Isolated Hot Stars in the Galactic Center Vicinity

Abstract

Using near-infrared imaging and spectroscopy, we discuss the discovery of six emission-line sources within ~20 pc of Sgr A West but outside of the central parsec. The objects are coincident with stars seen in the J, H, and K' images; all have Brγ (2.166 μm) in emission, several also have He I (2.058 and 2.112/3 μm), and some have He II (2.189 μm) emission lines. Comparison of the H- and K-band spectra of the newly discovered stars with recently published infrared spectral atlases of optically classified stars suggests that most of these stars are similar to massive stars in transition (e.g., Ofpe/WN9, B[e], and LBV), although one is definitely a WN6 star. Two of the potential stars are associated with the radio emission regions A-D near Sgr A East, three are near or within the radio emission regions H1-H8 (nomenclature from Yusef-Zadeh & Morris), the last is near G0.10+0.02 and is likely to be associated with the G0.12+0.02 (Arches) cluster of stars, discussed in a previous paper. The stars are shown to be significant sources of ionization for their associated radio emission regions, with several capable of completely ionizing the regions. These results provide additional support for the idea that these thermal radio regions, and similar such regions in the Galactic center, are indeed photoionized by hot young stars.