The Complex Organic Molecular Content in the L1498 Starless Core

Jiménez-Serra, Izaskun; Vasyunin, A. I.; Spezzano, S.; Caselli, P.; Cosentino, Giuliana; Viti, S.

doi:10.3847/1538-4357/ac024c

Cited by 27 publications

(10 citation statements)

References 65 publications

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“…Complex organic molecules (COMs), consisting of more than six atoms with one carbon atom at least, are important species for understanding the molecular evolution in the universe. They have extensively been found in various environments of low-mass star formation: quiescent dense clouds, pre-stellar cores (e.g., Bacmann et al 2012;Cernicharo et al 2012;Ceccarelli et al 2017;Soma et al 2018;Scibelli & Shirley 2020;Jiménez-Serra et al 2021;Scibelli et al 2021), disk/envelope systems of protostellar cores (e.g., Cazaux et al 2003;Bottinelli et al 2004;Kuan et al 2004;Pineda et al 2012;Jørgensen et al 2016;Oya et al 2016Oya et al , 2018Lee et al 2019;Imai et al 2019;Bianchi et al 2020;Manigand et al 2020;van Gelder et al 2020;Martín-Doménech et al 2021;Nazari et al 2021;Tychoniec et al 2021;Chahine et al 2022), and outflow shock regions around protostars (e.g., Arce et al 2008;Sugimura et al 2011;Codella et al 2020;De Simone et al 2020). A chemical differentiation between nitrogen-bearing and oxygen-bearing species has long been recognized in high-mass protostellar clusters (e.g., Blake et al 1987;Beuther et al 2005;Fontani et al 2007;Crockett et al 2015;Feng et al 2015;Wright et al 1996;Wyrowski et al 1999) and a low-mass binary source (Kuan et al 2004;Caux et al 2011;…”

Section: Introductionmentioning

confidence: 99%

Chemical Differentiation and Temperature Distribution on a Few au Scale around the Protostellar Source B335

Okoda

Oya

Imai

et al. 2022

ApJ

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Resolving physical and chemical structures in the vicinity of a protostar is of fundamental importance for elucidating their evolution to a planetary system. In this context, we have conducted 1.2 mm observations toward the low-mass protostellar source B335 at a resolution of 0.″03 with the Atacama Large Millimeter/submillimeter Array. More than 20 molecular species including HCOOH, NH2CHO, HNCO, CH3OH, CH2DOH, CHD2OH, and CH3OD are detected within a few tens au around the continuum peak. We find a systematic chemical differentiation between oxygen-bearing and nitrogen-bearing organic molecules by using the principal component analysis for the image cube data. The distributions of the nitrogen-bearing molecules are more compact than those of the oxygen-bearing ones except for HCOOH. The temperature distribution of the disk/envelope system is revealed by a multiline analysis for each of HCOOH, NH2CHO, CH3OH, and CH2DOH. The rotation temperatures of CH3OH and CH2DOH at the radius of 0.″06 along the envelope direction are derived to be 150–165 K. On the other hand, those of HCOOH and NH2CHO, which have a smaller distribution, are 75–112 K, and are significantly lower than those for CH3OH and CH2DOH. This means that the outer envelope traced by CH3OH and CH2DOH is heated by additional mechanisms rather than protostellar heating. We here propose the accretion shock as the heating mechanism. The chemical differentiation and the temperature structure on a scale of a few au provide us with key information to further understand chemical processes in protostellar sources.

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Section: Introductionmentioning

confidence: 99%

Chemical Differentiation and Temperature Distribution on a Few au Scale around the Protostellar Source B335

Okoda

Oya

Imai

et al. 2022

ApJ

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“…Complex organic molecules (COMs), molecules with six or more atoms (see Herbst & van Dishoeck 2009;Jørgensen et al 2020, for reviews), are commonly observed toward both lowmass and high-mass young embedded protostellar systems (e.g., Belloche et al 2013;Ceccarelli et al 2014;Jørgensen et al 2016;Bøgelund et al 2019;Nazari et al 2021;Yang et al 2021). They are also detected in protostellar outflows (e.g., Arce et al 2008;Codella et al 2017;Tychoniec et al 2021) and in low abundances in cold clouds (Bacmann et al 2012;Sci-belli et al 2021;Jiménez-Serra et al 2021). The simplest COMs such as methanol (CH 3 OH) and methyl cyanide (CH 3 CN) have also been detected toward more evolved low-mass Class II systems (Walsh et al 2014;Öberg et al 2015), in some cases pointing at inheritance between prestellar cores and protoplanetary disks (Booth et al 2021;van der Marel et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Importance of source structure on complex organics emission. I. Observations of CH$_3$OH from low-mass to high-mass protostars

