Hcn(1-0) Observations of Starless Cores

Sohn, Jungjoo; Lee, C. W.; Lee, H. M.; Park, Y.-S.; Myers, P. C.; Lee, Y.; Tafalla, M.

doi:10.5303/jkas.2004.37.4.261

Cited by 11 publications

(7 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It also shows that HC 3 N, DCO + , and HCN survive in the gas phase up to higher densities than most other species, and this makes them interesting line tracers of the middle layers of dense cores. Recent infall searches in starless cores Sohn et al 2004), do use this property of DCO + and HCN to penetrate deeper than using traditional tracers like CS or HCO + (e.g., Lee et al 2001). Our L1498 and L1517B analysis, however, shows that HCN and DCO + are no substitute for N 2 H + or NH 3 , as they end up depleting at densities of about 10 5 cm −3 .…”

Section: Comparison Between Moleculesmentioning

confidence: 71%

See 1 more Smart Citation

On the internal structure of starless cores

Tafalla¹,

Santiago-García²,

Myers

et al. 2006

A&A

Self Cite

183

256

View full text Add to dashboard Cite

Context. Low mass starless cores present an inhomogeneous chemical composition. Species like CO and CS deplete at their dense interiors, while N 2 H + and NH 3 survive in the gas phase. As molecular line observations are used to determine the physical conditions and kinematics of the core gas, chemical inhomogeneities can introduce a serious bias. Aims. We have carried out a molecular survey towards two starless cores, L1498 and L1517B. These cores have been selected for their relative isolation and close-to-round shape. They have been observed in a number of lines of 13 molecular species in order to determine a self-consistent set of abundance profiles. Methods. In a previous paper we modeled the physical structure of L1498 and L1517B. Here we use this work together with a spherically-symmetric Monte Carlo radiative transfer code to determine the radial profile of abundance for each species in the survey. Our model aims to fit simultaneously the radial profile of integrated intensity and the emerging spectrum from the core center. Results. L1498 and L1517B present similar abundance patterns, with most species suffering a significant drop toward the core center. This occurs for CO, CS, CH 3 OH, SO, C 3 H 2 , HC 3 N, C 2 S, HCN, H 2 CO, HCO + , and DCO + , which we fit with profiles having a sharp central hole. The size of this hole varies with molecule: DCO + , HCN, and HC 3 N have the smallest holes, while SO, C 2 S and CO have the largest holes. Only N 2 H + and NH 3 seem present in the gas phase at the core centers. Conclusions. From the different behavior of molecules, we select SO, C 2 S, and CH 3 OH as the most sensitive tracers of molecular depletion. Comparing our abundance determinations with the predictions from current chemical models we find order of magnitude discrepancies. Finally, we show how the "contribution function" can be used to study the formation of line profiles from the different regions of a core.

show abstract

Section: Comparison Between Moleculesmentioning

confidence: 71%

“…The HCN(1-0) spectra show evidence for self absorption towards both L1498 and L1517B (see also Sohn et al 2004). The HCN emission is therefore dominated by the core outer layers and it cannot be used to derive an abundance profile inside the core.…”

mentioning

confidence: 99%

On the internal structure of starless cores

Tafalla¹,

Santiago-García²,

Myers

et al. 2006

A&A

Self Cite

183

256

View full text Add to dashboard Cite

show abstract

“…It also shows that HC 3 N, DCO + , and HCN survive in the gas phase up to higher densities than most other species, and this makes them interesting line tracers of the middle layers of dense cores. Recent infall searches in starless cores (Lee et al 2004;Sohn et al 2004), do use this property of DCO + and HCN to penetrate deeper than using traditional tracers like CS or HCO + (e.g., Lee et al 2001). Our L1498 and L1517B analysis, however, shows that HCN and DCO + are no substitute for N 2 H + or NH 3 , as they end up depleting at densities of about 10 5 cm −3 .…”

Section: Comparison Between Moleculesmentioning

confidence: 76%

“…HCN and H 13 CN. The HCN(1-0) spectra show evidence for self absorption towards both L1498 and L1517B (see also Sohn et al 2004). The HCN emission is therefore dominated by the core outer layers and it cannot be used to derive an abundance profile inside the core.…”

Section: Fitting Proceduresmentioning

confidence: 93%

On The Internal Structure Of Starless Cores. Physical and Chemical Properties of L1498 and L1517B

