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Start Over Subject radio astronomy Content Level Research
691. HCN, HNC and DNC spectra of 27 sources
ID:
ivo://CDS.VizieR/J/A+A/609/A129
Title:
HCN, HNC and DNC spectra of 27 sources
Short Name:
J/A+A/609/A129
Date:
21 Oct 2021
Publisher:
CDS
Description:
The ratio between the two stable isotopes of nitrogen, ^14^N and ^15^N, is well measured in the terrestrial atmosphere (~272), and for the pre-solar nebula (~441, deduced from the solar wind). Interestingly, some pristine solar system materials show enrichments in 15N with respect to the pre-solar nebula value. However, it is not yet clear if and how these enrichments are linked to the past chemical history because we have only a limited number of measurements in dense star-forming regions. In this respect, dense cores, which are believed to be the precursors of clusters and also contain intermediate- and high-mass stars, are important targets because the solar system was probably born within a rich stellar cluster, and such clusters are formed in high-mass star-forming regions. The number of observations in such high-mass dense cores has remained limited so far. In this work, we show the results of IRAM-30m observations of the J=1-0 rotational transition of the molecules HCN and HNC and their 15N-bearing counterparts towards 27 intermediate- and high-mass dense cores that are divided almost equally into three evolutionary categories: high-mass starless cores, high-mass protostellar objects, and ultra-compact Hii regions. We have also observed the DNC(2-1) rotational transition in order to search for a relation between the isotopic ratios D/H and ^14^N/^15^N. We derive average ^14^N/^15^N ratios of 359+/-16 in HCN and of 438+/-21 in HNC, with a dispersion of about 150-200. We find no trend of the ^14^ N/^15^ N ratio with evolutionary stage. This result agrees with what has been found for N_2_H^+^ and its isotopologues in the same sources, although the ^14^N/^15^N ratios from N2H+ show a higher dispersion than in HCN/HNC, and on average, their uncertainties are larger as well. Moreover, we have found no correlation between D/H and ^14^N/^15^N in HNC. These findings indicate that (1) the chemical evolution does not seem to play a role in the fractionation of nitrogen, and that (2) the fractionation of hydrogen and nitrogen in these objects is not related.
692. H13CN/HN13C linelist
ID:
ivo://CDS.VizieR/VI/131
Title:
H13CN/HN13C linelist
Short Name:
VI/131
Date:
21 Oct 2021
Publisher:
CDS
Description:
A linelist of vibration-rotation transitions for ^13^C substituted HCN is presented. The line list is constructed using known experimental levels where available, calculated levels and ab initio line intensities originally calculated for the major isotopologue. Synthetic spectra are generated and compared with observations for cool carbon star WZ Cas. It is suggested that high resolution HCN spectra recorded near 14um should be particularly sensitive to the ^13^C-^12^C ratio.
693. HC_3_N in Orion KL
ID:
ivo://CDS.VizieR/J/A+A/559/A51
Title:
HC_3_N in Orion KL
Short Name:
J/A+A/559/A51
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a study of cyanoacetylene (HC_3_N) and cyanodiacetylene (HC_5_N) in Orion KL, using observations from two line surveys performed with the IRAM 30-m telescope and the HIFI instrument onboard the Herschel telescope. The frequency ranges covered are 80-280GHz and 480-1906GHz. This study (divided by families of molecules) is part of a global analysis of the physical conditions of Orion KL and the molecular abundances in the different components of this cloud. We modeled the observed lines of HC_3_N, HC_5_N, their isotopologues (including DC_3_N), and vibrational modes using a non-local thermodynamic equilibrium (non-LTE) radiative transfer code. In addition, to investigate the chemical origin of HC_3_N and DC_3_N in Orion KL, we used a time-dependent chemical model.
694. H_2_CO and H{alpha} observations of UC HII
ID:
ivo://CDS.VizieR/J/ApJ/587/714
Title:
H_2_CO and H{alpha} observations of UC HII
Short Name:
J/ApJ/587/714
Date:
21 Oct 2021
Publisher:
CDS
Description:
Fifty-four ultracompact (UC) HII regions in the GLIMPSE survey region (|b|<1{deg} and 30{deg}<l<70{deg}) were observed in H_2_CO and H110{alpha} using the 305 m Arecibo telescope. By analyzing H_2_CO absorption against the UC H II region continuum emission, we resolve the distance ambiguity toward 44 sources. This determination is critical to measure global physical properties of UC H II regions (e.g., luminosity, size, mass) and properties of the Galaxy (e.g., spiral structure, abundance gradients). We find that the distribution of UC H II regions in this survey is consistent with a ``local spur'', the Perseus, Sagittarius, and Scutum arms as delineated by Taylor & Cordes. However, departures from model velocities produce distance uncertainties only slightly smaller than the proposed arm separations.
