2,134 research outputs found
Star formation around mid-infrared bubble N37: Evidence of cloud-cloud collision
We have performed a multi-wavelength analysis of a mid-infrared (MIR) bubble
N37 and its surrounding environment. The selected 1515 area around
the bubble contains two molecular clouds (N37 cloud; V37-43 km
s, and C25.29+0.31; V43-48 km s) along the line of
sight. A total of seven OB stars are identified towards the bubble N37 using
photometric criteria, and two of them are spectroscopically confirmed as O9V
and B0V stars. Spectro-photometric distances of these two sources confirm their
physical association with the bubble. The O9V star is appeared to be the
primary ionizing source of the region, which is also in agreement with the
desired Lyman continuum flux analysis estimated from the 20 cm data. The
presence of the expanding HII region is revealed in the N37 cloud which could
be responsible for the MIR bubble. Using the CO line data and
photometric data, several cold molecular condensations as well as clusters of
young stellar objects (YSOs) are identified in the N37 cloud, revealing ongoing
star formation (SF) activities. However, the analysis of ages of YSOs and the
dynamical age of the HII region do not support the origin of SF due to the
influence of OB stars. The position-velocity analysis of CO data reveals
that two molecular clouds are inter-connected by a bridge-like structure,
favoring the onset of a cloud-cloud collision process. The SF activities (i.e.
the formation of YSOs clusters and OB stars) in the N37 cloud are possibly
influenced by the cloud-cloud collision.Comment: 18 pages, 13 figures, 2 tables, Accepted for publication in the Ap
Effect of Hedging-Integrated Rule Curves on the Performance of the Pong Reservoir (India) During Scenario-Neutral Climate Change Perturbations
This study has evaluated the effects of improved, hedging-integrated reservoir rule
curves on the current and climate-change-perturbed future performances of the Pong reservoir,
India. The Pong reservoir was formed by impounding the snow- and glacial-dominated Beas
River in Himachal Pradesh. Simulated historic and climate-change runoff series by the
HYSIM rainfall-runoff model formed the basis of the analysis. The climate perturbations used
delta changes in temperature (from 0° to +2 °C) and rainfall (from −10 to +10 % of annual
rainfall). Reservoir simulations were then carried out, forced with the simulated runoff
scenarios, guided by rule curves derived by a coupled sequent peak algorithm and genetic
algorithms optimiser. Reservoir performance was summarised in terms of reliability, resilience,
vulnerability and sustainability. The results show that the historic vulnerability reduced from
61 % (no hedging) to 20 % (with hedging), i.e., better than the 25 % vulnerability often
assumed tolerable for most water consumers. Climate change perturbations in the rainfall
produced the expected outcomes for the runoff, with higher rainfall resulting in more runoff
inflow and vice-versa. Reduced runoff caused the vulnerability to worsen to 66 % without
hedging; this was improved to 26 % with hedging. The fact that improved operational practices
involving hedging can effectively eliminate the impacts of water shortage caused by climate
change is a significant outcome of this study
Dual-Frequency Observations of 140 Compact, Flat-Spectrum Active Galactic Nuclei for Scintillation-Induced Variability
The 4.9 GHz Micro-Arcsecond Scintillation-Induced Variability (MASIV) Survey
detected a drop in Interstellar Scintillation (ISS) for sources at redshifts z
> 2, indicating an apparent increase in angular diameter or a decrease in flux
density of the most compact components of these sources, relative to their
extended emission. This can result from intrinsic source size effects or
scatter broadening in the Intergalactic Medium (IGM), in excess of the expected
(1+z)^0.5 angular diameter scaling of brightness temperature limited sources
due to cosmological expansion. We report here 4.9 GHz and 8.4 GHz observations
and data analysis for a sample of 140 compact, flat-spectrum sources which may
allow us to determine the origin of this angular diameter-redshift relation by
exploiting their different wavelength dependences. In addition to using ISS as
a cosmological probe, the observations provide additional insight into source
morphologies and the characteristics of ISS. As in the MASIV Survey, the
variability of the sources is found to be significantly correlated with
line-of-sight H-alpha intensities, confirming its link with ISS. For 25
sources, time delays of about 0.15 to 3 days are observed between the
scintillation patterns at both frequencies, interpreted as being caused by a
shift in core positions when probed at different optical depths. Significant
correlation is found between ISS amplitudes and source spectral index; in
particular, a large drop in ISS amplitudes is observed at spectral indices of <
-0.4 confirming that steep spectrum sources scintillate less. We detect a
weakened redshift dependence of ISS at 8.4 GHz over that at 4.9 GHz, with the
mean variance at 4-day timescales reduced by a factor of 1.8 in the z > 2
sources relative to the z < 2 sources, as opposed to the factor of 3 decrease
observed at 4.9 GHz. This suggests scatter broadening in the IGM.Comment: 30 pages, 14 figures, accepted for publication in the Astronomical
Journa
The ionizing sources of luminous compact HII regions in the RCW106 and RCW122 clouds
Given the rarity of young O star candidates, compact HII regions embedded in
dense molecular cores continue to serve as potential sites to peer into the
details of high-mass star formation. To uncover the ionizing sources of the
most luminous and compact HII regions embedded in the RCW106 and RCW122 giant
molecular clouds, known to be relatively nearby (2-4 kpc) and isolated, thus
providing an opportunity to examine spatial scales of a few hundred to a
thousand AU in size. High spatial resolution (0.3"), mid-infrared spectra
(R=350), including the fine structure lines [ArIII] and [NeII], were obtained
for four luminous compact HII regions, embedded inside the dense cores within
the RCW106 and RCW122 molecular cloud complexes. At this resolution, these
targets reveal point-like sources surrounded by nebulosity of different
morphologies, uncovering details at spatial dimensions of <1000AU. The
point-like sources display [ArIII] and [NeII] lines - the ratios of which are
used to estimate the temperature of the embedded sources. The derived
temperatures are indicative of mid-late O type objects for all the sources with
[ArIII] emission. Previously known characteristics of these targets from the
literature, including evidence of disk or accretion suggest that the identified
sources may grow more to become early-type O stars by the end of the star
formation process
Epitaxial strain modulated electronic properties of interface controlled nickelate superlattice
Perovskite nickelate heterostructure consisting of single unit cell of
EuNiO and LaNiO have been grown on a set of single crystalline
substrates by pulsed laser interval deposition to investigate the effect of
epitaxial strain on electronic and magnetic properties at the extreme interface
limit. Despite the variation of substrate in-plane lattice constants and
lattice symmetry, the structural response to heterostructuring is primarily
controlled by the presence of EuNiO layer. In sharp contrast to bulk
LaNiO or EuNiO, the superlattices grown under tensile strains exhibit
metal to insulator transition (MIT) below room temperature. The onset of
magnetic and electronic transitions associated with the MIT can be further
separated by application of large tensile strain. Furthermore, these
transitions can be entirely suppressed by very small compressive strain. X-ray
resonant absorption spectroscopy measurements reveal that such
strain-controlled MIT is directly linked to strain induced self-doping effect
without any chemical doping.Comment: Accepted in Phys. Rev.
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