240 research outputs found
Water emission from the high-mass star-forming region IRAS 17233-3606. High water abundances at high velocities
We investigate the physical and chemical processes at work during the
formation of a massive protostar based on the observation of water in an
outflow from a very young object previously detected in H2 and SiO in the IRAS
17233-3606 region. We estimated the abundance of water to understand its
chemistry, and to constrain the mass of the emitting outflow. We present new
observations of shocked water obtained with the HIFI receiver onboard Herschel.
We detected water at high velocities in a range similar to SiO. We
self-consistently fitted these observations along with previous SiO data
through a state-of-the-art, one-dimensional, stationary C-shock model. We found
that a single model can explain the SiO and H2O emission in the red and blue
wings of the spectra. Remarkably, one common area, similar to that found for H2
emission, fits both the SiO and H2O emission regions. This shock model
subsequently allowed us to assess the shocked water column density,
N(H2O)=1.2x10^{18} cm^{-2}, mass, M(H2O)=12.5 M_earth, and its maximum
fractional abundance with respect to the total density, x(H2O)=1.4x10^{-4}. The
corresponding water abundance in fractional column density units ranges between
2.5x10^{-5} and 1.2x10^{-5}, in agreement with recent results obtained in
outflows from low- and high-mass young stellar objects.Comment: accepted for publication as a Letter in Astronomy and Astrophysic
A Direct Measurement of the Total Gas Column Density in Orion KL
The large number of high-J lines of C^(18)O available via the Herschel Space Observatory provide an unprecedented ability to model the total CO column density in hot cores. Using the emission from all the observed lines (up to J = 15-14), we sum the column densities in each individual level to obtain the total column after correcting for the population in the unobserved states. With additional knowledge of source size, V_(LSR), and line width, and both local thermodynamic equilibrium (LTE) and non-LTE modeling, we have determined the total C^(18)O column densities in the Extended Ridge, Outflow/Plateau, Compact Ridge, and Hot Core components of Orion KL to be 1.4 Ă 10^(16) cm^(â2), 3.5 Ă 10^(16) cm^(â2), 2.2 Ă 10^(16) cm^(â2), and 6.2 Ă 10^(16) cm^(â2), respectively. We also find that the C^(18)O/C^(17)O abundance ratio varies from 1.7 in the Outflow/Plateau, 2.3 in the Extended Ridge, 3.0 in the Hot Core, and to 4.1 in the Compact Ridge. This is in agreement with models in which regions with higher ultraviolet radiation fields selectively dissociate C^(17)O, although care must be taken when interpreting these numbers due to the size of the uncertainties in the C^(18)O/C^(17)O abundance ratio
Molecular line survey of the high-mass star-forming region NGC 6334I with Herschel/HIFI and the SMA
We aim at deriving the molecular abundances and temperatures of the hot
molecular cores in the high-mass star-forming region NGC 6334I and consequently
deriving their physical and astrochemical conditions. In the framework of the
Herschel guaranteed time key program CHESS, NGC 6334I is investigated by using
HIFI aboard the Herschel Space Observatory. A spectral line survey is carried
out in the frequency range 480-1907 GHz, and auxiliary interferometric data
from the SMA in the 230 GHz band provide spatial information for disentangling
the different physical components contributing to the HIFI spectrum. The
spectral lines are identified with the aid of former surveys and spectral line
catalogs. The observed spectrum is then compared to a simulated synthetic
spectrum with XCLASS, assuming local thermal equilibrium, and best fit
parameters are derived using the model optimization package MAGIX. A total of
46 molecules are identified, with 31 isotopologues, resulting in about 4300
emission and absorption lines. High- energy levels of the dominant emitter
methanol and vibrationally excited HCN are detected. The number of unidentified
lines remains low with 75, or less than 2 percent of the lines detected. The
modeling suggests that several spectral features need two or more components to
be fitted properly. Other components could be assigned to cold foreground
clouds or to outflows, most visible in the SiO emission. A chemical variation
between the two embedded hot cores is found, with more N-bearing molecules
identified in SMA1 and O-bearing molecules in SMA2. Spectral line surveys give
powerful insights into the study of the interstellar medium. Different
molecules trace different physical conditions like the inner hot core, the
envelope, the outflows or the cold foreground clouds. The derived molecular
abundances provide further constraints for astrochemical models.Comment: 30 pages including appendix, 49 figures, accepted for publication in
Astronomy and Astrophysic
âYou Can\u27t Self-Care Your Way out of a Broken Systemâ: the 2022 Urban Libraries Trauma Forum
The Urban Libraries Trauma Study (ULTS) conducted by Urban Librarians Unite (ULU) examines trauma that urban public library workers experience in the workforce through their work with the public and interlibrary relationships. Drawing on interviews, focus groups, and a trauma forum, this paper discusses the problem of trauma in the library. It demonstrates a grounded way to engage library staff in research and change. Finally, this paper concludes with ideas proposed by the forum participants to begin addressing trauma in the library workplace and provide areas to look to going forward
Molecular line survey of the high-mass star-forming region NGC 6334I with Herschel/HIFI and the Submillimeter Array
Aims. We aim at deriving the molecular abundances and temperatures of the hot molecular cores in the high-mass star-forming region NGC 6334I and consequently deriving their physical and astrochemical conditions.
