- ID:
- ivo://CDS.VizieR/J/A+A/425/767
- Title:
- HC_5_N vibrationally excited states
- Short Name:
- J/A+A/425/767
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The rotational spectrum of the semistable HC_5_N molecule has been investigated in the millimeter-wave region for eight excited bending states which lie below 500cm^-1^, namely v_11_=1, 2, 3, and 4, v_10_=1, v_9_=1, (v_10_=1, v_11_=1), and (v_10_=1, v_11_=2). Transitions up to J=101-100 were measured, reaching a frequency as high as 270GHz. The set of spectroscopic constants determined in the present work makes it possible to predict much improved rest frequencies of millimeter-wave lines produced by vibrationally excited HC_5_N in hot core molecular sources and circumstellar shells. The Tables list the measured frequencies and the corresponding residuals of the least-squares analyses of J+1<--J transitions, with J in the range 8-100, which occur in the centimeter- and millimeter-wave regions.
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- ID:
- ivo://CDS.VizieR/J/ApJ/652/1230
- Title:
- H_2_CO absorption toward Galactic anticenter
- Short Name:
- J/ApJ/652/1230
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out a blind search in the general direction of the Galactic anticenter for absorption of the cosmic microwave background (CMB) radiation near 4.83GHz by molecular clouds containing gaseous ortho-formaldehyde (H_2_CO). The observations were done using the 25m radio telescope at Onsala in Sweden and covered strips in Galactic latitude, 1{deg}<=b<=+1{deg}, at several longitudes in the region 170{deg}<=l<=190{deg}. Spectra were obtained in these strips with a grid spacing corresponding to the telescope resolution of 10'. We have detected H_2_CO CMB absorption at 10% of the survey pointings.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A130
- Title:
- HCO and CH_3_O in prestellar cores
- Short Name:
- J/A+A/587/A130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The recent unexpected detection of terrestrial complex organic molecules in the cold (~10K) gas has cast doubts on the commonly accepted formation mechanisms of these species. Standard gas-phase mechanisms are inefficient and tend to underproduce these molecules, and many of the key reactions involved are unconstrained. Grain-surface mechanisms, which were presented as a viable alternative, suffer from the fact that they rely on grain surface diffusion of heavy radicals, which is not possible thermally at very low temperatures. One of the simplest terrestrial complex organic molecules, methanol is believed to form on cold grain surfaces following from successive H atom additions on CO. Unlike heavier species, H atoms are very mobile on grain surfaces even at 10K. Intermediate species involved in grain surface methanol formation by CO hydrogenation are the radicals HCO and CH_3_O, as well as the stable species formaldehyde H_2_CO. These radicals are thought to be precursors of complex organic molecules on grain surfaces. We present new observations of the HCO and CH_3_O radicals in a sample of prestellar cores and carry out an analysis of the abundances of the species HCO, H_2_CO, CH_3_O, and CH_3_OH, which represent the various stages of grain- surface hydrogenation of CO to CH_3_OH. The abundance ratios between the various intermediate species in the hydrogenation reaction of CO on grains are similar in all sources of our sample, HCO:H_2_CO:CH_3_O:CH_3_OH~10:100:1:100. We argue that these ratios may not be representative of the primordial abundances on the grains but, rather, suggest that the radicals HCO and CH_3_O are gas-phase products of the precursors H_2_CO and CH_3_OH, respectively. Various gas-phase pathways are considered, including neutral-neutral and ion-molecule reactions, and simple estimates of HCO and CH_3_O abundances are compared to the observations. Critical reaction rate constants, branching ratios, and intermediate species are finally identified.
- ID:
- ivo://CDS.VizieR/J/A+A/551/A28
- Title:
- H2CO and CO in 4 molecular clouds
- Short Name:
- J/A+A/551/A28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We seek to understand how the 4.8GHz formaldehyde absorption line is distributed in the MON R2, S156, DR17/L906, and M17/M18 regions. More specifically, we look for the relationship among the H_2_CO, ^12^CO, and ^13^CO spectral lines. The four regions of MON R2 (60'x90'), S156 (50'x70'), DR17/L906 (40'x60'), and M17/M18 (70'x80') were observed for H_2_CO (beam 10'), H110{alpha} recombination (beam 10'), 6 cm continuum (beam 10'), ^12^CO (beam 1'), and ^13^CO (beam 1'). We compared the H_2_CO, ^12^CO, ^13^CO, and continuum distributions, and also the spectra line parameters of H_2_CO, ^12^CO, and ^13^CO. Column densities of H_2_CO, ^13^CO, and H_2_ were also estimated. We found out that the H_2_CO distribution is similar to the ^12^CO and the ^13^CO distributions on a large scale. The correlation between the ^13^CO and the H_2_CO distributions is better than between the ^12^CO and H_2_CO distributions. The H_2_CO and the ^13^CO tracers systematically provide consistent views of the dense regions. Their maps have similar shapes, sizes, peak positions, and molecular spectra and present similar central velocities and line widths. Such good agreement indicates that the H_2_CO and the ^13^CO arise from similar regions.
- 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.
- 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.
- 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.
- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/617/A31
- Title:
- HCO+, CN, and 13CO maps of R Mon
- Short Name:
- J/A+A/617/A31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To our knowledge, R Mon is the only B0 star in which a gaseous Keplerian disk has been detected. However, there is some controversy about the spectral type of R Mon. Some authors propose that it could be a later B8e star, where disks are more common. Our goal is to re-evaluate the R Mon spectral type and characterize its protoplanetary disk. The spectral type of R Mon has been re-evaluated using the available continuum data and UVES emission lines. We used a power-law disk model to fit previous ^12^CO 1-0 and 2-1 interferometric observations and the PACS CO data to investigate the disk structure. Interferometric detections of ^13^CO J=1-0, HCO^+^ 1-0, and CN 1-0 lines using the IRAM Plateau de Bure Interferometer (PdBI) are presented. The HCN 1-0 line was not detected. Our analysis confirms that R Mon is a B0 star. The disk model compatible with the ^12^CO 1-0 and 2-1 interferometric observations falls short of predicting the observed fluxes of the 14<Ju<31 PACS lines; this is consistent with the scenario in which some contribution to these lines is coming from a warm envelope and/or UV-illuminated outflow walls. More interestingly, the upper limits to the fluxes of the Ju>31 CO lines suggest the existence of a region empty of CO at R<=20au in the proto-planetary disk. The intense emission of the HCO^+^ and CN lines shows the strong influence of UV photons on gas chemistry. The observations gathered in this paper are consistent with the presence of a transition disk with a cavity of Rin>=20 au around R Mon. This size is similar to the photoevaporation radius that supports the interpretation that UV photoevaporation is main disk dispersal mechanism in massive stars
- 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.