110 research outputs found
HIFI observations of warm gas in DR21: Shock versus radiative heating
The molecular gas in the DR21 massive star formation region is known to be
affected by the strong UV field from the central star cluster and by a fast
outflow creating a bright shock. The relative contribution of both heating
mechanisms is the matter of a long debate. By better sampling the excitation
ladder of various tracers we provide a quantitative distinction between the
different heating mechanisms. HIFI observations of mid-J transitions of CO and
HCO+ isotopes allow us to bridge the gap in excitation energies between
observations from the ground, characterizing the cooler gas, and existing ISO
LWS spectra, constraining the properties of the hot gas. Comparing the detailed
line profiles allows to identify the physical structure of the different
components. In spite of the known shock-excitation of H2 and the clearly
visible strong outflow, we find that the emission of all lines up to > 2 THz
can be explained by purely radiative heating of the material. However, the new
Herschel/HIFI observations reveal two types of excitation conditions. We find
hot and dense clumps close to the central cluster, probably dynamically
affected by the outflow, and a more widespread distribution of cooler, but
nevertheless dense, molecular clumps.Comment: Accepted for publication by A&
Detection of interstellar oxidaniumyl: abundant H2O+ towards the star-forming regions DR21, Sgr B2, and NGC6334
We identify a prominent absorption feature at 1115 GHz, detected in first
HIFI spectra towards high-mass star-forming regions, and interpret its
astrophysical origin. The characteristic hyperfine pattern of the H2O+
ground-state rotational transition, and the lack of other known low-energy
transitions in this frequency range, identifies the feature as H2O+ absorption
against the dust continuum background and allows us to derive the velocity
profile of the absorbing gas. By comparing this velocity profile with velocity
profiles of other tracers in the DR21 star-forming region, we constrain the
frequency of the transition and the conditions for its formation. In DR21, the
velocity distribution of H2O+ matches that of the [CII] line at 158\mu\m and of
OH cm-wave absorption, both stemming from the hot and dense clump surfaces
facing the HII-region and dynamically affected by the blister outflow. Diffuse
foreground gas dominates the absorption towards Sgr B2. The integrated
intensity of the absorption line allows us to derive lower limits to the H2O+
column density of 7.2e12 cm^-2 in NGC 6334, 2.3e13 cm^-2 in DR21, and 1.1e15
cm^-2 in Sgr B2.Comment: Accepted for publication in A&
Herschel observations of EXtra-Ordinary Sources: The Terahertz spectrum of Orion KL seen at high spectral resolution
We present the first high spectral resolution observations of Orion KL in the
frequency ranges 1573.4 - 1702.8 GHz (band 6b) and 1788.4 - 1906.8 GHz (band
7b) obtained using the HIFI instrument on board the Herschel Space Observatory.
We characterize the main emission lines found in the spectrum, which primarily
arise from a range of components associated with Orion KL including the hot
core, but also see widespread emission from components associated with
molecular outflows traced by H2O, SO2, and OH. We find that the density of
observed emission lines is significantly diminished in these bands compared to
lower frequency Herschel/HIFI bands.Comment: Accepted for publication in the Herschel HIFI special issue of
Astronomy and Astrophysics Letters, 5 pages, 3 figure
Reversal of infall in SgrB2(M) revealed by Herschel/HIFI observations of HCN lines at THz frequencies
To investigate the accretion and feedback processes in massive star
formation, we analyze the shapes of emission lines from hot molecular cores,
whose asymmetries trace infall and expansion motions. The high-mass star
forming region SgrB2(M) was observed with Herschel/HIFI (HEXOS key project) in
various lines of HCN and its isotopologues, complemented by APEX data. The
observations are compared to spherically symmetric, centrally heated models
with density power-law gradient and different velocity fields (infall or
infall+expansion), using the radiative transfer code RATRAN. The HCN line
profiles are asymmetric, with the emission peak shifting from blue to red with
increasing J and decreasing line opacity (HCN to HCN). This is most
evident in the HCN 12--11 line at 1062 GHz. These line shapes are reproduced by
a model whose velocity field changes from infall in the outer part to expansion
in the inner part. The qualitative reproduction of the HCN lines suggests that
infall dominates in the colder, outer regions, but expansion dominates in the
warmer, inner regions. We are thus witnessing the onset of feedback in massive
star formation, starting to reverse the infall and finally disrupting the whole
molecular cloud. To obtain our result, the THz lines uniquely covered by HIFI
were critically important.Comment: A&A, HIFI special issue, accepte
Herschel observations of extra-ordinary sources: Detection of Hydrogen Fluoride in absorption towards Orion~KL
We report a detection of the fundamental rotational transition of hydrogen
fluoride in absorption towards Orion KL using Herschel/HIFI. After the removal
of contaminating features associated with common molecules ("weeds"), the HF
spectrum shows a P-Cygni profile, with weak redshifted emission and strong
blue-shifted absorption, associated with the low-velocity molecular outflow. We
derive an estimate of 2.9 x 10^13 cm^-2 for the HF column density responsible
for the broad absorption component. Using our best estimate of the H2 column
density within the low-velocity molecular outflow, we obtain a lower limit of
~1.6 x 10^-10 for the HF abundance relative to hydrogen nuclei, corresponding
to 0.6% of the solar abundance of fluorine. This value is close to that
inferred from previous ISO observations of HF J=2--1 absorption towards Sgr B2,
but is in sharp contrast to the lower limit of 6 x 10^-9 derived by Neufeld et
al. (2010) for cold, foreground clouds on the line of sight towards G10.6-0.4.Comment: 5 pages, 3 figures, paper to be published in the Herschel special
issue of A&A letter
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
Herschel observations of extra-ordinary sources: Detecting spiral arm clouds by CH absorption lines
We have observed CH absorption lines ()
against the continuum source Sgr~B2(M) using the \textit{Herschel}/HIFI
instrument. With the high spectral resolution and wide velocity coverage
provided by HIFI, 31 CH absorption features with different radial velocities
and line widths are detected and identified. The narrower line width and lower
column density clouds show `spiral arm' cloud characteristics, while the
absorption component with the broadest line width and highest column density
corresponds to the gas from the Sgr~B2 envelope. The observations show that
each `spiral arm' harbors multiple velocity components, indicating that the
clouds are not uniform and that they have internal structure. This
line-of-sight through almost the entire Galaxy offers unique possibilities to
study the basic chemistry of simple molecules in diffuse clouds, as a variety
of different cloud classes are sampled simultaneously. We find that the linear
relationship between CH and H column densities found at lower by UV
observations does not continue into the range of higher visual extinction.
