The enigma of GCIRS 3

J.-U. Pott (1,2) & A. Eckart(1) & A. Glindemann(2) & R. Schödel(1) & T. Viehmann(1) & M. Robberto(3)

(1) I. Physikalisches Institut, University of Cologne, Zülpicher Str. 77, D-50937 Köln, Germany,
(2) European Southern Observatory (ESO),=20 Karl-Schwarzschildstr. 2, D-85748 Garching bei München, Germany
(3) Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA

Paper: A&A accepted


EPrint Server: xxx


GCIRS 3 is the most prominent MIR-source in the central parsec of the Galaxy. NIR spectroscopy failed to solve the enigma of its nature. The properties and peculiarities of extreme individual objects of the central stellar cluster contribute to our knowledge of star and dust formation close to a supermassive black hole. We initiated an unprecedented interferometric experiment to understand the nature of GCIRS 3 and investigate its properties as spectroscopic and interferometric reference star at 10 micron . VLT/VISIR imaging separates a compact source from diffuse, surrounding emission. The VLTI/MIDI instrument was used to measure spectroscopically resolved visibility moduli at an angular resolution of 10 mas of that compact 10 micron source, still unresolved by a single VLT. Recent NIR/MIR photometry data were added to enable simple SED- and full radiative transfer-modeling of the data. The luminosity and size estimates show that IRS 3 is probably a cool carbon star enshrouded by a complex dust distribution. Blackbody temperatures were derived. The coinciding interpretation of single telescope and interferometric data confirm dust emission from several different spatial scales. The interferometric data resolve the inner rim of dust formation. Despite observed deep silicate absorption towards GCIRS 3 we favor a carbon rich circumstellar dust shell. The silicate absorption most probably takes place in the outer diffuse dust, which is mostly ignored by MIDI measurements, but well observable in complementary VLT/VISIR data. This indicates physically and chemically distinct conditions of the local dust, changing with the distance to GCIRS 3. We have demonstrated that optical long baseline interferometry at infrared wavelengths is an indispensable tool to investigate sources at the Galactic Center. Our findings suggest further studies of the composition of interstellar dust and the shape of the 10 micron silicate feature at this outstanding region.

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