895 research outputs found
Hierarchical stratification of Pareto sets
In smooth and convex multiobjective optimization problems the set of Pareto optima is diffeomorphic to an dimensional simplex, where is the number of objective functions. The vertices of the simplex are the optima of the individual functions and the -dimensional facets are the Pareto optimal set of functions subproblems. Such a hierarchy of submanifolds is a geometrical object called stratification and the union of such manifolds, in this case the set of Pareto optima, is called a stratified set. We discuss how these geometrical structures generalize in the non convex cases, we survey the known results and deduce possible suggestions for the design of dedicated optimization strategies
When there was no GIS system: rediscovering archaeological researches of the 19th century through the use of the drone. The case study of Mount Siri (Anzi, Basilicata)
Modern archaeologists often find it difficult to identify the exact position on the field (and on the maps) of the finds brought to light during archaeological excavations, particularly those conducted before the second half of the 20th century. In these cases, in fact, they are obliged to record data and information on their GIS as being unable to locate the correct place, or even the area, of those ancient archaeological investigations. This inability to be precise creates several problems from a topographical point of view and negatively influences the archaeological reconstruction of specific territories or sites. Therefore, how is it possible to correctly locate and, as a result, mark on the map what was discovered or excavated in the recent past? One possible solution is the 3D reconstruction of a modern landscape through the use of the UAV technology and some derived applications, such as digital techniques based on Structure from Motion and Imaged-Based methodologies. The 3D model can be analyzed using the GIS system, and through the analysis of the micro-relief and aerial photos it is possible to use an important tool to locate past archaeological investigations. In this paper, we present the case study of Mount Siri (Anzi, Basilicata), the location of several important archaeological discoveries which were made during the 19th century
The extended structure of the remote cluster B514 in M31. Detection of extra-tidal stars
We present a study of the density profile of the remote M31 globular cluster
B514, obtained from HST/ACS observations. Coupling the analysis of the
distribution of the integrated light with star counts we can reliably follow
the profile of the cluster out to r~35", corresponding to ~130pc. The profile
is well fitted, out to ~15 core radii, by a King Model having C=1.65. With an
estimated core radius r_c=0.38", this corresponds to a tidal radius of r_t~17"
(~65pc). We find that both the light and the star counts profiles show a
departure from the best fit King model for r>~8" - as a surface brightness
excess at large radii, and the star counts profile shows a clear break in
correspondence of the estimated tidal radius. Both features are interpreted as
the signature of the presence of extratidal stars around the cluster. We also
show that B514 has a half-light radius significantly larger than ordinary
globular clusters of the same luminosity. In the M_V vs. log r_h plane, B514
lies in a region inhabited by peculiar clusters, like Omega Cen, G1, NGC2419
and others, as well as by the nuclei of dwarf elliptical galaxies.Comment: 9 pages, 6 figures. Accepted for publication in Astronomy &
Astrophysic
Massive young clusters in the disc of M31
We have studied the properties of a sample of 67 very blue and likely young
massive clusters in M31 extracted from the Bologna Revised Catalog of globular
clusters, selected according to their color [(B-V) < 0.45] and/or to the
strength of their Hbeta spectral index (Hbeta > 3.5 A). Their existence in M31
has been noted by several authors in the past; we show here that these Blue
Luminous Compact Clusters (BLCCs) are a significant fraction (>~ 15%) of the
whole globular cluster system of M31. Compared to the global properties of the
M31 globular cluster system, they appear to be intrinsically fainter,
morphologically less concentrated, and with a shallower Balmer jump and
enhanced absorption in their spectra.
Empirical comparison with integrated properties of clusters with known age as
well as with theoretical SSP models consistently indicate that their typical
age is less than ~2 Gyr, while they probably are not so metal-poor as deduced
if considered to be old. Either selecting BLCCs by their (B-V) colors or by the
strength of their Hbeta index the cluster sample turns out to be distributed
onto the outskirts of M31 disc, sharing the kinematical properties of the thin,
rapidly rotating disc component.
If confirmed to be young and not metal-poor, these clusters indicate the
occurrence of a significant recent star formation in the thin disc of M31,
although they do not set constraints on the epoch of its early formation.Comment: Submitted for publication in the Astronomical Journal. Aastex Latex
file of 22 pages, 12 figures and 3 table
Different Characteristics of the Bright Branches of the Globular Clusters M3 and M13
We carried out wide-field BVI CCD photometric observations of the GCs M3 and
M13 using the BOAO 1.8 m telescope equipped with a 2K CCD. We present CMDs of
M3 and M13. We have found AGB bumps at V = 14.85 for M3 at V = 14.25 for M13.
