5,489 research outputs found
The Seven Sisters DANCe III: Projected spatial distribution
Methods. We compute Bayesian evidences and Bayes Factors for a set of
variations of the classical radial models by King (1962), Elson et al. (1987)
and Lauer et al. (1995). The variations incorporate different degrees of model
freedom and complexity, amongst which we include biaxial (elliptical) symmetry,
and luminosity segregation. As a by-product of the model comparison, we obtain
posterior distributions and maximum a posteriori estimates for each set of
model parameters. Results. We find that the model comparison results depend on
the spatial extent of the region used for the analysis. For a circle of 11.5
parsecs around the cluster centre (the most homogeneous and complete region),
we find no compelling reason to abandon Kings model, although the Generalised
King model, introduced in this work, has slightly better fitting properties.
Furthermore, we find strong evidence against radially symmetric models when
compared to the elliptic extensions. Finally, we find that including mass
segregation in the form of luminosity segregation in the J band, is strongly
supported in all our models. Conclusions. We have put the question of the
projected spatial distribution of the Pleiades cluster on a solid probabilistic
framework, and inferred its properties using the most exhaustive and least
contaminated list of Pleiades candidate members available to date. Our results
suggest however that this sample may still lack about 20% of the expected
number of cluster members. Therefore, this study should be revised when the
completeness and homogeneity of the data can be extended beyond the 11.5
parsecs limit. Such study will allow a more precise determination of the
Pleiades spatial distribution, its tidal radius, ellipticity, number of objects
and total mass.Comment: 39 pages, 31 figure
Quantum state reconstruction using binary data from on/off photodetection
The knowledge of the density matrix of a quantum state plays a fundamental
role in several fields ranging from quantum information processing to
experiments on foundations of quantum mechanics and quantum optics. Recently, a
method has been suggested and implemented in order to obtain the reconstruction
of the diagonal elements of the density matrix exploiting the information
achievable with realistic on/off detectors, e.g. silicon avalanche
photo-diodes, only able to discriminate the presence or the absence of light.
The purpose of this paper is to provide an overview of the theoretical and
experimental developments of the on/off method, including its extension to the
reconstruction of the whole density matrix.Comment: revised version, 11 pages, 6 figures, to appear as a review paper on
Adv. Science Let
The Seven Sisters DANCe. I. Empirical isochrones, Luminosity and Mass Functions of the Pleiades cluster
The DANCe survey provides photometric and astrometric (position and proper
motion) measurements for approximately 2 millions unique sources in a region
encompassing 80deg centered around the Pleiades cluster.
We aim at deriving a complete census of the Pleiades, and measure the mass
and luminosity function of the cluster. Using the probabilistic selection
method described in Sarro+2014, we identify high probability members in the
DANCe (14mag) and Tycho-2 (12mag) catalogues, and study the
properties of the cluster over the corresponding luminosity range. We find a
total of 2109 high probability members, of which 812 are new, making it the
most extensive and complete census of the cluster to date. The luminosity and
mass functions of the cluster are computed from the most massive members down
to 0.025M. The size, sensitivity and quality of the sample
result in the most precise luminosity and mass functions observed to date for a
cluster. Our census supersedes previous studies of the Pleiades cluster
populations, both in terms of sensitivity and accuracy.Comment: Language Edition Done. Final version to be published in A&A. Tables
will be published at CDS. Meanwhile, they can be requested to H. Bouy (hbouy
-at- cab . inta - csic . es
Incomplete quantum process tomography and principle of maximal entropy
The main goal of this paper is to extend and apply the principle of maximum
entropy (MaxEnt) to incomplete quantum process estimation tasks. We will define
a so-called process entropy function being the von Neumann entropy of the state
associated with the quantum process via Choi-Jamiolkowski isomorphism. It will
be shown that an arbitrary process estimation experiment can be reformulated in
a unified framework and MaxEnt principle can be consistently exploited. We will
argue that the suggested choice for the process entropy satisfies natural list
of properties and it reduces to the state MaxEnt principle, if applied to
preparator devices.Comment: 8 pages, comments welcome, references adde
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