Observational Study On Oxygen-rich Molecules Of Silicate Carbon Stars

In this dissertation,we report spectral line observations of O-rich molecule and Infrared envi-ronment analysis towards Latest silicate carbon stars,using the Shanghai Astronomical Observatory65m Tianma radio telescope?TMRT?,the 13.7m millimeter wave telescope at Qinghai station of Pur-ple Mountain Observatory?PMO?,National Astronomical Observatory of Japan NOBEYAMA,respectively.Carbon stars generally have a C-rich circumstellar envelope?CSE?because of material out-flow.The mainstream view of evolved stars is that most of the carbon atoms in CSE are enriched in CO with a large binding energy.However,there is a special type of carbon star,silicate carbon star,which is found in the infrared band.There are show O-rich characteristics in circumstellar en-velope,foreshadow large amounts of oxygen-rich material.Phenomenon that cannot be explained by the conventional stellar evolution theory has gradually become a research hotspot.We report ob-servations 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 H₂CO 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 H₂O 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 H₂O masers disappearing and H₂CO absorption arising.