On the Difference between Type E and Type A OH/IR Stars

The observed SEDs of a sample of 60 OH/IR stars are fitted using a radiativetransfer model of a dusty envelope. Among the whole sample, 21 stars havereliable phase-lag distances while the others have less accurate distances.L*-P,Mlr-P and Mlr-L* relations have been plotted for these stars. It is foundthat type E (with emission feature at 10um and type A (with absorption featureat 10um) OH/IR stars have different L*-P and Mlr-L* relations while both ofthem follow a single Mlr-P relation. The type E stars are proven to be locatedin the area without large scale dense interstellar medium while the type Astars are located probably in dense interstellar medium. It is argued here thatthis may indicate the two types of OH/IR stars have different chemicalcomposition or zero age main sequence mass and so evolve in different ways.This conclusion has reinforced the argument by Chen et al.(2001) who reached asimilar conclusion from the galactic distribution of about 1000 OH/IR starswith the IRAS low-resolution spectra (LRS).Comment: 6 pages, 9 figures, 2 table