The origin of massive O-type field stars

Free access article

Issue		A&A Volume 425, Number 3, October III 2004


Page(s)		937 - 948
Section		Galactic structure, stellar clusters and populations
DOI		http://dx.doi.org/10.1051/0004-6361:20040454

A&A 425, 937-948 (2004)
DOI: 10.1051/0004-6361:20040454

I. A search for clusters

W. J. de Wit¹, L. Testi¹, F. Palla¹, L. Vanzi² and H. Zinnecker³

¹ INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
e-mail: dewit@arcetri.astro.it
² ESO, Alonso de Cordova 3107, Santiago, Chile
³ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany

(Received 16 March 2004 / Accepted 12 May 2004)

Abstract
We present a study aimed at clarifying the birthplace for 43 massive O-type field stars. In this first paper we present the observational part: a search for stellar clusters near the target stars. We derive stellar density maps at two different resolving scales, viz. ~ 0.25 pc and ~1.0 pc from NTT and TNG imaging and the 2MASS catalogue. These scales are typical for cluster sizes. The main result is that the large majority of the O-type field population are isolated stars: only 12% (5 out of 43) of the O-type field stars is found to harbour a small-scale stellar cluster. We review the literature and aim at characterizing the stellar field of each O-type field star with the emphasis on star formation and the presence of known young stellar clusters. An analysis of the result of this paper and a discussion of the O-type field population as products of a dynamical ejection event is presented in an accompanying paper.

Key words: stars: early-type -- stars: formation

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