6 research outputs found
Evolution of complex organic molecules in hot molecular cores: Synthetic spectra at (sub-)mm wavebands
Hot molecular cores (HMCs) are intermediate stages of high-mass star
formation and are also known for their rich emission line spectra at (sub-)mm
wavebands. The observed spectral feature of HMCs such as total number of
emission lines and associated line intensities are also found to vary with
evolutionary stages. We developed various 3D models for HMCs guided by the
evolutionary scenarios proposed by recent empirical and modeling studies. We
then investigated the spatio-temporal variation of temperature and molecular
abundances in HMCs by consistently coupling gas-grain chemical evolution with
radiative transfer calculations. We explored the effects of varying physical
conditions on molecular abundances including density distribution and
luminosity evolution of the central protostar(s). The time-dependent
temperature structure of the hot core models provides a realistic framework for
investigating the spatial variation of ice mantle evaporation as a function of
evolutionary timescales. With increasing protostellar luminosity, the water ice
evaporation font (100K) expands and the spatial distribution of gas phase
abundances of these COMs also spreads out. We simulated the synthetic spectra
for these models at different evolutionary timescales to compare with
observations. A qualitative comparison of the simulated and observed spectra
suggests that these self-consistent hot core models can reproduce the notable
trends in hot core spectral variation within the typical hot core timescales of
10 year. These models predict that the spatial distribution of various
emission line maps will also expand with evolutionary time. The model
predictions can be compared with high resolution observation that can probe
scales of a few thousand AU in high-mass star forming regions such as from
ALMA.[Abridged]Comment: accepted for publication in A&
Kinematics of the Young Stellar Objects associated with the Cometary Globules in the Gum Nebula
An analysis of proper motion measurements of the Young Stellar Objects (YSOs)
associated with the Cometary Globules (CGs) in the Gum Nebula is presented.
While earlier studies based on the radial velocity measurements of the CGs
suggested expansion of the system of the CGs, the observed proper motion of the
YSOs shows no evidence for expansion. In particular the kinematics of two YSOs
embedded in CGs is inconsistent with the supernova explosion of the companion
of Pup about 1.5 Myr ago as the cause of the expansion of the CG
system. YSOs associated with the CGs share the average proper motion of the
member stars of the Vela OB2 association. A few YSOs that have relatively large
proper motions are found to show relatively low infrared excesses.Comment: 19 pages, 6 figures, 4 tables, Accepted for publication in MNRA
Triggered star formation and Young Stellar Population in Bright-Rimmed Cloud SFO 38
We have investigated the young stellar population in and around SFO 38, one
of the massive globules located in the northern part of the Galactic HII region
IC 1396, using the Spitzer IRAC and MIPS observations (3.6 to 24 micron) and
followed up with ground based optical photometric and spectroscopic
observations. Based on the IRAC and MIPS colors and H-alpha emission we
identify ~45 Young Stellar Objects (Classes 0/I/II) and 13 probable Pre Main
Sequence candidates. We derive the spectral types (mostly K- and M-type stars),
effective temperatures and individual extinction of the relatively bright and
optically visible Class II objects. Based on optical photometry and theoretical
isochrones, we estimate the spread in stellar ages to be between 1--8 Myr with
a median age of 3 Myr and a mass distribution of 0.3--2.2 Msun with a median
value around 0.5 Msun. Using the width of the H-alpha emission line measured at
10% peak intensity, we derive the mass accretion rates of individual objects to
be between 10^{-10} to 10^{-8} Msun/yr. From the continuum-subtracted H-alpha
line image, we find that the H-alpha emission of the globule is not spatially
symmetric with respect to the O type ionizing star HD 206267. We clearly detect
an enhanced concentration of YSOs closer to the southern rim of SFO~38 and
identify an evolutionary sequence of YSOs from the rim to the dense core of the
cloud, with most of the Class II objects located at the bright rim. The YSOs
appear to be aligned along two different directions towards the O6.5V type star
HD 206267 and the B0V type star HD 206773. This is consistent with the
Radiation Driven Implosion (RDI) model for triggered star formation. (Abridged)Comment: Accepted for publication in Ap
Efficacy of expressed breast milk alone or in combination with paracetamol in reducing pain during retinopathy of prematurity screening: A randomized controlled trial
Background: The aim of this study was to determine the efficacy of expressed breast milk (EBM) alone or in combination with oral paracetamol for pain reduction during retinopathy of prematurity (ROP) screening.
Methods: A randomized control trial was conducted in two departments of Bangabandhu Sheikh Mujib Medical University. A total of 60 preterm neonates who underwent ROP screening were randomized into three equal groups. Group A got nesting and swaddling as per institutional protocol (control). Group B received 2 ml EBM two minutes prior to the ROP screening and Group C received 15 mg/kg syrup paracetamol 30 minutes prior to the ROP screening and EBM like Group B. Premature infant pain profile (PIPP) scores was used prior, during and 2 minutes after ROP screening procedure.
Results: The three groups were similar in terms of baseline characteristics. The mean (standard deviation) PIPP scores during the procedure were 16.4 (1.1), 15.0 (1.8) and 13.4 (1.8) in control, EBM, and EBM with paracetamol groups respectively. The PIPP scores were significantly lower in the EBM and EBM with paracetamol groups during the procedure compared to control group. In the EBM and EBM with paracetamol groups, the mean difference in PIPP scores (between before and during the procedure) was also substantially lower.
Conclusion: Breast milk alone or in combination with paracetamol can reduce significant pain during ROP screening than control group.
Bangabandhu Sheikh Mujib Medical University Journal 2023;16(2): 106-11
Seeds of Life in Space (SOLIS). III. Zooming Into the Methanol Peak of the Prestellar Core L1544
International audienceToward the prestellar core L1544, the methanol (CH3OH) emission forms an asymmetric ring around the core center, where CH3OH is mostly in solid form, with a clear peak at 4000 au to the northeast of the dust continuum peak. As part of the NOEMA Large Project SOLIS (Seeds of Life in Space), the CH3OH peak has been spatially resolved to study its kinematics and physical structure and to investigate the cause behind the local enhancement. We find that methanol emission is distributed in a ridge parallel to the main axis of the dense core. The centroid velocity increases by about 0.2 km s(-1) and the velocity dispersion increases from subsonic to transonic toward the central zone of the core, where the velocity field also shows complex structure. This could be an indication of gentle accretion of material onto the core or the interaction of two filaments, producing a slow shock. We measure the rotational temperature and show that methanol is in local thermodynamic equilibrium (LTE) only close to the dust peak, where it is significantly depleted. The CH3OH column density, N-tot(CH3OH), profile has been derived with non-LTE radiative transfer modeling and compared with chemical models of a static core. The measured N (tot)(CH3OH) profile is consistent with model predictions, but the total column densities are one order of magnitude lower than those predicted by models, suggesting that the efficiency of reactive desorption or atomic hydrogen tunneling adopted in the model may be overestimated; or that an evolutionary model is needed to better reproduce methanol abundance