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Astron. Astrophys. 349, 276-282 (1999)

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Radial velocities of optical lines in three bright Galactic HII regions *

César Esteban 1 and Manuel Peimbert 2

1 Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Canary Islands, Spain (cel@ll.iac.es)
2 Instituto de Astronomía, UNAM Apdo. Postal 70-264, Mexico D.F. 04510, Mexico (peimbert@astroscu.unam.mx)

Received 31 March 1999 / Accepted 11 May 1999


We present heliocentric radial velocities for a large number of emission lines covering all the optical spectral range for two slit positions of the Galactic HII regions M 42 and M 17 and one slit position of M 8. We obtain a fairly similar relation between the heliocentric velocity and the ionization potential of the ions in all the observed slit positions. This general result indicates a similar behaviour of the velocity stratification along the line of sight in the three objects. We suggest that flows of ionized gas streaming away from the molecular clouds toward the observer can explain qualitatively the observations.

Key words: ISM: H ii regions – ISM: individual objects: M 17 – ISM: individual objects: M 42 – ISM: individual objects: M 8 – ISM: kinematics and dynamics

* Based on data obtained at the Observatorio Astronómico Nacional, SPM, B.C., Mexico

Send offprint requests to: C. Esteban

© European Southern Observatory (ESO) 1999

Online publication: August 25, 1999