======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@aoc.nrao.edu http://www.aoc.nrao.edu/~gcnews ======================================================================== Vol. 28, No. 8 Aug 15, 2008 Dear subscriber, Unfortunately our automated scripts were broken over the summer due to forced changes in the computer environment because of a couple of security breaches. As I have been traveling for a majority of this period, the break in the system was unnoticed. I think I have been able to recover all abstract submissions, but if you have submitted an abstract after the last flash (June 5), I would ask you to check below in the abstracts or on the GCNEWS web pages that it is there. While I have your attention I would also like to ask that you check your address at http://www.aoc.nrao.edu/~gcnews/home/subscriber.shtml to make sure we have your correct email address. Over the years some addresses have bounced too often to keep them listed, so if you find colleagues wondering about not getting the GCNEWS emails, please have them check their spam filters or resubscribe to GCNEWS. Also if there is an error in your data please resubscribe to GCNEWS. This would be a good time as the announcements for the upcoming Galactic Center 2009 conference in China should appear soon. Thanks for your help in keeping the GC community connected! Lorant Recently submitted papers: -------------------------- 1) The Rotating Nuclear Star Cluster in NGC 4244 (Seth et al., ApJ) 2) Dynamical evolution of the young stars in the Galactic center (Perets et al., Central) 3) Study of the Science Capabilities of PRIMA in the Galactic Center (Bartko et al., SPIE) 4) Two extremely luminous WN stars in the Galactic center with circumstellar emission from dust and gas (Barniske et al., A&A) 5) Absorption Line Survey of H_3^+ toward the Galactic Center Sources II., Eight Infrared Sources within 30 pc of the Galactic Center (Goto et al., ApJ) 6) Decaying Sterile Neutrinos as a Heating Source in the Milky Way Center (Chan & Chu, MNRAS) 7) Milliarcsecond angular resolution of reddened stellar sources in the vicinity of the Galactic Center (Richichi et al., A&A) 8) Milliarcsecond angular resolution of reddened stellar sources in the vicinity of the Galactic Center. II. Additional observations (Richichi et al., A&A) 9) Binary formation and mass function variations in fragmenting discs with short cooling times (Alexander et al., MNRAS) 10) Discovery and Interpretation of an X-ray Period in the Galactic Center Source CXOGC J174536.1-285638 (Mikles et al., ApJ) 11) Gas flow models in the Milky Way embedded bars (Rodriguez-Fernandez & Combes, A&A) 12) Interpretation of radio continuum and molecular line observations of Sgr B2: free-free and synchrotron emission, and implications for cosmic rays (Protheroe et al., MNRAS) 13) The Galactic Center as a laboratory for extreme mass ratio gravitational wave source dynamics (Alexander, Invited) 14) Origin of the S Stars in the Galactic Center (Loeckmann et al., ApJL) 15) On the Formation of Compact Stellar Disks Around Sgr A* (Wardle & Yusef-Zadeh, ApJL) 16) Massive Star Formation in the Molecular Ring Orbiting the Black Hole at the Galactic Center (Yusef-Zadeh et al., ApJL) ------------------------------------------------------------------------ Email : aseth@cfa.harvard.edu Title : The Rotating Nuclear Star Cluster in NGC 4244 Author(s): Anil C. Seth(1,2), Robert D. Blum(3), Nate Bastian(4), Nelson Caldwell(1), Victor P. Debattista(5) Institute: (1) Harvard-Smithsonian Center for Astrophysics, 60 Garden Street Cambridge, MA 02138 (2) Center for Astrophysics Fellow (3) National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ, 85721 (4) Institute of Astronomy, University of Cambridge (5) Centre For Astrophysics, University of Central Lancashire, Preston PR1 2HE, UK Paper : ApJ, November 2008, in press EPrint : 0807.3044 Web : http://xxx.lanl.gov/pdf/0807.3044v1 Abstract: We present observations of the nuclear star cluster in the nearby edge-on spiral galaxy NGC 4244 using the Gemini Near-Infrared Integral Field Spectrograph (NIFS) with laser guide star adaptive optics. From a previous study of edge-on galaxies, this nuclear star cluster was found to be one of a sample of clusters that appear flattened along the plane of their host galaxies disks. Such clusters show evidence for multiple morphological components, with younger/bluer