T. Paumard1, J.P. Maillard1, S. Stolovy2
1 Institut d'Astrophysique de Paris (CNRS), 98b
75014 Paris, France
2 SIRTF Science Center, CalTech, MS 220-6, Pasadena, CA 91125, USA
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See: A&A 366, 466-480 (2001)
The cluster of helium stars around SgrA has been re-examined from high resolution spectro-imagery data with the BEAR instrument in the 2.06um helium line, at a spectral resolution of 74kms-1. Sixteen stars were confirmed as helium stars, some of the earlier detections of such stars in the central cluster were discarded, and three new stars added. These observations led to the discovery of two distinct classes of hot stars. The first class is characterized by very broad line profiles (FWHM 1000kms-1) and by their relative faintness. The other, brighter in K by an average factor roughly of 9, has a much narrower emission component of width 200kms-1. Most of the emission lines show a P Cygni profile. From these results, we propose that the narrow-line group represents stars in or near the LBV phase, whereas the broad-line group represents stars in the WR stage. The division into two groups is also shown by their spatial distribution, with the narrow-line stars in a compact central cluster (IRS 16) and the broad-line group distributed at the periphery of the central cluster of hot stars. New BEAR data at higher resolution (42.9kms-1) and on a larger field ( 40'') confirm and complete this analysis. Helium stars farther in projection from Sgr A* which were found in the larger field have been added to the class of WR stars. The detection of the emission line stars from the HST-NICMOS data in Pa alpha (1.87um) in the same field provides by comparison to the HeI stars an additional element to characterize the two groups. Bright Pa alpha emitters are generally associated with the narrow-line class stars while the weak Pa alpha emitters are associated with the broad-line class stars. A few particular cases are discussed. This confirms the different evolutionary status of the two groups of massive, hot stars in the central cluster.