======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@aoc.nrao.edu http://www.aoc.nrao.edu/~gcnews ======================================================================== Vol. 29, No. 19 Jun 16, 2010 Recently submitted papers: -------------------------- 1) Two New and Remarkable Sightlines into the GC's Molecular Gas (Geballe & Oka, ApJ) 2) Disks in the Arches cluster - survival in a starburst environment (Stolte et al., ApJ) 3) Concerning the Distance to the Center of the Milky Way and its Structure (Majaess, Acta A.) 4) Dynamical constraints on the origin of the young B-stars in the Galactic center (Perets et al., arXiv:1004.2703) ------------------------------------------------------------------------ Email : TGeballe@gemini.edu Title : Two New and Remarkable Sightlines into the GC's Molecular Gas Author(s): T. R. Geballe(1), T. Oka(2) Institute: (1) Gemini Observatory, 670 N. A'ohoku Place, Hilo, HI 96720 (2) Department of Astronomy and Astrophysics, Department of Chemistry, and Enrico Fermi Institute, University of Chicago, Chicago, IL 60637. Paper : ApJ, 709, L70 EPrint : 09123885 Abstract: Until now the known sources in the Galactic center with sufficiently smooth spectra and of sufficient brightness to be suitable for high resolution infrared absorption spectroscopy of interstellar gas occupied a narrow range of longitudes, from the central cluster of hot stars to approximately 30 pc east of the center. In order to more fully characterize the gas within the r 180 pc central molecular zone it is necessary to find additional such sources that cover a much wider longitudinal range of sightlines. We are in the process of identifying luminous dust-embedded objects suitable for spectroscopy within 1.2^o in longitude and 0.1^o in latitude of Sgr A* using the Spitzer GLIMPSE and the Two Micron All Sky Survey catalogues. Here we present spectra of H_3^+ and CO towards two such objects, one located 140 pc west of Sgr A*, and the other located on a line of sight to the Sgr B molecular cloud complex 85 pc to the east of Sgr A*. The sightline to the west passes through two dense clouds of unusually high negative velocities and also appears to sample a portion of the expanding molecular ring. The spectra toward Sgr B reveal at least ten absorption components covering over 200 km s^-1 and by far the largest equivalent width ever observed in an interstellar H_3^+ line; they appear to provide the first near-infrared view into that hotbed of star formation. ------------------------------------------------------------------------ Email : astolte@ph1.uni-koeln.de Title : Disks in the Arches cluster - survival in a starburst environment Author(s): A. Stolte, M. R. Morris, A. M. Ghez, T. Do, J. R. Lu, S. A. Wright, C. Ballard, E. Mills, K. Matthews Institute: (1) I. Physikalisches Institut, Universitaet zu Koeln, Zuelpicher Str. 77, 50937 Koeln, Germany (2) Division of Astronomy and Astrophysics, UCLA, Los Angeles, CA 90095-1547 (3) Institute of Geophysics and Planetary Physics, UCLA, Los Angeles, CA 90095 (4) Caltech Optical Observatories, California Institute of Technology, MS 320-47, Pasadena, CA 91225 (5) UC Berkeley, Astronomy Department, 601 Campbell Hall, Berkeley, CA 94720-3411 (6) 14090 Robler Road, Sherman Oaks, CA 91423 Paper : ApJ, Aug 2010, in press EPrint : 1006.1004 Abstract: Deep Keck/NIRC2 HK'L' observations of the Arches cluster near the Galactic center reveal a significant population of near-infrared excess sources. We combine the L'-band excess observations with K'-band proper motions, which allow us to confirm cluster membership of excess sources in a starburst cluster for the first time. The robust removal of field contamination provides a reliable disk fraction down to our completeness limit of H=3D19 mag, or 5 M_o at the distance of the Arches. Of the 24 identified sources with K'-L' > 2.0 mag, 21 have reliable proper motion measurements, all of which are proper motion members of the Arches cluster. VLT/SINFONI K'-band spectroscopy of three excess sources reveals strong CO bandhead emission, which we interpret as the signature of dense circumstellar disks. The detection of strong disk emission from the Arches stars is surprising in view of the high mass of the B-type main sequence host stars of the disks and the intense starburst environment. We find a disk fraction of 6 +/- 2% among B-type stars in the Arches cluster. A radial increase in the disk fraction from 3 to 10% suggests rapid disk destruction in the immediate vicinity of numerous O-type stars in the cluster core. A comparison between the Arches and other high- and low-mass star-forming regions provides strong indication that disk