13,462 research outputs found

    Waves in a hot uniaxial plasma excited by a current source

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    The fields excited by a short dipole antenna in a hot uniaxially anisotropic plasma (B_0→∞) have been studied. When ω<ω_p, the dipole effectively excites two propagating waves, a slow wave and a fast wave, inside a cone of half‐cone angle sin^(−1)(ω/ω_p). Inside the cone a characteristic interference structure in the angular distribution of the fields is noted. Outside the cone fields fall off exponentially. The appearance of the cone and the characteristic interference structure in the field is useful from the viewpoint of laboratory diagnostics

    R-matrices and Tensor Product Graph Method

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    A systematic method for constructing trigonometric R-matrices corresponding to the (multiplicity-free) tensor product of any two affinizable representations of a quantum algebra or superalgebra has been developed by the Brisbane group and its collaborators. This method has been referred to as the Tensor Product Graph Method. Here we describe applications of this method to untwisted and twisted quantum affine superalgebras.Comment: LaTex 7 pages. Contribution to the APCTP-Nankai Joint Symposium on "Lattice Statistics and Mathematical Physics", 8-10 October 2001, Tianjin, Chin

    Disk M Dwarf Luminosity Function From HST Star Counts

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    We study a sample of 257 Galactic disk M dwarfs (8<M_V<18.5) found in images obtained using HST. These include 192 stars in 22 fields imaged with the repaired WFC2 with mean limiting mag I=23.7 and 65 stars in 162 fields imaged with the pre-repair Planetary Camera with mean limiting mag V=21.3. We find that the disk luminosity function (LF) drops sharply for M_V>12 (M<0.25 \ms), decreasing by a factor \gsim 3 by M_V~14 (M~0.14\ms). This decrease in the LF is in good agreement with the ground-based photometric study of nearby stars by Stobie et al. (1989), and in mild conflict with the most recent LF measurements based on local parallax stars by Reid et al. (1995). The local LF of the faint Galactic disk stars can be transformed into a local mass function using an empirical mass-M_V relation. The mass function can be represented analytically over the mass range 0.1\ms<M<1.6\ms by \log(\phi)=-1.35-1.34\log(M/\ms)-1.85 [\log(M/\ms)]^2 where \phi is the number density per logarithmic unit of mass. The total column density of M stars is only \Sigma_M=11.8\pm 1.8\ms\pc^{-2}, implying a total `observed' disk column density of \Sigma_\obs~=39\ms\pc^{-2}, lower than previously believed, and also lower than all estimates with which we are familiar of the dynamically inferred mass of the disk. The measured scale length for the M-star disk is 3.0\pm 0.4 kpc. The optical depth to microlensing toward the LMC by the observed stars in the Milky Way disk is \tau~1x10^{-8}, compared to the observed optical depth found in ongoing experiments \tau_\obs~ 10^{-7}. The M-stars show evidence for a population with characteristics intermediate between thin disk and spheroid populations. Approximating what may be a continuum of populations by two separate component, we find characteristic exponential scale heights of ~210 pc and ~740 pc.Comment: 30 pages, uuencoded postscript, includes 3 figures, 2 table

    Casimir invariants and characteristic identities for gl()gl(\infty )

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    A full set of (higher order) Casimir invariants for the Lie algebra gl()gl(\infty ) is constructed and shown to be well defined in the category OFSO_{FS} generated by the highest weight (unitarizable) irreducible representations with only a finite number of non-zero weight components. Moreover the eigenvalues of these Casimir invariants are determined explicitly in terms of the highest weight. Characteristic identities satisfied by certain (infinite) matrices with entries from gl()gl(\infty ) are also determined and generalize those previously obtained for gl(n)gl(n) by Bracken and Green.1,2^{1,2}Comment: 10 pages, PlainTe

    Infrared Line Emission from Planetary Nebulae. I - General Theory

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    General theory of infrared line emission from planetary nebul

    A New Photometric Model of the Galactic Bar using Red Clump Giants

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    We present a study of the luminosity density distribution of the Galactic bar using number counts of red clump giants (RCGs) from the OGLE-III survey. The data were recently published by Nataf et al. (2013) for 9019 fields towards the bulge and have 2.94×1062.94\times 10^6 RC stars over a viewing area of 90.25deg290.25 \,\textrm{deg}^2. The data include the number counts, mean distance modulus (μ\mu), dispersion in μ\mu and full error matrix, from which we fit the data with several tri-axial parametric models. We use the Markov Chain Monte Carlo (MCMC) method to explore the parameter space and find that the best-fit model is the E3E_3 model, with the distance to the GC is 8.13 kpc, the ratio of semi-major and semi-minor bar axis scale lengths in the Galactic plane x0,y0x_{0},y_{0}, and vertical bar scale length z0z_0, is x0:y0:z01.00:0.43:0.40x_0:y_0:z_0 \approx 1.00:0.43:0.40 (close to being prolate). The scale length of the stellar density profile along the bar's major axis is \sim 0.67 kpc and has an angle of 29.429.4^\circ, slightly larger than the value obtained from a similar study based on OGLE-II data. The number of estimated RC stars within the field of view is 2.78×1062.78 \times 10^6, which is systematically lower than the observed value. We subtract the smooth parametric model from the observed counts and find that the residuals are consistent with the presence of an X-shaped structure in the Galactic centre, the excess to the estimated mass content is 5.8\sim 5.8%. We estimate the total mass of the bar is 1.8×1010M\sim 1.8 \times 10^{10} M_\odot. Our results can be used as a key ingredient to construct new density models of the Milky Way and will have implications on the predictions of the optical depth to gravitational microlensing and the patterns of hydrodynamical gas flow in the Milky Way.Comment: 15 pages, 6 figures, 4 tables. MNRAS accepte
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