177 research outputs found
Large-field CO(1--0) observations toward the Galactic historical supernova remnants: a large cavity around Tycho's supernova remnant
The investigation of the interaction between the supernova remnants (SNRs)
and interstellar gas is not only necessary to improve our knowledge of SNRs,
but also to understand the nature of the progenitor systems. As a part of the
Milky Way Imaging Scroll Painting CO line survey (MWISP), we study the
interstellar gas surrounding the Galactic historical SNRs, using the PMO
13.7-meter telescope. In this work, we present large-field
(32) and high-sensitivity CO(1-0) molecular line
observations toward Tycho's SNR. The CO observations reveal, from the outside
in, large molecular clouds, stream-like structures, and an inner rim around
Tycho's SNR. We derived the basic properties (column density, mass, and
kinematics) of these objects based on the CO observations. The large molecular
clouds individually show an arc toward the remnant center, outlining a large
cavity with radii of 0.30.6 (or 13 pc 27
pc at a distance of 2.5 kpc) around the remnant. The CO line broadenings and
asymmetries detected in the surrounding clouds, the observed expansion of the
cavity, in concert with enhanced CO(2-1)/(1-0) intensity ratio detected
in previous studies, suggest the interaction of the large cavity with a wind in
the region. After excluding the scenario of a large bubble produced by bright
massive stars, we suggest that the large cavity could be explained by accretion
wind from the progenitor system of Tycho's supernova. Nevertheless, the
possibility of the random distribution of a large cavity around Tycho's SNR
cannot be ruled out thus far. Further observations are needed to confirm the
physical association of the large cavity with Tycho's SNR.Comment: 15 pages, 9 figures, updated according to the A&A proo
SMA CO(2-1) Observations of CG30: A Protostellar Binary System with a High-Velocity Quadrupolar Molecular Outflow
We present interferometric observations in the 12CO (2-1) line and at 1.3 mm
dust continuum of the low-mass protostellar binary system in the cometary
globule CG30, using the Submillimeter Array. The dust continuum images resolve
two compact sources (CG30N and CG30S), with a linear separation of ~8700 AU and
total gas masses of ~1.4 and ~0.6 M_sun, respectively. With the CO images, we
discover two high-velocity bipolar molecular outflows, driven by the two
sources. The two outflows are nearly perpendicular to each other, showing a
quadrupolar morphology. The northern bipolar outflow extends along the
southeast (redshifted, with a velocity up to ~23 km/s) and northwest
(blueshifted, velocity up to ~30 km/s) directions, while the southern pair has
an orientation from southwest (blueshifted, velocity up to 13 km/s) to
northeast (redshifted, velocity up to ~41 km/s). The outflow mass of the
northern pair, driven by the higher mass source CG30N, is ~9 times larger than
that of the southern pair. The discovery of the quadrupolar molecular outflow
in the CG30 protobinary system, as well as the presence of other quadrupolar
outflows associated with binary systems, demonstrate that the disks in (wide)
binary systems are not necessarily co-aligned after fragmentation.Comment: 12 pages, 3 figures, to be published by ApJL in October 200
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Role of Hydrogen Bonding in Green Fluorescent Protein-like Chromophore Emission.
The fluorescence emission from green fluorescent protein (GFP) is known to be heavily influenced by hydrogen bonding between the core fluorophore and the surrounding side chains or water molecules. Yet how to utilize this feature for modulating the fluorescence of GFP chromophore or GFP-like fluorophore still remains elusive. Here we present theoretical calculations to predict how hydrogen bonding could influence the excited states of the GFP-like fluorophores. These studies provide both a new perspective for understanding the photophysical properties of GFP as well as a solid basis for the rational design of GFP-based fluorophores
Real-Time Rotation-Invariant Face Detection with Progressive Calibration Networks
Rotation-invariant face detection, i.e. detecting faces with arbitrary
rotation-in-plane (RIP) angles, is widely required in unconstrained
applications but still remains as a challenging task, due to the large
variations of face appearances. Most existing methods compromise with speed or
accuracy to handle the large RIP variations. To address this problem more
efficiently, we propose Progressive Calibration Networks (PCN) to perform
rotation-invariant face detection in a coarse-to-fine manner. PCN consists of
three stages, each of which not only distinguishes the faces from non-faces,
but also calibrates the RIP orientation of each face candidate to upright
progressively. By dividing the calibration process into several progressive
steps and only predicting coarse orientations in early stages, PCN can achieve
precise and fast calibration. By performing binary classification of face vs.
