THE ORIGIN OF COMPLEX ORGANIC MOLECULES IN PRESTELLAR CORES

By C. Vastel, Cecilia Ceccarelli, Bertrand Lefloch, R. Bachiller. 2014

153 citations recorded by the source corpus.

Complex organic molecules (COMs) have been detected in a variety of environments including cold prestellar cores. Given the low temperatures of these objects, these detections challenge existing models. We report here new observations toward the prestellar core L1544. They are based on an unbiased spectral survey of the 3 mm band at the IRAM 30 m telescope as part of the Large Program ASAI. The observations allow us to provide a full census of the oxygen-bearing COMs in this source. We detected tricarbon monoxide, methanol, acetaldehyde, formic acid, ketene, and propyne with abundances varying from 5 × 10−11 to 6 × 10−9. The non-LTE analysis of the methanol lines shows that they are likely emitted at the border of the core at a radius of ∼8000 AU, where T ∼ 10 K and n ∼2 × 104 cm−3. Previous works have shown that water vapor is enhanced in the same region because of the photodesorption of water ices. We propose that a non-thermal desorption mechanism is also responsible for the observed emission of methanol and COMs from the same layer. The desorbed oxygen and a small amount of desorbed methanol and ethene are enough to reproduce the abundances of tricarbon monoxide, methanol, acetaldehyde, and ketene measured in L1544. These new findings open the possibility that COMs in prestellar cores originate in a similar outer layer rather than in the dense inner cores, as previously assumed, and that their formation is driven by the non-thermally desorbed species.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/9df8a8bee3e3a54a856ec4fc1f8930cde05d0883

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In Astronomy and Astrophysics

1. R. Garrod
2. P. Caselli
3. V. Wakelam
4. Cecilia Ceccarelli
5. K. Oberg
6. M. Ruaud
7. E. Bergin
8. H. Cuppen

In Instrumentation

1. R. Garrod
2. Cecilia Ceccarelli
3. E. Bergin
4. P. Caselli
5. K. Oberg
6. V. Wakelam
7. E. V. van Dishoeck
8. M. Ruaud

Citations in the corpus

• Astrochemistry and compositions of planetary systems (2020, background): “of this initial organic ice reservoir is converted into more complex organics in interstellar clouds (Öberg et al. 2010; Bacmann et al. 2012; Cernicharo et al. 2012; Vastel et al. 2014; Jiménez-Serra et al. 2016; Scibelli and Shirley 2020).”
• Binding energies: New values and impact on the efficiency of chemical desorption (2017, background): “The observation of complex organic molecules in cold and dense environments of the interstellar medium has increased the interest of the community onto such processes (Bacmann et al. 2012; Cernicharo et al. 2012; Vastel et al. 2014).”
• Formation of complex organic molecules in cold objects: the role of gas-phase reactions (2015, methodology): “More recent observations towards the pre-stellar core L1544 (Bizzocchi et al. 2014; Vastel et al. 2014) added a crucial information: the methanol emission originates from the outer shell of the cold core, where the H2 density is ∼ 3 × 104 cm−3 and the temperature is ∼ 10 K, and not from the inner…”
• Formation of Complex Molecules in Prestellar Cores: A Multilayer Approach (2017, background): “It has also been detected by Vastel et al. (2014) towards L1544, with fractional abundance of ∼10−10 wrt. H.”
• H-atom addition and abstraction reactions in mixed CO, H2CO and CH3OH ices – an extended view on complex organic molecule formation (2016, background): “Acetaldehyde and ketene were also detected in the cold pre-stellar core L1544 (Vastel et al. 2014).”
• Grain Surface Models and Data for Astrochemistry (2017, background): “High sensitivity observations have shown that complex organic molecules are also present in the gas phase in cold environments (∼ 10 K), albeit at a low level with respect to molecular hydrogen (Öberg et al. 2010, 2011; Cernicharo et al. 2012; Bacmann et al. 2012; Vastel et al. 2014).”