8,604 research outputs found
On the Fractal Distribution of HII Regions in Disk Galaxies
In this work we quantify the degree to which star-forming events are clumped.
We apply a precise and accurate technique to calculate the correlation
dimension Dc of the distribution of HII regions in a sample of disk galaxies.
Our reliable results are distributed in the range 1.5<Dc<2.0. We get
significant variations in the fractal dimension among galaxies, contrary to a
universal picture sometimes claimed in literature. The faintest galaxies tend
to distribute their HII regions in more clustered (less uniform) patterns.
Moreover, the fractal dimension for the brightest HII regions within the same
galaxy seems to be smaller than for the faintest ones suggesting some kind of
evolutionary effect.Comment: 6 pages including 4 figures. To appear in Highlights of Spanish
Astrophysics V: Proceedings of the VIII Scientific Meeting of the Spanish
Astronomical Society held in Santander, July 7-11, 200
Generalized Lagrangian Master Equations
We discuss the geometry of the Lagrangian quantization scheme based on
(generalized) Schwinger-Dyson BRST symmetries. When a certain set of ghost
fields are integrated out of the path integral, we recover the
Batalin-Vilkovisky formalism, now extended to arbitrary functional measures for
the classical fields. Keeping the ghosts reveals the crucial role played by a
natural connection on the space of fields.Comment: LaTeX, 12 pages, CERN--TH-7247/9
Stellar Open Clusters' Membership Probabilities: an N-Dimensional Geometrical Approach
We present a new geometrical method aimed at determining the members of open
clusters. The methodology estimates, in an N-dimensional space, the membership
probabilities by means of the distances between every star and the cluster
central overdensity. It can handle different sets of variables, which have to
satisfy the simple condition of being more densely distributed for the cluster
members than for the field stars (as positions, proper motions, radial
velocities and/or parallaxes are). Unlike other existing techniques, this fact
makes the method more flexible and so can be easily applied to different
datasets. To quantify how the method identifies the clus- ter members, we
design series of realistic simulations recreating sky regions in both position
and proper motion subspaces populated by clusters and field stars. The re-
sults, using different simulated datasets (N = 1, 2 and 4 variables), show that
the method properly recovers a very high fraction of simulated cluster members,
with a low number of misclassified stars. To compare the goodness of our
methodology, we also run other existing algorithms on the same simulated data.
The results show that our method has a similar or even better performance than
the other techniques. We study the robustness of the new methodology from
different subsamplings of the ini- tial sample, showing a progressive
deterioration of the capability of our method as the fraction of missing
objects increases. Finally, we apply all the methodologies to the real cluster
NGC 2682, indicating that our methodology is again in good agreement with
preceding studies.Comment: 15 pages, 9 figures, 6 tables, accepted for publication in MNRA
The Large- Limit of the Two-Hermitian-matrix model by the hidden BRST method
This paper discusses the large N limit of the two-Hermitian-matrix model in
zero dimensions, using the hidden BRST method. A system of integral equations
previously found is solved, showing that it contained the exact solution of the
model in leading order of large .Comment: 19 pages, Latex,CERN--TH-6531/9
Origin of Antifields in the Batalin-Vilkovisky Lagrangian Formalism
The antifields of the Batalin-Vilkovisky Lagrangian quantization are standard
antighosts of certain collective fields. These collective fields ensure that
Schwinger-Dyson equations are satisfied as a consequence of the gauge symmetry
algebra. The associated antibracket and its canonical structure appear
naturally if one integrates out the corresponding ghost fields. An analogous
Master Equation for the action involving these ghosts follows from the
requirement that the path integral gives rise to the correct Schwinger-Dyson
equations.Comment: 36 pages, LaTeX, CERN--TH-6788/9
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