Methods. In the framework of the Herschel guaranteed time key program CHESS (Chemical HErschel Surveys of Star forming regions), NGC 6334I is investigated by using the Heterodyne Instrument for the Far-Infrared (HIFI) aboard the Herschel Space Observatory. A spectral line survey is carried out in the frequency range 480â1907 GHz, and further auxiliary interferometric data from the Submillimeter Array (SMA) in the 230 GHz band provide spatial information for disentangling the different physical components contributing to the HIFI spectrum. The spectral lines in the processed Herschel data are identified with the aid of former surveys and spectral line catalogs. The observed spectrum is then compared to a simulated synthetic spectrum, assuming local thermal equilibrium, and best fit parameters are derived using a model optimization package.
Results. A total of 46 molecules are identified, with 31 isotopologues, resulting in about 4300 emission and absorption lines. High-energy levels (E_u > 1000 K) of the dominant emitter methanol and vibrationally excited HCN (Μ_2 = 1) are detected. The number of unidentified lines remains low with 75, or <2% of the lines detected. The modeling suggests that several spectral features need two or more components to be fitted properly. Other components could be assigned to cold foreground clouds or to outflows, most visible in the SiO and H_(2)O emission. A chemical variation between the two embedded hot cores is found, with more N-bearing molecules identified in SMA1 and O-bearing molecules in SMA2.
Conclusions. Spectral line surveys give powerful insights into the study of the interstellar medium. Different molecules trace different physical conditions like the inner hot core, the envelope, the outflows or the cold foreground clouds. The derived molecular abundances provide further constraints for astrochemical models
Herschel observations of extraordinary sources: Full Herschel/HIFI molecular line survey of Sagittarius B2(M)
We present a full analysis of a broadband spectral line survey of Sagittarius
B2 (Main), one of the most chemically rich regions in the Galaxy located within
the giant molecular cloud complex Sgr B2 in the Central Molecular Zone. Our
goal is to derive the molecular abundances and temperatures of the high-mass
star-forming region Sgr B2(M) and thus its physical and astrochemical
conditions. Sgr B2(M) was observed using the Heterodyne Instrument for the
Far-Infrared (HIFI) on board the Herschel Space Observatory in a spectral line
survey from 480 to 1907 GHz at a spectral resolution of 1.1 MHz, which provides
one of the largest spectral coverages ever obtained toward this high-mass
star-forming region in the submillimeter with high spectral resolution and
includes frequencies > 1 THz unobservable from the ground. We model the
molecular emission from the submillimeter to the far-IR using the XCLASS
program. For each molecule, a quantitative description was determined taking
all emission and absorption features of that species across the entire spectral
range into account. Additionally, we derive velocity resolved ortho / para
ratios for those molecules for which ortho and para resolved molecular
parameters are available. Finally, the temperature and velocity distributions
are analyzed and the derived abundances are compared with those obtained for
Sgr B2(N) from a similar HIFI survey. A total of 92 isotopologues were
identified, arising from 49 different molecules, ranging from free ions to
complex organic compounds and originating from a variety of environments from
the cold envelope to hot and dense gas within the cores. Sulfur dioxide,
methanol, and water are the dominant contributors. For the ortho / para ratios
we find deviations from the high temperature values between 13 and 27 %. In
total 14 % of all lines remain unidentified.Comment: 67 pages, 102 figures, submitted to A&
Herschel observations of deuterated water towards Sgr B2(M)
Observations of HDO are an important complement for studies of water, because
they give strong constraints on the formation processes -- grain surfaces
versus energetic process in the gas phase, e.g. in shocks. The HIFI
observations of multiple transitions of HDO in Sgr~B2(M) presented here allow
the determination of the HDO abundance throughout the envelope, which has not
been possible before with ground-based observations only. The abundance
structure has been modeled with the spherical Monte Carlo radiative transfer
code RATRAN, which also takes radiative pumping by continuum emission from dust
into account. The modeling reveals that the abundance of HDO rises steeply with
temperature from a low abundance () in the outer envelope
at temperatures below 100~K through a medium abundance () in
the inner envelope/outer core, at temperatures between 100 and 200~K, and
finally a high abundance () at temperatures above 200~K in
the hot core.Comment: A&A HIFI special issue, accepte
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