Subject: GCFLASH - Vol. 1, No. 3 (Apr 19, 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. 3 Apr 19, 1996 Dear Subscriber, the first edition of the Newsflash after our call for papers is already longer than initially planed thanks to the many submission we have received (we will try to keep it shorter in the future). After the first two days we also got about 50 subscribers which is a very good start. You can see the list of current subscribers and the abstracts on our web page. Some of the papers give web links which are also accessible through our web page listing. Thus a simple mouse click will make those papers appear on your screen. For some of the papers the Tex file (no figures) will be available from our server directly. Best regards The GCNEWS Team Recently submitted papers: -------------------------- Email : aage@astro.su.se Title : Millimeter Spectral Line Observations of the Galactic Centre Author(s): Aa. Sandqvist Institute: (1) Stockholm Obervatory, S-133 36 Saltsjobaden, Sweden. e-mail: sandqvis@astro.su.se Paper : to be published in 4th ESO/CTIO Workshop Proceedings on the Galactic Centre (ed. R. Gredel) ASP Conf Proc Abstract: We have surveyed the Sgr A region (roughly -12' to +18' in l and -12' to +3' in b), including the Radio Arc, in the 110-GHz lines of C^18O (J=1-0) and HNCO (J_kk'=5_05-4_04) using the SEST. We have observed 554 positions with a grid spacing of 45''. The observational data are presented in form of l-b, l-v and b-v maps, recently published in A \& AS 113, 257. Observations of selected regions in the Galactic Centre in the 220-GHz C^18O (J=2-1) line have also begun and the Circumnuclear Disk has been mapped with the SEST in the 268-GHz HCO^+ (J=3-2) line with a grid spacing of 10''. Future mapping programs are being planned in the 119-GHz O_2 line, as well as in submillimetre lines of O_2 (487-GHz) and H_2O (557-GHz), using the 1.1-m Odin satellite telescope, which has a launch date in the fall of 1997. The Odin satellite is a Swedish project in collaboration with Canada, Finland and France. ------------------------------------------------------------------------ Email : gerhard@astro.unibas.ch Title : Dynamics of the Bar at the Galactic Centre Author(s): Ortwin Gerhard Institute: (1) Astron.Inst, Univ.Basel, CH Paper : to appear in the Proceedings of IAU Symp. 167: Unsolved Problems of the Milky Way, ed. L. Blitz & P. Teuben, (Kluwer) Weblink : http://www.astro.unibas.ch/~gerhard/papers/thehague.ps.gz.uu Sissa : astro-ph/9604069 Abstract: There is now substantial evidence for a rotating bar in the inner Galaxy. This is an important change in our perception of the Galaxy because it changes the ways in which we have to think about its evolutionary history. The idea of a Galactic bar is not new; that motion on elliptic orbits in a barred potential might explain various aspects of the atomic and molecular gas observations near the Galactic Centre has been suggested a number of times (e.g., Peters 1975, Cohen \& Few 1976, Liszt \& Burton 1980, Gerhard \& Vietri 1986, Mulder \& Liem 1986, Sanders 1989). What has changed in the past few years is (i) that the evidence now comes from several fronts, including the NIR light distribution as measured by COBE, IRAS source counts, atomic and molecular gas kinematics, the first indications for triaxiality in the stellar kinematics of the bulge, and perhaps the large optical depth to microlensing in the OGLE experiment; and (ii) that there is a dynamical model which provides a physical basis for explaining a number of independent features in the observed gas kinematics, is consistent to zeroth order with the other pieces of evidence for a bar that we now have, and promises to be extendable towards including these into one coherent picture. In this review I give a brief summary of the current evidence for the bar in the inner Galaxy. Then I discuss in more detail the subject of gas flows in bars and in the Galactic Centre. The integrated NIR photometry is described in the paper by Dwek. Finally, several evolutionary processes are briefly discussed which become relevant for Galactic evolution because of the presence of the bar, such as gas infall, angular momentum transfer, subsequent central star formation, and the formation of peanut-bulge-like stellar systems from bars through a bending instability. ------------------------------------------------------------------------ Email : isg@da.saao.ac.za Title : Variable Stars Close to the Galactic Centre Author(s): I.S. Glass S. Matsumoto T. Ono K. Sekiguchi Institute: (1) South African