2,899 research outputs found
Star formation associated with a large-scale infrared bubble
Using the data from the Galactic Ring Survey (GRS) and Galactic Legacy
Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), we performed a study for a
large-scale infrared bubble with a size of about 16 pc at a distance of 2.0
kpc. We present the 12CO J=1-0, 13CO J=1-0 and C18O J=1-0 observations of HII
region G53.54-0.01 (Sh2-82) obtained at the the Purple Mountain Observation
(PMO) 13.7 m radio telescope to investigate the detailed distribution of
associated molecular material. The large-scale infrared bubble shows a
half-shell morphology at 8 um. H II regions G53.54-0.01, G53.64+0.24, and
G54.09-0.06 are situated on the bubble. Comparing the radio recombination line
velocities and associated 13CO J=1-0 components of the three H II regions, we
found that the 8 um emission associated with H II region G53.54-0.01 should
belong to the foreground emission, and only overlap with the large-scale
infrared bubble in the line of sight. Three extended green objects (EGOs, the
candidate massive young stellar objects), as well as three H II regions and two
small-scale bubbles are found located in the G54.09-0.06 complex, indicating an
active massive star-forming region. C18O J=1-0 emission presents four cloud
clumps on the northeastern border of H II region G53.54-0.01. Via comparing the
spectral profiles of 12CO J=1-0, 13CO J=1-0, and C18O J=1-0 peak at each clump,
we found the collected gas in the three clumps, except for the clump coincided
with a massive YSO (IRAS 19282+1814). Using the evolutive model of H II region,
we derived that the age of H II region G53.54-0.01 is 1.5*10^6 yr. The
significant enhancement of several Class I and Class II YSOs around G53.54-0.01
indicates the presence of some recently formed stars, which may be triggered by
this H II region through the collect and collapse (CC) process.Comment: 9 pages, 6 figures, accepted for publication in A&
Constraints on Unparticle Interactions from Invisible Decays of Z, Quarkonia and Neutrinos
Unparticles (\U) interact weakly with particles. The direct signature of
unparticles will be in the form of missing energy. We study constraints on
unparticle interactions using totally invisible decay modes of , vector
quarkonia and neutrinos. The constraints on the unparticle interaction
scale \Lambda_\U are very sensitive to the dimension d_\U of the
unparticles. From invisible and decays, we find that with d_\U close
to 1 for vector \U, the unparticle scale \Lambda_\U can be more than
TeV, and for d_\U around 2, the scale can be lower than one TeV. From
invisible neutrino decays, we find that if d_\U is close to 3/2, the scale
can be more than the Planck mass, but with d_\U around 2 the scale can be as
low as a few hundred GeV. We also study the possibility of using V (Z)\to
\gamma + \U to constrain unparticle interactions, and find that present data
give weak constraints.Comment: 12 pages, 4 figures, version to appear in JHEP
Mini-jet thermalization and diffusion of transverse momentum correlation in high-energy heavy-ion collisions
Transverse momentum correlation in azimuthal angle of produced hadrons due to
mini-jets are studied first within the HIJING Monte Carlo model in high-energy
heavy-ion collisions. Jet quenching in the early stage of thermalization is
shown to lead to significant diffusion (broadening) of the correlation.
Evolution of the transverse momentum density fluctuation that gives rise to
such correlation in azimuthal angle in the later stage of heavy-ion collisions
is further investigated within a linearized diffusion-like equation and is
shown to be determined by the shear viscosity of the evolving dense matter.
Such a diffusion equation for the transverse momentum fluctuation is solved
with initial values given by HIJING and together with the hydrodynamic equation
for the bulk medium. The final transverse momentum correlation in azimuthal
angle is calculated along the freeze-out hyper-surface and is found further
diffused for larger values of shear viscosity to entropy density ratio . Therefore the final transverse momentum correlation in azimuthal
angle can be used to study the thermalization of mini-jets in the early stage
of heavy-ion collisions and the viscous effect in the hydrodynamic evolution of
the strongly coupled quark gluon plasma.Comment: RevTex 4, 4 pages and 2 figures, the method to determine the
fluctuation in transverse fluid velocity in the initial time of the hydro
evolution has been improved. The relevant parts have been rewritten with some
discussions and references adde
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