arXiv subjects

Ye Xu

Publications and source records attributed to Ye Xu.

117 records · Page 7Linked to original sources

arXiv2011

C2H, HC3N and HNC Observations in OMC-2/3

For the first time, the OMC-2/3 region was mapped in C2H(1-0), HC3N(10-9) and HNC(1-0) lines. In general, the emissions from all the three molecular species reveal an extended filamentary structure. The distribution of C2H cores almost follows that of the 1300 $μ$m condensations, which might suggest that C2H is a good tracer to study the core structure of molecular clouds. The core masses traced by HNC are rather flat, ranging from 18.8 to 49.5 $M_{\odot}$, while present a large span for those from C2H, ranging from 6.4 to 36.0 $M_{\odot}$. The line widths of both HNC and C2H look very similar, and both are wider than that of HC3N. The line widths of the three lines are all wider than those from dark clouds, implying that the former is more active than the latter, and has larger turbulence caused by winds and UV radiation from the surrounding massive stars.

astro-ph.SR↗

arXiv2010

Revising the kinematics of 12GHz CH3OH masers in W3(OH)

We derive accurate proper motions of the CH3OH 12 GHz masers towards the W3(OH) UCHII region, employing seven epochs of VLBA observations spanning a time interval of about 10 yr. The achieved velocity accuracy is of the order of 0.1 km/s, adequate to precisely measure the relative velocities of most of the 12 GHz masers in W3(OH), with amplitude varying in the range 0.3 - 3 km/s. Towards W3(OH), the most intense 12 GHz masers concentrate in a small area towards the north (the northern clump) of the UCHII region. We have compared the proper motions of the CH3OH 12 GHz masers with those (derived from literature data) of the OH 6035 MHz masers, emitting from the same region of the methanol masers. In the northern clump, the two maser emissions emerge from nearby (but likely distinct) cloudlets of masing gas with, in general, a rather smooth variation of line-of-sight and sky-projected velocities, which suggests some connection of the environments and kinematics traced by both maser types. The conical outflow model, previously proposed to account for the 12 GHz maser kinematics in the northern clump, does not reproduce the new, accurate measurements of 12 GHz maser proper motions and has to be rejected. We focus on the subset of 12 GHz masers of the northern clump belonging to the "linear structure at P.A. = 130-140 degree", whose regular variation of LSR velocities with position presents evidence for some ordered motion. We show that the 3-dimensional velocities of this "linear distribution" of 12GHz masers can be well fitted considering a flat, rotating disk, seen almost edge-on.

astro-ph.SR↗

arXiv2009

A Search for Infall Evidence in EGOs I: the Northern Sample

We report the first systematic survey of molecular lines (including HCO+ (1-0) and 12CO, 13CO, C18O (1-0) lines at 3 mm band) towards a new sample of 88 massive young stellar object (MYSO) candidates associated with ongoing outflows (known as extended green objects or EGOs) identified from the Spitzer GLIMPSE survey in the northern hemisphere with the PMO-13.7 m radio telescope. By analyzing the asymmetries of the optically thick line HCO+ for 69 of 72 EGOs with HCO+ detection, we found 29 sources with blue asymmetric profiles and 19 sources with red asymmetric profiles. This results in a blue excess of 0.14, seen as a signature of collapsing cores in the observed EGO sample. The relatively small blue excess measured in our full sample due to that the observed EGOs are mostly dominated by outflows and at an earlier evolutionary phase associated with IRDCs and 6.7 GHz methanol masers. The physical properties of clouds surrounding EGOs derived from CO lines are similar to those of massive clumps wherein the massive star forming cores associated with EGOs possibly embedded. The infall velocities and mass infall rates derived for 20 infall candidates are also consistent with the typical values found in MYSOs. Thus our observations further support the speculation of Cyganowski et al. (2008) that EGOs trace a population with ongoing outflow activity and active rapid accretion stage of massive protostellar evolution from a statistical view, although there maybe have limitations due to single-pointing survey with a large beam.

astro-ph.SR↗

arXiv2009

A multiwavelength study of massive star-forming region IRAS 22506+5944

We present a multi-line study of the massive star-forming region IRAS 22506+5944. A new 6.7 GHz methanol maser was detected. 12CO, 13CO, C18O and HCO+ J = 1-0 transition observations reveal a star formation complex consisting mainly of two cores. The dominant core has a mass of more than 200 solar mass, while another one only about 35 solar mass. Both cores are obviously at different evolutionary stages. A 12CO energetic bipolar outflow was detected with an outflow mass of about 15 solar mass.

