A Radio Molecular Line Search for Evidence of an O-rich Environment Around Binary in Silicate Carbon Stars
Abstract
We report observations of oxygen-rich (O-rich) radio molecular line tracers, including H2CO, H2O, and HCO+ toward 28 silicate carbon stars (SCSs). SCSs are special evolved star systems that consist of a carbon star associated with peculiar O-rich circumstellar material. Absorption in the 6 cm ${{\rm{H}}}_{2}\mathrm{CO}$ transition was detected from seven SCSs using the Shanghai 65 m Tianma radio telescope. In order to further investigate their O-rich material, several 3 mm molecular lines including HCO+ and CO were also observed with the Purple Mountain Observatory 13.7 m telescope. Double-peak profiles in some of these lines suggest the possible presence of a companion in the SCS system. A negative association between H2O masers and H2CO absorption was found in our sample of SCSs. The ${{\rm{H}}}_{2}{\rm{O}}$ maser sources may correspond to an earlier evolutionary stage when the circumstellar envelope (CSE) material is O-rich and limited to a compact and denser region. As the star evolves the CSE gradually expands and carbon abundance is enhanced, resulting in the ${{\rm{H}}}_{2}{\rm{O}}$ masers disappearing and H2CO absorption arising.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 2020
- DOI:
- 10.3847/1538-4357/ab6594
- Bibcode:
- 2020ApJ...890...34Z
- Keywords:
-
- Evolved stars;
- Silicon stars;
- Circumstellar envelopes;
- Circumstellar matter;
- Binary stars;
- Asymptotic giant branch stars;
- Post-asymptotic giant branch stars;
- Carbon stars;
- Chemically peculiar stars;
- 481;
- 1459;
- 237;
- 241;
- 154;
- 2100;
- 2121;
- 199;
- 226