695. H_2_CO and H{alpha} observations of UC HII
ID:
ivo://CDS.VizieR/J/ApJS/138/63
Title:
H_2_CO and H{alpha} observations of UC HII
Short Name:
J/ApJS/138/63
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report observations of the H110{alpha} radio recombination line and H_2_CO (1_10_-1_11_) toward 21 ultracompact H II regions with the Arecibo 305m radio telescope. We detect the H110{alpha} line in 20 sources, and for each of these we also detect a H_2_CO absorption feature at nearly the same velocity, demonstrating the association between molecular and ionized gas. We determine kinematic distances and resolve the distance ambiguity for all observed HII regions, as well as for 19 intervening molecular clouds. A plot of the Galactic distribution of these objects traces part of the spiral structure in the first Galactic quadrant. We compare flux densities and velocities as measured with the Arecibo Telescope with interferometric measurements of our sample of ultracompact HII regions. In general, the single-dish fluxes exceed the interferometric values, consistent with an extended component of radio continuum emission.
696. HCO+ and HCN obs. toward Planck Galactic Cold Clumps
ID:
ivo://CDS.VizieR/J/ApJ/820/37
Title:
HCO+ and HCN obs. toward Planck Galactic Cold Clumps
Short Name:
J/ApJ/820/37
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the first survey of dense gas toward Planck Galactic Cold Clumps (PGCCs). Observations in the J=1-0 transitions of HCO^+^ and HCN toward 621 molecular cores associated with PGCCs were performed using the Purple Mountain Observatory's 13.7m telescope. Among them, 250 sources were detected, including 230 cores detected in HCO^+^ and 158 in HCN. Spectra of the J=1-0 transitions from ^12^CO, ^13^CO, and C^18^O at the centers of the 250 cores were extracted from previous mapping observations to construct a multi-line data set. The significantly low detection rate of asymmetric double-peaked profiles, together with the good consistency among central velocities of CO, HCO^+^, and HCN spectra, suggests that the CO-selected Planck cores are more quiescent than classical star-forming regions. The small difference between line widths of C^18^O and HCN indicates that the inner regions of CO-selected Planck cores are no more turbulent than the exterior. The velocity-integrated intensities and abundances of HCO^+^ are positively correlated with those of HCN, suggesting that these two species are well coupled and chemically connected. The detected abundances of both HCO^+^ and HCN are significantly lower than values in other low- to high-mass star-forming regions. The low abundances may be due to beam dilution. On the basis of an inspection of the parameters given in the PGCC catalog, we suggest that there may be about 1000 PGCC objects that have a sufficient reservoir of dense gas to form stars.
697. HCO+ and N2D+ dense cores in Perseus
ID:
ivo://CDS.VizieR/J/ApJ/819/143
Title:
HCO+ and N2D+ dense cores in Perseus
Short Name:
J/ApJ/819/143
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the results of an HCO^+^ (3-2) and N_2_D^+^ (3-2) molecular line survey performed toward 91 dense cores in the Perseus molecular cloud using the James Clerk Maxwell Telescope, to identify the fraction of starless and protostellar cores with systematic radial motions. We quantify the HCO^+^ asymmetry using a dimensionless asymmetry parameter {delta}_v_, and identify 20 cores with significant blue or red line asymmetries in optically thick emission indicative of collapsing or expanding motions, respectively. We separately fit the HCO^+^ profiles with an analytic collapse model and determine contraction (expansion) speeds toward 22 cores. Comparing the {delta}_v_ and collapse model results, we find that {delta}_v_ is a good tracer of core contraction if the optically thin emission is aligned with the model-derived systemic velocity. The contraction speeds range from subsonic (0.03km/s) to supersonic (0.40km/s), where the supersonic contraction speeds may trace global rather than local core contraction. Most cores have contraction speeds significantly less than their free-fall speeds. Only 7 of 28 starless cores have spectra well-fit by the collapse model, which more than doubles (15 of 28) for protostellar cores. Starless cores with masses greater than the Jeans mass (M/M_J_>1) are somewhat more likely to show contraction motions. We find no trend of optically thin non-thermal line width with M/M_J_, suggesting that any undetected contraction motions are small and subsonic. Most starless cores in Perseus are either not in a state of collapse or expansion, or are in a very early stage of collapse.