There, the curve flattens, which probably means that CH is depleted in the
denser cores of these clouds.Comment: Accepted for publication in A&A, HIFI Special Issu
The ESO Diffuse Interstellar Band Large Exploration Survey (EDIBLES)
The ESO Diffuse Interstellar Band Large Exploration Survey (EDIBLES) is a Large Programme that is collecting high-signal-to-noise (S/N) spectra with UVES of a large sample of O and B-type stars covering a large spectral range. The goal of the programme is to extract a unique sample of high-quality interstellar spectra from these data, representing different physical and chemical environments, and to characterise these environments in great detail. An important component of interstellar spectra is the diffuse interstellar bands (DIBs), a set of hundreds of unidentified interstellar absorption lines. With the detailed line-of- sight information and the high-quality spectra, EDIBLES will derive strong constraints on the potential DIB carrier molecules. EDIBLES will thus guide the laboratory experiments necessary to identify these interstellar “mystery molecules”, and turn DIBs into powerful diagnostics of their environments in our Milky Way Galaxy and beyond. We present some preliminary results showing the unique capabilities of the EDIBLES programme
Probing the competition among different coordination motifs in metal-ciprofloxacin complexes through IRMPD spectroscopy and DFT calculations
The vibrational spectra of ciprofloxacin complexes with monovalent (Li+, Na+, K+, Ag+) and polyvalent (Mg2+, Al3+) metal ions are recorded in the range 1000-1900 cm(-1) by means of infrared multiple-photon dissociation (IRMPD) spectroscopy. The IRMPD spectra are analyzed and interpreted in the light of density functional theory (DFT)-based quantum chemical calculations in order to identify the possible structures present under our experimental conditions. For each metal-ciprofloxacin complex, four isomers are predicted, considering different chelation patterns. A good agreement is found between the measured IRMPD spectrum and the calculated absorption spectrum of the most stable isomer for each complex. Metal ion size and charge are found to drive the competition among the different coordination motifs: small size and high charge density metal ions prefer to coordinate the quinolone between the two carbonyl oxygen atoms, whereas large-size metal ions prefer the carboxylate group as a coordination site. In the latter case, an intramolecular hydrogen bond compensates the weaker interaction established by these cations. The role of the metal cation on the stabilization of ionic and nonionic structures of ciprofloxacin is also investigated. It is found that large-size metal ions preferentially stabilize charge separated motifs and that the increase of metal ion charge has a stabilizing effect on the zwitterionic form of ciprofloxacin
A Proposed Taxonomy of Anaerobic Fungi (Class Neocallimastigomycetes) Suitable for Large-Scale Sequence-Based Community Structure Analysis
Anaerobic fungi are key players in the breakdown of fibrous plant material in the rumen, but not much is known about the composition and stability of fungal communities in ruminants. We analyzed anaerobic fungi in 53 rumen samples from farmed sheep (4 different flocks), cattle, and deer feeding on a variety of diets. Denaturing gradient gel electrophoresis fingerprinting of the internal transcribed spacer 1 (ITS1) region of the rrn operon revealed a high diversity of anaerobic fungal phylotypes across all samples. Clone libraries of the ITS1 region were constructed from DNA from 11 rumen samples that had distinctly different fungal communities. A total of 417 new sequences were generated to expand the number and diversity of ITS1 sequences available. Major phylogenetic groups of anaerobic fungi in New Zealand ruminants belonged to the genera Piromyces, Neocallimastix, Caecomyces and Orpinomyces. In addition, sequences forming four novel clades were obtained, which may represent so far undetected genera or species of anaerobic fungi. We propose a revised phylogeny and pragmatic taxonomy for anaerobic fungi, which was tested and proved suitable for analysis of datasets stemming from high-throughput next-generation sequencing methods. Comparing our revised taxonomy to the taxonomic assignment of sequences deposited in the GenBank database, we believe that >29% of ITS1 sequences derived from anaerobic fungal isolates or clones are misnamed at the genus level
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