Stellar Ionization of the Thermal Radio Emission Regions in the Galactic Center

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Session 66 -- Galactic Center
Oral presentation, Tuesday, 10, 1995, 2:00pm - 3:30pm

[66.02D] Stellar Ionization of the Thermal Radio Emission Regions in the Galactic Center

A.S. Cotera (Stanford University)

The Anglo-Australian Telescope (AAT) has been used to search for hot young stars within the inner $\sim$40 pc of the Galactic Center. The primary ionization mechanism of the GC filaments has been uncertain. For the Arched Filaments, it has been argued that the ionization is the result of an interaction between the magnetic field and a molecular cloud coincident with the filaments (ie. Morris \& Yusef-Zadeh 1989, ApJ, 343,703). Alternatively, it has been suggested that photoionization by hot stars is responsible for the observed radio emission (ie. Erickson {\rm{et~al.}} 1991, ApJ, 370, L69)

During this investigation we have discovered $\sim$20 emission lines stars lying adjacent to or coincident with the radio emission regions G0.15--0.04 (the \lq Pistol\rq), the E1 and E2 Filaments, G0.10+0.02, and the Sgr A regions A-D, H5, H2 and H8 (nomenclature from Morris \& Yusef-Zadeh 1989). Based on a comparison of H and K band spectra with optically classified stars, we believe these stars to be B[e], Ofpe/WN9 and WN7--9 stars with T$_{\rm eff} \sim$20,000-30,000 K and L$\sim 10^6 L_\odot$. If our classification of the GC stars as WN7--9 is correct, the new stars comprise $\sim$14\% of known galactic WN stars. Based on the calculated luminosity of the stars and comparisons with radio data, if all the ionizing photons emitted by the stars are absorbed by the radio regions, the stars could be largely responsible for the ionization of their respective radio emission regions, but their distances and geometry preclude them from being the only ionizing sources. Additional hot stars may be embedded in or adjacent to the thermal radio emission regions but are not detected by our observations because they lack significant infrared emission lines.

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