26,439 research outputs found
Infrared emission from interstellar dust cloud with two embedded sources: IRAS 19181+1349
Mid and far infrared maps of many Galactic star forming regions show multiple
peaks in close proximity, implying more than one embedded energy sources. With
the aim of understanding such interstellar clouds better, the present study
models the case of two embedded sources. A radiative transfer scheme has been
developed to deal with an uniform density dust cloud in a cylindrical geometry,
which includes isotropic scattering in addition to the emission and absorption
processes. This scheme has been applied to the Galactic star forming region
associated with IRAS 19181+1349, which shows observational evidence for two
embedded energy sources. Two independent modelling approaches have been
adopted, viz., to fit the observed spectral energy distribution (SED) best; or
to fit the various radial profiles best, as a function of wavelength. Both the
models imply remarkably similar physical parameters.Comment: 17 pages, 6 Figures, uses epsf.sty. To appear in Journal of
Astronophysics & Astronom
Star formation activity in the southern Galactic HII region G351.63-1.25
The southern Galactic high mass star-forming region, G351.6-1.3, is a HII
region-molecular cloud complex with a luminosity of 2.0 x 10^5 L_sun, located
at a distance of 2.4 kpc. In this paper, we focus on the investigation of the
associated HII region, embedded cluster and the interstellar medium in the
vicinity of G351.6-1.3. We address the identification of exciting source(s) as
well as the census of stellar populations. The ionised gas distribution has
been mapped using the Giant Metrewave Radio Telescope (GMRT), India at three
continuum frequencies: 1280, 610 and 325 MHz. The HII region shows an elongated
morphology and the 1280 MHz map comprises six resolved high density regions
encompassed by diffuse emission spanning 1.4 pc x 1.0 pc. The zero age
main-sequence (ZAMS) spectral type of the brightest radio core is O7.5. We have
carried out near-infrared observations in the JHKs bands using the SIRIUS
instrument on the 1.4 m Infrared Survey Facility (IRSF) telescope. The
near-infrared images reveal the presence of a cluster embedded in nebulous
fan-shaped emission. The log-normal slope of the K-band luminosity function of
the embedded cluster is found to be 0.27 +- 0.03 and the fraction of the
near-infrared excess stars is estimated to be 43%. These indicate that the age
of the cluster is consistent with 1 Myr. The champagne flow model from a flat,
thin molecular cloud is used to explain the morphology of radio emission with
respect to the millimetre cloud and infrared brightness.Comment: 18 pages, 8 figures, To be published in MNRA
Radio and infrared study of the star forming region IRAS 20286+4105
A multi-wavelength investigation of the star forming complex IRAS 20286+4105,
located in the Cygnus-X region, is presented here. Near-infrared K-band data is
used to revisit the cluster / stellar group identified in previous studies. The
radio continuum observations, at 610 and 1280 MHz show the presence of a HII
region possibly powered by a star of spectral type B0 - B0.5. The cometary
morphology of the ionized region is explained by invoking the bow-shock model
where the likely association with a nearby supernova remnant is also explored.
A compact radio knot with non-thermal spectral index is detected towards the
centre of the cloud. Mid-infrared data from the Spitzer Legacy Survey of the
Cygnus-X region show the presence of six Class I YSOs inside the cloud. Thermal
dust emission in this complex is modelled using Herschel far-infrared data to
generate dust temperature and column density maps. Herschel images also show
the presence of two clumps in this region, the masses of which are estimated to
be {\sim} 175 M{\sun} and 30 M{\sun}. The mass-radius relation and the surface
density of the clumps do not qualify them as massive star forming sites. An
overall picture of a runaway star ionizing the cloud and a triggered population
of intermediate-mass, Class I sources located toward the cloud centre emerges
from this multiwavelength study. Variation in the dust emissivity spectral
index is shown to exist in this region and is seen to have an inverse relation
with the dust temperature.Comment: 20 pages, 16 figures, accepted for publication in MNRA
Three flavour Quark matter in chiral colour dielectric model
We investigate the properties of quark matter at finite density and
temperature using the nonlinear chiral extension of Colour Dielectric Model
(CCM). Assuming that the square of the meson fields devlop non- zero vacuum
expectation value, the thermodynamic potential for interacting three flavour
matter has been calculated. It is found that remain zero
in the medium whereas changes in the medium. As a result, and
quark masses decrease monotonically as the temperature and density of the quark
matter is increased.In the present model, the deconfinement density and
temperature is found to be lower compared to lattice results. We also study the
behaviour of pressure and energy density above critical temperature.Comment: Latex file. 5 figures available on request. To appear in Phys. Rev.
Warm stellar matter with neutrino trapping
The properties of hybrid stars formed by hadronic and quark matter in
beta-equilibrium at fixed entropies are described by appropriate equations of
state (EOS) in the framework of relativistic mean-field theory. In this work we
include the possibility of neutrino trapped EOS and compare the star properties
with the ones obtained after deleptonization, when neutrinos have already
diffused out. We use the nonlinear Walecka model for the hadron matter with two
different sets for the hyperon couplings and the MIT Bag and the
Nambu-Jona-Lasinio models for the quark matter. The phase transition to a
deconfined quark phase is investigated. Depending on the model and the
parameter set used, the mixed phase may or may not exist in the EOS at high
densities.
The star properties are calculated for each equation of state. The maximum
mass stellar configurations obtained within the NJL have larger masses than the
ones obtained within the Bag model. The Bag model predicts a mixed phase in the
interior of the most massive stable stars while, depending on the hyperon
couplings, the NJL model predicts a mixed phase or pure quark matter. Comparing
with neutrino free stars, the maximum allowed baryonic masses for protoneutron
stars are larger for the Bag model and
larger for the NJL model when neutrino trapping is imposed.Comment: 8 pages, 8 figures, 1 tabl
Self-interaction effects on screening in three-dimensional QED
We have shown that self interaction effects in massive quantum
electrodynamics can lead to the formation of bound states of quark antiquark
pairs. A current-current fermion coupling term is introduced, which induces a
well in the potential energy profile. Explicit expressions of the effective
potential and renormalized parameters are provided
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