapse SN progenitors cannot arise from single-star channel
only, and both single and binary channels are at play in the production of
core-collapse SNe. [ABRIDGED]Comment: 18 pages, 10 figures, accepted to A&
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
Designing and Developing Dynamic Decision Support Information for Disaster Response
Recently, Japan has been struck by extremely heavy rains and serious floods. To plan for disaster response, it is needed to consider various information such as precipitation, water level of rivers, weather forecasts, and so on. However, it requires high skill to integrate this information to utilize. Our study aims to provide the decision support information for both the national and the local governments by dynamic risk analysis to enforce disaster resilience. To demonstrate the effectiveness of disaster dynamics analysis, we have developed the “Dynamic Decision Support System for Disaster Response (DDS4D)”. DDS4D synthesizes natural observation data, social observation data, and geospatial data to provide decision support information that fits decision maker's the situational awareness in real time. Verifying several information products generated by DDS4D in the actual flood in Japan, we confirmed that they could support decision making of government.</p
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
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