3,434 research outputs found
First measurements of 15N fractionation in N2H+ toward high-mass star forming cores
We report on the first measurements of the isotopic ratio 14N/15N in N2H+
toward a statistically significant sample of high-mass star forming cores. The
sources belong to the three main evolutionary categories of the high-mass star
formation process: high-mass starless cores, high-mass protostellar objects,
and ultracompact HII regions. Simultaneous measurements of 14N/15N in CN have
been made. The 14N/15N ratios derived from N2H+ show a large spread (from ~180
up to ~1300), while those derived from CN are in between the value measured in
the terrestrial atmosphere (~270) and that of the proto-Solar nebula (~440) for
the large majority of the sources within the errors. However, this different
spread might be due to the fact that the sources detected in the N2H+
isotopologues are more than those detected in the CN ones. The 14N/15N ratio
does not change significantly with the source evolutionary stage, which
indicates that time seems to be irrelevant for the fractionation of nitrogen.
We also find a possible anticorrelation between the 14N/15N (as derived from
N2H+) and the H/D isotopic ratios. This suggests that 15N enrichment could not
be linked to the parameters that cause D enrichment, in agreement with the
prediction by recent chemical models. These models, however, are not able to
reproduce the observed large spread in 14N/15N, pointing out that some
important routes of nitrogen fractionation could be still missing in the
models.Comment: 2 Figures, accepted for publication in ApJ
Ionization toward the high-mass star-forming region NGC 6334 I
Context. Ionization plays a central role in the gas-phase chemistry of
molecular clouds. Since ions are coupled with magnetic fields, which can in
turn counteract gravitational collapse, it is of paramount importance to
measure their abundance in star-forming regions. Aims. We use spectral line
observations of the high-mass star-forming region NGC 6334 I to derive the
abundance of two of the most abundant molecular ions, HCO+ and N2H+, and
consequently, the cosmic ray ionization rate. In addition, the line profiles
provide information about the kinematics of this region. Methods. We present
high-resolution spectral line observations conducted with the HIFI instrument
on board the Herschel Space Observatory of the rotational transitions with Jup
> 5 of the molecular species C17O, C18O, HCO+, H13CO+, and N2H+. Results. The
HCO+ and N2H+ line profiles display a redshifted asymmetry consistent with a
region of expanding gas. We identify two emission components in the spectra,
each with a different excitation, associated with the envelope of NGC 6334 I.
The physical parameters obtained for the envelope are in agreement with
previous models of the radial structure of NGC 6334 I based on submillimeter
continuum observations. Based on our new Herschel/HIFI observations, combined
with the predictions from a chemical model, we derive a cosmic ray ionization
rate that is an order of magnitude higher than the canonical value of 10^(-17)
s-1. Conclusions. We find evidence of an expansion of the envelope surrounding
the hot core of NGC 6334 I, which is mainly driven by thermal pressure from the
hot ionized gas in the region. The ionization rate seems to be dominated by
cosmic rays originating from outside the source, although X-ray emission from
the NGC 6334 I core could contribute to the ionization in the inner part of the
envelope.Comment: This paper contains a total of 10 figures and 3 table
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High-J CO line emission from young stellar objects: from ISO to FIRST
we present the CO pure rotational spectrum at high J (Jup14) obtained with the Long Wavelength Spectrometer (LWS) on board of the ISO satellite towards molecular outflows exciting sources in nearby star formation regions. The physical conditions, derived using an LVG model for the line emission, indicate the presence of warm and dense gas, probably shock excited. The model fits show that often the bulk of this CO emission is expected in the spectral range that will be covered by FIRST, indicating the potentiality of this satellite to trace the warm component of gas emission in young stellar objects
The HIFI spectral survey of AFGL 2591 (CHESS). II. Summary of the survey
This paper presents the richness of submillimeter spectral features in the
high-mass star forming region AFGL 2591. As part of the CHESS (Chemical
Herschel Survey of Star Forming Regions) Key Programme, AFGL 2591 was observed
by the Herschel/HIFI instrument. The spectral survey covered a frequency range
from 480 up to 1240 GHz as well as single lines from 1267 to 1901 GHz (i.e. CO,
HCl, NH3, OH and [CII]). Rotational and population diagram methods were used to
calculate column densities, excitation temperatures and the emission extents of
the observed molecules associated with AFGL 2591. The analysis was supplemented
with several lines from ground-based JCMT spectra. From the HIFI spectral
survey analysis a total of 32 species were identified (including
isotopologues). In spite of the fact that lines are mostly quite week, 268
emission and 16 absorption lines were found (excluding blends). Molecular
column densities range from 6e11 to 1e19 cm-2 and excitation temperatures range
from 19 to 175 K. One can distinguish cold (e.g. HCN, H2S, NH3 with
temperatures below 70 K) and warm species (e.g. CH3OH, SO2) in the protostellar
envelope.Comment: Accepted to A&
Quasi-classical rate coefficient calculations for the rotational (de)excitation of H2O by H2
The interpretation of water line emission from existing observations and
future HIFI/Herschel data requires a detailed knowledge of collisional rate
coefficients. Among all relevant collisional mechanisms, the rotational
(de)excitation of H2O by H2 molecules is the process of most interest in
interstellar space. To determine rate coefficients for rotational de-excitation
among the lowest 45 para and 45 ortho rotational levels of H2O colliding with
both para and ortho-H2 in the temperature range 20-2000 K. Rate coefficients
