6 Conclusions

A 25 $\mu$m survey of 81 late type main-sequence dwarfs using ISO and IRAS data showed that 5 (or 6%) of all stars in the sample exhibit significant infrared excess which can be attributed to a Vega-like dust disk. The low fraction and the fact that the disks have already been identified at 60 $\mu$m indicates that the bulk emission from Vega-like disks is from cool dust ( $T_{\rm d}< 120$ K).

From the detection limit of Vega-like disks we estimate a lower mass limit of ${M_{\rm dust}=~2\times10^{-5}}~M_{\oplus}$ for the disks not detected by us. The survey confirms that there seems to be an absence of detectable amounts of dust at close distances ${D~\loa}$ 20 AU from the stars.

Acknowledgements

The ISOPHOT data presented in this paper were reduced using PIA, which is a joint development by the ESA Astrophysics Division and the ISOPHOT Consortium. We thank the referee, Dr. R. Liseau, for helpful comments leading to improvement of the manuscript.