astro-ph.SR↗

arXiv2009

Probing unparticle theory via lepton flavor violating process $J/ψ\to ll'$ at BESIII

The lepton flavor violating process $J/ψ\to ll' (l\neq l')$ serves as an ideal place to probe the unparticle theory. Such process can only occur at loop level in the Standard model (SM), so that should be very suppressed, by contrast in unparticle scenario, it happens at tree level and its contribution may be sizable for practical measurement. Moreover, the BESIII will offer the largest database on $J/ψ$ which makes more accurate measurements possible. Furthermore, for such purely leptonic decays background is relatively low and signal would be cleaner. Our work carefully investigates the possibility of observing such processes from both theoretical and experimental aspects.

hep-ph↗

arXiv2009

Improving Application of Bayesian Neural Networks to Discriminate Neutrino Events from Backgrounds in Reactor Neutrino Experiments

The application of Bayesian Neural Networks(BNN) to discriminate neutrino events from backgrounds in reactor neutrino experiments has been described in Ref.\cite{key-1}. In the paper, BNN are also used to identify neutrino events in reactor neutrino experiments, but the numbers of photoelectrons received by PMTs are used as inputs to BNN in the paper, not the reconstructed energy and position of events. The samples of neutrino events and three major backgrounds from the Monte-Carlo simulation of a toy detector are generated in the signal region. Compared to the BNN method in Ref.\cite{key-1}, more $^{8}$He/$^{9}$Li background and uncorrelated background in the signal region can be rejected by the BNN method in the paper, but more fast neutron background events in the signal region are unidentified using the BNN method in the paper. The uncorrelated background to signal ratio and the $^{8}$He/$^{9}$Li background to signal ratio are significantly improved using the BNN method in the paper in comparison with the BNN method in Ref.\cite{key-1}. But the fast neutron background to signal ratio in the signal region is a bit larger than the one in Ref.\cite{key-1}.

physics.data-an↗

arXiv2008

Applying Bayesian Neural Network to Determine Neutrino Incoming Direction in Reactor Neutrino Experiments and Supernova Explosion Location by Scintillator Detectors

In the paper, it is discussed by using Monte-Carlo simulation that the Bayesian Neural Network(BNN) is applied to determine neutrino incoming direction in reactor neutrino experiments and supernova explosion location by scintillator detectors. As a result, compared to the method in Ref.\cite{key-1}, the uncertainty on the measurement of the neutrino direction using BNN is significantly improved. The uncertainty on the measurement of the reactor neutrino direction is about 1.0$^\circ$ at the 68.3% C.L., and the one in the case of supernova neutrino is about 0.6$^\circ$ at the 68.3% C.L.. Compared to the method in Ref.\cite{key-1}, the uncertainty attainable by using BNN reduces by a factor of about 20. And compared to the Super-Kamiokande experiment(SK), it reduces by a factor of about 8.

physics.data-an↗

arXiv2008

Applying Bayesian Neural Networks to Separate Neutrino Events from Backgrounds in Reactor Neutrino Experiments

A toy detector has been designed to simulate central detectors in reactor neutrino experiments in the paper. The samples of neutrino events and three major backgrounds from the Monte-Carlo simulation of the toy detector are generated in the signal region. The Bayesian Neural Networks(BNN) are applied to separate neutrino events from backgrounds in reactor neutrino experiments. As a result, the most neutrino events and uncorrelated background events in the signal region can be identified with BNN, and the part events each of the fast neutron and $^{8}$He/$^{9}$Li backgrounds in the signal region can be identified with BNN. Then, the signal to noise ratio in the signal region is enhanced with BNN. The neutrino discrimination increases with the increase of the neutrino rate in the training sample. However, the background discriminations decrease with the decrease of the background rate in the training sample.

physics.data-an↗

arXiv2008

Applying Bayesian Neural Networks to Event Reconstruction in Reactor Neutrino Experiments

A toy detector has been designed to simulate central detectors in reactor neutrino experiments in the paper. The electron samples from the Monte-Carlo simulation of the toy detector have been reconstructed by the method of Bayesian neural networks (BNN) and the standard algorithm, a maximum likelihood method (MLD), respectively. The result of the event reconstruction using BNN has been compared with the one using MLD. Compared to MLD, the uncertainties of the electron vertex are not improved, but the energy resolutions are significantly improved using BNN. And the improvement is more obvious for the high energy electrons than the low energy ones.

physics.data-an↗