A&A Supplement series, Vol. 123, May II 1997, 63-82
Received April 18; accepted September 11, 1996
M.E. van den Ancker - P.S. Thé - A. Feinstein - R.A. Vázquez - D. de Winter - M.R. Pérez
Send offprint request: M.E. van den Ancker(email@example.com)
Astronomical Institute "Anton Pannekoek'', University of Amsterdam, Kruislaan 403, NL-1098 SJ Amsterdam, The Netherlands - Observatorio Astronómico de La Plata, Paseo del Bosque, 1900 La Plata, Argentina
Member of Carrera del Investigador Cientifico, CONICET, Buenos Aires, Argentina
Visiting astronomer, Cerro Tololo Inter-American observatory, operated under contract No. AST 78-27879
Dpto. Física Téorica C-XI, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, E-28049 Madrid, Spain
Applied Research Corporation, Suite 1120, 8201 Corporate Dr., Landover MD 20785, U.S.A.
The distance and formation history of the very young open cluster NGC 6530 were investigated by studying a total of 132 probable member stars of this open cluster. It was concluded that the distance to NGC 6530 is , and its interstellar reddening E(B-V) is 030. Furthermore, we conclude that the extinction law of the intracluster material is normal (i.e. ), but anomalous extinction laws were found for several more embedded stars in the cluster. Of the 132 stars included in this study, 11 are suspected to be variable, five show H in emission and nine show an infrared excess. Among the member stars of NGC 6530, three were found to be part of the Herbig Ae/Be stellar class, whereas two others are possible members of this stellar group as well. Also, one cluster member is probably a new massive post-AGB star, whereas the same could possibly apply to another member star. Finally, from the distribution of post- and pre-main sequence stars in the cluster's HR-diagram, it was concluded that the process of star formation in NGC 6530 must have started a few times years ago and, for the less massive stars, is probably still going on today.
keywords: circumstellar matter -- stars: formation -- stars: pre-main sequence -- dust, extinction -- HII regions -- open clusters and associations: NGC 6530