======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@aoc.nrao.edu http://www.aoc.nrao.edu/~gcnews ======================================================================== Vol. 28, No. 7 Jun 5, 2008 Recently submitted papers: -------------------------- 1) First VLTI infrared spectro-interferometry on GCIRS 7 (Pott et al., A&A) 2) X-Ray Observations of the Sagittarius D HII Region toward the Galactic Center with Suzaku (Sawada et al., PASJ) ------------------------------------------------------------------------ Email : jpott@keck.hawaii.edu Title : First VLTI infrared spectro-interferometry on GCIRS 7 Author(s): J.-U. Pott(1,2,3), A. Eckart(3), A. Glindemann(4), S. Kraus(5), R. Schoedel(6), A. M. Ghez(2), J. Woillez(1), G. Weigelt(5), Institute: (1) W.M. Keck Observatory (WMKO), CARA, 65-1120 Mamalahoa Hwy., Kamuela, HI-96743, USA (2) University of California Los Angeles (UCLA), Department of Astronomy, 430 Portola Plaza, Los Angeles, CA 90095-1547, USA (3) I. Physikalisches Institut (PH1), University of Cologne, Zuelpicher Str. 77, D-50937 Koeln, Germany (4) European Southern Observatory (ESO), Karl-Schwarzschild Str. 2, D-85748 Garching bei Muenchen, Germany (5) Max-Planck-Institut fuer Radioastronomie (MPIfR), Auf dem Huegel 69, D-53121 Bonn, Germany (6) Instituto de Astrofisica de Andalucia (IAA), Camino Bajo de Huetor, 50, 18008 Granada, Spain Paper : A&A, 2008, in press EPrint : 0805.4408 Web : http://planetquest.jpl.nasa.gov/Keck/keck_index.cfm Abstract: The massive black hole Sgr A* at the very center of the Galaxy, and its immediate stellar and non-stellar environment, have been studied in the past decade with increasing intensity and wavelength coverage, revealing surprising results. This research requires the highest angular resolution available to avoid source confusion and to study the physical properties of the objects. GCIRS 7 is the dominating star of the central cluster in the NIR, so it has been used as wavefront and astrometric reference. Our studies investigate, for the first time, its properties at 2 and 10 micron using the VLTI. We aim at analyzing the suitability of GCIRS 7 as an interferometric phase-reference for the upcoming generation of dual-field facilities at optical interferometers. VLTI-AMBER and MIDI instruments were used to spatially resolve GCIRS 7 and to measure the wavelength dependence of the visibility using the low spectral resolution mode ( lambda / \Delta lambda 30) and projected baseline lengths of about 50 m, resulting in an angular resolution of about 9 mas and 45 mas for the NIR and MIR, respectively. The first K-band fringe detection of a GC star suggests that GCIRS 7 could be marginally resolved at 2 micron, which would imply that the photosphere of the supergiant is enshrouded by a molecular and dusty envelope. At 10 micron , GCIRS 7 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 micron -silicate absorption in excess of the usual extinction law with respect to the NIR extinction has been found. Our VLTI observations show that interferometric NIR phase-referencing experiments with mas resolution using GCIRS 7 as phase reference appear to be feasible, but more such studies are required to definitely characterize the close environment around this star. The MIR data confirm recent findings of a relatively enhanced, interstellar 9.8 micron -silicate absorption with respect to the NIR extinction towards another star in the central arc-seconds, suggesting an unusual dust composition in that region. We demonstrate that the resolution and sensitivity of modern large-aperture optical telescope arrays is required to resolve the innermost environment of stars at the Galactic center. ------------------------------------------------------------------------ Email : sawada@cr.scphys.kyoto-u.ac.jp Title : X-Ray Observations of the Sagittarius D HII Region toward the Galactic Center with Suzaku Author(s): Makoto Sawada(1), Masahiro Tsujimoto(2), Katsuji Koyama(1), Casey J. Law(3), Takeshi Go Tsuru(1), Yoshiaki Hyodo(1) Institute: (1) Department of Physics, Graduate School of Science, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502 (2) Department of Astronomy \& Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802, USA (3) Astronomical Institute ``Anton Pannekoek'', University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands Paper : PASJ, in press EPrint : 0805.2079 Web : http://www-cr.scphys.kyoto-u.ac.jp/member/sawada/paper/ms_Suz akuSgrD.pdf Abstract: We present a Suzaku X-ray study of the Sagittarius D (Sgr D) HII region in the Galactic center region. Two 18'*18' images by the X-ray Imaging Spectrometer (XIS) encompass the entire Sgr D complex. Thanks to the low background, XIS discovered two diffuse sources with low surface brightness and obtained their high signal-to-noise ratio spectra. One is associated with the core of the Sgr D HII region, arising from the young stellar cluster. The other is a new object in the vicinity of the region. We also present 3.5 cm and 6.0 cm radio continuum maps of the new source using the 100 m Green Bank Telescope. We conclude that the source is a new supernova remnant (SNR; G1.2-0.0) based on: (1) the 0.9+/-0.2 keV thermal X-ray spectrum with emission lines from highly ionized atoms; (2) the diffuse nature with an apparent extent of 10 pc at the Galactic center distance inferred from the X-ray absorption ( 8.5*10^22 cm^-2); and (3) the nonthermal radio continuum spectral index ( -0.5). Our discovery of an SNR in the Sgr D HII region leads to a revision of the view of this system, which had been considered to be a thermal HII region and its environment. ------------------------------------------------------------------------ (Older versions of the Newsflash can be found at the gcnews web-page) ======================================================================== Edited by Sera Markoff, Loránt Sjouwerman, Joseph Lazio, Cornelia Lang, Rainer Schödel, Masaaki Sakano, Feng Yuan - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - For Abstract submission please follow the instructions which are at http://www.aoc.nrao.edu/~gcnews/home/submission.shtml ========================================================================