62,222 research outputs found
Searching for chemical inhomogeneities in Open Clusters: Analysis of the CN and CH Molecular Band Strengths in NGC 2158, NGC 2420, NGC 2682, NGC 7789 and Berkeley 29
Context: The total mass of a cluster, being the main parameter determining
its ability to host more than one stellar generation, may constitute a
threshold below which the cluster is able to form only a single stellar
population. AIms: Our goal is to investigate the existence of star-to-star
variations of CN and CH band strengths, related to the N and C abundances,
respectively, among the stars in five open cluster (NGC 2158, NGC 2420, NGC
2682, NGC 7789 and Berkeley 29) similar to those observed in globular clusters
and linked with the existence of multiple populations therein. Since these
systems are less massive than globulars, our results may allow us to constrain
the lower mass necessary to form more than one stellar population. Methods: We
measured the strength of the CN and CH bands, which correlate with the C and N
abundances, using four molecular indices in low-resolution SDSS/SEGUE spectra.
Results: We found that for four of the open clusters (NGC 2158, NGC 2420, NGC
2682 and Berkeley 29) all the stars studied in each of them have similar CN and
CH band strengths within the uncertainties since neither anomalous spreads nor
bimodalities have been detected in their CN and CH distributions. In contrast,
for NGC 7789 we found an anomalous spread in the strength of the CN molecular
band at 3839 \AA which is larger than the uncertainties. However, the small
number of stars studied in this cluster implies that further analysis is needed
to confirm the existence of chemical inhomogeneities in this cluster.Comment: 11 pages, 9 figures, Accepted for publication in A&A, Tables 7, 8 and
9 will be publish onlin
Axioms for consensus functions on the n-cube
An elementary general result is proved that allows for simple
characterizations of well-known location/consensus functions (median, mean and
center) on the n-cube. In addition, alternate new characterizations are given
for the median and anti-median functions on the n-cube.Comment: 12 page
Diphoton decay for a GeV scalar boson in an model
In the context of a nonuniversal and anomaly free extension of the
standard model, we examine the decay of a GeV scalar singlet state,
, as a possible explanation of the observed diphoton excess
announced by the ATLAS and CMS collaborations at CERN-LHC collider. One-loop
decay to photons is allowed through three heavy singlet quarks and one charged
Higgs boson into the loop. We obtain, for different width approximations and
for masses of the exotic singlet quarks in the region GeV, a
production cross section compatible
with ATLAS and CMS collaborations data. We also include another scalar singlet,
, as a dark matter candidate that may couple with the 750 GeV scalar at
tree level with production cross sections in agreement with ATLAS and CMS.Comment: 5 figures, discussion extended, 2 new figure
Moments of inertia for solids of revolution and variational methods
We present some formulae for the moments of inertia of homogeneous solids of
revolution in terms of the functions that generate the solids. The development
of these expressions exploits the cylindrical symmetry of these objects, and
avoids the explicit use of multiple integration, providing an easy and
pedagogical approach. The explicit use of the functions that generate the solid
gives the possibility of writing the moment of inertia as a functional, which
in turn allows us to utilize the calculus of variations to obtain a new insight
into some properties of this fundamental quantity. In particular, minimization
of moments of inertia under certain restrictions is possible by using
variational methods.Comment: 6 pages, 6 figures, LaTeX2e. Two paragraphs added. Minor typos
corrected. Version to appear in European Journal of Physic
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