3,929 research outputs found
A deep and wide-field view at the IC 2944 / 2948 complex in Centaurus
We employed the ESO MPI wide-field camera and obtained deep images in the VIc
pass-bands in the region of the IC 2944/2948 complex (l ~ 294; b ~ -1), and
complemented them with literature and archival data. We used this material to
derive the photometric, spectroscopic and kinematic properties of the brightest
(V < 16) stars in the region. The VI deep photometry on the other end, helped
us to unravel the lower main sequence of a few, possibly physical, star groups
in the area.
Our analysis confirmed previous suggestions that the extinction toward this
line of sight follows the normal law (Rv = 3.1). We could recognize B-type
stars spread in distance from a few hundred pc to at least 2 kpc. We found two
young groups (age ~ 3 Myr) located respectively at about 2.3 and 3.2 kpc from
the Sun. They are characterized by a significant variable extinction (E(B-V)
ranging from 0.28 to 0.45 mag), and host a significant pre-main sequence
population. We computed the initial mass functions for these groups and
obtained slopes Gamma from -0.94 to -1.02 (e_Gamma = 0.3), in a scale where the
classical Salpeter law is -1.35. We estimated the total mass of both main
stellar groups in ~ 1100 Mo, respectively. Our kinematic analysis
indicated that both groups of stars deviate from the standard rotation curve of
the Milky Way, in line with literature results for this specific Galactic
direction.
Finally, along the same line of sight we identified a third group of
early-type stars located at ~ 8 kpc from the Sun. This group might be located
in the far side of the Sagittarius-Carina spiral arm.Comment: 13 pages, 11 figures, accepted for publication in MNRA
Real-time marker-less multi-person 3D pose estimation in RGB-Depth camera networks
This paper proposes a novel system to estimate and track the 3D poses of
multiple persons in calibrated RGB-Depth camera networks. The multi-view 3D
pose of each person is computed by a central node which receives the
single-view outcomes from each camera of the network. Each single-view outcome
is computed by using a CNN for 2D pose estimation and extending the resulting
skeletons to 3D by means of the sensor depth. The proposed system is
marker-less, multi-person, independent of background and does not make any
assumption on people appearance and initial pose. The system provides real-time
outcomes, thus being perfectly suited for applications requiring user
interaction. Experimental results show the effectiveness of this work with
respect to a baseline multi-view approach in different scenarios. To foster
research and applications based on this work, we released the source code in
OpenPTrack, an open source project for RGB-D people tracking.Comment: Submitted to the 2018 IEEE International Conference on Robotics and
Automatio
BVRIJHK photometry and proper motion analysis of NGC 6253 and the surrounding field
Context. We present a photometric and astrometric catalog of 187963 stars
located in the field around the old super-metal-rich Galactic open cluster NGC
6253. The total field-of-view covered by the catalog is 34' x 33'. In this
field, we provide CCD BVRI photometry. For a smaller region close to the
cluster's center, we also provide near-infrared JHK photometry. Aims. We
analyze the properties of NGC 6253 by using our new photometric data and
astrometric membership. Methods. In June 2004, we targeted the cluster during a
10 day multi-site campaign, which involved the MPG/ESO 2.2m telescope with its
wide-field imager and the Anglo-Australian 3.9m telescope, equipped with the
IRIS2 near-infrared imager. Archival CCD images of NGC 6253 were used to derive
relative proper motions and to calculate the cluster membership probabilities.
Results. We have refined the cluster's fundamental parameters, deriving
(V_0-M_v)=11.15, E(B - V)=0.15, E(V - I)=0.25, E(V - J)=0.50, and E(V -
H)=0.55. The color excess ratios obtained using both the optical and near
infrared colors indicate a normal reddening law in the direction of NGC 6253.
The age of NGC 6253 at 3.5 Gyr, determined from our best-fitting isochrone
appears to be slightly older than the previous estimates. Finally, we estimated
the binary fraction among the cluster members to be \sim20%-30% and identified
11 blue straggler candidates.Comment: 16 pages, 13 figures, 11 tables. Accepted for publication in A&A.
