  Investigating the environment of the massive black hole SgrA* at the center
of the Galaxy requires the highest angular resolution available to avoid source
confusion and to study the physical properties of the individual objects.
GCIRS7 has been used as wavefront and astrometric reference. Our studies
investigate, for the first time, its properties at 2&10um using VLTI/AMBER and
MIDI. We aim at analyzing the suitability of IRS7 as an IF-phase-reference for
the upcoming generation of dual-field facilities at optical interferometers. We
observed with (R~30) and 50m (proj.) baseline, resulting in 9 and 45mas
resolution for NIR and MIR, resp. The first K-band fringe detection of a GC
star suggests that IRS7 could be marginally resolved at 2um, which would imply
that the photosphere of the supergiant is enshrouded by a molecular and dusty
envelope. At 10um, IRS7 is strongly resolved with a visibility of approximately
0.2. The MIR is dominated by moderately warm (200 K), extended dust, mostly
distributed outside of a radius of about 120 AU (15 mas) around the star. A
deep 9.8-silicate absorption in excess of the usual extinction law with respect
to the NIR extinction has been found. This confirms recent findings of a
relatively enhanced, interstellar 9.8-silicate absorption with respect to the
NIR extinction towards another star in the central arcsec, suggesting an
unusual dust composition in that region. Our VLTI observations show that
interferometric NIR phase-referencing experiments with mas resolution using
IRS7 as phase-reference appear to be feasible, but more such studies are
required to definitely characterize the close environment around this star. We
demonstrate that interferometry is required to resolve the innermost
environment of stars at the Galactic center.
