717 research outputs found
CH^+(1–0) and ^(13)CH^+(1–0) absorption lines in the direction of massive star-forming regions
We report the detection of the ground-state rotational transition of the methylidyne cation CH^+ and its isotopologue ^(13)CH^+ toward the remote
massive star-forming regions W33A, W49N, and W51 with the HIFI instrument onboard the Herschel satellite. Both lines are seen only in
absorption against the dust continuum emission of the star-forming regions. The CH^+ absorption is saturated over almost the entire velocity
ranges sampled by the lines-of-sight that include gas associated with the star-forming regions (SFR) and Galactic foreground material. The CH^+
column densities are inferred from the optically thin components. A lower limit of the isotopic ratio [^(12)CH^+]/[^(13)CH^+] > 35.5 is derived from
the absorptions of foreground material toward W49N. The column density ratio, N(CH^+)/N(HCO^+), is found to vary by at least a factor 10,
between 4 and >40, in the Galactic foreground material. Line-of-sight ^(12)CH^+ average abundances relative to total hydrogen are estimated. Their
average value, N(CH^+)/N_H > 2.6 × 10^(−8), is higher than that observed in the solar neighborhood and confirms the high abundances of CH^+ in
the Galactic interstellar medium. We compare this result to the predictions of turbulent dissipation regions (TDR) models and find that these high
abundances can be reproduced for the inner Galaxy conditions. It is remarkable that the range of predicted N(CH^+)/N(HCO^+) ratios, from 1 to
~50, is comparable to that observed
Nitrogen hydrides in interstellar gas: Herschel/HIFI observations towards G10.6-0.4 (W31C)
The HIFI instrument on board the Herschel Space Observatory has been used to observe interstellar nitrogen hydrides along the sight-line towards
G10.6−0.4 in order to improve our understanding of the interstellar chemistry of nitrogen. We report observations of absorption in NH N = 1 ← 0,
J = 2 ← 1 and ortho-NH_2 1_(1,1) ← 0_(0,0). We also observed ortho-NH_3 1_0 ← 0_0, and 2_0 ← 1_0, para-NH_3 2_1 ← 1_1, and searched unsuccessfully for
NH^+. All detections show emission and absorption associated directly with the hot-core source itself as well as absorption by foreground material
over a wide range of velocities. All spectra show similar, non-saturated, absorption features, which we attribute to diffuse molecular gas. Total
column densities over the velocity range 11−54 km s^(−1) are estimated. The similar profiles suggest fairly uniform abundances relative to hydrogen,
approximately 6 × 10^(−9), 3 × 10^(−9), and 3 × 10^(−9) for NH, NH_2, and NH_3, respectively. These abundances are discussed with reference to models of
gas-phase and surface chemistry
Interstellar CH absorption in the diffuse interstellar medium along the sight-lines to G10.6–0.4 (W31C), W49N, and W51
We report the detection of the ground state N, J = 1, 3/2 → 1, 1/2 doublet of the methylidyne radical CH at ~532 GHz and ~536 GHz with
the Herschel/HIFI instrument along the sight-line to the massive star-forming regions G10.6–0.4 (W31C), W49N, and W51. While the molecular
cores associated with these massive star-forming regions show emission lines, clouds in the diffuse interstellar medium are detected in absorption
against the strong submillimeter background. The combination of hyperfine structure with emission and absorption results in complex profiles,
with overlap of the different hyperfine components. The opacities of most of the CH absorption features are linearly correlated with those of CCH,
CN, and HCO^+ in the same velocity intervals. In specific narrow velocity intervals, the opacities of CN and HCO^+ deviate from the mean trends,
giving rise to more opaque absorption features. We propose that CCH can be used as another tracer of the molecular gas in the absence of better
tracers, with [CCH]/[H_2] ~3.2 ± 1.1 × 10^(−8). The observed [CN]/[CH], [CCH]/[CH] abundance ratios suggest that the bulk of the diffuse matter
along the lines of sight has gas densities n_H = n(H) + 2n(H_2) ranging between 100 and 1000 cm^(−3)
Excitation and abundance of C_3 in star forming cores: Herschel/HIFI observations of the sight-lines to W31C and W49N
We present spectrally resolved observations of triatomic carbon (C_3) in several ro-vibrational transitions between the vibrational ground state and
the low-energy ν_2 bending mode at frequencies between 1654−1897 GHz along the sight-lines to the submillimeter continuum sources W31C
and W49N, using Herschel’s HIFI instrument. We detect C_3 in absorption arising from the warm envelope surrounding the hot core, as indicated
by the velocity peak position and shape of the line profile. The sensitivity does not allow to detect C_3 absorption due to diffuse foreground clouds.