disk components and older/redder spheroidal components. Our new observations of NGC 4244 show clear rotation of 30 km s^-1 within the central 10 pc (0.5'') of the cluster. The central velocity dispersion is found to be 28+/-2 km s^-1. The multiple stellar populations inferred from the optical colors and spectra are seen as variations in the CO line strength in the NIFS spectra. The rotation is clearly detected even in the older, more spheroidal stellar ------------------------------------------------------------------------ Email : hagai.perets@weizmann.ac.il Title : Dynamical evolution of the young stars in the Galactic center Author(s): Hagai. B. Perets(1), Alessia Gualandris(2), David Merritt(2) and Tal Alexander(1) Institute: (1) Benoziyo Center for Astrophysics, Weizmann Institute of Science and Center for Computational Relativity and Gravitation, Rochester Institute of Technology Paper : Central Kiloparsec conference proceedings, 2008 Abstract: Recent observations of the Galactic center revealed a nuclear disk of young OB stars near the massive black hole (MBH), in addition to many similar outlying stars with higher eccentricities and/or high inclinations relative to the disk (some of them possibly belonging to a second disk). In addition, observations show the existence of young B stars (the 'S-cluster') in an isotropic distribution in the close vicinity of the MBH (<0.04 pc). We use extended N-body simulations to probe the dynamical evolution of these two populations. We show that the stellar disk could have evolved to its currently observed state from a thin disk of stars formed in a gaseous disk, and that the dominant component in its evolution is the interaction with stars in the cusp around the MBH. We also show that the currently observed distribution of the S-stars could be consistent with a capture origin through 3-body binary-MBH interactions. In this scenario the stars are captured at highly eccentric orbits, but scattering by stellar black holes could change their eccentricity distribution to be consistent with current observations. ------------------------------------------------------------------------ Email : hendrik.bartko@googlemail.com Title : Study of the Science Capabilities of PRIMA in the Galactic Center Author(s): H. Bartko(1), O. Pfuhl(1), F. Eisenhauer(1), R. Genzel(1,2), S. Gillessen(1), S. Rabien(1), R. Abuter(3), G. v. Belle(3), F. Delplancke(3), S. Menardi(3), J. Sahlmann(3,4) Institute: (1) Max-Planck-Institute for Extraterrestrial Physics, Garching, Germany; (2) Department of Physics, University of California, Berkeley, USA; (3) ESO, Garching, Germany;, (4) Observatoire de Geneve, Sauverny, Switzerland. Paper : SPIE 325 Abstract: The Phase-Referenced Imaging and Micro-arcsecond Astrometry (PRIMA) facility is scheduled for installation in the Very Large Telescope Interferometer observatory in Paranal, Chile, in the second half of 2008. Its goal is to provide astrometric accuracy in the micro-arcsecond range. High precision astrometry can be applied to explore the dynamics of the dense stellar cluster. Especially models for the formation of stars near super massive black holes or the fast transfer of short-lived massive stars into the innermost parsec of our galaxy can be tested. By measuring the orbits of stars close to the massive black hole one can probe deviations from a Keplerian motion. Such deviations could be due to a swarm of dark, stellar mass objects that perturb the point mass solution. At the same time the orbits are affected by relativistic corrections which thus can be tested. The ultimate goal is to test the effects of general relativity in the strong gravitational field. The latter can be probed with the near infrared flares of SgrA* which are most likely due to accretion phenomena onto the black hole. We study the expected performance of PRIMA for astrometric measurements in the Galactic Center based on laboratory measurements and discuss possible observing strategies. ------------------------------------------------------------------------ Email : jott@nrao.edu Paper : MNRAS in press Abstract: Recent ammonia (1,1) inversion line data on the Galactic star forming region Sgr B2 show that the column density is consistent with a radial Gaussian density profile with a standard deviation of 2.75 pc. Deriving a formula for the virial mass of spherical Gaussian clouds, we obtain M_vir =1.9 * 10^6 M_o for Sgr B2. For this matter distribution, a reasonable magnetic field and an impinging flux of cosmic rays of solar neighbourhood intensity, we predict the expected synchrotron emission from the Sgr B2 giant molecular cloud due to secondary electrons and positrons resulting from cosmic ray interactions, including effects of losses due to pion production collisions during diffusive propagation into the cloud complex. We assemble radio continuum data at frequencies between 330 MHz and 230 GHz. From the spectral energy distribution the emission appears to be thermal at all frequencies. Before using these data to constrain the predicted synchrotron flux, we first model the spectrum as free-free emission from the known ultra compact H ii regions plus emission from an envelope or wind with a radial density gradient, and obtain an excellent fit. We thus find the spectrum at all frequencies to be dominated by thermal emission, and this severely constrains the possible synchrotron emission by secondary electrons to quite low flux levels. The absence of a significant contribution by secondary electrons is almost certainly due to multi-GeV energy cosmic rays being unable to penetrate far into giant molecular clouds. This would also explain why 100 MeV-GeV gamma-rays (from neutral pion decay or bremsstrahlung by secondary electrons) were not observed from Sgr B2 by EGRET, while TeV energy gamma-rays were observed, being produced by higher energy cosmic rays which more readily penetrate giant molecular clouds. ------------------------------------------------------------------------ Email : lida@astro.physik.uni-potsdam.de Title : Two extremely luminous WN stars in the Galactic center with circumstellar emission from dust and gas Author(s): A. Barniske, L. M. Oskinova, and W.-R. Hamann Institute: (1) Potsdam University, Am Neuen Palais 10, Potsdam, 14469 Germany Paper : A&A 486/3, 2008, in press Web : http://www.spitzer.caltech.edu/Media/releases/ssc2008-13/ Abstract: The central region of our Galaxy contains a large population of young massive stars. These stars are concentrated in three large star clusters, as well as being scattered in the field. Strong ionizing radiation and stellar winds of massive stars are the essential feedback agents that determine the physics of the ISM in the Galactic center. The aim is to study relatively isolated massive WN-type stars in the Galactic center in order to explore their properties and their influence on the ISM. The K-band spectra of two WN stars in the Galactic center, WR 102ka and WR 102c, are exploited to infer the stellar parameters and to compute synthetic stellar spectra using the Potsdam Wolf-Rayet (PoWR) model atmosphere code. These models are combined with dust-shell models for analyzing the Spitzer IRS spectra of these objects. Archival IR images complement the interpretation. We report that WR 102ka and WR 102c are among the most luminous stars in the Milky Way. They critically influence their immediate environment by strong mass loss and intense UV radiation, and thus set the physical conditions for their compact circumstellar nebula. The mid-IR continua for both objects are dominated by dust emission. For the first time we report the presence of dust in the close vicinity of WN stars. Also for the first time, we have detected lines of pure-rotational transitions of molecular hydrogen in a massive-star nebula. A peony-shaped nebula around WR 102ka is resolved at 24 micron by the Spitzer MIPS camera. We attribute the formation of this IR-bright nebula to the recent evolutionary history of WR 102ka. ------------------------------------------------------------------------ Email : mgoto@mpia-hd.mpg.de Title : Absorption Line Survey of H_3^+ toward the Galactic Center Sources II., Eight Infrared Sources within 30 pc of the Galactic Center Author(s): Miwa Goto(1) T. Usuda(2) T. Nagata(3) T. R. Geballe(4) B. J. McCall(5) N. Indriolo(5) H. Suto(6) Th. Henning(1) C. P. Morong(7) Takeshi Oka Institute: (1) Max-Planck-Institut fuer Astronomie (2) Subaru Telescope (3) Kyoto University (4) Gemini Observatory (5) University of Illinois at Urbana-Champaign (6) NAOJ (7) Max-Planck-Institut fuer Astronomie (8) University of Chicago Paper : ApJ, accepted EPrint : 0807.4522 Abstract: Infrared absorption lines of H_3^+, including the metastable R(3,3)^l line, have been observed toward eight bright infrared