Exploring the <sup>13</sup>CO/C<sup>18</sup>O abundance ratio towards Galactic young stellar objects and HII regions

Areal, M. B.; Paron, S.; Peña, M.; Ortega, M. E.

doi:10.1051/0004-6361/201732067

Cited by 14 publications

(13 citation statements)

References 19 publications

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“…general, the higher values of X 13/18 are located mainly at the borders, or close to them, of regions with ionized gas, where the far-UV photons are likely escaping and selectively photodissociating the C 18 O species as found in previous works (e.g. Areal et al 2018;Kong et al 2015;Shimajiri et al 2014). This is the case of the northeastern region of the UC Hii region, where there are many pixels with high X 13/18 values (about 8), while towards the southwest, in coincidence with a dark cloud, X 13/18 is low (about 3).…”

Section: Discussionsupporting

confidence: 56%

“…This avoids the use of indirect estimations from known elemental abundances, such as the case of the 13 CO/C 18 O abundance ratio (X 13/18 ), that in general it is estimated from a double ratio between the 12 C/ 13 C and 16 O/ 18 O ratios given by Wilson & Rood (1994). In a previous paper (Areal et al 2018), using 12 CO, 13 CO, and C 18 O J=3-2 data we studied the X 13/18 towards a large sample of young stellar objects (YSOs) and Hii regions distributed along the first Galactic quadrant, finding ratios systematically lower than the predicted from the mentioned elemental abundance relations. We also found that the ratios depend not only on the distance to the Galactic center, as shown by Wilson & Rood (1994), but also on the type of source or region observed.…”

Section: Introductionmentioning

confidence: 99%

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Mapping the ¹³CO/C¹⁸O abundance ratio in the massive star-forming region G29.96−0.02

Paron

Areal

Ortega

2018

A&A

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Aims. Estimating molecular abundances ratios from the direct measurement of the emission of the molecules towards a variety of interstellar environments is indeed very useful to advance in our understanding of the chemical evolution of the Galaxy, and hence of the physical processes related to the chemistry. It is necessary to increase the sample of molecular clouds, located at different distances, in which the behaviour of molecular abundance ratios, such as the 13 CO/C 18 O ratio, is studied in detail. Methods. We selected the well-studied high-mass star-forming region G29.96−0.02, located at a distance of about 6.2 kpc, which is an ideal laboratory to perform this kind of studies. To study the 13 CO/C 18 O abundance ratio (X 13/18 ) towards this region it was used 12 CO J=3-2 data obtained from the CO High-Resolution Survey, 13 CO and C 18 O J=3-2 data from the 13 CO/C 18 O (J=3-2) Heterodyne Inner Milky Way Plane Survey, and 13 CO and C 18 O J=2-1 data retrieved from the CDS database which were observed with the IRAM 30 m telescope. The distribution of column densities and X 13/18 throughout the extension of the analyzed molecular cloud was studied based on LTE and non-LTE methods.Results. Values of X 13/18 between 1.5 to 10.5, with an average of about 5, were found across the studied region, showing that, besides the dependency between X 13/18 and the galactocentric distance, the local physical conditions may strongly affect this abundance ratio. We found that correlating the X 13/18 map with the location of the ionized gas and dark clouds allows us to suggest in which regions the far-UV radiation stalls in dense gaseous components, and in which ones it escapes and selectively photodissociates the C 18 O isotope.The non-LTE analysis shows that the molecular gas has very different physical conditions, not only spatially across the cloud, but also along the line of sight. This kind of studies may represent a tool to indirectly estimate (from molecular lines observations) the degree of photodissociation in molecular clouds, which is indeed useful to study the chemistry in the interstellar medium.

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Section: Discussionsupporting

confidence: 56%

Section: Introductionmentioning

confidence: 99%

Mapping the ¹³CO/C¹⁸O abundance ratio in the massive star-forming region G29.96−0.02

Paron

Areal

Ortega

2018

A&A

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“…As mentioned in Sect. 5.7, the 13 CO/C 18 O abundance ratio increases in regions of enhanced UV field (Shimajiri et al 2014;Ishii et al 2019;Areal et al 2018). This variation is interpreted in terms of the selective photodissociation and isotopic fractionation (see Bron et al 2018;Fuente et al 2019).…”

Section: Comparison Between Taurus Perseus and Orionmentioning

confidence: 98%

Gas phase Elemental abundances in Molecular cloudS (GEMS)

