======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@mpifr-bonn.mpg.de http://www.mpifr-bonn.mpg.de/gcnews ======================================================================== Vol. 11, No. 5 Mar 16, 2000 Recently submitted papers: -------------------------- 1) 2 micron Spectroscopy within 0.''3 of Sgr A* (Figer et al., ApJL) 2) Bipolar-Hyper-Shell Galactic Center Starburst Model: Further Evidence from ROSAT Data and New Radio and X-ray Simulations (SOFUE, ApJ) 3) Stellar Iron Abundances at the Galactic Center (Ramirez et al., ApJ) ------------------------------------------------------------------------ Email : figer@stsci.edu Title : 2 micron Spectroscopy within 0.''3 of Sgr A* Author(s): Donald F. Figer(1), E. E. Becklin(2), Ian S. McLean(2), Andrea M. Gilbert(3), James R. Graham(3), James E. Larkin(2), N. A. Levenson(4), Harry I. Teplitz(5,6), Mavourneen K. Wilcox(2), Mark Morris(2) Institute: (1) Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218; figer@stsci.edu (2) Department of Physics and Astronomy, University of California, Los Angeles, Division of Astronomy, Los Angeles, CA, 90095-1562 (3) Department of Astronomy, University of California, Berkeley, 601 Campbell Hall, Berkeley, CA, 94720-3411 (4) Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (5) Laboratory for Astronomy and Solar Physics, Code 681, Goddard Space Flight Center, Greenbelt MD 20771 (6) NOAO Research Associate Paper : ApJ Letters, April 10th Issue Abstract: We present moderate (R 2,700) and high resolution (R 22,000) 2.0-2.4 micron spectroscopy of the central 0.1 square arcseconds of the Galaxy obtained with NIRSPEC, the facility near-infrared spectrometer for the Keck II telescope. The composite spectra do not have any features attributable to the brightest stars in the central cluster, i.e. after background subtraction, W_^12CO(2-0) < 2 \AA. This stringent limit leads us to conclude that the majority, if not all, of the stars are hotter than typical red giants. Coupled with previously reported photometry, we conclude that the sources are likely OB main sequence stars. In addition, the continuum slope in the composite spectrum is bluer than that of a red giant and is similar to that of the nearby hot star, IRS16NW. It is unlikely that they are late-type giants stripped of their outer envelopes because such sources would be much fainter than those observed. Given their inferred youth ( tau _age < 20 \Myr), we suggest the possibility that the stars have formed within 0.1 pc of the supermassive black hole. We find a newly-identified broad-line component (V_FWHM 1,000 km/sec ) to the 2.2178 micron [\ionFe3] line located within a few arcseconds of Sgr A^*. A similar component is not seen in the Br- gamma emission. ------------------------------------------------------------------------ Email : sofue@mtk.ioa.s.u-tokyo.ac.jp Title : Bipolar-Hyper-Shell Galactic Center Starburst Model: Further Evidence from ROSAT Data and New Radio and X-ray Simulations Author(s): Yoshiaki SOFUE Institute: Institute of Astronomy, University of Tokyo, Mitaka, Tokyo 181-8588 Paper : ApJ, in press Abstract: Using the all-sky ROSAT soft X-ray and 408-MHz radio continuum data, we show that the North Polar Spur and its western and southern counter-spurs draw a giant dumbbell-shape necked at the galactic plane. We interpret these features as due to a shock front originating from a starburst 15 million years ago with a total energy of the order of 10^56 ergs or 10^5 type II supernovae. We simulate all-sky distributions of radio continuum and soft X-ray intensities based on the bipolar-hyper-shell galactic center starburst model. The simulations can well reproduce the radio NPS and related spurs, as well as radio spurs in the tangential directions of spiral arms. Simulated X-ray maps in 0.25, 0.75 and 1.5 keV bands reproduce the ROSAT X-ray NPS, its western and southern counter-spurs, and the absorption layer along the galactic plane. We propose to use the ROSAT all-sky maps to probe the physics of gas in the halo-intergalactic interface, and to directly date and measure the energy of a recent Galactic Center starburst. ------------------------------------------------------------------------ Email : solange@astronomy.ohio-state.edu Title : Stellar Iron Abundances at the Galactic Center Author(s): Solange V. Ramirez(1), K. Sellgren(1), John S. Carr(2), Suchitra C. Balachandran(3), Robert Blum(4), Donald M. Terndrup(5), & Adam Steed(5) Institute: (1) Department of Astronomy, The Ohio State University (2) Naval Research Laboratory (3) Department of Astronomy, University of Maryland (4) Cerro Tololo Inter-American Observatory (5) Department of Astronomy, The Ohio State University Paper : ApJ in press EPrint : astro-ph/0002062 Abstract: We present measurements of [Fe/H] for six M supergiant stars and three giant stars within 0.5 pc of the Galactic Center (GC) and one M supergiant star within 30 pc of the GC. The results are based on high-resolution ( lambda / Delta lambda = 40,000) K-band spectra, taken with CSHELL at the NASA Infrared Telescope Facility. We determine the iron abundance by detailed abundance analysis, performed with the spectral synthesis program MOOG. The mean [Fe/H] of the GC stars is determined to be near solar, [Fe/H] = +0.12 +/- 0.22. Our analysis is a differential analysis, as we have observed and applied the same analysis technique to eleven cool, luminous stars in the solar neighborhood with similar temperatures and luminosities as the GC stars. The mean [Fe/H] of the solar neighborhood comparison stars, [Fe/H] = +0.03 +/- 0.16, is similar to that of the GC stars. The width of the GC [Fe/H] distribution is found to be narrower than the width of the [Fe/H] distribution of Baade's Window in the bulge but consistent with the width of the [Fe/H] distribution of giant and supergiant stars in the solar neighborhood. ------------------------------------------------------------------------ (Older versions of the Newsflash can be found at the gcnews web-page) ======================================================================== Edited by Angela Cotera Heino Falcke (cotera@ipac.caltech.edu) (hfalcke@mpifr-bonn.mpg.de) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - For Abstract submission please send the (La)Tex file of your paper to gcnews@mpifr-bonn.mpg.de ========================================================================