sources associated with hot and massive stars located in and between the Galactic Center Cluster and the Quintuplet Cluster 30 pc to the east. The absorption lines with high velocity dispersion arise in the Galaxy's Central Molecular Zone (CMZ) as well as in foreground spiral arms. The temperature and density of the gas in the CMZ, as determined from the relative strengths of the H_3^+ lines, are T=200 - 300 K and n<=50 - 200 cm^-3. The detection of high column densities of H_3^+ toward all eight stars implies that this warm and diffuse gaseous environment is widespread in the CMZ. The products of the ionization rate and path length for these sight lines are 1000 and 10 times higher than in dense and diffuse clouds in the Galactic disk, respectively, indicating that the ionization rate, \zeta, is not less than 10^-15 s^-1 and that L is at least on the order of 50 pc. The warm and diffuse gas is an important component of the CMZ, in addition to the three previously known gaseous environments: (1) cold molecular clouds observed by radio emission of CO and other molecules, (2) hot (T = 10^4 - 10^6 K) and highly ionized diffuse gas (n_e = 10 - 100 cm^-3) seen in radio recombination lines, far infrared atomic lines, and radio-wave scattering, and (3) ultra-hot (T = 10^7 - 10^8 K) X-ray emitting plasma. Its prevalence significantly changes the understanding of the environment of the CMZ. The sight line toward GC IRS 3 is unique in showing an additional H_3^+ absorption component, which is interpreted as due to either a cloud associated with circumnuclear disk or the ``50 km s^-1 cloud'' known from radio observations. An infrared pumping scheme is examined as a mechanism to populate the (3,3) metastable level in this cloud. ------------------------------------------------------------------------ Email : mhchan@sun1.phy.cuhk.edu.hk Title : Decaying Sterile Neutrinos as a Heating Source in the Milky Way Center Author(s): M. H. Chan and M. -C. Chu Institute: Department of Physics and Institute of Theoretical Physics, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China Paper : MNRAS in press EPrint : 0806.1311 Abstract: Recent Chandra and Newton observations indicate that there are two-temperature components (T 8 keV, 0.8 keV) of the diffuse x-rays emitted from deep inside the center of Milky Way. We show that this can be explained by the existence of sterile neutrinos, which decay to emit photons that can be bound-free absorbed by the isothermal hot gas particles in the center of Milky Way. The model can account for a stable configuration of the two-temperature components hot gas naturally as well as the energy needed to maintain the 8 keV temperature in the hot gas. The predicted sterile neutrino mass is between 16-18 keV. ------------------------------------------------------------------------ Email : octavi.fors@gmail.com Title : Milliarcsecond angular resolution of reddened stellar sources in the vicinity of the Galactic Center Author(s): A. Richichi(1), O. Fors(2,3), E. Mason(4), J. Stegmaier(1), T. Chandrasekhar(5) Institute: (1) European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei Muenchen, Germany (2) Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Marti i Franques 1, 08028 Barcelona, Spain (3) Observatori Fabra, Cami de l'Observatori s/n, 08035 Barcelona, Spain (4) European Southern Observatory, Santiago, Chile (5) Physical Research Laboratory, 380009 Ahmedabad, India Paper : A&A, Jul 2008, in press EPrint : 0807.2646 Abstract: For the first time, the lunar occultation technique has been employed on a very large telescope in the near-IR with the aim of achieving systematically milliarcsecond resolution on stellar sources. We have demonstrated the burst mode of the ISAAC instrument, using a fast read-out on a small area of the detector to record many tens of seconds of data at a time on fields of few squared arcseconds. We have used the opportunity to record a large number of LO events during a passage of the Moon close to the Galactic Center in March 2006. We have developed and employed for the first time a data pipeline for the treatment of LO data, including the automated estimation of the main data analysis parameters using a wavelet-based method, and the preliminary fitting and plotting of all light curves. We recorded 51 LO events over about four hours. Of these, 30 resulted of sufficient quality to enable a