are calculated on a recent high-accuracy H2O-H2 potential energy surface using
quasi-classical trajectory calculations. Trajectories are sampled by a
canonical Monte-Carlo procedure. H2 molecules are assumed to be rotationally
thermalized at the kinetic temperature. By comparison with quantum calculations
available for low lying levels, classical rates are found to be accurate within
a factor of 1-3 for the dominant transitions, that is those with rates larger
than a few 10^{-12}cm^{3}s^{-1}. Large velocity gradient modelling shows that
the new rates have a significant impact on emission line fluxes and that they
should be adopted in any detailed population model of water in warm and hot
environments.Comment: 8 pages, 2 figures, 1 table (the online material (4 tables) can be
obtained upon request to [email protected]
Broad N2H+ emission towards the protostellar shock L1157-B1
We present the first detection of N2H+ towards a low-mass protostellar
outflow, namely the L1157-B1 shock, at about 0.1 pc from the protostellar
cocoon. The detection was obtained with the IRAM 30-m antenna. We observed
emission at 93 GHz due to the J = 1-0 hyperfine lines. The analysis of the
emission coupled with the HIFI CHESS multiline CO observations leads to the
conclusion that the observed N2H+(1-0) line originates from the dense (> 10^5
cm-3) gas associated with the large (20-25 arcsec) cavities opened by the
protostellar wind. We find a N2H+ column density of few 10^12 cm-2
corresponding to an abundance of (2-8) 10^-9. The N2H+ abundance can be matched
by a model of quiescent gas evolved for more than 10^4 yr, i.e. for more than
the shock kinematical age (about 2000 yr). Modelling of C-shocks confirms that
the abundance of N2H+ is not increased by the passage of the shock. In summary,
N2H+ is a fossil record of the pre-shock gas, formed when the density of the
gas was around 10^4 cm-3, and then further compressed and accelerated by the
shock.Comment: ApJ, in pres
Hypospadias: clinical approach, surgical technique and long-term outcome
Background: Hypospadias is one of the most common congenital abnormalities in male newborn. There is no universal approach to hypospadias surgical repair, with more than 300 corrective procedures described in current literature. The reoperation rate within 6–12 months of the initial surgery is most frequently used as an outcome measure. These short-term outcomes may not reflect those encountered in adolescence and adult life. This study aims to identify the long-term cosmetic, functional and psychosexual outcomes. Methods: Medical records of boys who had undergone surgical repair of hypospadias by a single surgical team led by the same surgeon at a single centre between August 2001 and December 2017 were reviewed. Families were contacted by telephone and invited to participate. Surgical outcome was assessed by combination of clinical examination, a life-related interview and 3 validated questionnaires (the Penile Perception Score-PPS, the Hypospadias Objective Score Evaluation-HOSE, the International Index of Erectile Function-5-IIEF5). Outcomes were compared according to age, severity of hypospadias, and respondent (child, parent and surgeon). Results: 187 children and their families agreed to participate in the study. 46 patients (24.6%) presented at least one complication after the repair, with a median elapsed time of 11.5 months (6.5–22.5). Longitudinal differences in surgical corrective procedures (p < 0.01), clinical approach (p < 0.01), hospitalisation after surgery (p < 0.01) were found. Cosmetic data from the PPS were similar among children and parents, with no significant differences in child’s age or the type of hypospadias: 83% of children and 87% of parents were satisfied with the cosmetic result. A significant difference in functional outcome related to the type of hypospadias was reflected responses to HOSE amongst all groups of respondents: children (p < 0.001), parents (p=0.02) and surgeon (p < 0.01). The child’s HOSE total score was consistently lower than the surgeon (p < 0.01). The HOSE satisfaction rate on functional outcome was 89% for child and 92% for parent respondents. Conclusion: Surgeons and clinicians should be cognizant of the long-term outcomes following hypospadias surgical repair and this should be reflected in a demand for a standardised approach to repair and follow-up
Confirmation of a recent bipolar ejection in the very young hierarchical multiple system IRAS 16293-2422
We present and analyze two new high-resolution (approx 0.3 arcsec),
high-sensitivity (approx 50 uJy beam-1) Very Large Array 3.6 cm observations of
IRAS 16293-2422 obtained in 2007 August and 2008 December. The components
A2alpha and A2beta recently detected in this system are still present, and have
moved roughly symmetrically away from source A2 at a projected velocity of
30-80 km s-1. This confirms that A2alpha and A2beta were formed as a
consequence of a very recent bipolar ejection from A2. Powerful bipolar
ejections have long been known to occur in low-mass young stars, but this is
-to our knowledge-- the first time that such a dramatic one is observed from
its very beginning. Under the reasonable assumption that the flux detected at
radio wavelengths is optically thin free-free emission, one can estimate the
mass of each ejecta to be of the order of 10^-8 Msun. If the ejecta were
created as a consequence of an episode of enhanced mass loss accompanied by an
increase in accretion onto the protostar, then the total luminosity of IRAS
16293-2422 ought to have increased by 10-60% over the course of at least
several months. Between A2alpha and A2beta, component A2 has reappeared, and
the relative position angle between A2 and A1 is found to have increased
significantly since 2003-2005. This strongly suggests that A1 is a protostar
rather than a shock feature, and that the A1/A2 pair is a tight binary system.
Including component B, IRAS 16293-2422 therefore appears to be a very young
hierarchical multiple system.Comment: Accepted for publication in The Astrophysical Journa
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