EDP Sciences
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Volume 406, Number 1, July IV 2003
Page(s) 119 - 130
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20030605

A&A 406, 119-130 (2003)
DOI: 10.1051/0004-6361:20030605

Stellar tracers of the Cygnus Arm

I. Spectroscopic study of bright photometric candidates
I. Negueruela1, 2 and A. Marco2

1  Observatoire de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, France
2  Dpto. de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain

(Received 7 March 2003 / Accepted 14 April 2003)

We present medium-resolution spectroscopy of a sample of stars in the second Galactic quadrant selected from the literature because their colours suggest that they are moderately-reddened early-type stars at very large distances. From the derived spectral types and observed colours, we calculate distances to all these objects. For a sizable fraction of our sample, we find distances well in excess of what is expected for Perseus Arm objects, even allowing for rather generous errors. In the interval $l=150\degr{-}180\degr$, there is a large number of objects with distances in excess of 4 kpc, which are likely tracing the Outer or Cygnus Arm. In particular, we find that the association Cam OB3 is placed on this Arm. Based on our results, the extent and definition of the associations Cas OB4 and Aur OB2 need to be reevaluated.

Key words: stars: early-type -- stars: distances -- Galaxy: structure -- open clusters and associations: general

Offprint request: I. Negueruela, ignacio@dfists.ua.es

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© ESO 2003