detailed fitting. We detected two binaries with subarcsecond projected separation and three stars with a marginally resolved angular diameter of about 2 milliarcseconds. Two more stars, which are cross-identified with SiO maser, were found to be resolved and in one case we could recover the brightness profile of the extended emission, which is well consistent with an optically thin shell. The remaining unresolved stars were used to characterize the performance of the method. The LO technique at a very large telescope is a powerful and efficient method to achieve angular resolution, sensitivity, and dynamic range that are among the best possible today with any technique. The selection of targets is naturally limited and LOs are fixed-time events, however each observation requires only a few minutes including overheads. As such, LOs are ideally suited to fill small gaps of idle time between standard observations. ------------------------------------------------------------------------ Email : octavi.fors@gmail.com Title : Milliarcsecond angular resolution of reddened stellar sources in the vicinity of the Galactic Center. II. Additional observations Author(s): A. Richichi(1), O. Fors(2,3), E. Mason(4) Institute: (1) European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei Muenchen, Germany (2) Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Marti i Franques 1, 08028 Barcelona, Spain (3) Observatori Fabra, Cami de l'Observatori s/n, 08035 Barcelona, Spain (4) European Southern Observatory, Santiago, Chile Paper : A&A, Jul 2008, in press EPrint : 0807.2650 Abstract: We present lunar occultation (LO) observations obtained in August 2006 with the recently demonstrated burst mode of the ISAAC instrument at the ESO VLT. The results presented here follow the previously reported observations carried out in March 2006 on a similar but unrelated set of sources. Interstellar extinction in the inner regions of the galactic bulge amounts to tens of magnitudes at visual wavelengths. As a consequence, the majority of sources in that area are poorly studied and large numbers of potentially interesting sources such as late-type giants with circumstellar shells, stellar masers, infrared stars, remain excluded from the typical investigations which are carried out in less problematic regions. Also undetected are a large numbers of binaries. By observing LO events in this region, we gain the means to investigate at least a selected number of sources with an unprecedented combination of sensitivity and angular resolution. The LO technique permits to achieve milliarcsecond resolution with a sensitivity of K 12 mag at a very large telescope. We have used the opportunity of a favorable passage of the Moon over a crowded region in the general direction of the Galactic Center to observe 78 LO events of heavily reddened stellar sources. We have detected six new binary and one triple star, with typical projected separation of 0.''01. We have also detected the compact circumstellar emission around one maser and one central star of a planetary nebula. Additionally we have measured the diameter and/or circumstellar shell of two carbon stars and other IR sources. We have used the upper limits on the size of about 60 unresolved or marginally resolved sources to establish the performance of the method. In agreement with our previous result, we conclude that lunar occultations in fast read-out mode on a detector subwindow at an 8 m-class telescope can achieve an angular resolution close to 0.''001 with a sensitivity K 12 mag. ------------------------------------------------------------------------ Email : rda@strw.leidenuniv.nl Title : Binary formation and mass function variations in fragmenting discs with short cooling times Author(s): R.D. Alexander (1,2), P.J. Armitage (2,3) and J. Cuadra (3) Institute: (1) Sterrewacht Leiden, Universiteit Leiden, Niels Bohrweg 2, 2300 RA, Leiden, the Netherlands (2) JILA, University of Colorado, Boulder, CO 80309-0440, USA (3) Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309-0391, USA Paper : MNRAS, in press EPrint : 0807.1731 Abstract: Accretion discs at sub-pc distances around supermassive black holes are likely to cool rapidly enough that self-gravity results in fragmentation. Here, we use high-resolution hydrodynamic simulations of a simplified disc model to study how the outcome of fragmentation depends upon numerical