637 research outputs found
Extremal projectors for contragredient Lie (super)symmetries (short review)
A brief review of the extremal projectors for contragredient Lie
(super)symmetries (finite-dimensional simple Lie algebras, basic classical Lie
superalgebras, infinite-dimensional affine Kac-Moody algebras and
superalgebras, as well as their quantum -analogs) is given. Some
bibliographic comments on the applications of extremal projectors are
presented.Comment: 21 pages, LaTeX; typos corrected, references adde
Astrometry with MCAO: HST-GeMS proper motions in the globular cluster NGC 6681
Aims: for the first time the astrometric capabilities of the Multi-Conjugate
Adaptive Optics (MCAO) facility GeMS with the GSAOI camera on Gemini-South are
tested to quantify the accuracy in determining stellar proper motions in the
Galactic globular cluster NGC 6681. Methods: proper motions from HST/ACS for a
sample of its stars are already available, and this allows us to construct a
distortion-free reference at the epoch of GeMS observations that is used to
measure and correct the temporally changing distortions for each GeMS exposure.
In this way, we are able to compare the corrected GeMS images with a
first-epoch of HST/ACS images to recover the relative proper motion of the
Sagittarius dwarf spheroidal galaxy with respect to NGC 6681. Results: we find
this to be (\mu_{\alpha}cos\delta, \mu_{\delta}) = (4.09,-3.41) mas/yr, which
matches previous HST/ACS measurements with a very good accuracy of 0.03 mas/yr
and with a comparable precision (r.m.s of 0.43 mas/yr). Conclusions: this study
successfully demonstrates that high-quality proper motions can be measured for
quite large fields of view (85 arcsec X 85 arcsec) with MCAO-assisted,
ground-based cameras and provides a first, successful test of the performances
of GeMS on multi-epoch data.Comment: 5 pages, 4 figures. Accepted for publication by A&A Letter
Q-power function over Q-commuting variables and deformed XXX, XXZ chains
We find certain functional identities for the Gauss q-power function of a sum
of q-commuting variables. Then we use these identities to obtain two-parameter
twists of the quantum affine algebra U_q (\hat{sl}_2) and of the Yangian
Y(sl_2). We determine the corresponding deformed trigonometric and rational
quantum R-matrices, which then are used in the computation of deformed XXX and
XXZ Hamiltonians.Comment: LaTeX, 12 page
M13 multiple stellar populations seen with the eyes of Stromgren photometry
We present a photometric study of M13 multiple stellar populations over a wide field of view, covering approximately 6.5 half-light radii, using archival Isaac Newton Telescope observations to build an accurate multiband Strömgren catalogue. The use of the Strömgren index cy permits us to separate the multiple populations of M13 on the basis of their position on the red giant branch. The comparison with medium and high resolution spectroscopic analysis confirms the robustness of our selection criterion. To determine the radial distribution of stars in M13, we complemented our data set with Hubble Space Telescope observations of the cluster core, to compensate for the effect of incompleteness affecting the most crowded regions. From the analysis of the radial distributions, we do not find any significant evidence of spatial segregation. Some residuals may be present in the external regions where we observe only a small number of stars. This finding is compatible with the short dynamical time-scale of M13 and represents, to date, one of the few examples of fully spatially mixed multiple populations in a massive globular cluster
The power of teaming up HST and Gaia:The first proper motion measurement of the distant cluster NGC 2419
Aims: We present the first measurement of the proper motion and orbit of the
very distant and intriguing globular cluster NCG 2419. Methods: We have
combined data from HST and Gaia DR1 to derive the relative proper motions of
stars in the direction to the cluster. To tie to an absolute reference frame we
have used a background galaxy located in the field. Results: We find the
absolute proper motion of NGC 2419 to be ,
)=() mas/yr. We have integrated the
orbit of the cluster in a Galactic potential and found it to oscillate between
53 kpc and 98 kpc on a nearly polar orbit. This makes it very
likely that NGC 2419 is a former cluster of the Sagittarius dwarf spheroidal
galaxy, also because it shares the same sense of rotation around the Milky Way.Comment: 5 pages, 4 figures, accepted for publication by A&A Letter
Generalized Paraxial Ray Trace Procedure Derived from Geodesic Deviation
