Does Cyg OB2 harbour any open cluster?

¹ Universidade Federal do Rio Grande do Sul, Instituto de Física, CP 15051, Porto Alegre 91501-970, RS, Brazil
² Universidade de São Paulo, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, CP 3386, São Paulo 01060-970, SP, Brazil
³ Universidade Estadual do Rio Grande do Sul, Unidade São Borja, Rua Bompland 512, São Borja 97670-000, RS, Brazil

Corresponding author: Ch. Bonatto, charles@if.ufrgs.br

Received: 21 November 2002
Accepted: 6 May 2003

Abstract

We report the detection of three new open cluster candidates located in Cygnus. Two of them are projected near the center of the rich compact association Cyg OB2. These two objects have been found during an optical inspection of that region with Digitized Sky Survey images. Using 2MASS photometry we determined their fundamental parameters. We assumed an age of 1–4 Myr and obtained a distance from the Sun  kpc for both objects. Reddening values for Objects 1 and 2 are and , respectively. A normal luminosity function is observed down to A0 stars, similar to that of NGC 6910. The two open cluster candidates may form a physical pair in Cyg OB2, similar to Tr 14/Tr 16 in Car OB1. Subsequently, we carried out a systematic search with 2MASS in a region encompassing Cyg OB2. A third uncatalogued object resulted from this search which is projected just outside Cyg OB2.