======================================================================== 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. 8, No. 12 Jul 1, 1998 Please don't forget: the GC98 conference registration deadline is in two weeks. The abstract deadline for contributed papers has just passed and evaluation of the submitted abstracts will start soon. Preparations for the next GCNEWS volume are also well under way. Recently submitted papers: -------------------------- 1) Massive Stars in the Quintuplet Cluster (Figer et al., ApJ) 2) Stellar Gas Flows Into A Dark Cluster Potential At The Galactic Center (Melia & Coker, ApJ) ------------------------------------------------------------------------ Email : figer@gc.astro.ucla.edu Title : Massive Stars in the Quintuplet Cluster Author(s): Donald F. Figer(1), Ian S. McLean(1), Mark Morris(1) Institute: (1) University of California, Los Angeles, Division of Astronomy, Department of Physics \& Astronomy, Los Angeles, CA 90095-1562 Paper : submitted to ApJ Weblink : http://www.astro.ucla.edu/~figer/papers.html Abstract: We present near-infrared photometry and K-band spectra of newly-identified stars in the Quintuplet Cluster, one of the three known massive clusters projected within 50 pc of the Galactic Center. We find that the cluster contains a variety of massive stars, including more unambiguously identified Wolf-Rayet stars than any other cluster in the Galaxy, and over a dozen other stars in earlier stages of evolution, i.e., LBV, Ofpe/WN9, and OBI. One newly identified star may be the second ``Luminous Blue Variable'' identified in the cluster, after the ``Pistol Star.'' While we are unable to provide certain spectral classifications for the five enigmatic Quintuplet-proper stars, we tentatively propose that they are extremely dusty versions of the WC stars found elsewhere in the cluster, and similar to the dozen or so known examples in the Galaxy. Given the evolutionary stages of the identified stars, the cluster appears to be about 3.5 Myr old. The total mass is estimated to be ~ 10^4 \Msun, and the mass density in stars is >~ a few thousand M_sun pc^-3. The newly-identified stars increase the estimated ionizing flux from this cluster by about an order of magnitude with respect to earlier estimates, to 10^50.9 photons s^-1, or roughly what is required to ionize the nearby ``Sickle'' HII region (G0.18-0.04). The total luminosity from the massive cluster stars is ~ 10^7.5 L_sun, enough to account for the heating of the nearby molecular cloud, M0.20-0.033. We propose a picture which integrates most of the major features in this part of the sky, excepting the non-thermal filaments. We compare the cluster to other young massive clusters and globular clusters, finding that it is unique in stellar content and age, except, perhaps, for the young cluster in the central parsec of the Galaxy. In addition, we find that the cluster is comparable to small ``super star clusters.'' ------------------------------------------------------------------------ Email : rfc@physics.Arizona.EDU Title : Stellar Gas Flows Into A Dark Cluster Potential At The Galactic Center Author(s): Fulvio Melia^\dag(1) and Robert Coker^*(2) Institute: (1) ^\dagPhysics Department and Steward Observatory, The University of Arizona, Tucson, AZ 85721 (2) ^*Physics Department, The University of Arizona, Tucson, AZ 85721 (3) Presidential Young Investigator. (4) NASA, GSRP Fellow. Paper : ApJ, submitted EPrint : astro-ph/9806195 Abstract: The evidence for the presence of a concentration of dark matter at the Galactic center is now very compelling. There is no question that the stellar and gas kinematics within ~ 0.01 pc is dominated by under-luminous matter in the form of either a massive black hole, a highly condensed distribution of stellar remnants, or a more exotic source of gravity. The unique, compact radio source Sgr A* appears to be coincident with the center of this region, but its size (less than about 3* 10^14 cm at lambda 1.35 cm) is still significantly smaller than the current limiting volume enclosing this mass. Sgr A* may be the black hole, if the dark matter distribution is point-like. If not, we are left with a puzzle regarding its nature, and a question of why this source should be so unique and lie only at the Galactic center. In this paper, we examine an alternative to the black hole paradigm--that the gravitating matter is a condensed cluster of stellar remnants--and study the properties of the Galactic center wind flowing through this region. Some of this gas is trapped in the cluster potential, and we study in detail whether this hot, magnetized gas is in the proper physical state to produce Sgr A*'s spectrum. We find that at least for the Galactic center environment, the temperature of the trapped gas never attains the value required for significant GHz emission. In addition, continuum (mostly bremsstrahlung) emission at higher frequencies is below the current measurements and upper limits for this source. We conclude that the cluster potential is too shallow for the trapped Galactic center wind to account for Sgr A*'s spectrum, which instead appears to be produced only within an environment that has a steep-gradient potential like that generated by a black hole. ------------------------------------------------------------------------ (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 ========================================================================