Molecular Gas in 21 and 30 μm Sources: The 2 mm and 1.3 mm Spectra of IRAS 21318+5631 and 22272+5435
Abstract
The carriers of the 21 and 30 μm emission features in infrared spectra of circumstellar envelopes are a long-standing enigma. In this paper, we present the results of molecular line observations toward two circumstellar envelopes exhibiting the 21 and/or 30 μm features, IRAS 21318+5631 and 22272+5435. We investigate whether they have unusual gas-phase chemistry and search for a possible gas-phase precursor of the carriers of the two dust features. The spectra cover several discrete frequency ranges of 130-164 GHz and 216.5-273 GHz, resulting in a detection of 13 molecular species and isotopologues in each object. A rotation-diagram analysis is carried out to determine the molecular abundances, column densities, and excitation temperatures. We did not discover any molecular species that would be unexpected in a normal C-rich star. Nevertheless, there exists subtle differences between their molecular abundances. IRAS 22272+5435 shows stronger SiC2 and HC3N lines and weaker SiS lines than IRAS 21318+5631, suggesting that this 21 μm source is more carbon-rich and has experienced more efficient dust formation. We discuss the potential implications of the results for the carriers of the 21 μm and 30 μm features.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2020
- DOI:
- 10.3847/1538-4357/ab9b80
- arXiv:
- arXiv:2006.07044
- Bibcode:
- 2020ApJ...898..151Z
- Keywords:
-
- Spectral line identification;
- Circumstellar matter;
- Interstellar molecules;
- Asymptotic giant branch;
- Post-asymptotic giant branch;
- 2073;
- 241;
- 849;
- 108;
- 1287;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 43 pages, 6 figures, Accepted for publication in ApJ