The Nearby Evolved Stars Survey – IV. Mapping cold gas in the circumstellar envelopes of evolved stars with 12CO and 13CO ( <i>J</i> = 1 → 0) emission

ABSTRACT We have performed mapping observations of 42 AGB stars, of which 23 and 14 stars were detected in $^{12}$CO and $^{13}$CO ($J = 1 \rightarrow 0$) emission, respectively, using 45 m telescope of Nobeyama Radio Observatory. Our aim is to reveal distributions of extended cold gas in circumstellar envelopes and test a possibility of detecting shell structures with high $^{12}$CO/$^{13}$CO ratios caused by thermal pulses and third dredge-ups. By comparing our maps with those of $^{12}$CO ($J = 3 \rightarrow 2$) emission obtained with James Clerk Maxwell Telescope at the same angular resolution, we found that envelopes of $^{12}$CO ($J = 1 \rightarrow 0$) emission has at least twice the sizes of $^{12}$CO ($J = 3 \rightarrow 2$) emission. Among 14 stars detected in both $^{12}$CO and $^{13}$CO emission, nine stars show radial variations of $^{12}$CO/$^{13}$CO ratio along radial direction in their envelopes, which is likely caused by selective photodissociation by interstellar ultraviolet radiation, not thermal pulses or third dredge ups. Based on radiative transfer simulations, we conclude that optical depths are small (typically $\tau \lesssim 0.5$), ruling out the possibility that the absence of detected shells in our data is due to optical depth. This implies no signatures of thermal pulses or third dredge ups in the last $\sim$1500–13 000 yr. We further confirmed aspherical envelope morphologies of o Cet, WX Psc, and RAFGL 618, which were likely formed by bipolar outflows and photodissociation. The elongated morphology of SV Peg that we newly found is subject to study.

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Journal
Monthly Notices of the Royal Astronomical Society
Published
2025-12-18
DOI
https://doi.org/10.1093/mnras/staf2239
Primary Topic
Astrophysics and Star Formation Studies
Type
article
Field-Weighted Citation Impact
0.00

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article

The Nearby Evolved Stars Survey – IV. Mapping cold gas in the circumstellar envelopes of evolved stars with 12CO and 13CO ( J = 1 → 0) emission

Christopher J. R. Clark, F. Kemper, Hyosun Kim, A. A. Zijlstra et al.
Monthly Notices of the Royal Astronomical Society
Astrophysics and Star Formation Studies
article

The Nearby Evolved Stars Survey – IV. Mapping cold gas in the circumstellar envelopes of evolved stars with 12CO and 13CO ( J = 1 → 0) emission

Christopher J. R. Clark, F. Kemper, Hyosun Kim, A. A. Zijlstra, Kei Amada, J. Cami, R. Wesson, S. Srinivasan, S. T. Zeegers, Gioia Rau, Naomi Hirano, S Fukaya, Iain McDonald, J. P. Marshall, T. E. Dharmawardena, A. Trejo-Cruz, Peter Scicluna, S. H. J. Wallström, Hiroshi Imai, Hiroko Shinnaga, Olivia Jones, J. A. Toalá, Jinhua He
article en

Abstract

ABSTRACT We have performed mapping observations of 42 AGB stars, of which 23 and 14 stars were detected in $^{12}$CO and $^{13}$CO ($J = 1 \rightarrow 0$) emission, respectively, using 45 m telescope of Nobeyama Radio Observatory. Our aim is to reveal distributions of extended cold gas in circumstellar envelopes and test a possibility of detecting shell structures with high $^{12}$CO/$^{13}$CO ratios caused by thermal pulses and third dredge-ups. By comparing our maps with those of $^{12}$CO ($J = 3 \rightarrow 2$) emission obtained with James Clerk Maxwell Telescope at the same angular resolution, we found that envelopes of $^{12}$CO ($J = 1 \rightarrow 0$) emission has at least twice the sizes of $^{12}$CO ($J = 3 \rightarrow 2$) emission. Among 14 stars detected in both $^{12}$CO and $^{13}$CO emission, nine stars show radial variations of $^{12}$CO/$^{13}$CO ratio along radial direction in their envelopes, which is likely caused by selective photodissociation by interstellar ultraviolet radiation, not thermal pulses or third dredge ups. Based on radiative transfer simulations, we conclude that optical depths are small (typically $\tau \lesssim 0.5$), ruling out the possibility that the absence of detected shells in our data is due to optical depth. This implies no signatures of thermal pulses or third dredge ups in the last $\sim$1500–13 000 yr. We further confirmed aspherical envelope morphologies of o Cet, WX Psc, and RAFGL 618, which were likely formed by bipolar outflows and photodissociation. The elongated morphology of SV Peg that we newly found is subject to study.

Monthly Notices of the Royal Astronomical SocietyVol. 547(2)
Kagoshima University (JP), Institució Catalana de Recerca i Estudis Avançats (ES), Western University (CA), Space Telescope Science Institute (US), Space Science Institute (US), U.S. National Science Foundation (US), Institute of Astronomy and Astrophysics, Academia Sinica (TW), Institute of Space Sciences (ES), University of Hertfordshire (GB), Chinese Academy of Sciences (CN), The Open University (GB), Korea Astronomy and Space Science Institute (KR), Yunnan Observatories (CN), University of Manchester (GB), Philip Morris International (United States) (US), Chinese Academy of Science South America Center for Astronomy (CL), Institut d'Estudis Espacials de Catalunya (ES), ASIS Foundation (US), Royal Observatory (GB), Max Planck Institute for Astronomy (DE), Institute of Space Sciences (ES), Université Bourgogne Franche-Comté (FR), European Southern Observatory (CL), Instituto de Geofísica y Astronomía (CU), National Astronomical Observatory of Japan (JP), National Astronomical Observatories (CN), European Space Research and Technology Centre (NL), University College London (GB), Space Research Organisation Netherlands (NL), UK Astronomy Technology Centre (GB), University of Chile (CL), Search for Extraterrestrial Intelligence (US), KU Leuven (BE)
Kagoshima University, Ministerio de Ciencia, Innovación y Universidades, National Research Foundation, National Natural Science Foundation of China, Chinese Academy of Sciences, Fonds Wetenschappelijk Onderzoek, Korea Astronomy and Space Science Institute, National Research Foundation of Korea, National Astronomical Observatory of Japan, Vlaamse regering, Ministry of Science and ICT, South Korea, National Science and Technology Council, Science and Technology Facilities Council, Japan Society for the Promotion of Science, Agencia Estatal de Investigación
Openalex Percentile: Top 71%
Astrophysics and Star Formation Studies
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