From the column densities of the rotational levels in the vibrational ground state probed by the absorption we derive a rotation temperature (T_(rot))
of ~50−70 K, which is a good measure of the kinetic temperature of the absorbing gas, as radiative transitions within the vibrational ground state
are forbidden. It is also in good agreement with the dust temperatures for W31C and W49N. Applying the partition function correction based on
the derived T_(rot), we get column densities N(C_3) ~ 7−9 × 10^(14) cm^(−2) and abundance x(C_3) ~ 10^(−8) with respect to H_2. For W31C, using a radiative
transfer model including far-infrared pumping by the dust continuum and a temperature gradient within the source along the line of sight we find
that a model with x(C_3) = 10^(−8), T_(kin) = 30−50 K, N(C_3) = 1.5 × 10^(15) cm^(−2) fits the observations reasonably well and provides parameters in very
good agreement with the simple excitation analysis
Discovery of Hydrogen Fluoride in the Cloverleaf Quasar at z = 2.56
We report the first detection of hydrogen fluoride (HF) toward a high
redshift quasar. Using the Caltech Submillimeter Observatory (CSO) we detect
the HF J = 1 - 0 transition in absorption toward the Cloverleaf, a broad
absorption line (BAL) quasi-stellar object (QSO) at z=2.56. The detection is
statistically significant at the ~ 6 sigma level. We estimate a lower limit of
4 \times 1014 cm-2 for the HF column density and using a previous estimate of
the hydrogen column density, we obtain a lower limit of 1.7 \times 10-9 for the
HF abundance. This value suggests that, assuming a Galactic N(HF)/NH ratio, HF
accounts for at least ~10% of the fluorine in the gas phase along the line of
sight to the Cloverleaf quasar. This observation corroborates the prediction
that HF should be a good probe of the molecular gas at high redshift.
Measurements of the HF abundance as a function of redshift are urgently needed
to better constrain the fluorine nucleosynthesis mechanism(s)
Effect of periodontal dressing on nonâ surgical periodontal treatment outcomes: a systematic review
BackgroundPeriodontal dressing has been advocated and showed some positive outcomes for placing over the surgical site after periodontal surgery. However, little is known about its effect on nonâ surgical therapy.PurposeThe aim of this review was to assess the clinical effect of periodontal dressing when used after nonâ surgical therapy.Material and methodsTwo examiners performed an electronic search in several databases for relevant articles published in English up to November 2013. Selected studies were randomized human clinical trials (prospective or retrospective trials) with the clear aim of investigating the effect of periodontal dressing placement upon periodontal nonâ surgical mechanical therapy. Data were extracted from the included articles for analysis.ResultsThree randomized clinical trials fulfilled the inclusion criteria and thus were included in the data analysis. Statistical analysis could not be carried out due to the lack of clear data of the included studies. However, descriptive analysis showed its effectiveness in improving clinical parameters such as gain of clinical attachment level and reduction of probing pocket depth.ConclusionPlacement of periodontal dressing right after nonâ surgical mechanical therapy can be beneficial in improving overall shortâ term clinical outcomes, although more controlled studies are still needed to validate this finding.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/122435/1/idh12130.pd
Hydrogen chloride in diffuse interstellar clouds along the line of sight to W31C (G10.6-0.4)
We report the detection of hydrogen chloride, HCl, in diffuse molecular clouds on the line of sight toward the star-forming region W31C (G10.6-0.4). The J = 1-0 lines of the two stable HCl isotopologues, H^(35)Cl and H^(37)Cl, are observed using the 1b receiver of the Heterodyne Instrument for the Far-Infrared (HIFI) on board the Herschel Space Observatory. The HCl line is detected in absorption, over a wide range of velocities associated with diffuse clouds along the line of sight to W31C. The analysis of the absorption strength yields a total HCl column density of a few 10^(13) cm^(–2), implying that HCl accounts for ~0.6% of the total gas-phase chlorine, which exceeds the theoretical model predictions by a factor of ~6. This result is comparable to those obtained from the chemically related species H_2Cl^+ and HCl^+, for which large column densities have also been reported on the same line of sight. The source of discrepancy between models and observations is still unknown; however, the detection of these Cl-bearing molecules provides key constraints for the chlorine chemistry in the diffuse gas
Herschel observations of EXtraordinary Sources: Analysis of the full Herschel/HIFI molecular line survey of Sagittarius B2(N)
A sensitive broadband molecular line survey of the Sagittarius B2(N)
star-forming region has been obtained with the HIFI instrument on the Herschel
Space Observatory, offering the first high-spectral resolution look at this
well-studied source in a wavelength region largely inaccessible from the ground
(625-157 um). From the roughly 8,000 spectral features in the survey, a total
of 72 isotopologues arising from 44 different molecules have been identified,
ranging from light hydrides to complex organics, and arising from a variety of
environments from cold and diffuse to hot and dense gas. We present an LTE
model to the spectral signatures of each molecule, constraining the source
sizes for hot core species with complementary SMA interferometric observations,
and assuming that molecules with related functional group composition are
cospatial. For each molecule, a single model is given to fit all of the
emission and absorption features of that species across the entire 480-1910 GHz
spectral range, accounting for multiple temperature and velocity components
when needed to describe the spectrum. As with other HIFI surveys toward massive
star forming regions, methanol is found to contribute more integrated line
intensity to the spectrum than any other species. We discuss the molecular
abundances derived for the hot core, where the local thermodynamic equilibrium
approximation is generally found to describe the spectrum well, in comparison
to abundances derived for the same molecules in the Orion KL region from a
similar HIFI survey.Comment: Accepted to ApJ. 64 pages, 14 figures. Truncated abstrac
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