======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@aoc.nrao.edu http://www.aoc.nrao.edu/~gcnews ======================================================================== Vol. 21, No. 3 May 5, 2005 Recently submitted papers: -------------------------- 1) IRS 16SW - A New Comoving Group of Young Stars in the Central Parsec of the Milky Way (Lu et al., ) 2) Theoretical Isochrones with Extinction in the K-Band (Kim et al., 2005) ------------------------------------------------------------------------ Email : jlu@astro.UCLA.EDU Title : IRS 16SW - A New Comoving Group of Young Stars in the Central Parsec of the Milky Way Author(s): J. R. Lu, A. M. Ghez(1), S. D. Hornstein, M. Morris, E. E. Becklin Institute: UCLA Department of Physics and Astronomy, Los Angeles, CA 90095-1562 (1) UCLA Institute of Geophysics and Planetary Physics, Los Angeles, CA 90095-1565 Abstract: One of the most perplexing problems associated with the supermassive black hole at the center of our Galaxy is the origin of the young stars in its close vicinity. Using proper motion measurements and stellar number density counts based on 9 years of diffraction-limited K(2.2 micron )-band speckle imaging at the W. M. Keck 10-meter telescopes, we have identified a new comoving group of stars, which we call the IRS 16SW comoving group, located 1.''9 (0.08 pc, in projection) from the central black hole. Four of the five members of this comoving group have been spectroscopically identified as massive young stars, specifically He I emission-line stars and OBN stars. This is the second young comoving group within the central parsec of the Milky Way to be recognized and is the closest, by a factor of 2, in projection to the central black hole. These comoving groups may be the surviving cores of massive infalling star clusters that are undergoing disruption in the strong tidal field of the central supermassive black hole. ------------------------------------------------------------------------ Email : sungsoo.kim@khu.ac.kr Title : Theoretical Isochrones with Extinction in the K-Band Author(s): Sungsoo S. Kim(1), Donald F. Figer(2), Myung Gyoon Lee(3), and Seungkyung Oh(1) Institute: (1) Dept. of Astronomy \& Space Science, Kyung Hee University, Yongin-shi, Kyungki-do 449-701, Korea; sskim@ap.khu.ac.kr (2) Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218; figer@stsci.edu (3) Astronomy Program, SEES, Seoul National University, Seoul 151-742, Korea; mglee@astrog.snu.ac.kr Paper : 2005 PASP, 117, 445 Abstract: We calculate theoretical isochrones, in a consistent way, for five filters in the atmospheric window between 1.9 micron and 2.5 micron , K, K', K_s, F205W, and F222M, using the Padova stellar evolutionary models by Girardi et al. Even when displayed in the same Vega magnitude system, the near-infrared colors of the same isochrone can differ by up to 0.18 mag at its bright end, depending on the filter. We present magnitude transformations between K-band filters as a function of color from H \& K band filters. Isochrones with extinction at K of up to 6 mag are also presented. We find that care is needed when comparing extinction values that are estimated using different filter sets in the K-band, in particular when comparing those between atmospheric and space filter sets: extinction values for space filters can be in error by up to 0.3 mag. To reduce this error, we introduce an ``effective extinction slope'' for each filter set and isochrone model, which describes the extinction behaviour of isochrones in the color-magnitude diagram more correctly than the actual extinction law. Our calculation also suggests that the extinction law implied by the observations of Rieke, Rieke, \& Paul for wavelengths between H and K bands is better described by a power-law function with an exponent of 1.61, instead of 1.55, which is commonly used with an assumption that the transmission functions of H and K filters are Dirac delta functions. ------------------------------------------------------------------------ (Older versions of the Newsflash can be found at the gcnews web-page) ======================================================================== Edited by Sera Markoff, Loránt Sjouwerman, Joseph Lazio, Cornelia Lang, Rainer Schödel, Robin Herrnstein - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - For Abstract submission please follow the instructions which are at http://www.aoc.nrao.edu/~gcnews/home/submission.shtml ========================================================================