High-velocity stars in the cores of globular clusters: the illustrative case of NGC 2808

Context. We report the detection of five high-velocity stars in the core of the globular cluster NGC 2808. The stars lie on the red giant branch and show total velocities between 40 and 45 kms(-1). For a core velocity dispersion sigma(c) = 13.4 kms(-1), this corresponds to up to 3.4 sigma(c). These velocities are close to the estimated escape velocity (similar to 50 km s(-1)) and suggest an ejection from the core. Two of these stars have been confirmed in our recent integral field spectroscopy data and we will discuss them in more detail here. These two red giants are located at a projected distance of similar to 0.3 pc from the center. According to their positions on the color magnitude diagram, both stars are cluster members.

[1]  N. Neumayer,et al.  Central kinematics of the globular cluster NGC 2808: upper limit on the mass of an intermediate-mass black hole , , 2012, 1204.4074.

[2]  E. Dalessandro,et al.  THE BINARY FRACTION IN THE GLOBULAR CLUSTER M10 (NGC 6254): COMPARING CORE AND OUTER REGIONS , 2011, 1108.5675.

[3]  K. Gebhardt,et al.  Kinematic signature of an intermediate-mass black hole in the globular cluster NGC 6388 , 2011, 1107.4243.

[4]  T. Lebzelter,et al.  Long period variables and mass loss in the globular clusters NGC 362 and NGC 2808 , 2011, 1103.5299.

[5]  A. Gualandris,et al.  Very massive runaway stars from three-body encounters , 2010 .

[6]  J. Kruijssen.  The evolution of the stellar mass function in star clusters , 2009, 0910.4579.

[7]  S. Zwart,et al.  On the origin of high‐velocity runaway stars , 2009, 0903.0738.

[8]  D. Heggie,et al.  A search for spectroscopic binaries in the Galactic globular cluster M4 Based on 5973 individual spectra collected at VLT , 2008, 0810.1897.

[9]  K. Long,et al.  Combined Chandra, XMM-Newton, and Hubble Space Telescope observations of the Galactic globular cluster NGC 2808 , 2008, 0808.2661.

[10]  J. Anderson,et al.  DEEP ADVANCED CAMERA FOR SURVEYS IMAGING IN THE GLOBULAR CLUSTER NGC 6397: THE BINARY FRACTION , 2008 .

[11]  Michele Cappellari,et al.  Measuring the inclination and mass-to-light ratio of axisymmetric galaxies via anisotropic Jeans models of stellar kinematics , 2008, 0806.0042.

[12]  Karl Gebhardt,et al.  Gemini and Hubble Space Telescope Evidence for an Intermediate-Mass Black Hole in ω Centauri , 2008 .

[13]  J. Anderson,et al.  DEEP ADVANCED CAMERA FOR SURVEYS IMAGING IN THE GLOBULAR CLUSTER NGC 6397: THE BINARY FRACTION , 2008, 0803.0005.

[14]  A. D. Mackey,et al.  A double main-sequence turn-off in the rich star cluster NGC 1846 in the Large Magellanic Cloud , 2007, 0704.3360.

[15]  J. Anderson,et al.  A Triple Main Sequence in the Globular Cluster NGC 2808 , 2007, astro-ph/0703767.

[16]  V.V.Gvaramadze,et al.  Hyperfast pulsars as the remnants of massive stars ejected from young star clusters , 2007, astro-ph/0702735.

[17]  Karl Gebhardt,et al.  Evidence for an Intermediate Mass Black Hole in Omega Centauri , 2006, 0801.2782.

[18]  S. Zwart,et al.  "Ejection of hypervelocity stars from the Galactic Centre by intermediate-mass black holes" , 2006, astro-ph/0607455.

[19]  R. O’Shaughnessy,et al.  Binary Mergers and Growth of Black Holes in Dense Star Clusters , 2005, astro-ph/0508224.

[20]  L. Ho,et al.  An Intermediate-Mass Black Hole in the Globular Cluster G1: Improved Significance from New Keck and Hubble Space Telescope Observations , 2005, astro-ph/0508251.

[21]  S. Zwart,et al.  Three-body encounters in the Galactic Centre: the origin of the hypervelocity star SDSS J090745.0+024507 , 2005, astro-ph/0507365.

[22]  P. University,et al.  The fingerprint of binary intermediate‐mass black holes in globular clusters: suprathermal stars and angular momentum alignment , 2005, astro-ph/0506405.

[23]  T. Lebzelter,et al.  Long period variables in the globular cluster 47 Tuc: Radial velocity variations , 2005, astro-ph/0501336.