Paraxial ray tracing procedures have become widely accepted techniques for
acoustic models in seismology and underwater acoustics. To date a generic form
of these procedures including fluid motion and time dependence has not appeared
in the literature. A detailed investigation of the characteristic curves of the
equations of hydrodynamics allows for an immediate generalization of the
procedure to be extracted from the equation form geodesic deviation. The
general paraxial ray trace equations serve as an ideal supplement to ordinary
ray tracing in predicting the deformation of acoustic beams in random
environments. The general procedure is derived in terms of affine
parameterization and in a coordinate time parameterization ideal for
application to physical acoustic ray propagation. The formalism is applied to
layered media, where the deviation equation reduces to a second order
differential equation for a single field with a general solution in terms of a
depth integral along the ray path. Some features are illustrated through
special cases which lead to exact solutions in terms of either ordinary or
special functions.Comment: Original; 40 pages (double spaced), 1 figure Replaced version; 36
pages single spaced, 7 figures. Expanded content; Complete derivation of the
equations from the equations of hydrodynamics, introduction of an auxiliary
basis for three dimensional wave-front modeling. Typos in text and equations
correcte
The Chemical and Dynamical Evolution of Isolated Dwarf Galaxies
Using a suite of simulations (Governato et al. 2010) which successfully
produce bulgeless (dwarf) disk galaxies, we provide an analysis of their
associated cold interstellar media (ISM) and stellar chemical abundance
patterns. A preliminary comparison with observations is undertaken, in order to
assess whether the properties of the cold gas and chemistry of the stellar
components are recovered successfully. To this end, we have extracted the
radial and vertical gas density profiles, neutral hydrogen velocity dispersion,
and the power spectrum of structure within the ISM. We complement this analysis
of the cold gas with a brief examination of the simulations' metallicity
distribution functions and the distribution of alpha-elements-to-iron.Comment: To appear in the proceedings of the JENAM 2010 Symposium "Dwarf
Galaxies: Keys to Galaxy Formation and Evolution" (Lisbon, 9-10 September
2010), P. Papaderos, S. Recchi, G. Hensler (eds.), Springer Verlag (2011), in
pres
Basic Twist Quantization of osp(1|2) and kappa-- Deformation of D=1 Superconformal Mechanics
The twisting function describing a nonstandard (super-Jordanian) quantum
deformation of is given in explicite closed form. The quantum
coproducts and universal R-matrix are presented. The non-uniqueness of the
twisting function as well as two real forms of the deformed
superalgebras are considered. One real quantum superalgebra is
interpreted as describing the -deformation of D=1, N=1 superconformal
algebra, which can be applied as a symmetry algebra of N=1 superconformal
mechanics.Comment: 13 pages,LaTeX, v2. References added, typos correcte
The Stellar Populations of the Cetus Dwarf Spheroidal Galaxy
We present Hubble Space Telescope Wide Field Planetary Camera 2 photometry in
the V and I passbands of the recently discovered Local Group dwarf spheroidal
galaxy in Cetus. Our color-magnitude diagram extends from above the first
ascent red giant branch (RGB) tip to approximately half a magnitude below the
horizontal branch (HB). Adopting a reddening of E(B-V) = 0.03, the magnitude of
the RGB tip yields a distance modulus of (m-M)o = 24.46 +/- 0.14. After
applying the reddening and distance modulus, we have utilized the color
distribution of RGB stars to determine a mean metal abundance of [Fe/H] = -1.7
on the Zinn & West scale with an intrinsic internal abundance dispersion of
+/-0.2 dex. An indirect calculation of the HB morphology of Cetus based on the
mean dereddened HB color yields (B-R)/(B+V+R) = -0.91 +/- 0.09, which
represents an HB that is redder than what can be attributed solely to Cetus'
metal abundance. As such, Cetus suffers from the `second parameter effect' in
which another parameter besides metallicity is controlling the HB morphology.
If we adopt the conventional `age hypothesis' explanation for the second
parameter effect, then this implies that Cetus is 2-3 Gyr younger than Galactic
globular clusters at its metallicity.Comment: 13 pages, 8 figures, Accepted for publication in the March 10, 2002
Ap
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