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Astron. Astrophys. 333, 613-618 (1998)

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5. Energy distribution

In order to investigate physical properties of Tc-rich and Tc-deficient S stars in more detail, the broad band energy distributions from B or V band to 60 µm or 100 µm can be plotted simply by using the single or double blackbody fitting proposed by Xiong et al. (1994). One example of energy distribution for the typical Tc-deficient S star, GZ Peg and Tc-rich S star, W And is plotted in Fig. 5 and Fig. 6, respectively, while the others could be made accessible in electronic form in Fig. 5a and Fig. 6a, respectively. It is very clear that all Tc-deficient S stars can be fitted by a single blackbody curve which reflects the photospheric properties whereas many Tc-rich ones in the LRS group E request double blackbody fitting which reflects the photospheric and circumstellar properties. Again this implies that Tc-deficient S stars have no or little infrared excess whereas Tc-rich ones usually have, hence are more evolved objects.

[FIGURE] Fig. 5. Energy distribution of typical Tc-deficient S star GZ Peg

[FIGURE] Fig. 6. Energy distribution of typical Tc-rich S star W And

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© European Southern Observatory (ESO) 1998

Online publication: April 20, 1998