resolution and cooling time, and to investigate the incidence of binary formation within fragmenting discs. We investigate a range of cooling times, from the relatively long cooling time-scales that are marginally unstable to fragmentation down to highly unstable cooling on a time-scale that is shorter than the local dynamical time. The characteristic mass of fragments decreases with reduced cooling time, though the effect is modest and dependent upon details of how rapidly bound clumps radiate. We observe a high incidence of capture binaries, though we are unable to determine their final orbits or probability of survival. The results suggest that faster cooling in the parent disc results in an increased binary fraction, and that a high primordial binary fraction may result from disc fragmentation. We discuss our results in terms of the young massive stars close to the Galactic Centre, and suggest that observations of some stellar binaries close to the Galactic Centre remain consistent with formation in a fragmenting accretion disc. ------------------------------------------------------------------------ Email : reba@astro.ufl.edu Title : Discovery and Interpretation of an X-ray Period in the Galactic Center Source CXOGC J174536.1-285638 Author(s): Valerie J. Mikles(1), Stephen S. Eikenberry(1), Reba M. Bandyopadhyay(1), Michael P. Muno(2) Institute: (1) Department of Astronomy, University of Florida, Gainesville, FL 32611 (2) Space Radiation Laboratory, Caltech, Pasadena, CA 91125 Paper : ApJ, 2008, in press EPrint : 0807.0657 Abstract: We present X-ray and infrared observations of the X-ray source CXOGC J174536.1-285638. Previous observations suggest that this source may be an accreting binary with a high-mass donor (HMXB) or a colliding wind binary (CWB). Based on the Chandra and XMM-Newton light curve, we have found an apparent 189 +/- 6 day periodicity with better than 99.997% confidence. We discuss several possible causes of this periodicity, including both orbital and superorbital interpretations. We explore in detail the possibility that the X-ray modulation is related to an orbital period and discuss the implications for two scenarios; one in which the variability is caused by obscuration of the X-ray source by a stellar wind, and the other in which it is caused by an eclipse of the X-ray source. We find that in the first case, CXOGC J174536.1-285638 is consistent with both CWB and HMXB interpretations, but in the second, CXOGC J174536.1-285638 is more likely a HMXB. ------------------------------------------------------------------------ Email : rodrigue@iram.fr Title : Gas flow models in the Milky Way embedded bars Author(s): N. J. Rodriguez-Fernandez(1), F. Combes(2) Institute: (1) IRAM, 300 rue de la Piscine, 38406 St. Martin d'Heres, France (2) LERMA, Observatoire de Paris, 61 Av de l'Observatoire, 75014 Paris, France Paper : A&A in press EPrint : 0806.4252 Abstract: present many unknowns as the origin of the asymmetry of the lv-diagram of the Central Molecular Zone (CMZ). On the other hand, there are recent evidences in the stellar component of the presence of a nuclear bar that could be slightly lopsided. Our goal is to characterize the nuclear bar observed in 2MASS maps and to study the gas dynamics in the inner Milky Way taking into account this secondary bar. We have derived a realistic mass distribution by fitting the 2MASS star counts map of Alard (2001) with a model including three components (disk, bulge and nuclear bar) and we have simulated the gas dynamics, in the deduced gravitational potential, using a sticky-particles code. Our simulations of the gas dynamics reproduce successfully the main characteristics of the Milky Way for a bulge orientation of 20 DEG-35 DEG with respect to the Sun-Galactic Center (GC) line and a pattern speed of 30-40 km/s/kpc. In our models the Galactic Molecular Ring (GMR) is not an actual ring but the inner parts of the spiral arms, while the 3-kpc arm and its far side counterpart are lateral arms that contour the bar. Our simulations reproduce, for the first time, the parallelogram shape of the lv-diagram of the CMZ as the gas response to the nuclear bar. This bar should be oriented by an angle of 60 DEG-75 DEG with respect to the Sun-GC line and its mass amounts to (2-5.5) 10^9 \Msun. We show that the observed asymmetry of the CMZ cannot be due to lopsidedness of the nuclear bar