The enigma of GCIRS 3 - Constraining the properties of the mid-infrared reference star of the central parsec of the Milky Way with optical long baseline interferometry

Abstract

GCIRS3 is the most prominent MIR source in the central pc of the Galaxy. NIR spectroscopy failed to solve the enigma of its nature. The properties 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 interferometric experiment to understand IRS3 and investigate its properties as spectroscopic and interferometric reference star at 10um. VISIR imaging separates a compact source from diffuse, surrounding emission. The VLTI/MIDI instrument was used to measure visibilities at 10mas resolution of that compact 10um source, still unresolved by a single VLT. Photometry data were added to enable simple SED- and full radiative transfer-models of the data. The luminosity and size estimates show that IRS3 is probably a cool carbon star enshrouded by a complex dust distribution. Dust temperatures were derived. The coinciding interpretation of multiple datasets confirm dust emission at several spatial scales. The IF data resolve the innermost area of dust formation. Despite observed deep silicate absorption towards IRS3 we favor a carbon rich chemistry of the circumstellar dust shell. The silicate absorption most probably takes place in the outer diffuse dust, which is mostly ignored by MIDI measurements. This indicates physically and chemically distinct conditions of the local dust, changing with the distance to IRS3. 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 10um silicate feature at this outstanding region.

arXiv commentaccepted by A&A, now in press; 19 pages, 22 figures, 5 tables

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Cited by in corpus (13)

• The Milky Way's Supermassive Black Hole: How good a case is it? A Challenge for Astrophysics & Philosophy of Science
• Absorption Line Survey of H3+ toward the Galactic Center Sources II. Eight Infrared Sources within 30 pc of the Galactic Center
• Approaching hell's kitchen: Molecular daredevil clouds in the vicinity of Sgr A*
• M-Band Spectra of Dust Embedded Sources at the Galactic Center
• Absorption at 11 microns in the interstellar medium and embedded sources: evidence for crystalline silicates
• ALMA and VLA observations of emission from the environment of Sgr A*
• High spectral resolution spectroscopy of the SiO fundamental lines in red giants and red supergiants with VLT/VISIR
• X3: a high-mass Young Stellar Object close to the supermassive black hole Sgr~A*
• First VLTI infrared spectro-interferometry on GCIRS 7 - Characterizing the prime reference source for Galactic center observations at highest angular resolution
• Candidate Young Stellar Objects in the S-cluster: The Kinematic Analysis of a Sub-population of the Low-mass G-objects close to Sgr A*
• Mapping the aliphatic hydrocarbon content of interstellar dust in the Galactic plane
• Modelling the mid-infrared polarization in dust around young stars
• Composition of the galactic center star cluster: Population analysis from adaptive optics narrow band spectral energy distributions