6 Summary

  With the aim of searching for young star clusters around intermediate mass stars, we have selected a sample of 45 Herbig AeBe stars, 43 of which cover almost uniformly the spectral range from O9 to A7. From data existing in the literature we have selected a set of stellar parameters (spectral type, distance from the Sun, V-magnitude and B-V colour), from which we have calculated effective temperature and bolometric luminosity for each star. Using the theoretical PMS evolutionary tracks of Palla & Stahler (1993), we have evaluated the age of almost all the stars with spectral type later than B5.

The field around each star has been imaged in the near-infrared with a moderately large field of view and sensitivity. In 22 fields we found a group of stars likely associated with the Herbig AeBe star and determined the two richness indicators ${\cal N}_{K}$ and $I_{\rm C}$,as well as the radius of the group. The typical size of the detected groups is $\sim0.2$ pc. This value is in agreement with that found by other authors in various young stellar clusters (Hillenbrand 1995; Carpenter et al. 1997). It is remarkable that stellar groups with a few to several hundred members share similar sizes, which in turn correspond to the typical sizes of dense cores in molecular clouds.

The observations presented in this paper constitute the dataset for our study of the clustering around Herbig AeBe stars (Paper I; Testi et al. 1998).

Acknowledgements

We thank the TIRGO and ARNICA staff, especially Filippo Mannucci, for nice scheduling and service observing. LT would like to thank the NOT staff for help and hospitality. Special thanks are due to Colin Aspin, Leslie Hunt, Amanda Kaas and Ruggero Stanga who made the NOT run a very pleasent and fruitfull one. The NOT observing run has been partially supported by the Dipartimento di Astronomia e Scienza dello Spazio of the Università di Firenze. This work was partly supported by ASI grant ARS-96-66 and CNR grant 97.00018.CT02 to the Osservatorio di Arcetri. Support from C.N.R.-N.A.T.O. Advanced Fellowship program and from NASA's Origins of Solar Systems program (through grant NAGW-4030) is gratefully aknowledged. This search has made use of the Simbad database, operated at CDS, Strasbourg, France.