English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The carriers of the 21 and 30\,$\mu$m emission features in infrared spectraof circumstellar envelopes are a long-standing enigma. In this paper, wepresent the results of molecular line observations toward two circumstellarenvelopes exhibiting the 21 and/or 30\,$\mu$m features, IRAS\,21318+5631 and22272+5435, aiming at investigating whether they have unusual gas-phasechemistry and searching for possible gas-phase precursor of the carriers of thetwo dust features. The spectra cover several discrete frequency ranges of130--164\,GHz and 216.5--273\,GHz, resulting in a detection of 13 molecularspecies and isotopologues in each object. Rotation-diagram analysis is carriedout to determine the molecular abundances, column densities, and excitationtemperatures. We did not discover any molecular species that is unexpected in anormal C-rich star. Nevertheless, there exists subtle difference between theirmolecular abundances. IRAS\,22272+5435 shows stronger SiC$_2$ and HC$_3$N linesand weaker SiS lines than IRAS\,21318+5631, presumably suggesting that this21\,$\mu$m source is more carbon rich and has experienced a more efficient dustformation. We discuss the potential implications of the results for thecarriers of the 21\,$\mu$m and 30\,$\mu$m features.

Molecular gas in 21 and 30 micron sources: the 2\,mm and 1.3\,mm spectra of IRAS\,21318+5631 and 22272+5435