123223236
Fitting formulae for cross sections of tidal capture binary formation
Tidal captures can produce objects that are obser- vationally and dynamically important in dense stellar systems. Recent discoveries of compact young clusters in and out of the Galaxy have prompted the studies of dynamics of star clusters with a large range in stellar masses. The tidal interactions be- tween high and low mass stars are found to be rather frequent in such clusters. In this Research Note, we present fitting formulae for the cross sections of tidal capture binary formation between two stars with a large mass ratio. We present the cases between two main-sequence stars, and between a degenerate star and a main-sequence star.
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.
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.
123122242
OBSERVATION OF THE TOP QUARK
Top-quark production is observed in collisions at at the Fermilab Tevatron. The CDF and DO collaborations observe signals consistent with to but inconsistent with the background prediction by 4.8σ (CDF) and 4.6σ (DO). Additional evidence for the top quark is provided by a peak in the reconstructed mass distribution. The kinematic properties of the excess events are consistent with the top-quark decay. The top-quark mass has been measured to be 176±8(stat.) ±10(sys.)GeV/c2 (CDF) and ±22(sys.)GeV/c2 (DO), and the -production cross section to be and 6.4±2.2 pb (DO).
122861815
Beam test of the CsI(Tl) calorimeter for the BELLE detector at the KEK-B factory
We studied the performance of a prototype electromagnetic calorimeter for the BELLE detector at the KEK proton synchrotron for an energy range of 0.25-3.5 GeV. The prototype consisted of an array of 6 x 5 CsI(Tl) crystals with 30 cm length (16.2 radiation lengths) and about 6 cm x 6 cm cross section. The scintillation light of each CsI(Tl) crystal was read out by two large-area PIN photodiodes and charge-sensitive preamplifiers attached at the rear face of the crystal. We measured the energy and position resolution for electrons and the e/pi separation for two sets of matrix configurations: one corresponded to the center and the other to the edge of the barrel calorimeter. The overall performance measured by the test proves that the prototype calorimeter is satisfactory for the use in the BELLE detector.
18632800
Soliton and Domain Wall in the Self-Dual Ferromagnet
We perform the dimensional reduction of a uniaxial planar ferromagnet system coupled to an Abelian Chern-Simons gauge field in the self-dual limit, and investigate the soliton and domain wall solutions of the emerging 1+1 dimensional self-dual system. This self-dual ferromagnet is the usual inhomogeneous Landau-Lifshitz system with an extra non-local term supplementing the anisotropic potential energy. The Hamiltonian is Bogomol’nyi bounded from below and has four adjusting parameters. The Bogomol’nyi equation is described in detail in analogy with the Newtonian equation of motion and its numerical solution is presented. PACS codes: 11.10.Lm, 11.27.+d
119276928
Measurement of central exclusive $\pi^+ \pi^-$ production in $p\bar{p}$ collisions at $\sqrt{s} = 0.9$ and 1.96 TeV at CDF
We measure exclusive π+π- production in proton-antiproton collisions at center-of-mass energies s=0.9 and 1.96 TeV in the Collider Detector at Fermilab. We select events with two oppositely charged particles, assumed to be pions, with pseudorapidity |η|<1.3 and with no other particles detected in |η|<5.9. We require the π+π- system to have rapidity |y|<1.0. The production mechanism of these events is expected to be dominated by double pomeron exchange, which constrains the quantum numbers of the central state. The data are potentially valuable for isoscalar meson spectroscopy and for understanding the pomeron in a region of transition between nonperturbative and perturbative quantum chromodynamics. The data extend up to dipion mass M(π+π-)=5000  MeV/c2 and show resonance structures attributed to f0 and f2(1270) mesons. From the π+π- and K+K- spectra, we place upper limits on exclusive χc0(3415) production.
124082673
Data compression and transmission algorithms for CMS FRPC muon chambers