van Gelder,

Nazari,

Tabone

et al. 2022

Preprint

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Context. Complex organic molecules (COMs) are often observed toward embedded Class 0 and I protostars. However, not all Class 0 and I protostars exhibit COMs emission. Aims. The aim is to study variations in methanol (CH 3 OH) emission and use this as an observational tracer of hot cores to test if absence of CH 3 OH emission can be linked to source properties. Methods. A sample of 148 low-mass and high-mass protostars is investigated using new and archival observations with the Atacama Large Millimeter/submillimeter Array (ALMA) that contain lines of CH 3 OH and its isotopologues. Data for an additional 36 sources are added from the literature giving a total of 184 different sources. The warm (T 100 K) gaseous CH 3 OH mass, M CH 3 OH , is determined for each source using primarily optically thin isotopologues and compared to a simple toy model of a spherically symmetric infalling envelope that is passively heated the central protostar.Results. A scatter of more than four orders of magnitude is found for M CH 3 OH among the low-mass protostars with values ranging between 10 −7 M and 10 −11 M . On average, Class I protostellar systems seem to have less warm M CH 3 OH ( 10 −10 M ) than younger Class 0 sources (∼ 10 −7 M ). High-mass sources in our sample show higher warm M CH 3 OH up to ∼ 10 −7 − 10 −3 M . To take into account the effect of the source's overall mass on M CH 3 OH , a normalized CH 3 OH mass is defined as M CH 3 OH /M dust,0 , where M dust,0 is the cold + warm dust mass in the disk and inner envelope within a fixed radius measured from the ALMA dust continuum. A correlation between M CH 3 OH /M dust,0 and L bol is found. Excluding upper limits, a simple power-law fit to the normalized warm CH 3 OH masses results in M CH 3 OH /M dust,0 ∝ L 0.70±0.05 bol over an L bol range of 10 −1 − 10 6 L . This is in good agreement with the toy model which predicts that the normalized M CH 3 OH increases with L 0.75 bol due to the snowline moving outward. Sources for which the size of the disk is equivalent or smaller than the estimated 100 K radius fall within the 3σ range of the best-fit power-law model, whereas sources with significantly larger disks show up to two orders of magnitude lower normalized warm CH 3 OH masses. Conclusions. The agreement between sources that are rich in CH 3 OH with the toy model of a spherically symmetric infalling envelope implies that the thermal structure of the envelopes in these sources is likely not strongly affected by a disk. However, based on the disagreement between the toy model and sources showing less warm CH 3 OH mass, we suggest that source structure such as a disk can result in colder gas and thus fewer COMs in the gas phase. Additionally, optically thick dust can hide the emission of COMs. Advanced modeling is necessary to quantify the effects of a disk and/or continuum optical depth on the presence of gaseous COMs in young protostellar systems.

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“…Another interesting discussion from this work concerns the prevalence of OH over other reactive radicals (in this work represented by NH 2 and CH 3 ) may be an explanation for the segregation of O-bearing and N-bearing COMs in cold cores (Jiménez-Serra et al 2021). Very briefly, and taking as an example the L1498 prestellar core, N-bearing molecules (such as CH 3 CN or CH 2 CHCN) were located in the outer shell of the core, while -O bearing molecules were not and are expected towards the more accreted center of the core.…”

Section: Discussionmentioning

confidence: 85%

Radical Addition and H Abstraction Reactions in C2H2, C2H4 and C2H6: A Gateway for Ethyl and Vinyl Bearing Molecules in the Interstellar Medium

Molpeceres,

Rivilla

2022

Preprint

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Context. Recent interstellar detections include a significant number of molecules containing vinyl (C 2 H 3 ) and ethyl (C 2 H 5 ) groups in their structure. For several of these molecules, there is not a clear experimental or theoretical evidence that support their formation from simpler precursors Aims. We carried out a systematic search of viable reactions starting from closed shell hydrocarbons containing two carbon atoms (ethane, C 2 H 6 ; ethylene, C 2 H 4 ; and acetylene, C 2 H 2 ) with the goal of determining viable chemical routes for the formation of vinyl and ethyl molecules on top of interstellar dust grains. Methods. We used density functional theory calculations in combination with semiclassical instanton theory to derive the rate coefficients for the radical-neutral surface reactions. The effect of a surface was modelled through an implicit surface approach, profiting from the weak interaction between the considered hydrocarbons and the dust surfaces. Results. Our results show that both H and OH radicals are key in converting acetylene and ethylene into more complex radicals that are susceptible to continue reacting and forming interstellar complex organic molecules. The relevant reactions, for example OH additions, present rate constants above 10 1 s −1 that are likely competitive with OH diffusion on grains. Similarly, H atom addition to acetylene and ethylene is a very fast process with rate constants above 10 4 s −1 in all cases, and greatly enhanced by quantum tunneling. Hydrogen abstraction reactions are less relevant, but may play a role in specific cases involving the OH radical. Reactions with other radicals NH 2 , CH 3 are likely to have a much lesser impact in the chemistry of ethyl and vinyl bearing molecules. Conclusions. The effective formation at low temperatures of four radicals (C 2 H 3 , C 2 H 5 , C 2 H 2 OH, and C 2 H 4 OH) through our proposed mechanism opens the gate for the formation of complex organic molecules and indicates a potential prevalence of OH bearing molecules on the grain. Following our suggested reaction pathway, we explain the formation of many of the newly detected molecules, and propose new molecules for detection. Our results reinforce the recent view on the importance of the OH radical in the interstellar surface chemistry.

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The Complex Organic Molecular Content in the L1498 Starless Core

Cited by 27 publications

References 65 publications

Chemical Differentiation and Temperature Distribution on a Few au Scale around the Protostellar Source B335

Chemical Differentiation and Temperature Distribution on a Few au Scale around the Protostellar Source B335

Importance of source structure on complex organics emission. I. Observations of CH$_3$OH from low-mass to high-mass protostars

Radical Addition and H Abstraction Reactions in C2H2, C2H4 and C2H6: A Gateway for Ethyl and Vinyl Bearing Molecules in the Interstellar Medium

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