379 research outputs found
Spatially Resolving Substructures within the Massive Envelope around an Intermediate-mass Protostar: MMS 6/OMC-3
With the Submillimeter Array, the brightest (sub)millimeter continuum source
in the OMC-2/3 region, MMS 6, has been observed in the 850 um continuum
emission with approximately 10 times better angular resolution than previous
studies (~0.3"; ~120 AU at Orion). The deconvolved size, the mass, and the
column density of MMS 6-main are estimated to be 0.32"x0.29" (132 AUx120 AU),
0.29 Mo, and 2.1x10^{25} cm^{-2}, respectively. The estimated extremely high
mean number density, 1.5x10^{10} cm^{-3}, suggests that MMS 6-main is likely
optically thick at 850 um. We compare our observational data with three
theoretical core models: prestellar core, protostellar core + disk-like
structure, and first adiabatic core. These comparisons clearly show that the
observational data cannot be modeled as a simple prestellar core with a gas
temperature of 20 K. A self-luminous source is necessary to explain the
observed flux density in the (sub)millimeter wavelengths. Our recent detection
of a very compact and energetic outflow in the CO (3-2) and HCN (4-3) lines,
supports the presence of a protostar. We suggest that MMS 6 is one of the first
cases of an intermediate mass protostellar core at an extremely young stage. In
addition to the MMS 6-main peak, we have also spatially resolved a number of
spiky structures and sub-clumps, distributed over the central 1000 AU. The
masses of these sub-clumps are estimated to be 0.066-0.073 Mo, which are on the
order of brown dwarf masses. Higher angular resolution and higher sensitivity
observations with ALMA and EVLA will reveal the origin and nature of these
structures such as whether they are originated from fragmentations, spiral
arms, or inhomogeneity within the disk-like structures/envelope.Comment: Accepted to Ap
A Linear Programming Approach for Molecular QSAR analysis
Small molecules in chemistry can be represented as graphs. In a quantitative structure-activity relationship (QSAR) analysis, the central task is to find a regression function that predicts the activity of the molecule in high accuracy. Setting a QSAR as a primal target, we propose a new linear programming approach to the graph-based regression problem. Our method extends the graph classification algorithm by Kudo et al. (NIPS 2004), which is a combination of boosting and graph mining. Instead of sequential multiplicative updates, we employ the linear programming boosting (LP) for regression. The LP approach allows to include inequality constraints for the parameter vector, which turns out to be particularly useful in QSAR tasks where activity values are sometimes unavailable. Furthermore, the efficiency is improved significantly by employing multiple pricing
Angular Momentum Exchange by Gravitational Torques and Infall in the Circumbinary Disk of the Protostellar System L1551 NE
We report the ALMA observation of the Class I binary protostellar system
L1551 NE in the 0.9-mm continuum, C18O (3-2), and 13CO (3-2) lines at a ~1.6
times higher resolution and a ~6 times higher sensitivity than those of our
previous SMA observations, which revealed a r ~300 AU-scale circumbinary disk
in Keplerian rotation. The 0.9-mm continuum shows two opposing U-shaped
brightenings in the circumbinary disk, and exhibits a depression between the
circumbinary disk and the circumstellar disk of the primary protostar. The
molecular lines trace non-axisymmetric deviations from Keplerian rotation in
the circumbinary disk at higher velocities relative to the systemic velocity,
where our previous SMA observations could not detect the lines. In addition, we
detect inward motion along the minor axis of the circumbinary disk. To explain
the newly-observed features, we performed a numerical simulation of gas orbits
in a Roche potential tailored to the inferred properties of L1551 NE. The
observed U-shaped dust features coincide with locations where gravitational
torques from the central binary system are predicted to impart angular momentum
to the circumbinary disk, producing shocks and hence density enhancements seen
as a pair of spiral arms. The observed inward gas motion coincides with
locations where angular momentum is predicted to be lowered by the
gravitational torques. The good agreement between our observation and model
indicates that gravitational torques from the binary stars constitute the
primary driver for exchanging angular momentum so as to permit infall through
the circumbinary disk of L1551 NE.Comment: 38 pages, 11 figures, accepted for publication in Ap
Space-efficient Feature Maps for String Alignment Kernels
String kernels are attractive data analysis tools for analyzing string data.
