Pei-sheng Chen

A further identification of silicate carbon stars

A new cross identification of 22 silicate carbon stars is made using the GCGCS, IRAS, PSC, HST/GSC and USNO catalogues. More precise positions for the sources are given for further study and cases of unconfirmed identification listed.

A study of the infrared emission of three H II regions S 140–142☆

Abstract The infrared emission of the H II region-molecular cloud complexes S 140, S 141 and S 142 is examined using the IRAS Sky Survey Atlases. The IRAF and Skyview software are used to draw the contour maps of infrared intensity, color temperature and optical depth of each source. The total infrared luminosity and dust distribution in the complexes are given. Compact clumps where star formation probably takes place are identified. The exciter star of S 141 is analyzed.

OH/IR stars with SiC circumstellar envelopes

From the LRS spectra of almost 2000 IRAS sources showing the 1612 MHz OH emission we found 9 candidates for OH/IR stars with SiC features in their envelopes. Further study indicates that 6 of these are definitely or very probably carbon star with the 11.3 mu m SiC emission feature in addition of being OH/IR stars showing the 1612 MHz OH maser emission.

IRAS 17213-3841: A late-type carbon-rich star or an early-type emission-line star?

IRAS 17213-3841 is listed in a new edition of the Catalogue of Carbon Stars as a, carbon-rich star. However, the IRAS low-resolution spectrum of the star shows the oxygen-rich silicate emission feature. Spectral observations show that the star is an early-type emission-line star near the zero age main sequence with spectral type O9/B0, and is not a carbon star. Therefore it should be removed from the catalogue of carbon stars. The near infrared-IRAS two-colour diagram method used to identify IRAS 17213-3841 as a carbon star is not completely reliable and care should be exercised when using it for identification of carbon stars.

Infrared spectra of T Tauri stars

We present IRAS low-resolution spectra for 26 T Tauri stars and, based on the spectra, discuss the properties and environment of these stars. The analysis reveals that silicate dust is a common material in the circumstellar shells of T Tauri stars.

A discussion on the mass loss formulae for OH/IR stars

It is found that the mass loss rate derived from S-25/S-12 is generally greater;than that from the OH flux. This suggests an increasing loss rate with time. It is found that the gas-to-dust ratio decreases during the evolution Of OH/IR stars. An empirical relation between the gas-to-dust ratio and the dust mass loss rate is derived, leading to a formula for calculating the total mass loss rate directly from the IRAS 60 mum flux. OH/IR stars with silicate emission have a larger range of mass loss ratio, from 10(-7) to 10(-5) M-circle dot/yr; those with silicate absorption, a smaller range between 10(-5) and 10(-4) M-circle dot/yr. So a large increase in the mass loss rate takes place during the emission phase.

Infrared observation and the energy distribution of silicate carbon stars

Near-infrared photometry of all II silicate carbon stars north of declination -10 degrees is made. Combined with available data in the visible range and from IRAS, we discuss their distribution on the infrared two-color diagrams and their spectral distribution, and we compare with the results for normal carbons and so ascertain their evolutionary status.

IRAS identifications of new S stars

Abstract Of the 75 new S stars published in 1990, 41 have been identified with objects in IRAS Point Source Catalog and 12 with stars in Hubble Space Telescope Guide Star Catalog.

Infrared observational study of MS and CS stars

Abstract We give the results of JHK observation of a set of MS and CS stars. Combining IRAS, PSC and LRS data we discuss their properties throughout the infrared and point out their roles as intermediate types between the M and S stars and between the S and C stars, showing the possible existence of an evolutionary series in the late type stars, M→MS→S→SC→C.