104,886 research outputs found
An updated catalog of M31 globular-like clusters: UBVRI photometry, ages, and masses
We present an updated UBVRI photometric catalog containing 970 objects in the
field of M31, selected from the Revised Bologna Catalog (RBC v.4.0), including
965, 967, 965, 953, and 827 sources in the individual UBVRI bands,
respectively, of which 205, 123, 14, 126, and 109 objects do not have
previously published photometry. Photometry is performed using archival images
from the Local Group Galaxies Survey, which covers 2.2 deg^2 along the major
axis of M31. We focus on 445 confirmed `globular-like' clusters and candidates,
comprising typical globular and young massive clusters. The ages and masses of
these objects are derived by comparison of their observed spectral-energy
distributions with simple stellar population synthesis. Approximately half of
the clusters are younger than 2 Gyr, suggesting that there has been significant
recent active star formation in M31, which is consistent with previous results.
We note that clusters in the halo (r_ projected>30kpc) are composed of two
different components, older clusters with ages >10 Gyr and younger clusters
with ages around 1 Gyr. The spatial distributions show that the young clusters
(<2 Gyr) are spatially coincident with the galaxy's disk, including the `10 kpc
ring,' the `outer ring,' and the halo of M31, while the old clusters (> 2 Gyr)
are spatially correlated with the bulge and halo. We also estimate the masses
of the 445 confirmed clusters and candidates in M31 and find that our estimates
agree well with previously published values. We find that none of the young
disk clusters can survive the inevitable encounters with giant molecular clouds
in the galaxy's disk and that they will eventually disrupt on timescales of a
few Gyr. Specifically, young disk clusters with a mass of 10^4 M_\odot are
expected to dissolve within 3.0 Gyr and will, thus, not evolve to become
globular clusters.Comment: 35 pages, 20 figures and 5 tables, accepted for publication in Ap
Star clusters in M33: updated UBVRI photometry, ages, metallicities, and masses
The photometric characterization of M33 star clusters is far from complete.
In this paper, we present homogeneous photometry of 708 star clusters
and cluster candidates in M33 based on archival images from the Local Group
Galaxies Survey, which covers 0.8 deg along the galaxy's major axis. Our
photometry includes 387, 563, 616, 580, and 478 objects in the bands,
respectively, of which 276, 405, 430, 457, and 363 do not have previously
published photometry. Our photometry is consistent with previous
measurements (where available) in all filters. We adopted Sloan Digital Sky
Survey photometry for complementary purposes, as well as Two Micron
All-Sky Survey near-infrared photometry where available. We fitted the
spectral-energy distributions of 671 star clusters and candidates to derive
their ages, metallicities, and masses based on the updated {\sc parsec} simple
stellar populations synthesis models. The results of our minimization
routines show that only 205 of the 671 clusters () are older than 2 Gyr,
which represents a much smaller fraction of the cluster population than that in
M31 (), suggesting that M33 is dominated by young star clusters (
Gyr). We investigate the mass distributions of the star clusters---both open
and globular clusters---in M33, M31, the Milky Way, and the Large Magellanic
Cloud. Their mean values are , 5.43, 2.72, and
4.18, respectively. The fraction of open to globular clusters is highest in the
Milky Way and lowest in M31. Our comparisons of the cluster ages, masses, and
metallicities show that our results are basically in agreement with previous
studies (where objects in common are available); differences can be traced back
to differences in the models adopted, the fitting methods used, and stochastic
sampling effects.Comment: 32 pages, 12 figures, 2 tables, accepted for publication in ApJ
Determinants and dimensions of firm growth
Firm growth is an important indicator of a thriving economy. Although the determinants of firm growth have been studied in various disciplines, an integrated analysis is still lacking. This paper attempts to provide such an analysis. Many determinants of firm growth are summarized and classified into three dimensions: individual, organizational, and environmental determinants. By conducting an empirical study using 523 Dutch small and medium sized firms, we identify the determinants of firm growth which is measured by employment growth. Our findings show that environmental determinants do not affect firm growth. Individual ones do: entrepreneurs with growth motivation and having technical knowledge are more likely to grow their firms while entrepreneurs characterized by a strong need of achievement are less likely to engage in firm growth. Organizational determinants have the most influence on firm growth: the older thefirm, the less likely it is to grow. Availability of financial capital is found to be crucial to firm growth. Finally, the firm’s scalability (its preparedness to grow) is found to have a positive impact on firm growth.
Fateev-Zamolodchikov and Kashiwara-Miwa models: boundary star-triangle relations and surface critical properties
The boundary Boltzmann weights are found by solving the boundary
star-triangle relations for the Fateev-Zamolodchikov and Kashiwara-Miwa models.
We calculate the surface free energies of the models. The critical surface
exponent \alpha_s of the Kashiwara-Miwa model is given and satisfies the
scaling relation \alpha_b=2\alpha_s-2, where \alpha_b is the bulk exponent.Comment: 17 pages, no ps figures, latex fil
The limit of massive gravity
Lorentz-invariant massive gravity is usually associated with a strong
coupling scale . By including non-trivial effects from the
Stueckelberg modes, we show that about these vacua, one can push the strong
coupling scale to higher values and evade the linear vDVZ-discontinuity. For
generic parameters of the theory and generic vacua for the Stueckelberg fields,
the -decoupling limit of the theory is well-behaved and free of any
ghost or gradient-like instabilities. We also discuss the implications for
nonlinear sigma models with Lorentzian target spaces.Comment: 38 pages, 1 figure, JHEP version, minor change
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