743 research outputs found
Resolved Stellar Populations at the Distance of Virgo
Top of the wish list of any astronomer who wants to understand galaxy
formation and evolution is to resolve the stellar populations of a sample of
giant elliptical galaxies: to take spectra of the stars and make
Colour-Magnitude Diagrams going down to the oldest main sequence turn-offs. It
is only by measuring the relative numbers of stars on Main Sequence Turnoffs at
ages ranging back to the time of the earliest star formation in the Universe
that we can obtain unambiguous star formation histories. Understanding star
formation histories of individual galaxies underpins all our theories of galaxy
formation and evolution. To date we only have detailed star formation histories
for the nearest-by objects in the Local Group, namely galaxies within 700kpc of
our own. This means predominantly small diffuse dwarf galaxies in a poor group
environment. To sample the full range of galaxy types and to consider galaxies
in a high density environment (where much mass in the Universe resides) we need
to be able to resolve stars at the distance of the Virgo (~17Mpc) or Fornax
(~18Mpc) clusters. This ambitious goal requires an Extremely Large Telescope
(ELT), with a diameter of 50-150m, operating in the optical/near-IR at its
diffraction limit.Comment: proceedings IAU 232 "Extremely Large Telescopes", eds Whitelock,
Leibundgut and Dennefel
Modified Affine Hecke Algebras and Drinfeldians of Type A
We introduce a modified affine Hecke algebra \h{H}^{+}_{q\eta}({l})
(\h{H}_{q\eta}({l})) which depends on two deformation parameters and
. When the parameter is equal to zero the algebra
\h{H}_{q\eta=0}(l) coincides with the usual affine Hecke algebra
\h{H}_{q}(l) of type , if the parameter q goes to 1 the algebra
\h{H}^{+}_{q=1\eta}(l) is isomorphic to the degenerate affine Hecke algebra
\Lm_{\eta}(l) introduced by Drinfeld. We construct a functor from a category
of representations of into a category of representations of
Drinfeldian which has been introduced by the first author.Comment: 11 pages, LATEX. Contribution to Proceedings "Quantum Theory and
Symmetries" (Goslar, July 18-22, 1999) (World Scientific, 2000
Neutral hydrogen in the starburst galaxy NGC3690/IC694
Researchers made observations of the neutral hydrogen (HI) emission structure surrounding the very deep absorption peak (observed earlier by Dickey (1986)) in the galaxy pair NGC3690/IC694. This galaxy pair is highly luminous in the far infrared, and known to exhibit extensive star formation as well as nuclear activity. Knowledge of the spatial distribution and velocity structure of the HI emission is of great importance to the understanding of the dynamics of the interaction and the resulting environmental effects on the galaxies
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
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
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
On Some Lie Bialgebra Structures on Polynomial Algebras and their Quantization
We study classical twists of Lie bialgebra structures on the polynomial
current algebra , where is a simple complex
finite-dimensional Lie algebra. We focus on the structures induced by the
so-called quasi-trigonometric solutions of the classical Yang-Baxter equation.
It turns out that quasi-trigonometric -matrices fall into classes labelled
by the vertices of the extended Dynkin diagram of . We give
complete classification of quasi-trigonometric -matrices belonging to
multiplicity free simple roots (which have coefficient 1 in the decomposition
of the maximal root). We quantize solutions corresponding to the first root of
.Comment: 41 pages, LATE
Stellar Populations in the Phoenix Dwarf (dIrr/dSph) Galaxy as Observed by HST/WFPC2
We present HST/WFPC2 photometry of the central regions of the Phoenix dwarf.
Accurate photometry allows us to: 1) confirm the existence of the horizontal
branch previously detected by ground-based observations, and use it to
determine a distance to Phoenix, 2) clearly detect the existence of multiple
ages in the stellar population of Phoenix, 3) determine a mean metallicity of
the old red giant branch stars in Phoenix, and suggest that Phoenix has evolved
chemically over its lifetime, 4) extract a rough star formation history for the
central regions which suggests that Phoenix has been forming stars roughly
continuously over its entire lifetime.Comment: Accepted by AJ, 22 pages including 6 figures + 1 figure in JPEG
forma
Manganese in dwarf spheroidal galaxies
We provide manganese abundances (corrected for the effect of the hyperfine
structure) for a large number of stars in the dwarf spheroidal galaxies
Sculptor and Fornax, and for a smaller number in the Carina and Sextans dSph
galaxies. Abundances had already been determined for a number of other elements
in these galaxies, including alpha and iron-peak ones, which allowed us to
build [Mn/Fe] and [Mn/alpha] versus [Fe/H] diagrams. The Mn abundances imply
sub-solar [Mn/Fe] ratios for the stars in all four galaxies examined. In
Sculptor, [Mn/Fe] stays roughly constant between [Fe/H]\sim -1.8 and -1.4 and
decreases at higher iron abundance. In Fornax, [Mn/Fe] does not vary in any
significant way with [Fe/H]. The relation between [Mn/alpha] and [Fe/H] for the
dSph galaxies is clearly systematically offset from that for the Milky Way,
which reflects the different star formation histories of the respective
galaxies. The [Mn/alpha] behavior can be interpreted as a result of the
metal-dependent Mn yields of type II and type Ia supernovae. We also computed
chemical evolution models for star formation histories matching those
determined empirically for Sculptor, Fornax, and Carina, and for the Mn yields
of SNe Ia, which were assumed to be either constant or variable with
metallicity. The observed [Mn/Fe] versus [Fe/H] relation in Sculptor, Fornax,
and Carina can be reproduced only by the chemical evolution models that include
a metallicity-dependent Mn yield from the SNe Ia.Comment: 19 pages, 10 figures, accepted for publication in Astronomy &
Astrophysic
The early days of the Sculptor dwarf spheroidal galaxy
We present the high resolution spectroscopic study of five -3.9<=[Fe/H]<=-2.5
stars in the Local Group dwarf spheroidal, Sculptor, thereby doubling the
number of stars with comparable observations in this metallicity range. We
carry out a detailed analysis of the chemical abundances of alpha, iron peak,
light and heavy elements, and draw comparisons with the Milky Way halo and the
ultra faint dwarf stellar populations. We show that the bulk of the Sculptor
metal-poor stars follows the same trends in abundance ratios versus metallicity
as the Milky Way stars. This suggests similar early conditions of star
formation and a high degree of homogeneity of the interstellar medium. We find
an outlier to this main regime, which seems to miss the products of the most
massive of the TypeII supernovae. In addition to its value to help refining
galaxy formation models, this star provides clues to the production of cobalt
and zinc. Two of our sample stars have low odd-to-even barium isotope abundance
ratios, suggestive of a fair proportion of s-process; we discuss the
implication for the nucleosynthetic origin of the neutron capture elements.Comment: Replacement after language editio
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