Volume 372, Number 3, June IV 2001
|Page(s)||833 - 850|
|Published online||15 June 2001|
Kinematics of young stars*
II. Galactic spiral structure
Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Av. Diagonal 647, 08028 Barcelona, Spain
2 IEEC (Institut d'Estudis Espacials de Catalunya), Edif. Nexus-104, Gran Capità 2-4, 08034 Barcelona, Spain
Corresponding author: D. Fernández, firstname.lastname@example.org
Accepted: 8 March 2001
The young star velocity field is analysed by means of a galactic model which takes into account solar motion, differential galactic rotation and spiral arm kinematics. We use two samples of Hipparcos data, one containing O- and B-type stars and another one composed of Cepheid variable stars. The robustness of our method is tested through careful kinematic simulations. Our results show a galactic rotation curve with a classical value of A Oort constant for the O and B star sample (-13.8 km s-1 kpc-1) and a higher value for Cepheids (-16.9 km s-1 kpc-1, depending on the cosmic distance scale chosen). The second-order term is found to be small, compatible with a zero value. The study of the residuals shows the need for a K-term up to a heliocentric distance of 4 kpc, obtaining a value (1-3) km s-1 kpc-1. The results obtained for the spiral structure from O and B stars and Cepheids show good agreement. The Sun is located relatively near the minimum of the spiral perturbation potential (-20°) and very near the corotation circle. The angular rotation velocity of the spiral pattern was found to be km s-1 kpc-1.
Key words: Galaxy: kinematics and dynamics / Galaxy: solar neighbourhood / Galaxy: structure / stars: early-type / stars: kinematics / stars: variables: Cepheids
© ESO, 2001
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