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Spectral types are determined from low resolution optical spectra of 40 IRAS sources with far-infrared colours similar to planetary nebulae. The presence of circumstellar dust, high galactic latitude, and early supergiant or giant spectral type, sometimes with emission in the Balmer lines, indicate that some of these stars are low mass stars in the post-AGB stage of evolution.
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Parthasarathy et al. (2000) studied this question.
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