Astr. Observatory, PO Box 9, Observatory, South Africa (2) Institute of Astr., University of Tokyo, Bunkyo-ku, Tokyo 113, Japan (3) Nishi-Harima Astr. Observatory, Sayo-cho, Hyogo 679-53, Japan (4) National Astr. Observatory, Mitaka, Tokyo 181, Japan Paper : proceedings of the 4th ESO/CTIO workskop "The Galactic Center" Abstract: A large-format infrared camera has been used for repeated observations of a 24 * 24 arcmin^2 region around the Galactic Centre. The survey is carried out at \it K (2.2\mum), with single-epoch coverage at \it H (1.65\mum) and \it J (1.25\mum). So far, the observations have extended over two seasons and it is intended that they will continue for one more. The brightest ~200 objects within each 5 * 5 arcmin^2 sub-field have been examined for variability. Preliminary processing of the data has revealed about 280 likely variables in the overall field. Their positions have been determined relative to stars in the STScI Guide Star Catalog. They include several previously known OH/IR stars. ------------------------------------------------------------------------ Email : rblum@casa.Colorado.EDU Title : JHKL Photometry and the K-band Luminosity Function at the Galactic Center Author(s): R. D. Blum(1,2,3), K. Sellgren(1,4), and D. L. DePoy(1) Institute: (1) Department of Astronomy, The Ohio State University, 174 W. 18th Ave., Columbus, Oh, 43210, Visiting Astronomer, Cerro Tololo Inter--American Observatory, National Optical Astronomy Observatories, which are operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation. (2) Hubble Fellow (3) Current address: University of Colorado, JILA, Campus Box 440, Boulder CO, 80309 (4) Alfred P. Sloan Research Fellow Paper : accepted by ApJ Weblink : ftp://degobah.colorado.edu/pub/rblum/RCS1/ Abstract: J, H, K, and L photometry for the stars in the central ~ 2' (~ 5 pc) of the Galaxy are presented. Using the observed J-H, H-K, and K-L colors and assumed intrinsic colors, we determine the interstellar extinction at 2.2 \mic (A_K) for approximately 1100 individual stars. The mean A_K (= 3.3 mag) is similar to previous results, but we find that the reddening is highly variable and some stars are likely to be seen through A_K > 6 mag. The de--reddened K-band luminosity function points to a significantly brighter component to the stellar population (> 1.5 mag at K) than found in the stellar population in Baade's window, confirming previous work done at lower spatial resolution. The observed flux of all Galactic center stars with estimated K_o (de--reddened magnitude) <=q 7.0 mag is ~ 25 % of the total in the 2' * 2' field. Our observations confirm the recent finding that several bright M stars in the Galactic center are variable. Our photometry also establishes the near--infrared variability of the M1--2 supergiant, IRS 7. ------------------------------------------------------------------------ Email : tagger@cea.fr Title : Non-linear generation of warps by spiral waves in galactic disks Author(s): F. Masset and M. Tagger Institute: (1) DSM/DAPNIA/Service d'Astrophysique (URA 2052 associ\'ee au CNRS), CEA Saclay, 91191 Gif-sur-Yvette, France Paper : A&A in press Abstract: We present a new mechanism to explain the frequently observed and thus certainly permanent warping of spiral galaxies. We consider the possibility of non-linear coupling between the spiral wave of the galaxy and two warp waves, such that the former, which is linearly unstable and extracts energy and angular momentum from the inner regions of the galactic disk, can continuously feed the latter. We derive an expression for the coupling coefficient in the WKB approximation. We show that the coupling is too weak in the stellar disk, except at the Outer Lindblad Resonance where the spiral slows down and is efficiently coupled to warp waves. There, the spiral can be almost completely converted into ``transmitted'' warps, which we can observe in HI, and a ``reflected'' one, which we can observe as a corrugation. Our mechanism reproduces the observed amplitudes of the warp and of the corrugation, and might explain related phenomena such as the behavior of the line of nodes of the warp. Furthermore we show that the energy and momentum fluxes of observed spirals and warps are of the same order of magnitude, adding a strong point in favor of this model. ------------------------------------------------------------------------ (Older versions of the Newsflash can be found at the gcnew wep-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 ========================================================================