Subject: GCFLASH - Vol. 2, No. 9 (Jul 22, 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. 2, No. 9 Jul 22, 1996 Dear Subscriber, this are the last abstracts for Vol. 2 of the Newsletter which was just completed and which will be distributed tomorrow. The long anticipated paper by Genzel et al. on the dark mass concentration (did anyone say black hole?) in the GC and the MIR observations of the Sgr A* region reported by Stolovy et al. make this certainly an exceptional finish for the current issue. What makes this even more exciting, is that much more is to be expected within the next year for both, the mass and the (possible) IR spectrum of Sgr A*. Your GCNEWS Team Recently submitted papers: -------------------------- 1) The Dark Mass Concentration in the Central Parsec of the Milky Way (Genzel et al., ApJ) 2) The First Mid-Infrared Detection of a Source Coincident with Sagittarius A* (Stolovy et al., ApJL) Email : GENZEL@MPE-GARCHING.MPG.DE Title : The Dark Mass Concentration in the Central Parsec of the Milky Way Author(s): R. Genzel and N. Thatte and A. Krabbe and H. Kroker and L.E. Tacconi-Garman Institute: Max-Planck-Institut fuer extraterrestrische Physik, Garching, Germany Paper : ApJ, in press Abstract: We report ~1" resolution K-band (2 micron ) imaging spectroscopy of the central parsec of our Galaxy. The derived radial velocities for 223 early and late type stars probe thenuclear mass distribution to spatial scales of 0.1 pc. We find a statistically very significant increase of projected stellar velocity dispersion from about 55 km/s at p~5 pc to 180 km/s at p~0.1 pc. The stars are also rotating about the dynamic center. The late type stars follow general Galactic rotation, while the early type stars show counter- rotation. Fitting simultaneously the observed projected surface densities and velocity dispersions we derive the intrinsic volume densities and radial velocity dispersion as a function of distance from the dynamic center for both types of stars. We then derive the mass distribution between 0.1 and 5 pc from the Jeans equation assuming an isotropic velocity field. Our analysis requires a compact central dark mass of 2.5 to 3.2*10^6, at 6 to 8\sigma significance. The dark mass has a density of 1-9 M_opc^-3 or greater and a mass to 2 micron luminosity of >=100. The increase in mass to luminosity ratio can be reduced but not eliminated even if extreme anisotropic velocity distributions are considered. The dark mass cannot be a cluster of solar mass remnants (such as neutron stars). It is either a compact cluster of 10-20 M_o black holes or a single massive black hole. ------------------------------------------------------------------------ Email : stolovy@astrosun.tn.cornell.edu Title : The First Mid-Infrared Detection of a Source Coincident with Sagittarius A* Author(s): Susan R. Stolovy, T. L. Hayward, and Terry Herter Institute: (1) Department of Astronomy, Cornell University, Ithaca, NY 14853,Electronic mail: stolovy, hayward, herter@astrosun.tn.cornell.edu Paper : to appear in ApJ Letters; accepted July 1996 Weblink : http://astrosun.tn.cornell.edu/SC10/pubs/gc.html Abstract: We present the first mid-infrared detection of a source coincident ith the black hole candidate Sgr A* in a deep image of the inner parsec of the Galaxy. These data were obtained with SpectroCam-10 at the 200-inch Hale telescope. The source was detected at 8.7 micron on two separate occasions using different observing techniques. The spatial resolution is ~ 0.''7 and the noise level is 1.6 mJy beam^-1 in the combined mosaic near Sgr A*. A source at Sgr A* is weakly apparent in the raw data, but is difficult to identify due to strong diffuse dust emission with a mean flux density of 500 mJy arcsec^-2. Several deconvolution techniques were applied to achieve the diffraction limit of 0.''44, all of which revealed a peak on a narrow NW-SE ridge of emission. The peak is coincident with Sgr A* within the +/-0.''3 uncertainty in locating Sgr A* relative to IRS 7. We estimate the flux density of the Sgr A* source above the ridge to be 25 +/- 5 mJy. The extinction-corrected 8.7 micron flux density of ~ 100 mJy is significantly greater than what is predicted by dustless accretion disk models. The excess emission is best explained by warm dust which may be associated with Sgr A* or heated by local stellar sources. ------------------------------------------------------------------------ (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 ========================================================================