[24]  P. Hut,et al.  Which Globular Clusters Contain Intermediate-Mass Black Holes? , 2004, astro-ph/0410597.

[25]  Livermore,et al.  N‐body simulations of stars escaping from the Orion nebula , 2004, astro-ph/0401451.

[26]  Eric Emsellem,et al.  Parametric Recovery of Line‐of‐Sight Velocity Distributions from Absorption‐Line Spectra of Galaxies via Penalized Likelihood , 2003, astro-ph/0312201.

[27]  A. Robin,et al.  A synthetic view on structure and evolution of the Milky Way , 2003, astro-ph/0401052.

[28]  M. Colpi,et al.  Probing the Presence of a Single or Binary Black Hole in the Globular Cluster NGC 6752 with Pulsar Dynamics , 2003, astro-ph/0309017.

[29]  J. Makino,et al.  Dynamical evolution of star clusters in tidal fields , 2002, astro-ph/0211471.

[30]  Monica Colpi,et al.  The Case of PSR J1911–5958A in the Outskirts of NGC 6752: Signature of a Black Hole Binary in the Cluster Core? , 2002, astro-ph/0204291.

[31]  M. Miller,et al.  Production of intermediate-mass black holes in globular clusters , 2001, astro-ph/0106188.

[32]  D. Merritt,et al.  A Fundamental Relation between Supermassive Black Holes and Their Host Galaxies , 2000, astro-ph/0006053.

[33]  K. Gebhardt,et al.  Canada-France-Hawaii Telescope Adaptive Optics Observations of the Central Kinematics in M15 , 1999, astro-ph/9912172.

[34]  D. Heggie,et al.  The time-scale of escape from star clusters , 1999, astro-ph/9910468.

[35]  J. Cassinelli,et al.  Introduction to Stellar Winds by Henny J. G. L. M. Lamers , 1999 .

[36]  J. Cassinelli,et al.  Introduction to Stellar Winds , 1999 .

[37]  T. Lebzelter,et al.  Infrared Velocities of Long Period Variables: CO delta(upsilon)=3 in Four Miras and Five SR Variables , 1997 .

[38]  C. Bailyn,et al.  Hubble Space Telescope Observations of the Post-Core-Collapse Globular Cluster NGC 6752. II. A Large Main-Sequence Binary Population , 1997 .

[39]  William E. Harris,et al.  A Catalog of Parameters for Globular Clusters in the Milky Way , 1996 .

[40]  P. Hut,et al.  Binary--Single-Star Scattering. VI. Automatic Determination of Interaction Cross Sections , 1996, astro-ph/9604015.

[41]  D. Heggie,et al.  Binary--Single-Star Scattering. VII. Hard Binary Exchange Cross Sections for Arbitrary Mass Ratios: Numerical Results and Semianalytic FITS , 1996, astro-ph/9604016.

[42]  Steinn Sigurdsson,et al.  Binary-single star interactions in globular clusters , 1993 .

[43]  Steinn Sigurdsson,et al.  Primordial black holes in globular clusters , 1993, Nature.

[44]  Piet Hut,et al.  Stellar black holes in globular clusters , 1993, Nature.

[45]  G. Meylan,et al.  Two high-velocity stars shot out from the core of the globular cluster 47 Tucanae , 1991 .

[46]  J. N. Bahcall,et al.  Estimated number of field stars toward Galactic globular clusters and Local Group Galaxies , 1985 .

[47]  John N. Bahcall,et al.  Binary-single star scattering. I: Numerical experiments for equal masses , 1983 .

[48]  S. Ridgway,et al.  Time series infrared spectroscopy of the Mira variable chi Cygni , 1982 .

[49]  J. Hills,et al.  Computer simulations of close encounters between single stars and hard binaries , 1980 .

[50]  J. Gunn,et al.  Dynamical studies of globular clusters based on photoelectric radial velocities of individual stars. I. M3. , 1979 .

[51]  P. Wood,et al.  Pulsation and mass loss in Mira variables , 1979 .

[52]  K. Hinkle.  Infrared spectroscopy of Mira variables. I. R Leonis: The CO and OH vibration-rotation overtone bands , 1978 .

[53]  Douglas C. Heggie,et al.  Binary evolution in stellar dynamics , 1975 .

[54]  I. King,et al.  The structure of star clusters. VI. Observed radii and structural parameters in globular clusters. , 1975 .

[55]  W. Harris.  The unusual horizontal branch of NGC 2808 , 1974 .