Among them, alignment kernels are known for their high prediction accuracies in
string classifications when tested in combination with SVM in various
applications. However, alignment kernels have a crucial drawback in that they
scale poorly due to their quadratic computation complexity in the number of
input strings, which limits large-scale applications in practice. We address
this need by presenting the first approximation for string alignment kernels,
which we call space-efficient feature maps for edit distance with moves
(SFMEDM), by leveraging a metric embedding named edit sensitive parsing (ESP)
and feature maps (FMs) of random Fourier features (RFFs) for large-scale string
analyses. The original FMs for RFFs consume a huge amount of memory
proportional to the dimension d of input vectors and the dimension D of output
vectors, which prohibits its large-scale applications. We present novel
space-efficient feature maps (SFMs) of RFFs for a space reduction from O(dD) of
the original FMs to O(d) of SFMs with a theoretical guarantee with respect to
concentration bounds. We experimentally test SFMEDM on its ability to learn SVM
for large-scale string classifications with various massive string data, and we
demonstrate the superior performance of SFMEDM with respect to prediction
accuracy, scalability and computation efficiency.Comment: Full version for ICDM'19 pape
Evolutionary Status of Brightest and Youngest Source in the Orion Molecular Cloud-3 Region
The brightest continuum source in the Orion Molecular Cloud-3 region (OMC-3),
MMS 6, was observed with the Very Large Array (VLA), the Nobeyama Millimeter
Array (NMA), and the Submillimeter Array (SMA). Our data were supplemented by
near- to mid-infrared archival data taken by Spitzer Space Telescope. The
compact continuum source, MMS 6-main, was detected with an H_2 mass of 3.0 Msun
with a size of 510 AU. Despite its compact and well condensed appearance,
neither clear CO outflow, radio jet, nor infrared sources (at a wave-length
shorter than 8 um) were detected at MMS 6-main even with the present
high-spatial resolution and high-sensitivity observations. The derived H_2
column density, 2.6x10^25 cm^-2, corresponds to a visual extinction of
A_v~15000 mag., and the derived number density is at least two orders of
magnitude higher than for the other OMC-2/3 continuum sources. The volume
density profile of the source was estimated to have a power-law index of 2 or
steeper down to a radius of ~450 AU. The time scale to form a protostar at the
center or the time scale elapsed after its formation is estimated to be 830 to
7600 yr. This is much shorter than the typical lifetime of the Class 0/I
protostars, which is ~10^(4-5) yr, suggesting that MMS 6-main is probably in
either the earliest stage of the proto-stellar core or in the latest stage of
the pre-stellar phase.Comment: 34 pages, 7 figures, accepted to Ap
FORMATION OF THE UNEQUAL-MASS BINARY PROTOSTARS IN L1551NE BY ROTATIONALLY DRIVEN FRAGMENTATION
We present observations at 7 mm that fully resolve the two circumstellar
disks, and a reanalyses of archival observations at 3.5 cm that resolve along
their major axes the two ionized jets, of the class I binary protostellar
system L1551 NE. We show that the two circumstellar disks are better fit by a
shallow inner and steep outer power-law than a truncated power-law. The two
disks have very different transition radii between their inner and outer
regions of 18.6 AU and 8.9 AU respectively. Assuming that they are
intrinsically circular and geometrically thin, we find that the two
circumstellar disks are parallel with each other and orthogonal in projection
to their respective ionized jets. Furthermore, the two disks are closely
aligned if not parallel with their circumbinary disk. Over an interval of
10 yr, source B (possessing the circumsecondary disk) has moved
northwards with respect to and likely away from source A, indicating an orbital
motion in the same direction as the rotational motion of their circumbinary
disk. All the aforementioned elements therefore share the same axis for their
angular momentum, indicating that L1551 NE is a product of rotationally-driven
fragmentation of its parental core. Assuming a circular orbit, the relative
disk sizes are compatible with theoretical predictions for tidal truncation by
a binary system having a mass ratio of 0.2, in agreement with the
reported relative separations of the two protostars from the center of their
circumbinary disk. The transition radii of both disks, however, are a factor of
1.5 smaller than their predicted tidally-truncated radii.Comment: Accepted for publication in Ap
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