======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@aoc.nrao.edu http://www.aoc.nrao.edu/~gcnews ======================================================================== Vol. 20, No. 4 Feb 11, 2005 Recently submitted papers: -------------------------- 1) Stellar Bowshocks in the Northern Arm of the Galactic Center: More Members and Kinematics of the Massive Star Population (Tanner et al., ApJ) 2) Accretion of cool stellar winds on Sgr A*: another puzzle of the Galactic Centre? (Cuadra et al., MNRASL) 3) A Distinct Structure Inside the Galactic Bar (Nishiyama et al., ApJL) ------------------------------------------------------------------------ Email : Angelle.M.Tanner-120278@mailhub.jpl.nasa.gov Title : Stellar Bowshocks in the Northern Arm of the Galactic Center: More Members and Kinematics of the Massive Star Population Author(s): A. Tanner, A. M. Ghez, and M. R. Morris J. C. Christou Institute: (1) UCLA Department of Physics and Astronomy, Los Angeles, CA 90095-1562 (2) Center for Adaptive Optics, Santa Cruz, CA Paper : ApJ May 2005 in press EPrint : astro-ph/0412494 Abstract: We present new 2.2 micron diffraction-limited images from the W. M. Keck 10 m and Gemini 8 m telescopes of the cool Galactic Center sources, IRS 1W, 5, 8, 10W, and 21 along with new proper motions for IRS 1W, 10W and 21. These observations were carried out to test the bowshock hypothesis presented by Tanner et al. as an alternative to a very recent (10^4 yr) epoch of star formation within the tidal stream of gas and dust known as the Northern Arm. Resolved asymmetric structure is detected in all the sources, with bowshock morphologies associated with IRS 1W, 5, 8 and 10W. For IRS 1W and 10W, there is an agreement between the position angle of the asymmetry and that of the inferred relative velocity vector of the near-infrared source with respect to the Northern Arm gas, strengthening the bowshock hypothesis. We therefore conclude that the observed morphology is indeed a bowshock generated by sources plowing through the Northern Arm. Furthermore, the large extent of the resolved structures (310-1340 AU), along with their luminosities ( 10^4-5 L_\sun), suggests that their central sources are Wolf-Rayet stars, comparable to the broad He emission-line stars, which have strong winds on the order of 1000 km s^-1. The bowshock geometry, along with the proper motion measurements, provide three-dimensional orbital solutions for this enigmatic class of objects. The orientations of the orbital planes of IRS 1W and 10W are consistent with that of the putative clockwise plane which has been proposed as a solution for the He I emission-line stars. While these observations eliminate the need to invoke star formation within the Northern Arm, they increase by 10% the total known population of massive, young stars with strong winds, whose origin remains unexplained in the context of the nearby supermassive black hole. ------------------------------------------------------------------------ Email : jcuadra@ibm-2.MPA-Garching.MPG.DE Title : Accretion of cool stellar winds on Sgr A*: another puzzle of the Galactic Centre? Author(s): J. Cuadra, S. Nayakshin, V. Springel, \& T. Di Matteo Paper : MNRAS Letters, submitted EPrint : astro-ph/0502044 Web : http://www.mpa-garching.mpg.de/~jcuadra/Winds/ Abstract: Sgr A* is currently being fed by winds from a cluster of gravitationally bound young mass-loosing stars. Using observational constraints on the orbits, mass loss rates and wind velocities of these stars, we numerically model the distribution of gas in the 0.1-10'' region around Sgr A*. We find that radiative cooling of recently discovered slow winds leads to the formation of many cool filaments and blobs, and to a thin and rather light accretion disc with a scale of about an arcsecond. The disc however does not extend all the way to our inner boundary. Instead, hot X-ray emitting gas dominates the inner arcsecond. In our simulations, cool streams of gas frequently enter this region on low angular momentum orbits, and are then disrupted and heated up to the ambient hot gas temperature. The accreting gas around Sgr A* is thus two-phase, with a hot component, observable at X-ray wavelengths, and a cool component, which may be responsible for the majority of time variability of Sgr A* emission on hundred and thousand years time-scales. ------------------------------------------------------------------------ Email : shogo@z.phys.nagoya-u.ac.jp Title : A Distinct Structure Inside the Galactic Bar Author(s): Shogo Nishiyama(1), Tetsuya Nagata(2), Daisuke Baba(1), Yasuaki Haba(1), Ryota Kadowaki(1), Daisuke Kato(1), Mikio Kurita(1), Chie Nagashima(1), Takahiro Nagayama(2), Yuka Murai(2), Yasushi Nakajima(3), Motohide Tamura(3), Hidehiko Nakaya(4), Koji Sugitani(5), Takahiro Naoi(6), Noriyuki Matsunaga(7), Toshihiko Tanabe(7), Nobuhiko Kusakabe(8), Shuji Sato(1) Institute: (1) Department of Astrophysics, Nagoya University, Nagoya, 464-8602, Japan (2) Department of Astronomy, Kyoto University, Kyoto, 606-8502, Japan (3) National Astronomical Observatory of Japan, Mitaka, 181-8588, Japan (4) Subaru Telescope, National Astronomical Observatory of Japan, 650 North A'ohoku Place, Hilo, HI 96720, U.S.A. (5) Institute of Natural Science, Nagoya City University, Nagoya, 464-8602, Japan (6) Department of Earth and Planetary Sciences The University of Tokyo, Tokyo, 113-0033, Japan (7) Institute of Astronomy, School of Science, The University of Tokyo, Tokyo, 181-0015, Japan (8) Department of Astronomy and Earth Sciences, Tokyo Gakugei University, Tokyo, 184-8501, Japan Paper : ApJL, accepted EPrint : astro-ph/0502058 Web : http://www.z.phys.nagoya-u.ac.jp/~shogo/papers/DistinctStruct ure.pdf Abstract: We present the result of a near-infrared (J H K_S) survey along the Galactic plane, -10.5 <= l <= 10.5 and b=+1 DEG, with the IRSF 1.4m telescope and the SIRIUS camera. K_S vs. H-K_S color-magnitude diagrams reveal a well-defined population of red clump (RC) stars whose apparent magnitude peak changes continuously along the Galactic plane, from K_S=13.4 at l=-10 DEG to K_S=12.2 at l=10 DEG after dereddening. This variation can be explained by the bar-like structure found in previous studies, but we find an additional inner structure at \mid l \mid< 4^o, where the longitude - apparent magnitude relation is distinct from the outer bar, and the apparent magnitude peak changes by only \thickapprox 0.1 mag over the central 8^o. The exact nature of this inner structure is as yet uncertain. ------------------------------------------------------------------------ (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 ========================================================================