as suggested by the 2MASS maps. We do not find clear evidences of lopsidedness in the stellar potential. We propose that the observed asymmetry of the central gas layer can be due to the infalling of gas into the CMZ in the l=1.3 DEG-complex. ------------------------------------------------------------------------ Email : rprother@physics.adelaide.edu.au Title : Interpretation of radio continuum and molecular line observations of Sgr B2: free-free and synchrotron emission, and implications for cosmic rays Author(s): R.J. Protheroe^1, J. Ott^2,3, R.D. Ekers^4, D.I. Jones^1,4, R.M. Crocker^5 Institute: ^1 Department of Physics, School of Chemistry \& Physics, University of Adelaide, South Australia 5000, Australia., ^2 National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA, ^3 California Institute of Technology, 1200 E. California Blvd., Caltech Astronomy, 105-24, Pasadena, CA, 91125, USA., ^4 Australia Telescope National Facility, CSIRO, P.O. BOX 76 Epping, NSW 1710, Australia., ^5 J.L. William Fellow, School of Physics, Monash University, Victoria, Australia. Paper : MNRAS in press EPrint : arXiv:0807.0127 Abstract: Recent ammonia (1,1) inversion line data on the Galactic star forming region Sgr B2 show that the column density is consistent with a radial Gaussian density profile with a standard deviation of 2.75 pc. Deriving a formula for the virial mass of spherical Gaussian clouds, we obtain M_vir =1.9 * 10^6 M_o for Sgr B2. For this matter distribution, a reasonable magnetic field and an impinging flux of cosmic rays of solar neighbourhood intensity, we predict the expected synchrotron emission from the Sgr B2 giant molecular cloud due to secondary electrons and positrons resulting from cosmic ray interactions, including effects of losses due to pion production collisions during diffusive propagation into the cloud complex. We assemble radio continuum data at frequencies between 330 MHz and 230 GHz. From the spectral energy distribution the emission appears to be thermal at all frequencies. Before using these data to constrain the predicted synchrotron flux, we first model the spectrum as free-free emission from the known ultra compact H ii regions plus emission from an envelope or wind with a radial density gradient, and obtain an excellent fit. We thus find the spectrum at all frequencies to be dominated by thermal emission, and this severely constrains the possible synchrotron emission by secondary electrons to quite low flux levels. The absence of a significant contribution by secondary electrons is almost certainly due to multi-GeV energy cosmic rays being unable to penetrate far into giant molecular clouds. This would also explain why 100 MeV-GeV gamma-rays (from neutral pion decay or bremsstrahlung by secondary electrons) were not observed from Sgr B2 by EGRET, while TeV energy gamma-rays were observed, being produced by higher energy cosmic rays which more readily penetrate giant molecular clouds. ------------------------------------------------------------------------ Email : tal.alexander@weizmann.ac.il Title : The Galactic Center as a laboratory for extreme mass ratio gravitational wave source dynamics Author(s): Tal Alexander Institute: (1) Weizmann Institute of Science Paper : Invited talk 2nd Kolkata conf. on BHs EPrint : 0807.1929 Abstract: The massive Galactic black hole and the stars around it are a unique laboratory for studying how relaxation processes lead to close interactions of stars and compact remnants with the central massive black hole, in particular those leading to the emission of gravitational waves. I review new results on the processes of strong mass segregation and loss-cone refilling by massive perturbers and resonant relaxation; describe observational evidence that these processes play a role in the Galactic Center and can be studied there; and discuss some of the implications for Extreme Mass Ration Inspiral event rates and their properties. ------------------------------------------------------------------------ Email : uloeck@astro.uni-bonn.de Title : Origin of the S Stars in the Galactic Center Author(s): Ulf Loeckmann, Holger Baumgardt, and Pavel Kroupa Institute: (1) Argelander-Institut fuer Astronomie, Universitaet Bonn, Auf dem Huegel 71, 53121 Bonn, Germany Paper : ApJ Letters, August 2008, in press EPrint : 0807.2239 Web : http://www.journals.uchicago.edu/doi/ref/10.1086/591734 