======================================================================== 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. 12, No. 22 Jan 8, 2001 Recently submitted papers: -------------------------- 1) Starburst Clusters in Galactic Nuclei (Figer & Morris, conference) 2) UHECR Production by a Compact Black-Hole Dynamo: Application to Sgr A* (Levinson & Boldt, Astroparticle Physics) 3) Database of Geneva stellar evolution tracks and isochrones for (UBV)_J(RI)_C JHKLL'M, HST-WFPC2, Geneva and Washington photometric systems (Lejeune et al., A&A) ------------------------------------------------------------------------ Email : figer@stsci.edu Title : Starburst Clusters in Galactic Nuclei Author(s): Donald F. Figer(1), Mark Morris(2) Institute: (1) STScI, 3700 San Martin Drive, Baltimore, MD 21218;,JHU, 3400 Charles Street, Baltimore, MD 21218 (2) UCLA, Division of Astronomy, 405 Hilgard Avenue, LA CA 90095-1562 Paper : conference proceedings, Modes of Star Weblink : http://nemesis.stsci.edu/~figer/web/papers.html EPrint : astro-ph/0012500 Abstract: Galactic nuclei often harbor a disproportionately large amount of star formation activity with respect to their surrounding disks. Not coincidentally, the density of molecular material in galactic nuclei is often also much greater than that in disks (Table 1 in Kennicutt 1998). The interplay between rich populations of young stars and dense molecular environments is evident in our own Galactic center, which hosts over 10% of Galactic star formation activity within only <0.1% of the volume of the Galactic disk. Data obtained with the VLA and HST reveal a variety of star forming sites in the Galactic Center, including a substantial population of stars that are formed in very dense and massive clusters, while other stars are formed in somewhat sparsely populated associations of massive stars. Indeed, three of the stellar clusters are the most massive and densest in the Galaxy. In this paper, we discuss the Galactic center environment and its compact young star clusters, and compare them to their counterparts in star forming galactic nuclei, concluding that dense molecular environments and large velocity dispersions combine to alter star formation activity in both cases, particularly as regards massive young clusters. ------------------------------------------------------------------------ Email : levinson@wise1.tau.ac.il Title : UHECR Production by a Compact Black-Hole Dynamo: Application to Sgr A* Author(s): Amir Levinson (1), Elihu Boldt (2) Institute: (1) School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel (2) Laboratory for High Energy Astrophysics, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA Paper : Astroparticle Physics, submitted EPrint : astro-ph/0012314 Abstract: The possibility that the excess cosmic ray (CR) flux near 10^18 eV, reported recently by the AGASA group, is due to a compact black hole dynmo associated with the Sgr A* source is considered. Under the assumption that the Galactic center black hole rotates with nearly maximal spin, and that the magnetic field threading the horizon is in rough equipartition with matter accreted by the hole, the spectra and total fluxes of accelerated CRs and their associated curvature emission depend only on accretion rate. For the accretion rate estimated on the basis of observations of stellar winds near Sgr A* ( 10^-3 Eddington), the maximum proton energy achievable by this mechanism is of the order of 10^18 eV, and the corresponding CR power is 10^41 alpha _CR erg s^-1, where alpha _CR<<1 is the CR production efficiency. The corresponding spectrum of curvature photons peaks at several hundreds GeV, with a total luminosity comparable to the CR power released. For much lower accretion rates both the CR and gamma-ray fluxes predicted are completely insignificant. Upcoming gamma-ray experiments, such as HESS and GLAST, can be used to probe the parameters of this system. ------------------------------------------------------------------------ Email : schaerer@ast.obs-mip.fr Title : Database of Geneva stellar evolution tracks and isochrones for (UBV)_J(RI)_C JHKLL'M, HST-WFPC2, Geneva and Washington photometric systems Author(s): Thibault Lejeune, Daniel Schaerer Paper : A&A, in press Weblink : http://webast.ast.obs-mip.fr/stellar/ EPrint : astro-ph/00114497 Abstract: We have used an updated version of the empirically and semi-empirically calibrated BaSeL library of synthetic stellar spectra of Lejeune et al. (1997, 1998) and Westera et al. (1999) to calculate synthetic photometry in the (UBV)_J(RI)_C JHKLL'M, HST-WFPC2, Geneva, and Washington systems for the entire set of non-rotating Geneva stellar evolution models covering masses from 0.4-0.8 to 120-150 M_o and metallicities Z=0.0004 (1/50 Z_o) to 0.1 (5 Z_o). The results are provided in a database which includes all individual stellar tracks and the corresponding isochrones covering ages from 10^3 yr to 16-20 Gyr in time steps of \Delta \log t= 0.05 dex. The database also includes a new grid of stellar tracks of very metal-poor stars (Z=0.0004) from 0.8 - 150 M_o calculated with the Geneva stellar evolution code. The full database will be available in electronic form at the CDS, http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/(vol)/(page) and at, http://webast.ast.obs-mip.fr/stellar/. ------------------------------------------------------------------------ (Older versions of the Newsflash can be found at the gcnews web-page) ======================================================================== Edited by Angela Cotera Heino Falcke & Sera Markoff (cotera@as.arizona.edu) (hfalcke,smarkoff@mpifr-bonn.mpg.de) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - For Abstract submission please send the (La)Tex file of your paper to gcnews@mpifr-bonn.mpg.de ========================================================================