Catalog avaiable via CD
The effect of spatial resolution on optical and near-IR studies of stellar clusters: Implications for the origin of the red excess
Recent ground based near-IR studies of stellar clusters in nearby galaxies
have suggested that young clusters remain embedded for 7-10Myr in their
progenitor molecular cloud, in conflict with optical based studies which find
that clusters are exposed after 1-3Myr. Here, we investigate the role that
spatial resolution plays in this apparent conflict. We use a recent catalogue
of young (~\msun) clusters in the nearby spiral
galaxy, M83, along with Hubble Space Telescope (HST) imaging in the optical and
near-IR, and ground based near-IR imaging, to see how the colours (and hence
estimated properties such as age and extinction) are affected by the aperture
size employed, in order to simulate studies of differing resolution. We find
that the near-IR is heavily affected by the resolution, and when aperture sizes
~pc are used, all young/blue clusters move red-ward in colour space, which
results in their appearance as heavily extincted clusters. However, this is due
to contamination from nearby sources and nebular emission, and is not an
extinction effect. Optical colours are much less affected by resolution. Due to
the larger affect of contamination in the near-IR, we find that, in some cases,
clusters will appear to show near-IR excess when large (~pc) apertures are
used. Our results explain why few young (~Myr), low extinction (\av <
1~mag) clusters have been found in recent ground based near-IR studies of
cluster populations, while many such clusters have been found in higher
resolution HST based studies. Additionally, resolution effects appear to (at
least partially) explain the origin of the near-IR excess that has been found
in a number of extragalactic YMCs.Comment: 8 pages, 5 figures, accepted for publication in MNRA
An optical and near IR study of the old open cluster NGC 2141
We report on CCD optical (B and V passbands) and near IR (J and K bands)
observations in the region of the old open cluster NGC 2141. By combining the
two sets of photometry (500 stars in common) we derive new estimates of the
cluster fundamental parameters. We confirm that the cluster is 2.5 Gyrs old,
but, with respect to previous investigations, we obtain a slightly larger
reddening (E(B-V)=0.40), and a slightly shorter distance (3.8 kpc) from the
Sun. Finally we present Luminosity Function (LF) in the V band, which is
another age indicator. We provide a good fit for the age range inferred from
isochrones by assuming the Kroupa et al. (1993) IMF up to =5.0. We
interpret the disagreemt at fainter magnitudes as an evidence of mass
segregation.Comment: 8 pages, 8 figures, accepted for publication in Astronomy and
Astrophysic
Endogenous Minimum Participation in International Environmental Treaties
Many international treaties come into force only after a minimum number of countries have signed and ratified the treaty. Why do countries agree to introduce a minimum participation constraint among the rules characterising an international treaty? This question is particularly relevant in the case of environmental treaties dealing with global commons, where free-riding incentives are strong. Is a minimum participation rule a way to offset these free-riding incentives? Why do countries that know they have an incentive to free-ride accept to tie their hands through the introduction of a minimum participation constraint? This paper addresses the above questions by analysing a three-stage non-cooperative coalition formation game. In the first stage, countries set the minimum coalition size that is necessary for the treaty to come into force. In the second stage, countries decide whether to sign the treaty. In the third stage, the equilibrium values of the decision variables are set. At the equilibrium, both the minimum participation constraint and the number of signatories the coalition size are determined. This paper shows that a non-trivial partial coalition, sustained by a binding minimum participation constraint, forms at the equilibrium. This paper thus explains why in international negotiations all countries often agree on a minimum participation rule even when some of them do not intend to sign the treaty. The paper also analyses the optimal size of the minimum participation constraint
Age Determination of Fifteen Old to Intermediate-Age Small Magellanic Cloud Star Clusters
We present CMDs in the V and I bands for fifteen star clusters in the Small
Magellanic Cloud (SMC) based on data taken with the Very Large Telescope (VLT,
Chile). We selected these clusters from our previous work, wherein we derived
cluster radial velocities and metallicities from Calcium II infrared triplet
(CaT) spectra also taken with the VLT. We discovered that the ages of six of
our clusters have been appreciably underestimated by previous studies, which
used comparatively small telescopes, graphically illustrating the need for
large apertures to obtain reliable ages of old and intermediate-age SMC star
clusters. In particular, three of these clusters, L4, L6 and L110, turn out to
be amongst the oldest SMC clusters known, with ages of 7.9 +- 1.1, 8.7 +- 1.2
and 7.6 +- 1.0 Gyr, respectively, helping to fill a possible "SMC cluster age
gap" (Glatt et al. 2008). Using the present ages and metallicities from Parisi
et al. (2009), we analyze the age distribution, age gradient and age
metallicity relation (AMR) of a sample of SMC clusters measured homogeneously.
There is a suggestion of bimodality in the age distribution but it does not
show a constant slope for the first 4 Gyr (Piatti 2011), and we find no
evidence for an age gradient. Due to the improved ages of our cluster sample,
we find that our AMR is now better represented in the intermediate/old period
than that we derived in Parisi et al. (2009), where we simply took ages
available in the literature. Additionally, clusters younger than aprox. 4 Gyr
now show better agreement with the bursting model, but we confirm that this
model is not a good representation of the AMR during the intermediate-age/old
period. A more complicated model is needed to explain the SMC chemical
evolution in that period.Comment: 76 pages, 32 figures. Accepted for publication in A
Giant Quantum Reflection of Neon Atoms from a Ridged Silicon Surface
The specular reflectivity of slow, metastable neon atoms from a silicon
surface was found to increase markedly when the flat surface was replaced by a
grating structure with parallel narrow ridges. For a surface with ridges that
have a sufficiently narrow top, the reflectivity was found to increase more
than two orders of magnitude at the incident angle of 10 mRad from the surface.
The slope of the reflectivity vs the incident angle near zero was found to be
nearly an order of magnitude smaller than that of a flat surface. A grating
with 6.5% efficiency for the first-order diffraction was fabricated by using
the ridged surface structure.Comment: 5 pages, 4 figures. To be published in J. Phys. Soc. Jp
Pinning and Tribology of Tethered Monolayers on Disordered Substrates
We study the statistical mechanics and dynamics of crystalline films with a
fixed internal connectivity on a random substrate. Defect free triangular
lattices exhibit a sharp transition to a low temperature glassy phase with
anomalous phonon fluctuations and a nonlinear force-displacement law with a
continuously variable exponent, similar to the vortex glass phase of directed
lines in 1+1 dimensions. The periodicity of the tethered monolayer acts like a
filter which amplifies particular Fourier components of the disorder. However,
the absence of annealed topological defects like dislocations is crucial: the
transition is destroyed when the constraint of fixed connectivity is relaxed
and dislocations are allowed to proliferate.Comment: revtex, preprint style, 27 pages. This submission is a revision of
cond-mat/9607184. The revisions affect only Appendix B, Appendix C, and Eqs.
2.27, 2.28, 2.3
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