Revised distances of Northern HII regions ^*,**

¹ LAM, 2 Place Le Verrier, 13248 Marseille Cedex 04, France e-mail: delphine.russeil@oamp.fr
² LAM, Traverse du Siphon-Les trois Lucs, BP 8, 13376 Marseille Cedex 12, France

Received: 17 July 2006
Accepted: 19 April 2007

Abstract

Aims.Our aim is to determine the distance of outer Galaxy star-forming complexes in order to model the kinematic structure of our Galaxy.

Methods.We searched for exciting star(s) of HII regions, with poor or unknown stellar distance, in the second and third galactic quadrants. We carried out spectroscopic and photometric (when necessary) observations in order to establish their spectral type and their U, B and V magnitudes. From these data, complemented with literature data, we determine the spectro-photometric distance of their associated complexes.

Results.We (re)established the stellar distance of 23 star forming complexes. Reinvestigating the kinematics of the Perseus and Cygnus arms, we determined the velocity departures from circular rotation and we interpreted them as streaming motions in the spiral arms. Indeed, in addition to the Perseus arm where such departures were known for a long time, we added evidence for velocity deviations in the Cygnus arm. Most significant is that we found the opposite sign for these departures in the Perseus and Cygnus arms, which suggests that the co-rotation radius is located between these two arms at ~13 kpc from the galactic center.