16,106 research outputs found
Gravitational Slingshot of Young Massive Stars in Orion
The Orion Nebula Cluster (ONC) is the nearest region of massive star
formation and thus a crucial testing ground for theoretical models. Of
particular interest amongst the ONC's ~1000 members are: \theta^1 Ori C, the
most massive binary in the cluster with stars of masses 38 and 9 MSun (Kraus et
al. 2009); the Becklin-Neugebauer (BN) object, a 30 km/s runaway star of ~8
MSun (Tan 2004); and the Kleinmann-Low (KL) nebula protostar, a
highly-obscured, ~15 MSun object still accreting gas while also driving a
powerful, apparently "explosive" outflow (Allen & Burton 1993). The unusual
behavior of BN and KL is much debated: How did BN acquire its high velocity?
How is this related to massive star formation in the KL nebula? Here we report
the results of a systematic survey using ~ 10^7 numerical experiments of
gravitational interactions of the \theta^1C and BN stars. We show that
dynamical ejection of BN from this triple system at its observed velocity
leaves behind a binary with total energy and eccentricity matching those
observed for \theta^1C. Five other observed properties of \theta^C are also
consistent with it having ejected BN and altogether we estimate there is only a
<~ 10^{-5} probability that \theta^1C has these properties by chance. We
conclude that BN was dynamically ejected from the \theta^1C system about 4,500
years ago. BN has then plowed through the KL massive-star-forming core within
the last 1,000 years causing its recently-enhanced accretion and outflow
activity.Comment: 16 pages, 9 figures, 1 table, accepted to Ap
IN-SYNC. VIII. Primordial Disk Frequencies in NGC 1333, IC 348, and the Orion A Molecular Cloud
In this paper, we address two issues related to primordial disk evolution in
three clusters (NGC 1333, IC 348, and Orion A) observed by the INfrared Spectra
of Young Nebulous Clusters (IN-SYNC) project. First, in each cluster, averaged
over the spread of age, we investigate how disk lifetime is dependent on
stellar mass. The general relation in IC 348 and Orion A is that primordial
disks around intermediate mass stars (2--5) evolve faster than those
around loss mass stars (0.1--1), which is consistent with previous
results. However, considering only low mass stars, we do not find a significant
dependence of disk frequency on stellar mass. These results can help to better
constrain theories on gas giant planet formation timescales. Secondly, in the
Orion A molecular cloud, in the mass range of 0.35--0.7, we provide
the most robust evidence to date for disk evolution within a single cluster
exhibiting modest age spread. By using surface gravity as an age indicator and
employing 4.5 excess as a primordial disk diagnostic, we observe a
trend of decreasing disk frequency for older stars. The detection of
intra-cluster disk evolution in NGC 1333 and IC 348 is tentative, since the
slight decrease of disk frequency for older stars is a less than 1-
effect.Comment: 25 pages, 26 figures; submitted for publication (ApJ
Investigating the PageRank and sequence prediction based approaches for next page prediction
Discovering unseen patterns from web clickstream is an upcoming research area. One of the meaningful approaches for making predictions is using sequence prediction that is typically the improved compact prediction tree (CPT+). However, to increase this method's effectiveness, combining it with at least other methods is necessary. This work investigates such PageRank-based methods related to sequence prediction as All-K-Markov, DG, Markov 1st, CPT, CPT+. The experimental results proved that the integration of CPT+ and PageRank is the right solution for next page prediction in terms of accuracy, which is more than a standard method of approximately 0.0621%. Still, the size of the newly created sequence database is reduced up to 35%. Furthermore, our proposed solution has an accuracy that is much higher than other ones. It is intriguing for the next phase (testing one) to make the next page prediction in terms of time performance
The Core Mass Function in the Massive Protocluster G286.21+0.17 revealed by ALMA
We study the core mass function (CMF) of the massive protocluster
G286.21+0.17 with the Atacama Large Millimeter/submillimeter Array via 1.3~mm
continuum emission at a resolution of 1.0\arcsec\ (2500~au). We have mapped a
field of 5.3\arcmin5.3\arcmin\ centered on the protocluster clump. We
measure the CMF in the central region, exploring various core detection
algorithms, which give source numbers ranging from 60 to 125, depending on
parameter selection. We estimate completeness corrections due to imperfect flux
recovery and core identification via artificial core insertion experiments. For
masses , the fiducial dendrogram-identified CMF can be fit
with a power law of the form
with , slightly shallower than, but still consistent with, the
index of the Salpeter stellar initial mass function of 1.35.
Clumpfind-identified CMFs are significantly shallower with
. While raw CMFs show a peak near ,
completeness-corrected CMFs are consistent with a single power law extending
down to , with only a tentative indication of a shallowing
of the slope around . We discuss the implications of these
results for star and star cluster formation theories.Comment: 11 pages, accepted by Ap
IN-SYNC. VII. Evidence for a decreasing spectroscopic binary fraction from 1 to 100 Myr within the IN-SYNC sample
We study the occurrence of spectroscopic binaries in young star-forming
regions using the INfrared Spectroscopy of Young Nebulous Clusters(IN-SYNC)
survey, carried out in SDSS-III with the APOGEE spectrograph. Multi-epoch
observations of thousands of low-mass stars in Orion A, NGC 2264, NGC 1333, IC
348, and the Pleiades have been carried out, yielding H-band spectra with a
nominal resolution of R=22,500 for sources with H 12 mag. Radial velocity
precisions of 0.3 were achieved, which we use to identify
radial velocity variations indicative of undetected companions. We use Monte
Carlo simulations to assess the types of spectroscopic binaries to which we are
sensitive, finding sensitivity to binaries with orbital periods d,
for stars with and 100 . Using Bayesian inference, we find evidence
for a decline in the spectroscopic binary fraction, by a factor of 3-4 from the
age of our pre-main-sequence sample to the Pleiades age . The significance of
this decline is weakened if spot-induced radial-velocity jitter is strong in
the sample, and is only marginally significant when comparing any one of the
pre-main-sequence clusters against the Pleiades. However, the same decline in
both sense and magnitude is found for each of the five pre-main-sequence
clusters, and the decline reaches statistical significance of greater than 95%
confidence when considering the pre-main-sequence clusters jointly. Our results
suggest that dynamical processes disrupt the widest spectroscopic binaries
( d) as clusters age, indicating that this
occurs early in the stars' evolution, while they still reside within their
nascent clusters.Comment: 21 pages, 9 Figure
A Vertically Resolved MSE Framework Highlights the Role of the Boundary Layer in Convective Self-Aggregation
Convective self-aggregation refers to a phenomenon in which random convection
can self-organize into large-scale clusters over an ocean surface with uniform
temperature in cloud-resolving models. Previous literature studies convective
aggregation primarily by analyzing vertically integrated (VI) moist static
energy (MSE) variance. That is the global MSE variance, including both the
local MSE variance at a given altitude and the covariance of MSE anomalies
between different altitudes. Here we present a vertically resolved (VR) MSE
framework that focuses on the local MSE variance to study convective
self-aggregation. Using a cloud-resolving simulation, we show that the
development of self-aggregation is associated with an increase of local MSE
variance, and that the diabatic and adiabatic generation of the MSE variance is
mainly dominated by the boundary layer (BL). The results agree with recent
numerical simulation results and the available potential energy analyses
showing that the BL plays a key role in the development of self-aggregation. We
further present a detailed comparison between the global and local MSE variance
frameworks in their mathematical formulation and diagnostic results,
highlighting their differences.Comment: 50 pages, 2 tables, 12 figures, submitted to the Journal of the
Atmospheric Science
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