425 research outputs found
Star Cluster Candidates in M81
We present a catalog of extended objects in the vicinity of M81 based a set
of 24 Hubble Space Telescope Advanced Camera for Surveys (ACS) Wide Field
Camera (WFC) F814W (I-band) images. We have found 233 good globular cluster
candidates; 92 candidate HII regions, OB associations, or diffuse open
clusters; 489 probable background galaxies; and 1719 unclassified objects. We
have color data from ground-based g- and r-band MMT Megacam images for 79
galaxies, 125 globular cluster candidates, 7 HII regions, and 184 unclassified
objects. The color-color diagram of globular cluster candidates shows that most
fall into the range 0.25 < g-r < 1.25 and 0.5 < r-I < 1.25, similar to the
color range of Milky Way globular clusters. Unclassified objects are often
blue, suggesting that many of them are likely to be HII regions and open
clusters, although a few galaxies and globular clusters may be among them.Comment: 35 pages, 11 figures, submitted to A
Edge States and Entanglement Entropy
It is known that gauge fields defined on manifolds with spatial boundaries
support states localized at the boundaries. In this paper, we demonstrate how
coarse-graining over these states can lead to an entanglement entropy. In
particular, we show that the entanglement entropy of the ground state for the
quantum Hall effect on a disk exhibits an approximate ``area " law.Comment: 16 pages, minor corrections and futher details adde
Edge States in Gauge Theories: Theory, Interpretations and Predictions
Gauge theories on manifolds with spatial boundaries are studied. It is shown
that observables localized at the boundaries (edge observables) can occur in
such models irrespective of the dimensionality of spacetime. The intimate
connection of these observables to charge fractionation, vertex operators and
topological field theories is described. The edge observables, however, may or
may not exist as well-defined operators in a fully quantized theory depending
on the boundary conditions imposed on the fields and their momenta. The latter
are obtained by requiring the Hamiltonian of the theory to be self-adjoint and
positive definite. We show that these boundary conditions can also have nice
physical interpretations in terms of certain experimental parameters such as
the penetration depth of the electromagnetic field in a surrounding
superconducting medium. The dependence of the spectrum on one such parameter is
explicitly exhibited for the Higgs model on a spatial disc in its London limit.
It should be possible to test such dependences experimentally, the above Higgs
model for example being a model for a superconductor. Boundary conditions for
the 3+1 dimensional system confined to a spatial ball are studied. Their
physical meaning is clarified and their influence on the edge states of this
system (known to exist under certain conditions) is discussed. It is pointed
out that edge states occur for topological solitons of gauge theories such as
the 't Hooft-Polyakov monopoles.Comment: 36 pages, LATEX File (revised because figures had problems
A Genuine Intermediate-Age Globular Cluster in M33
We present deep integrated-light spectroscopy of nine M33 globular clusters
taken with the Hectospec instrument at the MMT Observatory. Based on our
spectroscopy and previous deep color-magnitude diagrams obtained with
HST/WFPC2, we present evidence for the presence of a genuine intermediate-age
globular cluster in M33. The analysis of Lick line indices indicates that all
globular clusters are metal-poor ([Z/H] <~ -1.0) and that cluster M33-C38 is
about 5-8 Gyr younger than the rest of the sample M33 star clusters. We find no
evidence for a population of blue horizontal branch stars in the CMD of
M33-C38, which rules out the possibility of an artificially young spectroscopic
age due to the presence of hot stars. We infer a total mass of 5-9 x 10^4 M_sol
for M33-C38, which implies that M33-C38 has survived ~2-3 times longer than
some dynamical evolution model predictions for star clusters in M33, although
it is not yet clear to which dynamical component of M33 - thin disk, thick
disk, halo - the cluster is associated.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letter
Towards a calibration of SSP models from the optical to the mid-infrared
Our knowledge about unresolved stellar systems comes from comparing
integrated-light properties to SSP models. Therefore it is crucial to calibrate
the latter as well as possible by integrated-light colors of clusters that have
reliable ages and metallicities (deep CMDs and/or spectroscopy of individual
giants). This is especially true for the NIR and MIR, which contain important
population synthesis diagnostics and are often used to derive masses of stellar
systems at hight redshifts. Here we present integrated colors of MC clusters
using new VRI photometry and 2MASS data. In the imminent future we will include
MIR data from Spitzer/IRAC. We compare our new colors with popular SSP models
to illustrate their strengths and weaknesses.Comment: 2 pages, 1 figure, to appear in the proceedings of IAU Symposium
No241 "Stellar Populations as building blocks of galaxies", A. Vazdekis & R.
Peletier, ed
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