depletion is significantly more rapid in compact starburst clusters than in moderate star-forming environments. ------------------------------------------------------------------------ Email : dmajaess@ap.stmarys.ca Title : Concerning the Distance to the Center of the Milky Way and its Structure Author(s): Daniel J. Majaess Institute: (1) Saint Mary's University, Halifax, Nova Scotia, Canada (2) The Abbey Ridge Observatory, Stillwater Lake, Nova Scotia, Canada Paper : Acta A., vol.60 no.1 (2010) EPrint : 1002.2743 Abstract: The distance to the Galactic center inferred from OGLE RR Lyrae variables observed in the direction of the bulge is R_0=8.1+/-0.6 kpc. An accurate determination of R_0 is hindered by countless effects that include an ambiguous extinction law, a bias for smaller values of R_0 because of a preferential sampling of variable stars toward the near side of the bulge owing to extinction, and an uncertainty in characterizing how a mean distance to the group of variable stars relates to R_0. A VI-based period-reddening relation for RR Lyrae variables is derived to map extinction throughout the bulge. The reddening inferred from RR Lyrae variables in the Galactic bulge, LMC, SMC, and IC 1613 match that established from OGLE red clump giants and classical Cepheids. RR Lyrae variables obey a period-colour (VI) relation that is relatively insensitive to metallicity. Edge-on and face-on illustrations of the Milky Way are constructed by mapping the bulge RR Lyrae variables in tandem with cataloged red clump giants, globular clusters, planetary nebulae, classical Cepheids, young open clusters, HII regions, and molecular clouds. The sample of RR Lyrae variables do not trace a prominent Galactic bar or triaxial bulge oriented at phi 25 DEGr. ------------------------------------------------------------------------ Email : hperets@cfa.harvard.edu Title : Dynamical constraints on the origin of the young B-stars in the Galactic center Author(s): Hagai B. Perets(1), Alessia Gualandris(2) Institute: (1) CfA fellow, Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Camridge, MA 02138, USA (2) Max-Planck Institut fr Astrophysik, Karl-Schwarzschild-Str. 1, D-85741 Garching, Germany Paper : arXiv:1004.2703 Web : http://adsabs.harvard.edu/abs/2010arXiv1004.2703P Abstract: Regular star formation is thought to be inhibited close to the massive black hole (MBH) in the Galactic center. Nevertheless, tens of young main sequence B stars have been observed in an isotropic distribution close to it. These stars are observed to have an apparently continuous distribution from very close to the MBH <0.01 pc and up to at least 0.5 pc, suggesting a common origin. Various models have been suggested for the formation of the B-stars closest to the MBH (<0.05 pc; the S-stars), typically involving the migration of these stars from their original birthplace to their currently observed position. Here we explore the orbital phase space distribution of the B-stars throughout the central pc expected from the various suggested models for the origin of the B-stars. We find that most of these models have difficulties in explaining, by themselves, both the population of the S-stars (<0.05 pc), and the population of the young B-stars further away (up to 0.5 pc). Most models grossly over-predict the number of B-stars up to 0.5 pc, given the observed number of S-stars. Such models include the intermediate-mass black hole assisted cluster inspiral scenario, Kozai-like perturbations by two disks, spiral density waves migration in a gaseous disk, and some of the eccentric disk instability models. We focus on one of the other models, the massive perturber induced binary disruption, which is consistent with both the S-stars and the extended population of B-stars further away. For this model we use analytical arguments and N-body simulations to provide further observational predictions. These could be compared with future observations to further support this model, constrain it or refute it. These predictions include the radial distribution of the young B-stars, their eccentricity distribution and its dependence on distance from the MBH (higher eccentricities at larger distances from the MBH), as well as less specific expectations regarding their mass function. ------------------------------------------------------------------------ (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, Masaaki Sakano, Feng Yuan - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - For Abstract submission please follow the instructions which are at http://www.aoc.nrao.edu/~gcnews/home/submission.shtml ========================================================================