119002004
Massive Stars in the Arches Cluster
We present and use new spectra and narrow-band images, along with previously published broad-band images, of stars in the Arches cluster to extract photometry, astrometry, equivalent width, and velocity information. The data are interpreted with a wind/atmosphere code to determine stellar temperatures, luminosities, mass-loss rates, and abundances. We have doubled the number of known emission-line stars, and we have also made the first spectroscopic identification of the main sequence for any population in the Galactic Center. We conclude that the most massive stars are bona-fide Wolf-Rayet (WR) stars and are some of the most massive stars known, having M_{initial} > 100 Msun, and prodigious winds, Mdot > 10^{-5} Msun yr^{-1}, that are enriched with helium and nitrogen; with these identifications, the Arches cluster contains about 5% of all known WR stars in the Galaxy. We find an upper limit to the velocity dispersion of 22 kms^{-1}, implying an upper limit to the cluster mass of 7(10^4) Msun within a radius of 0.23 pc; we also estimate the bulk heliocentric velocity of the cluster to be v_{cluster,odot} approximately +95 kms^{-1}.
13909300
The Stream-Stream Collision after the Tidal Disruption of a Star around a Massive Black Hole
A star can be tidally disrupted around a massive black hole. It is known that the debris forms a precessing stream, which may collide with itself. The stream collision is a key process in determining the subsequent evolution of the stellar debris: if the orbital energy is efficiently dissipated, the debris will eventually form a circular disk (or torus). In this paper, we have numerically studied such a stream collision resulting from the encounter between a 106 M☉ black hole and a 1 M☉ normal star with a pericenter radius of 100 R☉. A simple treatment for radiative cooling has been adopted for both optically thick and optically thin regions. We have found that approximately 10% to 15% of the initial kinetic energy of the streams is converted into thermal energy during the collision. The spread in angular momentum of the incoming stream is increased by a factor of 2 to 3, and such an increase, together with the decrease in kinetic energy, significantly helps the circularization process. The initial luminosity burst produced by the collision may reach as high as 1041 ergs s-1 in 104 s, after which the luminosity increases again (but slowly this time) to a steady value of a few 1040 ergs s-1 in a few times 105 s. The radiation from the system is expected to be close to Planckian, with an effective temperature of ~105 K.
119456102
Theoretical isochrones with extinction in the K band. II. J - K versus K
ABSTRACT We calculate theoretical isochrones in a consistent way for five filter pairs near the J and K band atmospheric windows ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $J-K$ \end{document} , \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcom...
119489565
Core-Collapse Times of Two-Component Clusters
We examine the corecollapse times of isolated, two-mass-component star clusters using Fokker-Planck models. With initial condition of Plummer models, we find that the corecollapse times of clusters with M_1/M_2 >> 1 are well correlated with (N_1/N_2)^{1/2}(m_1/m_2)^{2} t_{rh}, where M_1/M_2 and m_1/m_2 are the light to heavy component total and individual mass ratios, respectively, N_1/N_2 is the number ratio, and t_{rh} is the initial half-mass relaxation time scale. We also find two-component cluster parameters that best match multi-component (thus more realistic) clusters with power-law mass functions.
118942465
The Arches Cluster Mass Function
We have analyzed H- and Ks-band images of the Arches cluster obtained using the NIRC2 instrument on Keck with the laser guide star adaptive optics (LGS AO) system. With the help of the LGS AO system, we were able to obtain the deepest ever photometry for this cluster and its neighborhood and derive the background-subtracted present-day mass function down to 1.3 M☉ for the 5''-9'' annulus of the cluster. We find that the previously reported turnover at 6 M☉ is simply due to a local bump in the mass function (MF), and that the MF continues to increase down to our 50% completeness limit (1.3 M☉) with a power-law exponent of Γ = -0.91 for the mass range of 1.3 < M/M☉ < 50. Our numerical calculations for the evolution of the Arches cluster show that the Γ-values for our annulus increase by 0.1-0.2 during the lifetime of the cluster and thus suggest that the Arches cluster initially had Γ of -1.0 to 1.1, which is only slightly shallower than the Salpeter value.
17473739
Stellar collisions and mergers in the galactic center
Stars are most likely to merge or collide in regions of the highest stellar densities, and our own Galactic Center contains many stars packed into a relatively small volume -- even the ambient stellar number density in the central 50 pc is quite high, ~10^3 stars pc^{-3}. More striking, the three compact young clusters in this region have central densities as high as 10^6 stars pc^{-3}. We discuss these extreme environments and the possibility that stellar mergers and collisions have recently occured there. In particular, we predict that at least one massive star in the Arches cluster has already experienced a stellar merger in its short lifetime. Further, the Pistol Star, in the nearby Quintuplet cluster, might owe its apparent relative youth to a rejuvinating stellar merger. Finally, the apparently young stars in the central arcsecond could be products of either collisions, inducing atmospheric stripping, or mergers.
123024842
XMASS EXPERIMENT II
120964777
New results from the KIMS experiment
The Korea Invisible Mass Search (KIMS) collaboration has performed experiments on dark matter searches and double beta decay searches at the Yangyang underground laboratory. Recent results of KIMS as well as the status of the R&D on various detectors are presented. For the WIMP search KIMS ruled out the recoil of 127I of DAMA signal region unambiguously and set the most stringent limit on spin dependent WIMP interactions in the case of pure proton coupling. New limits on neutrino-less double beta decays of 112Sn, 124Sn, 64Zn is also reported.
118368147
Counterterms in gravity in the light-front formulation and a D = 2 conformal-like symmetry in gravity
A bstractIn this paper we discuss gravity in the light-front formulation (light-cone gauge) and show how possible counterterms arise. We find that Poincaré invariance is not enough to find the three-point counterterms uniquely. Higher-spin fields can intrude and mimic three-point higher derivative gravity terms. To select the correct term we have to use the remaining reparametrization invariance that exists after the gauge choice. We finally sketch how the corresponding programme for N = 8 Supergravity should work.
17174387
N-flation: Observable predictions from the random matrix mass spectrum
We carry out numerical investigations of the perturbations in N-flation models where the mass spectrum is generated by random matrix theory. The tensor-to-scalar ratio and non-Gaussianity are already known to take the single-field values, and so the density perturbation spectral index is the main parameter of interest. We study several types of random field initial conditions and compute the spectral index as a function of mass spectrum parameters. Comparison with microwave anisotropy data from the Wilkinson Microwave Anisotropy Probe shows that the model is currently viable in the majority of its parameter space.
119294901
E8(8) in Light Cone Superspace
We derive the non-linear action of E-8(8) on the constrained chiral superfield in the light-cone superspace with eight complex Grassmann variables. We construct (to lowest order in the coupling) the sixteen dynamical supersymmetries which generate a Hamiltonian with E-8(8) invariance in three space-time dimensions, and show that it has only interactions with even powers of the coupling constant.