Rodríguez-Baras

Fuente

Riviére-Marichalar

et al. 2021

A&A

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Gas phase Elemental abundances in Molecular CloudS (GEMS) is an IRAM 30 m Large Program designed to provide estimates of the S, C, N, and O depletions and gas ionization degree, X(e−), in a selected set of star-forming filaments of Taurus, Perseus, and Orion. Our immediate goal is to build up a complete and large database of molecular abundances that can serve as an observational basis for estimating X(e−) and the C, O, N, and S depletions through chemical modeling. We observed and derived the abundances of 14 species (13CO, C18O, HCO+, H13CO+, HC18O+, HCN, H13CN, HNC, HCS+, CS, SO, 34SO, H2S, and OCS) in 244 positions, covering the AV ~3 to ~100 mag, n(H2) ~ a few 103 to 106 cm−3, and Tk ~10 to ~30 K ranges in these clouds, and avoiding protostars, HII regions, and bipolar outflows. A statistical analysis is carried out in order to identify general trends between different species and with physical parameters. Relations between molecules reveal strong linear correlations which define three different families of species: (1) 13CO and C18O isotopologs; (2) H13CO+, HC18O+, H13 CN, and HNC; and (3) the S-bearing molecules. The abundances of the CO isotopologs increase with the gas kinetic temperature until TK ~ 15 K. For higher temperatures, the abundance remains constant with a scatter of a factor of ~3. The abundances of H13 CO+, HC18 O+, H13 CN, and HNC are well correlated with each other, and all of them decrease with molecular hydrogen density, following the law ∝ n(H2)−0.8 ± 0.2. The abundances of S-bearing species also decrease with molecular hydrogen density at a rate of (S-bearing/H)gas ∝ n(H2)−0.6 ± 0.1. The abundances of molecules belonging to groups 2 and 3 do not present any clear trend with gas temperature. At scales of molecular clouds, the C18O abundance is the quantity that better correlates with the cloud mass. We discuss the utility of the 13CO/C18O, HCO+/H13CO+, and H13 CO+/H13CN abundance ratios as chemical diagnostics of star formation in external galaxies.

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“…To calculate the mass of the sources, we need to take the abundance of C 18 O with respect to H 2 into account. There is a substantial uncertainty in this, which moreover depends on the type of region observed (e.g., PDR regions vs. YSO vs. HII regions), with some authors suggesting lower (Areal et al 2018) or higher (Shimajiri et al 2014) C 18 O versus H 2 abundances that can lead to significantly different results. We adopted the calibration of Frerking et al (1982) for high-density enviroments in ρ Ophiuchus.…”

Section: Gas Temperatures and Column Densitiesmentioning

confidence: 99%

IRAM and Gaia views of multi-episodic star formation in IC 1396A

Sicilia‐Aguilar

Patel

Fang

et al. 2019

A&A

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Context. IC 1396A is a cometary globule that contains the Class 0 source IC 1396A-PACS-1, which was discovered with Herschel. Aims. We use IRAM 30m telescope and Gaia DR2 data to explore the star formation history of IC 1396A and investigate the possibilities of triggered star formation. Methods. IRAM and Herschel continuum data were used to obtain dust temperature and column density maps. Heterodyne data reveal the velocity structure of the gas. Gaia DR2 proper motions for the stars complete the kinematics of the region. Results. IC 1396A-PACS-1 presents molecular emission similar to a hot corino with warm carbon chain chemistry due to the UV irradiation. The source is embedded in a dense clump surrounded by gas at velocities that are significantly different from the velocities of the Tr 37 cluster. CN emission reveals photoevaporation, while continuum data and high-density tracers (C18O, HCO+, DCO+, and N2D+) reveal distinct gaseous structures with a range of densities and masses. Conclusions. By combining the velocity, column density, and temperature information and Gaia DR2 kinematics, we confirm that the globule has experienced various episodes of star formation. IC 1396A-PACS-1 is probably the last intermediate-mass protostar that will form within IC 1396A; it shows evidence of being triggered by radiation-driven implosion. Chemical signatures such as CCS place IC 1396A-PACS-1 among the youngest known protostars. Gaia DR2 data reveal velocities in the plane of the sky ~4 km s−1 for IC 1396A with respect to Tr 37. The total velocity difference (8 km s−1) between the Tr 37 cluster and IC 1396A is too small for IC 1396A to have undergone substantial rocket acceleration, which imposes constraints on the distance to the ionizing source in time and the possibilities of triggered star formation. The three stellar populations in the globule reveal that objects located within relatively close distances (<0.5 pc) can be formed in various star-forming episodes within ~1–2 Myr. Once the remaining cloud disperses, we expect substantial differences in evolutionary stage and initial conditions for the resulting objects and their protoplanetary disks, which may affect their evolution. Finally, evidence for short-range feedback from the embedded protostars, and in particular, the A-type star V390 Cep, is also observed.

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Exploring the ¹³CO/C¹⁸O abundance ratio towards Galactic young stellar objects and HII regions

Cited by 14 publications

References 19 publications

Mapping the ¹³CO/C¹⁸O abundance ratio in the massive star-forming region G29.96−0.02

Mapping the ¹³CO/C¹⁸O abundance ratio in the massive star-forming region G29.96−0.02

Gas phase Elemental abundances in Molecular cloudS (GEMS)

IRAM and Gaia views of multi-episodic star formation in IC 1396A

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Exploring the 13CO/C18O abundance ratio towards Galactic young stellar objects and HII regions

Cited by 14 publications

References 19 publications

Mapping the 13CO/C18O abundance ratio in the massive star-forming region G29.96−0.02

Mapping the 13CO/C18O abundance ratio in the massive star-forming region G29.96−0.02

Gas phase Elemental abundances in Molecular cloudS (GEMS)

IRAM and Gaia views of multi-episodic star formation in IC 1396A

Contact Info

Product

Resources

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Exploring the ¹³CO/C¹⁸O abundance ratio towards Galactic young stellar objects and HII regions

Mapping the ¹³CO/C¹⁸O abundance ratio in the massive star-forming region G29.96−0.02

Mapping the ¹³CO/C¹⁸O abundance ratio in the massive star-forming region G29.96−0.02