Tafalla

Myers

Caselli

et al. 2004

Astrophysics and Space Science

Self Cite

View full text Add to dashboard Cite

Context. Low mass starless cores present an inhomogeneous chemical composition. Species like CO and CS deplete at their dense interiors, while N2H + and NH3 survive in the gas phase. As molecular line observations are used to determine the physical conditions and kinematics of the core gas, chemical inhomogeneities can introduce a serious bias. Aims. We have carried out a molecular survey towards two starless cores, L1498 and L1517B. These cores have been selected for their relative isolation and close-to-round shape. They have been observed in a number of lines of 13 molecular species in order to determine a self-consistent set of abundance profiles. Methods. In a previous paper we modeled the physical structure of L1498 and L1517B. Here we use this work together with a spherically-symmetric Monte Carlo radiative transfer code to determine the radial profile of abundance for each species in the survey. Our model aims to fit simultaneously the radial profile of integrated intensity and the emerging spectrum from the core center.Results. L1498 and L1517B present similar abundance patterns, with most species suffering a significant drop toward the core center. This occurs for CO, CS, CH3OH, SO, C3H2, HC3N, C2S, HCN, H2CO, HCO + , and DCO + , which we fit with profiles having a sharp central hole. The size of this hole varies with molecule: DCO + , HCN, and HC3N have the smallest holes, while SO, C2S and CO have the largest holes. Only N2H + and NH3 seem present in the gas phase at the core centers. Conclusions. From the different behavior of molecules, we select SO, C2S, and CH3OH as the most sensitive tracers of molecular depletion. Comparing our abundance determinations with the predictions from current chemical models we find order of magnitude discrepancies. Finally, we show how the "contribution function" can be used to study the formation of line profiles from the different regions of a core.

show abstract

“…Other studies have also reported no evidence of HCN depletion. Sohn et al (2004) found that the intensity of the F = 0 → 1 hyperfine component of HCN(1-0) correlates strongly with the intensity of N 2 H + , a molecule that does not show depletion in prestellar cores at the scales sampled by single-dish telescopes. In a detailed analysis of the HCN emission toward two contracting cores, Lee et al (2007) also obtained a flat HCN abundance profile in L694-2, at 7×10 −9 relative to H 2 , while they derived an increase from 1.7 to 3.5 ×10 −9 in L1197 when moving inward.…”

Section: Depletion Of Hcn From the Gas Phasementioning

confidence: 96%

Abundance of HCN and its C and N isotopologues in L1498

Magalhaes

Hily-Blant

Fauré

et al. 2018

A&A

View full text Add to dashboard Cite

The isotopic ratio of nitrogen in nearby protoplanetary disks, recently measured in CN and HCN, indicates that a fractionated reservoir of volatile nitrogen is available at the earliest stage of comet formation. This reservoir also presents a 3:1 enrichment in 15 N relative to the elemental ratio of 330, identical to that between the solar system comets and the protosun, suggesting that similar processes are responsible for the fractionation in the protosolar nebula (PSN) and in these PSN analogs. However, where, when, and how the fractionation of nitrogen takes place is an open question. Previously obtained HCN/HC 15 N abundance ratios suggest that HCN may already be enriched in 15 N in prestellar cores, although doubts remain on these measurements, which rely on the double-isotopologue method. Here we present direct measurements of the HCN/H 13 CN and HCN/HC 15 N abundance ratios in the L1498 prestellar core based on spatially resolved spectra of HCN(1-0), (3-2), H 13 CN(1-0), and HC 15 N(1-0) rotational lines. We use state-of-the-art radiative transfer calculations using ALICO, a 1D radiative transfer code capable of treating hyperfine overlaps. From a multiwavelength analysis of dust emission maps of L1498, we derive a new physical structure of the L1498 cloud. We also use new, high-accuracy HCN-H 2 hyperfine collisional rates, which enable us to quantitatively reproduce all the features seen in the line profiles of HCN(1-0) and HCN(3-2), especially the anomalous hyperfine line ratios. Special attention is devoted to derive meaningful uncertainties on the abundance ratios. The obtained values, HCN/H 13 CN=45±3 and HCN/HC 15 N=338±28, indicate that carbon is heavily fractionated in HCN, but nitrogen is not. For the H 13 CN/HC 15 N abundance ratio, our detailed study validates to some extent analyses based on the single excitation temperature assumption. Comparisons with other measurements from the literature suggest significant core-to-core variability. Furthermore, the heavy 13 C enrichment we found in HCN could explain the superfractionation of nitrogen measured in solar system chondrites.

show abstract

Hcn(1-0) Observations of Starless Cores

Cited by 11 publications

References 11 publications

On the internal structure of starless cores

On the internal structure of starless cores

On The Internal Structure Of Starless Cores. Physical and Chemical Properties of L1498 and L1517B

Abundance of HCN and its C and N isotopologues in L1498

Contact Info

Product

Resources

About