Subject: GCFLASH - Vol. 1, No. 5 (Apr 28, 1996) ======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@astro.umd.edu http://www.astro.umd.edu/~gcnews ======================================================================== Vol. 1, No. 5 Apr 28, 1996 Just after the last Newsflash was sent out we got six more papers. So we had to quickly send out another one. For the ESO/CTIO conference participants this is no surprise: the deadline for papers is in two days, and half of the papers today are for those proceedings. Remember: for many papers the text or even a full PS version is available through our webpage (quite useful if you have to write your own paper and you were a bit lazy in taking notes). Recently submitted papers: -------------------------- 1.) Hot Stars in the Quintuplet (Figer et al.) 2.) A Varying Mass-To-Light Ratio in the Galactic Center Cluster? (Saha et al.) 3.) A New Eclipsing X-Ray Burster near the Galactic Center: A Quiescent State of the Old Transient A1742-289 (Maeda et al.) 4.) A new sample of OH/IR stars in the Galactic center (Sjouerman et al.) 5.) Radio Continuum and Molecular Gas in the Galactic Center (Sofue) 6.) The interaction of the G359.54+0.18 Nonthermal Filaments with the Ambient Medium (Staguhn et al.) ------------------------------------------------------------------------ Email : figer@bnkl01.astro.ucla.edu Title : Hot Stars in the Quintuplet Author(s): Donald F. Figer, Mark Morris, and Ian S. McLean Institute: Division of Astronomy, Department of Physics \& Astronomy, University of California, Los Angeles, CA 90095 Paper : to appear in the 4th ESO/CTIO Workshop on the Galactic Center Proceedings Weblink : http://www.astro.ucla.edu/~figer/papers.html Abstract: We present K-band spectra of newly identified hot stars in the Quintuplet cluster, as well as template spectra for 34 Galactic Wolf-Rayet stars. Five of the new stars are WR types (3 WC and 2 WN), while 14 others are OB supergiants; three of the WR stars are probably the hottest identified stars within 50 pc of the Galactic Center. The newly identified stars increase the estimated ionizing flux from this cluster by about an order of magnitude with respect to earlier estimates, to 8.2(10^49) photons s^-1, or about one third of what is required to ionize the ``Sickle'' (G0.18-0.04). In addition, we propose that the 5 original enigmatic members of the Quintuplet-proper are dusty WCL stars, similar to the dozen or so known examples in the Galaxy. ------------------------------------------------------------------------ Email : gvb@maths.anu.edu.au Title : A Varying Mass-To-Light Ratio in the Galactic Center Cluster? Author(s): Prasenjit Saha (1), Geoffrey V. Bicknell (2), and Peter J. McGregor (1) Institute: (1) Mt. Stromlo \& Siding Spring Observatories, Weston PO, ACT 2611, Australia; \hfill\break email: saha@mso.anu.edu.au, peter@mso.anu.edu.au (2) ANU Astrophysical Theory Centre. Australian National University, Canberra, ACT 0200, Australia. email: geoff@wintermute.anu.edu.au. The ANUATC is operated jointly by the Mt. Stromlo and Siding Spring Observatories and the School of Mathematical Sciences. Paper : ApJ, in press Sissa : astro-ph/9604153 Abstract: We reanalyze published kinematic and photometric data for the cool star population in the central 10 pc (240'') of the Galaxy, while (a) isolating the photometric data appropriate to this population, and (b) properly allowing for projection effects. Under the assumptions that the system is spherical and isotropic, we find that M/L_K varies from <=q 1 outside a radius of 0.8 pc to > 2 at 0.35 pc. This behavior cannot be due to the presence of a central massive black hole. We suggest that such a varying M/L_K may be due to an increasing concentration of stellar remnants towards the Galactic center. Our derived mass-radius curve confirms the existence of ~ 3 * 10^6 M_solar within 0.35 pc of the Galactic center, and ~ 1.5 * 10^6 M_solar within 0.2 pc. However, the latter estimate is subject to the uncertain distribution of cool stars in this region. We also consider the dynamics of the hot star population close to the Galactic center and show that the velocity dispersion of the He I stars and the surface brightness distribution of the hot stars are consistent with the mass distribution inferred from the cool stars. ------------------------------------------------------------------------ Email : maeda@cr.scphys.kyoto-u.ac.jp Title : A New Eclipsing X-Ray Burster near the Galactic Center: A Quiescent State of the Old Transient A1742-289 Author(s): Yoshitomo Maeda, Katsuji Koyama, Masaaki Sakano, (Department of Physics, Faculty of Science, Kyoto University, Sakyo-ku, Kyoto, 606-01 Japan, E-mail (YM) maeda@cr.scphys.kyoto-u.ac.jp) Toshiaki Takeshima, (Laboratory for High Energy Astrophysics, NASA/Goddard Space Flight Center, Greenbelt,MD 20771), and, Shigeo Yamauchi, (Faculty of Humanities and Social Sciences, Iwate University, 3-18-34, Ueda, Morioka, Iwate 020) Paper : PASJ 48 (1996), in press Abstract: With ASCA, we found highly absorbed X-rays from the position of the bright transient source A1742-289, with variable flux ranging from 8*10^-12 to 4*10^-11 erg s^-1cm^-2 in the 3-10 keV band. We discovered an X-ray burst and eclipses from A1742-289, establishing that A1742-289 is an eclipsing low mass X-ray binary. Using the black body radius during the X-ray burst, we estimated the distance of A1742-289 to be about 10 kpc, or near the