non-face with gradually decreasing RIP ranges, PCN can accurately detect faces
with full RIP angles. Such designs lead to a real-time
rotation-invariant face detector. The experiments on multi-oriented FDDB and a
challenging subset of WIDER FACE containing rotated faces in the wild show that
our PCN achieves quite promising performance.Comment: Accepted by The IEEE Conference on Computer Vision and Pattern
Recognition (CVPR 2018). Code: \url{https://github.com/Jack-CV/PCN
OVRO N2H+ Observations of Class 0 Protostars: Constraints on the Formation of Binary Stars
We present the results of an interferometric study of the N2H+(1--0) emission
from nine nearby, isolated, low-mass protostellar cores, using the OVRO
millimeter array. The main goal of this study is the kinematic characterization
of the cores in terms of rotation, turbulence, and fragmentation. Eight of the
nine objects have compact N2H+ cores with FWHM radii of 1200 -- 3500 AU,
spatially coinciding with the thermal dust continuum emission. The only more
evolved (Class I) object in the sample (CB 188) shows only faint and extended
N2H+ emission. The mean N2H+ line width was found to be 0.37 km/s. Estimated
virial masses range from 0.3 to 1.2 M_sun. We find that thermal and turbulent
energy support are about equally important in these cores, while rotational
support is negligible. The measured velocity gradients across the cores range
from 6 to 24 km/s/pc. Assuming these gradients are produced by bulk rotation,
we find that the specific angular momenta of the observed Class 0 protostellar
cores are intermediate between those of dense (prestellar) molecular cloud
cores and the orbital angular momenta of wide PMS binary systems. There appears
to be no evolution (decrease) of angular momentum from the smallest prestellar
cores via protostellar cores to wide PMS binary systems. In the context that
most protostellar cores are assumed to fragment and form binary stars, this
means that most of the angular momentum contained in the collapse region is
transformed into orbital angular momentum of the resulting stellar binary
systems.Comment: 35 pages, 9 figures (one in color), 6 tables. Accepted by ApJ (to
appear in Nov. 2007
IRAM-PdBI Observations of Binary Protostars I: The Hierarchical System SVS13 in NGC1333
We present millimeter interferometric observations of the young stellar
object SVS13 in NCG1333 in the N2H+(1-0) line and at 1.4 and 3mm dust
continuum, using the IRAM Plateau de Bure interferometer. The results are
complemented by infrared data from the Spitzer Space Telescope. The millimeter
dust continuum images resolve four sources (A, B, C, and VLA3) in SVS13. With
the dust continuum images, we derive gas masses of 0.2-1.1 M_sun for the
sources. N2H+(1-0) line emission is detected and spatially associated with the
dust continuum sources B and VLA3. The observed mean line width is ~0.48 km/s
and the estimated virial mass is ~0.7 M_sun. By simultaneously fitting the
seven hyperfine line components of N2H+, we derive the velocity field and find
a symmetric velocity gradient of about 28 km/s/pc across sources B and VLA3,
which could be explained by core rotation. The velocity field suggests that
sources B and VLA3 are forming a physically bound protobinary system embedded
in a common N2H+ core. Spitzer images show mid-infrared emission from sources A
and C, which is spatially associated with the mm dust continuum emission. No
infrared emission is detected from source B, implying that the source is deeply
embedded. Based on the morphologies and velocity structure, we propose a
hierarchical fragmentation picture for SVS13 where the three sources (A, B, and
C) were formed by initial fragmentation of a filamentary prestellar core, while
the protobinary system (sources B and VLA3) was formed by rotational
fragmentation of a single collapsing sub-core.Comment: 26 pages, 9 figures, accepted by Ap
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