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EPoS |
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EPoS Contribution
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Chemical Evolution in Embedded Protostars: Ice Chemistry Unveiled by JWST
Yao-Lun Yang RIKEN, Wako-shi, JP | |
| Chemical evolution in prestellar and protostellar phases not only determines the initial chemical composition of protostellar disks but also provides a laboratory to study the fundamentals of interstellar chemistry. In recent years, common detection of gas-phase complex organic molecules (COMs) suggests extensive chemical reactions already taken place in the early phase of star formation. While some protostars have abundant gas-phase COMs, many protostars still show no sign of COM emission. This contrast of their gas-phase chemical signatures begs the question: Does the diverse gas-phase chemistry represent distinctively different chemical evolution? and what processes govern the chemical evolution in the early phase of star formation? In our CORINOS program, we aim to address these questions by probing the ice compositions with JWST. Ices represent the more pristine chemistry with minimum contaminations from gas-phase reactions. With the unprecedented sensitivity of JWST, we can trace the shape of ice absorption profiles, constraining its mixing with other species and detecting minor species. In all four CORINOS sources, we detect likely features of icy COMs regardless of the presence of gaseous COMs. If these signatures indeed represent icy COMs, we would get similar abundance in ice- and gas-phase. Moreover, the sources with little gaseous COMs also tend to have less ice. These findings suggest a similar ice chemistry despite that these protostars have distinct gas-phase appearance; also, the apparent deficiency of gaseous COMs is due to inefficient desorption processes rather than different chemical evolution. We also argue that prestellar chemistry plays a dominant role in determining the chemical compositions of protostellar cores. In this talk, I will overview the major results of the CORINOS program, including a detailed ice inventory of an extremely young protostar. Furthermore, whereas JWST provides extremely sensitive spectra, interpretations of ice absorption features still face several challenges. The absorption features are intrinsically blended and isolating each species is not trivial. Furthermore, spectra of embedded protostars suffer from substantial extinction by dust and ice, which hinders straightforward measurements of a continuum for deriving absorption. I will discuss the approaches we took to mitigate these challenges as well as the limitations. Robust characterizations of ice compositions would require an iterative process between observations, modeling, and laboratory experiments. | |
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| Caption: Ice features in four embedded protostar with contrasting gas-phase chemistry detected by JWST. The top panels show the MIRI/MRS spectra and the bottom three panels show the derived optical depth spectra at 7 um, 10 um, and 15 um, probing the absorption features of icy COMs, NH3 and CH3OH, and CO2, respectively. | |
| Collaborators: J.B. Bergner, Berkeley, US L.I. Cleeves, UVA, US E.F. van Dishoeck, Leiden, NL N.J. Evans II, UT-Austin, US R.T. Garrod, UVA, US J.D. Green, STScI, US R. Gross, UVA, US M. Jin, Goddard, US C.-H. Kim, SNU, KR J. Kim, KASI, KR J.-E. Lee, SNU, KR Y. Okoda, RIKEN, JP K.M. Pontoppidan, JPL, US W.R.M. Rocha, Leiden, NL N. Sakai, RIKEN, JP C.N. Shingledecker, BenedictineU, US C. Salyk, VassarU, US B. Shope, UVA, US J.J. Tobin, NRAO, US |
Key publication
Relevant topic(s): Chemistry Disks Low-Mass SF |
| Relevant Big Question: What processes determine the molecular chemistry in embedded protostars? | |