Galactic Center. Then the burst peak flux was found below the Eddington limit of a neutron star. Excess soft X-rays during the eclipse were detected, which are interpreted to be a scattering by interstellar dust-grains. Since A1742-289 was found to be an X-ray emitter even in the quiescent state with a moderate but variable flux, and since A1742-289 is lying only 1.3' from the Galactic center, previously reported X-ray fluxes of the Galactic center (Sgr A*) with non-imaging instruments might have been suffered by possible contamination of A1742-289. ------------------------------------------------------------------------ Email : sjouwerm@sigyn.oso.chalmers.se Title : A new sample of OH/IR stars in the Galactic center Author(s): Lorant Sjouwerman^1,2, Anders Winnberg^1, Huib Jan van Langevelde^3, Harm Habing^2 and Michael Lindqvist^1,2 Institute: (1) ^1Onsala Space Observatory, 439 92 Onsala, Sweden ^2Sterrewacht Leiden, P.O. Box 9513, 2300 RA Leiden, the Netherlands ^3Joint Institute for VLBI in Europe, P.O. Box 2, 7990 AA Dwingeloo, the Netherlands Paper : to appear in the 4th ESO/CTIO workshop on the Galactic center Weblink : http://www.oso.chalmers.se/~sjouwerm/4thCTIO.ps Abstract: We report on the preliminary results of an extensive search for OH/IR stars in the Galactic center region. The main goal is to use the larger sample of OH/IR stars to probe the gravitational potential in the Galactic center (see Lindqvist, Habing & Winnberg 1992b). The search in the 1612 MHz line of OH was performed by observations taken with the Australia Telescope Compact Array and by means of concatenating Very Large Array data sets used for a monitoring program (Van Langevelde et al. 1993). The volume surveyed is over 80 pc in diameter centered on Sgr A^* and has a velocity coverage of -550 to +600 km s^-1. The 1\sigma noise is about 5 mJy, at least four times as deep as earlier surveys. So far we have found about 50 new OH/IR stars, almost as many as we expected. The newly found OH/IR stars seem to be similar in their observable properties to the OH/IR stars already known in the Galactic center. In our data we have found OH counterparts for two H_2O masers detected by Levine et al. (1995) and by Yusef-Zadeh & Mehringer (1995). These H_2O masers are not the argued clues for recent star formation: the objects are old OH/IR stars (Sjouwerman & Van Langevelde 1996). ------------------------------------------------------------------------ Email : sofue@mtk.ioa.s.u-tokyo.ac.jp Title : Radio Continuum and Molecular Gas in the Galactic Center Author(s): Yoshiaki Sofue, Institute of Astronomy, University of Tokyo, Mitaka, Tokyo 181, Japan, E-mail: sofue@mtk.ioa.s.u-tokyo.ac.jp Paper : to appear in the Proc. of the Nobel Symp. 98 "Barred Galaxies and Circumnuclear Activity", (ed.) A. Sandquist Sissa : astro-ph/9604062 Abstract: Nonthermal radio emission in the galactic center reveals a number of vertical structures across the galactic plane, which are attributed to poloidal magnetic field and/or energetic outflow. Thermal radio emission comprises star forming regions distributed in a thin, dense thermal gas disk. The thermal region is associated with dense molecular gas disk, in which the majority of gas is concentrated in a rotating molecular ring. Outflow structures like the radio lobe is associated with rotating molecular gas at high speed, consistent with a twisted magnetic cylinder driven by accretion of a rotating gas disk. To appear in the proceedings of Nobel Symposium 98 "Barred galaxies and circumnuclear activity" (Nov 30-Dec 3, Stockholm, ed. Aa Sandqvist, Springer Verlag) ------------------------------------------------------------------------ Email : staguhn@Newton.ph1.Uni-Koeln.DE Title : The interaction of the G359.54+0.18 Nonthermal Filaments with the Ambient Medium Author(s): J. Staguhn and J. Stutzki (1), F. Yusef-Zadeh (2), K. I. Uchida (3) Institute: (1) Universitaet zu Koeln, 1. Physikalisches Instituet Zuelpicher Str. 77, 50937 Koeln, Germany (2) Dearborne Observatory, Northwestern University, 2131 Sheridan Road, Evanston, IL 60208, USA (3) Max Planck Institut fuer Radioastronomie, Auf dem Huegel 69, 53121 Bonn, Germany Paper : to appear in the proceedings of the 4th ESO/CTIO workshop "The Galactic Center" Abstract: We present a study of the Galactic Center nonthermal filament system G359.54+0.18 located to the north of the Sgr C region. We find evidence in support of the suggestion by Serabyn & Morris that the nonthermal filaments are the manifestations of large-scale vertical magnetic field lines illuminated by collisions with molecular clouds. Included in the study are observations of, (1) the 3 mm emission lines of CS, HCO^+ and other molecular species with the SEST, (2) several lines of ^12CO and ^13CO with the 3-m KOSMA antenna, (3) 5 GHz radio continuum emission with the VLA, and (4) H79alpha recombination line emission with the 100-m antenna at Effelsberg. ------------------------------------------------------------------------ (Older versions of the Newsflash can be found at the gcnews web-page) ======================================================================== Edited by Angela Cotera Heino Falcke (cotera@ipac.caltech.edu) (hfalcke@astro.umd.edu) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - For Abstract submission please send the (La)Tex file of your paper to gcnews@astro.umd.edu ========================================================================