Statistics of Effective Temperatures and Spectral Types of Carbon-Enhanced Metal-Poor(CEMP)Stars in the SDSS-DR7

The fraction of CEMP(Carbon-Enhanced Metal-Poor)stars among metal-poor stars according to the SDSS(The Sloan Digital Sky Survey)DR7(Data Release 7)is about 11%.The effective temperatures of CEMP stars calculated with the SSPP(The SEGUE Stellar Parameter Pipeline)are mostly in the range 6000K to 9000K.After recalculating the temperatures and the spectral types of CEMP stars by using the PLSR (Partial Least Squares Regression)method, we find that the results given by SSPP have larger random errors.In addition, the random deviotions bias in effective temperature between PLSR and SSPP cannot be ignored when the temperature is above 7500K.These are consistent with the estimates from different methods in the SSPP.Based on color-color and color-magnitude diagrams, CEMP stars can be divided into two categories:BHB/BS and F(F Turn-Off), with the former category including stars of higher temperatures and larger errors in temperature values.The BHB and BS CEMP stars can also be separated in a log(g)-color diagram.Finally, possible origins of the carbon element in the two categories of CEMP stars are discussed.