It is found that AGB stars in M3 are more concentrated near the bump, while
those in M13 are scattered along the AGB sequence. We identified the RGB bump
of M3 at V = 15.50 and that of M13 at V = 14.80. We have estimated the ratios R
and R2 for M3 and M13 and found that of R for M3 is larger than that for M13
while R2's for M3 and M13 are similar when only normal HB stars are used in R
and R2 for M13. However, we found that R's for M3 and M13 are similar while R2
for M3 is larger than that for M13 when all the HB stars are included in R and
R2 for M13. We have compared the observed RGB LFs of M3 and M13 with the
theoretical RGB LF of Bergbusch & VandenBerg at the same radial distances from
the cluster centers as used in R and R2 for M3 and M13. We found "extra stars"
belonging to M13 in the comparison of the observed RGB LF of M13 and the
theoretical RGB LF of Bergbusch & VandenBerg. In the original definition of R
of Buzzoni et al., N(HB) corresponds to the lifetime of HB stars in the RR
Lyrae instability strip at log T_eff = 3.85. So, the smaller R value resulting
for M13 compared with that for M3 in the case where only normal HB stars are
included in R and R2 for M13 may be partially caused by "extra stars", and the
similar R's for M3 and M13 in the case where the all HB stars are included in R
and R2 for M13 may be caused by "extra stars" in the upper RGB of M13. If
"extra stars" in the upper RGB of M13 are caused by an effective "deep mixing"
these facts support the contention that an effective "deep mixing" could lead
to different HB morphologies between M3 and M13 and subsequent sequences.Comment: 24 pages, 7 figures, to be published in the A
The Star Formation History of the Carina Dwarf Galaxy
We have analyzed deep B and V photometry of the Carina dwarf spheroidal
reaching below the old main-sequence turnoff to about V = 25. Using simulated
color-magnitude diagrams to model a range of star formation scenarios, we have
extracted a detailed, global star formation history. Carina experienced three
significant episodes of star formation at about 15 Gyr, 7 Gyr, and 3 Gyr.
Contrary to the generic picture of galaxy evolution, however, the bulk of star
formation, at least 50%, occured during the episode 7 Gyr ago, which may have
lasted as long as 2 Gyr. For unknown reasons, Carina formed only 10-20% of its
stars at an ancient epoch and then remained quiescent for more than 4 Gyr. The
remainder (~30%) formed relatively recently, only 3 Gyr ago. Interest in the
local population of dwarf galaxies has increased lately due to their potential
importance in the understanding of faint galaxy counts. We surmise that objects
like Carina, which exhibits the most extreme episodic behavior of any of the
dwarf spheroidal companions to the Galaxy, are capable of contributing to the
observed excess of blue galaxies at B = 24 only if the star formation occurred
instantaneously.Comment: 23 pages of text, 20 figures, 8 tables. AJ, in pres
HST-NICMOS Observations of Terzan 5: Stellar Content and Structure of the Core
We report results from HST-NICMOS imaging of the extremely dense core of the
globular cluster Terzan 5. This highly obscured bulge cluster has been
estimated to have one of the highest collision rates of any galactic globular
cluster, making its core a particularly conducive environment for the
production of interacting binary systems. We have reconstructed high-resolution
images of the central 19"x19" region of Terzan 5 by application of the drizzle
algorithm to dithered NIC2 images in the F110W, F187W, and F187N near-infrared
filters. We have used a DAOPHOT/ALLSTAR analysis of these images to produce the
deepest color-magnitude diagram (CMD) yet obtained for the core of Terzan 5. We
have also analyzed the parallel 11"X11" NIC1 field, centered 30" from the
cluster center and imaged in F110W and F160W, and an additional NIC2 field that
is immediately adjacent to the central field. This imaging results in a clean
detection of the red-giant branch and horizontal branch in the central NIC2
field, and the detection of these plus the main-sequence turnoff and the upper
main sequence in the NIC1 field. We have constructed an H versus J-H CMD for
the NIC1 field. We obtain a new distance estimate of 8.7 kpc, which places
Terzan 5 within less than 1 kpc of the galactic center. We have also determined
a central surface-density profile which results in a maximum likelihood
estimate of 7.9" +/- 0.6" for the cluster core radius. We discuss the
implications of these results for the dynamical state of Terzan 5.Comment: 17 pages, 9 figures, accepted for publication in ApJ, for May 20,
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