======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@aoc.nrao.edu http://www.aoc.nrao.edu/~gcnews ======================================================================== Vol. 27, No. 6 Aug 23, 2007 Recently submitted papers: -------------------------- 1) GRO J1744-28, search for the counterpart: infrared photometry and spectroscopy (Gosling et al., MNRAS) 2) Spitzer IRS Observations of the Galactic Center: Shocked Gas in the Radio Arc Bubble (Simpson et al., ApJ) 3) Do flares in Sagittarius A* reflect the last stage of tidal capture? (Cadez et al., AIP) ------------------------------------------------------------------------ Email : ajgosling@gmail.com Title : GRO J1744-28, search for the counterpart: infrared photometry and spectroscopy Author(s): A.J. Gosling,^1 R.M. Bandyopadhyay,^2 J.C.A. Miller-Jones^3 and S.A. Farrell,^4,5 Institute: ^1Department of Astrophysics, University of Oxford, Keble Road, Oxford, OX1 3RH, UK ^2Department of Astronomy, University of Florida, Gainesville, FL 32611, USA ^3Astronomical Institute `Anton Pannekoek', University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands ^4School of PEMS, UNSW@ADFA, Northcott Drive, Canberra, ACT 2600, Australia ^5Centre d'Etude Spatiale des Rayonnements, 9 Avenue du Colonel Roche, 31028 Toulouse Cedex 4, France CNRS/UPS Paper : MNRAS in press EPrint : astro-ph/0703692 Web : http://www-astro.physics.ox.ac.uk/~ajg/papers/groj.pdf Abstract: Using VLT/ISAAC, we have detected 2 candidate counterparts to the bursting pulsar \groj, one bright and one faint, both within the X-ray error circles found using XMM-Newton and Chandra. In determining the spectral types of the counterparts we applied 3 different extinction corrections; one for an all-sky value, one for a Galactic Bulge value and one for a local value. We find that the local value, with an extinction law of alpha = 3.23 +/- 0.01 is the only correction that results in colours and magnitudes for both the bright and faint counterparts that are consistent with a small range of spectral types, and in the case of the bright counterpart are also consistent with the spectroscopic identification. Photometry of the fainter candidate then indicates it is a K7/M0 V star at a distance of 3.75+/-1 kpc. Such a star would require a very low inclination angle (i<9^o) to satisfy the mass-function constraints; however this source cannot be excluded as the counterpart without follow-up spectroscopy to detect emission signatures of accretion. Photometry and spectroscopy of the bright candidate indicate that it is most likely a G/K III star. The spectrum does not show \brg emission, a known indicator of accretion. The bright star's magnitudes are in agreement with the constraints placed on the probable counterpart by the calculations of \citetrapp97 for an evolved star that has had its envelope stripped. The mass-function indicates the most likely counterpart has M < 0.3 M_sol for an inclination of i >= 15 DEGr; a stripped giant, or a main sequence M3+ V star would be consistent with this mass-function constraint. In both cases mass-transfer, if present, will be by wind-accretion as the counterpart will not fill its Roche lobe given the observed orbital period. In this case, the derived magnetic field strength of 2.4 * 10^11 G is sufficient to inhibit accretion of captured material by the propeller effect, hence the quiescent state of the system. ------------------------------------------------------------------------ Email : jsimpson@mail.arc.nasa.gov Title : Spitzer IRS Observations of the Galactic Center: Shocked Gas in the Radio Arc Bubble Author(s): Janet P. Simpson(1,2), Sean W. J. Colgan(1), Angela S. Cotera(2), Edwin F. Erickson(1), David J. Hollenbach(3), Michael J. Kaufman(4), and Robert H. Rubin(1,5) Institute: (1) NASA Ames Research Center, Mail Stop 245-6, Moffett Field, CA 94035-1000, USA (2) SETI Institute, 515 N Whisman Road, Mountain View, CA 94043, USA (3) NASA Ames Research Center, Mail Stop 245-3, Moffett Field, CA 94035-1000, USA (4) Dept of Physics, San Jose State University, One Washington Square, San Jose, CA 95192, USA (5) Orion Enterprises Paper : ApJ, Dec 2007, in press EPrint : astro-ph/0708.2103 Abstract: We present Spitzer IRS spectra (R 600, 10 - 38 micron ) of 38 positions in the Galactic Center (GC), all at the same Galactic longitude and spanning +/- 0.3^o in latitude. Our positions include the Arches Cluster, the Arched Filaments, regions near the Quintuplet Cluster, the ``Bubble'' lying along the same line-of-sight as the molecular cloud G0.11-0.11, and the diffuse interstellar gas along the line-of-sight at higher Galactic latitudes. From measurements of the [\ionO4], [\ionNe2], [\ionNe3], [\ionSi2], [\ionS3], [\ionS4], [\ionFe2], [\ionFe3], and H_2 S(0), S(1), and S(2) lines we determine the gas excitation and ionic abundance ratios. The Ne/H and S/H abundance ratios are 1.6 times that of the Orion Nebula. The main source of excitation is photoionization, with the Arches Cluster ionizing the Arched Filaments and the Quintuplet Cluster ionizing the gas nearby and at lower Galactic latitudes including the far side of the Bubble. In addition, strong shocks ionize gas to O^+3 and destroy dust grains, releasing iron into the gas phase (Fe/H 1.3 * 10^-6 in the Arched Filaments and Fe/H 8.8 * 10^-6 in the Bubble). The shock effects are particularly noticeable in the center of the Bubble, but O^+3 is present in all positions. We suggest that the shocks are due to the winds from the Quintuplet Cluster Wolf-Rayet stars. On the other hand, the H_2 line ratios can be explained with multi-component models of warm molecular gas in photodissociation regions without the need for H_2 production in shocks. ------------------------------------------------------------------------ Email : uros.kostic@fmf.uni-lj.si Title : Do flares in Sagittarius A* reflect the last stage of tidal capture? Author(s): A. Cadez M. Calvani A. Gomboc U. Kostic Paper : AIP Conf.Proc. 861 (2006) 566-571 EPrint : astro-ph/0708.2696 Web : http://astro.ago.uni-lj.si/bh/pmwiki.php?n=Main.Publications Abstract: In recent years the case for the presence of 3-4* 10^6 M_o black hole in our Galactic Centre has gain strenght from results of stellar dynamics observations and from the detection of several rapid X-ray and IR flares observed in the Sagittarius A* from 2000 to 2004. Here we explore the idea that such flares are produced when the central black hole tidaly captures and disrupts a small body - e.g. a comet or an asteroid. ------------------------------------------------------------------------ (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 ========================================================================