698. H_2_CO & H110{alpha} obs. toward Aquila
ID:
ivo://CDS.VizieR/J/ApJ/874/172
Title:
H_2_CO & H110{alpha} obs. toward Aquila
Short Name:
J/ApJ/874/172
Date:
21 Oct 2021
Publisher:
CDS
Description:
The formaldehyde H_2_CO(1_10_-1_11_) absorption line and H110{alpha} radio recombination line have been observed toward the Aquila Molecular Cloud using the Nanshan 25m telescope operated by the Xinjiang Astronomical Observatory CAS. These first observations of the H_2_CO (1_10_-1_11_) absorption line determine the extent of the molecular regions that are affected by the ongoing star formation in the Aquila molecular complex and show some of the dynamic properties. The distribution of the excitation temperature Tex for H_2_CO identifies the two known star formation regions W40 and Serpens South as well as a smaller new region Serpens 3. The intensity and velocity distributions of H_2_CO and ^13^CO(1-0) do not agree well with each other, which confirms that the H_2_CO absorption structure is mostly determined by the excitation of the molecules resulting from the star formation rather than by the availability of molecular material as represented by the distribution. Some velocity-coherent linear ^13^CO(1-0) structures have been identified in velocity channel maps of H2CO and it is found that the three star formation regions lie on the intersect points of filaments. The H110{alpha} emission is found only at the location of the W40 HII region and spectral profile indicates a redshifted spherical outflow structure in the outskirts of the HII region. Sensitive mapping of H_2_CO absorption of the Aquila Complex has correctly identified the locations of star formation activity in complex molecular clouds and the spectral profiles reveal the dominant velocity components and may identify the presence of outflows.
699. HCOOCH3 map of Orion-KL
ID:
ivo://CDS.VizieR/J/A+A/532/A32
Title:
HCOOCH3 map of Orion-KL
Short Name:
J/A+A/532/A32
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Orion Kleinmann-Low nebula (Orion-KL) is a complex region of star formation. Whereas its proximity allows studies on a scale of a few hundred AU, spectral confusion makes it difficult to identify molecules with low abundances. We studied an important oxygenated molecule, HCOOCH3, to characterize the physical conditions, temperature, and density of the different molecular source components.
700. HCOO^13^CH_3_ rotational spectrum
ID:
ivo://CDS.VizieR/J/A+A/568/A58
Title:
HCOO^13^CH_3_ rotational spectrum
Short Name:
J/A+A/568/A58
Date:
21 Oct 2021
Publisher:
CDS
Description:
An astronomical survey of interstellar molecular clouds needs a previous analysis of the spectra in the microwave and sub-mm energy range of organic molecules to be able to identify them. We obtained very accurate spectroscopic constants in a comprehensive laboratory analysis of rotational spectra. These constants can be used to predict the transitions frequencies very precisely that were not measured in the laboratory. We present the experimental study and its theoretical analysis for two ^13^C-methyl formate isotopologues to detect these two isotopologues for the first time in their excited torsional states, which lie at 130/cm (200K) in Orion-KL. New spectra of HCO-O-^13^CH_3_ (^13^C_2_) methyl formate were recorded with the mm- and submm-wave spectrometer in Lille from 50 to 940GHz. A global fit for v_t_=0 and 1 was accomplished with the BELGI program to reproduce the experimental spectra with greater accuracy. We analysed 5728 and 2881 new lines for v_t_=0 and 1 for HCOO^13^CH_3_. These new lines were globally fitted with 846 previously published lines for v_t_=0. In consequence, 52 parameters of the RAM Hamiltonian were accurately determined and the value of the barrier height (V_3_=369.93168(395)/cm) was improved. We report the detection of the first excited torsional states (v_t_=1) in Orion-KL for the ^13^C_2_ and ^13^C_1_ methyl formate based on the present analysis and previously published data. We provide column densities, isotopic abundances, and vibrational temperatures for these species. Following this work, accurate prediction can be provided. This permits detecting 135 features of the first excited torsional states of ^13^C-methyl formate isotopologues in Orion-KL in the 80-280GHz frequency range, without missing lines.