Stellar Bow Shocks in the Northern Arm of the Galactic Center: More Members and Kinematics of the Massive Star Population

We present new 2.2 micron diffraction-limited images from the W. M. Keck 10 mand Gemini 8 m telescopes of the cool Galactic Center sources, IRS 1W, 5, 8,10W, and 21 along with new proper motions for IRS 1W, 10W and 21. Theseobservations were carried out to test the bowshock hypothesis presented byTanner et al. as an alternative to a very recent (10^4 yr) epoch of starformation within the tidal stream of gas and dust known as the Northern Arm.Resolved asymmetric structure is detected in all the sources, with bowshockmorphologies associated with IRS 1W, 5, 8 and 10W. For IRS 1W and 10W, there isan agreement between the position angle of the asymmetry and that of therelative velocity vector of the near-infrared source with respect to theNorthern Arm gas strengthening the bowshock hypothesis. We therefore concludethat the observed morphology is indeed a bowshock generated by sources plowingthrough the Northern Arm. Furthermore, the large extent of the resolvedstructures (310-1340 AU) along with their luminosities (~10^4-5 Lsun) suggeststhat their central sources are Wolf-Rayet stars, comparable to the broad Heemission-line stars, which have strong winds on the order of 1000 km/s. Thebowshock morphology, along with the proper motion measurements, providethree-dimensional orbital solutions for this enigmatic class of objects; IRS 1Wand 10W have orbital planes that are consistent with that of the putativeclockwise plane which has been proposed as a solution for the He Iemission-line stars. While these observations eliminate the need to invoke starformation within the Northern Arm, they increase by 14% the total knownpopulation of massive, young stars with strong winds, whose origin remainsunexplained in the context of the nearby supermassive black hole.Comment: Accepted by ApJ, 25 pages, 5 figure