======================================================================== 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. 9, No. 13 Jan 18, 1999 Recently submitted papers: -------------------------- 1) Luminous variables in the Quintuplet cluster (Glass et al., MNRAS) 2) Hot Expanding Shells in the Envelope of the Sagittarius B2 Molecular Cloud (Martin-Pintado et al., Proc.) 3) The hot gas and the cold dust in the Galactic Center clouds as seen by ISO (Martin-Pintado et al., Proc.) ------------------------------------------------------------------------ Email : isg@da.saao.ac.za Title : Luminous variables in the Quintuplet cluster Author(s): I.S. Glass^1, S. Matsumoto^2, B.S. Carter^3 and K. Sekiguchi^4, ^1 South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa,^2 Institute of Astronomy, University of Tokyo, Mitaka, Tokyo 181, Japan, ^3Carter Observatory, PO Box 2909, Wellington, New Zealand, ^4 Subaru Telescope, NAOJ, 650 North A'ohoku Place, Hilo, HI 96720, USA Paper : MNRAS, in press Abstract: We report observations of variability amongst the stars of the ``Quintuplet" cluster located about 30 pc in projection from the centre of the Galaxy. Two of the five cocoon star members, which may be protostars or peculiar Wolf-Rayets, are seen to vary slowly with moderate amplitude (0.4-0.5 mag). The bright star within the ``Pistol" H ii region, suspected of being a Luminous Blue Variable (LBV), has in fact been found to show variability, confirming its tentative classification. A second nearby presumed LBV also varies. One of the apparent Quintuplet members is likely to be a Mira variable along the same line of sight. ------------------------------------------------------------------------ Email : nemesio@oan.es Title : Hot Expanding Shells in the Envelope of the Sagittarius B2 Molecular Cloud Author(s): J. Martin-Pintado^1, R. A. Gaume^2, N. Rodriguez-Fernandez^1, P. de Vicente^1, and T. L. Wilson^3,4 Institute: ^1 Observatorio Astron\'omico Nacional, Apartado 1143, E-28800 Alcal\'a de Henares, Spain, ^2 U.S. Naval Observatory, 3450 Massachusetts Ave., NW, Washington, DC 20392-5420, ^3 Max Planck Institut fuer Radioastronomie, Postfach 2024, D-53010 Bonn, Germany, ^4 Sub-mm Telescope Observatory, Steward Observatory, The University of Arizona, Tucson, Az, 85721, Paper : to appear in "The Physics and Chemistry of the ISM" proc's Weblink : http://www.oan.es/preprints Abstract: We present high resolution images of the warm gas in the envelope of the Sagittarius B2 (Sgr B2) molecular cloud. These images reveal that the morphology of the Sgr B2 molecular envelope is dominated by several shells and incomplete shells expanding at low velocities ~10 km/sec ns. The sizes of the shells are between 1 and 2.6 pc and their thicknesses are between 0.2 and 0.4 pc. The shells are hot with kinetic temperatures, T_k, of 40 -150 K. The large number of masers in H_2CO, CH_3OH and the newly detected (3,3) \nht masers are correlated with the hot molecular shells. Associated with the shells, we have also detected new hot cores, suggesting that massive star formation has taken place very recently in the molecular envelope of Sgr B2. Wind-blown bubbles, driven by typical galactic Wolf-Rayet stars, could account for the kinetic energies and the momenta observed in the hot \nht shells. Shocks associated with the expanding bubbles provide the chemistry required to explain the large number of masers, and the heating of the molecular gas in the envelope of Sgr B2. ------------------------------------------------------------------------ Email : nemesio@oan.es Title : THE HOT GAS AND THE COLD DUST IN THE GALACTIC CENTER CLOUDS AS SEEN BY ISO Author(s): J. Martin-Pintado^1, N.J. Rodriguez-Fernandez^1, P. de Vicente^1, A. Fuente^1, T.L. Wilson^2, S. Huettemeister^3, D. Kunze^4 Institute: ^1 Observatorio Astronomico Nacional, Apartado 1143, E-28800, Alcala de Henares, Spain, ^2 Max-Planck Institut fuer Radioastronomie, Postfach 2024, D 53010 Bonn, Germany, ^3 Astronomische Institute, Auf dem Huegel 71, D-53121 Bonn Germany, ^4 MPE, Giesenbachstrasse 1, D-85748 Garching, Germany. Paper : to appear in The Universe as Seen by ISO Weblink : http://www.oan.es/preprints Abstract: We present the first results of the LWS and SWS ISO observations of 18 molecular clouds in the Galactic center (GC) region. H_2 emission from several rotational lines in the ground vibrational state has been detected toward all molecular clouds. The rotational temperatures derived from these lines are between 150 and 500 K. Remarkably, the derived column densities of the hot H_2, ~ 2 10^22 cm^-2, are similar to those obtained for the cold gas. the From the non-detection of the S(3) line at 9.7 micron , we find that the hot gas must be located behind more than 30 mag of visual extinction of cold gas and dust. The LWS continuum spectra indicate that the cold dust has temperatures of 25-35 K and column densities similar to those required to explain the extinction of the H_2 emission. Observations of the J=2-1 and J=1-0 lines of C^18O (J=2-1/J=1-0 line ratios of 0.7-1.4) seem to sample only the cold gas located in front of the hot gas. This indicates that the low J transitions of C^18O does not trace the total molecular gas in the GC. The LWS continuum spectra impose stringent limits (<= 1 per cent) to the hot dust associated to the hot H_2. Toward most of the clouds we also detected emission from the fine structure lines of ionized species such as SIII and NeII, and in some cases lines from NeIII and OIII. In contrast with the previous idea that the heating of the GC clouds is dominated by shocks, our data suggest that photoelectric heating by UV radiation can be the dominat mechanism. The effective temperature of the ionization radiation derived from the NeIII/NeII ratio is 35.000 K (typical of an O7 star). Our ISO data when combined with the upper limits to the intensities of the recombination lines measured at millimeter wavelengths indicate that the UV radiation is very diluted. Cavities with sizes larger than 2 pc surrounding the ionizing star(s) are required to explain the dilution. The origin of the ionized cavities and the implications of these findings on the heating of the molecular clouds in the GC are briefly discussed. ------------------------------------------------------------------------ (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 ========================================================================