Abstract: Over the last 15 years, around a hundred very young stars have been observed in the central parsec of our Galaxy. While the presence of young stars forming one or two stellar disks at 0.1 pc from the supermassive black hole (SMBH) can be understood through star formation in accretion disks, the origin of the S stars observed a factor of 10 closer to the SMBH has remained a major puzzle. Here we show the S stars to be a natural consequence of dynamical interaction of two stellar disks at larger radii. Due to precession and Kozai interaction, individual stars achieve extremely high eccentricities at random orientation. Stellar binaries on such eccentric orbits are disrupted due to close passages near the SMBH, leaving behind a single S star on a much tighter orbit. The remaining star may be ejected from the vicinity of the SMBH, thus simultaneously providing an explanation for the observed hypervelocity stars in the Milky Way halo. ------------------------------------------------------------------------ Email : wardle@ics.mq.edu.au Title : On the Formation of Compact Stellar Disks Around Sgr A* Author(s): Mark Wardle Farhad Yusef-Zadeh Institute: (1) Department of Physics, Macquarie University, Sydney NSW 2109, Australia (2) Department of Physics \& Astronomy, Northwestern University, Evanston, IL 60208, USA Paper : ApJ Letters, in press EPrint : 0805.3274 Abstract: The recent identification of one or two sub-parsec disks of young, massive stars orbiting the 4\ee 6 \msol black hole Sgr A* has prompted an ``in-situ'' scenario for star formation in disks of gas formed from a cloud captured from the Galactic center environment. To date there has been no explanation given for the low angular momentum of the disks relative to clouds passing close to the center. Here we show that the partial accretion of extended Galactic center clouds, such as the 50 km/sec giant molecular cloud, that temporarily engulf Sgr A* during their passage through the central region of the Galaxy provide a natural explanation for the angular momentum and surface density of the the observed stellar disks. The captured cloud material is gravitationally unstable and forms stars as it circularizes, potentially explaining the large eccentricity and range of inclinations of the observed stellar orbits. The application of this idea to the formation of the circumnuclear ring is also discussed. ------------------------------------------------------------------------ Email : zadeh@northwestern.edu Title : Massive Star Formation in the Molecular Ring Orbiting the Black Hole at the Galactic Center Author(s): Yusef-Zadeh, F.; Braatz, J.; Wardle, M.; Roberts, D. Paper : ApJL in press EPrint : arXiv:0807.1745 Abstract: A ring of dense molecular gas extending 2-7 pc orbits the supermassive black hole Sgr A* at the center of our Galaxy. Using the Green Bank Telescope, we detected water maser lines and both narrow (0.35 km/s) and broad (30 - 50 km/s) methanol emission from the molecular ring. Two of the strongest methanol lines at 44 GHz are confirmed as masers by interferometric observations. These class I methanol masers are collisionally excited and are signatures of early phases of massive star formation in the disk of the Galaxy, suggesting that star formation in the molecular ring is in its early phase. Close inspection of the kinematics of the associated molecular clumps in the HCN (J=1-0) line reveals broad red-shifted wings indicative of disturbance by protostellar outflows from young (few times 10^4 yr), massive stars embedded in the clumps. The thermal methanol profile has a similar shape, with a narrow maser line superimposed on a broad, red-shifted wing. Additional evidence for the presence of young massive protostars is provided by shocked molecular hydrogen and a number of striking ionized and molecular linear filaments in the vicinity of methanol sources suggestive of 0.5-pc scale protostellar jets. Given that the circumnuclear molecular ring is kinematically unsettled and thus is likely be the result of a recent capture, the presence of both methanol emission and broad, red-shifted HCN emission suggests that star formation in the circumnuclear ring is in its infancy. ------------------------------------------------------------------------ (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 ========================================================================