A multiwavelength study of star formation in the very young open cluster NGC 6530 ^*

¹ Astronomical Institute "Anton Pannekoek”, University of Amsterdam, Kruislaan 403, NL–1098 SJ Amsterdam, The Netherlands
² Observatorio Astronómico de La Plata, Paseo del Bosque, 1900 La Plata, Argentina
³ Member of Carrera del Investigador Cientifico, CONICET, Buenos Aires, Argentina
⁴ Visiting astronomer, Cerro Tololo Inter-American observatory, operated under contract No. AST 78-27879
⁵ Dpto. Física Téorica C–XI, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, E–28049 Madrid, Spain
⁶ Applied Research Corporation, Suite 1120, 8201 Corporate Dr., Landover MD 20785, U.S.A.

Send offprint request to: M.E. van den Ancker

Received: 18 April 1996
Accepted: 11 September 1996

Abstract

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 is 030. Furthermore, we conclude that the extinction law of the intracluster material is normal (i.e. R_V = 3.1), 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 Hα 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 10⁷ years ago and, for the less massive stars, is probably still going on today.