Isolated Wolf-Rayet Stars and O Supergiants Identified in the Galactic Center Region via Paschen-alpha Excess

Jon Mauerhan (1), Angela Cotera (2), Hui Dong (3), Mark Morris (4), Daniel Wang (3), Susan Stolovy (1), Cornelia Lang (5)

(1) Spitzer Science Center, California Institute of Technology, Pasadena, CA, USA
(2) SETI Institute, USA
(3) University of Massachusetts, USA
(4) University of California, Los Angeles, USA
(5) University of Iowa, USA

We report the discovery of 19 hot, evolved, massive stars near the Galactic center region (GCR). These objects were selected for spectroscopy owing to their detection as strong sources of Paschen-alpha emission-line excess, following a narrowband imaging survey of the central 0.65 x 0.25 degress (l, b) around Sgr A* with the Hubble Space Telescope. Discoveries include 6 carbon-type (WC) and 5 nitrogen-type (WN) Wolf-Rayet stars, 6 O supergiants, and 2 Be supergiants. Two of the O supergiants have X-ray counterparts having properties consistent with solitary O stars and colliding-wind binaries. The infrared photometry of 17 stars is consistent with the Galactic center distance, but 2 of them are located in the foreground. Several WC stars exhibit a relatively large infrared excess, which is possibly thermal emission from hot dust. Most of the stars appear scattered throughout the GCR, with no relation to the three known massive young clusters; several others lie near the Arches and Quintuplet clusters and may have originated within one of these systems. The results of this work bring the total sample of Wolf-Rayet stars in the GCR to 88. All sources of strong P-alpha excess have been identified in the area surveyed with HST, which implies that the sample of WN stars in this region is near completion, and is dominated by late (WNL) types. The current WC sample, although probably not complete, is almost exclusively dominated by late (WCL) types. The observed Wolf-Rayet subtype distribution in the GCR is a reflection of the intrinsic rarity of early subtypes (WNE and WCE) in the inner Galaxy, an effect that is driven by metallicity.

Reference: Astrophysical Journal
Status: Manuscript has been accepted