Pei-Sheng Chen

Newly Identified Silicate Carbon Stars from IRAS Low-Resolution Spectra

The discovery of silicate carbon star poses a challenge to the theory of stellar evolution in the late stage, hence it is important to look for more silicate carbon stars. To this end we have carried out cross-identifications between the new IRAS Low-Resolution Spectrum (LRS) database and the new carbon star catalog, CGCS3. We have found nine new silicate carbon stars with silicate features around 10 mu m and/or 18 mu m. These newly identified stars are located in the Regions IIIa and VII in the IRAS two-color diagram, which means they indeed have typical far infrared colors of silicate carbon stars. The infrared properties of each of these sources are discussed.

Infrared spectral evolution of carbon stars

We collected almost all Highly Processed Data Products (HPDP) of ISO SWS01 spectra for the Galactic visual carbon stars, infrared carbon stars, extreme carbon stars and carbon-rich proto-planetary nebulae (PPNs). Those infrared spectra are primarily analyzed and discussed. It is shown that either spectral shapes/peaks, or main molecular/dust features are evidenced to change in the sequence of visual carbon stars, infrared carbon stars, extreme carbon stars and carbon-rich PPNs. Statistically, in this sequence, continua are gradually changed from blue to red and locations of spectral peaks of continua are also gradually changed from short wavelengths to long wavelengths. In addition, in this sequence, intensities of main molecular/dust features are also gradually changed from prominent in the short wavelengths to prominent in the long wavelengths. Furthermore, from 2MASS and IRAS photometric data, the sequence is also proved. Results in this paper strongly support the previous suggestion for the evolution sequence of carbon-rich objects in our Galaxy, that is the sequence of visual carbon stars → infrared carbon stars → extreme carbon stars → carbon-rich PPNs.

On the Carbon-Star Status of Five Stars in a New Carbon Star Catalog

We find that five sources listed in the new carbon star catalog are not really carbon-rich objects but oxygen-rich stars, because they all have the prominent 10mum silicate features in absorption and the 1612 MHz OH maser emission or/and the SiO molecular features. These objects were considered as carbon stars in the catalog based only on their locations in the infrared two-color diagram. Therefore to use the infrared two-color diagram to distinguish carbon-rich stars from oxygen-rich stars must be done with caution, because, in general, it has only a statistical meaning.

IRAS 19111+2555 (=S Lyr): A Possible Silicate Carbon Star

The properties and classification of IRAS 19111+2555 have so far not been well determined. We collect all the available information and data of this star, and take the data obtained by IRAS LRS and ISO SWS to discuss its properties and classification. The star is found to have a 3.1µm feature in absorption and a 10µm feature in emission, so it is possibly a new silicate carbon star.

The Chemical Classification of the AGB Star IRAS 17515--2407

The chemical classification of IRAS 17515-2407 has been debated for a long time. Up to now there are two contenders, oxygen-rich or carbon-rich. We believe that IRAS 17515-2407 is an oxygen-rich source: because (i) it shows the silicate self-absorbed emission; (ii) in the near infrared-IRAS diagram it is located in the oxygen-rich object region and (iii) particularly, it has detected SiO maser emission.

An Infrared Photometric Study of Galaxies with Extragalactic H2O Maser Sources

All galaxies with extragalactic H2O maser sources observed so far are collected. With the 2MASS and the IRAS photometric data an infrared study is performed on those galaxies. By a comparison between the H2O maser detected sources and non-detected sources in the infrared it is indicated that infrared properties in the IRAS 12–25 μm and 60–100 μm are important for producing H2O masers in galaxies. It is also found that the H2O maser galaxies with different nuclear activity types have rather different infrared properties mainly in the IRAS 12–60 μm region.

Near infrared observation of carbon and S stars with silicate feature

The near infrared observations of carbon and S type stars with silicate feature are presented in this paper. By adding the IRAS data to the observations, the color-color diagrams and energy distributions are discussed to provide some evidence for the possible evolution status of such stars.