323 research outputs found
Software Model Checking via Large-Block Encoding
The construction and analysis of an abstract reachability tree (ART) are the
basis for a successful method for software verification. The ART represents
unwindings of the control-flow graph of the program. Traditionally, a
transition of the ART represents a single block of the program, and therefore,
we call this approach single-block encoding (SBE). SBE may result in a huge
number of program paths to be explored, which constitutes a fundamental source
of inefficiency. We propose a generalization of the approach, in which
transitions of the ART represent larger portions of the program; we call this
approach large-block encoding (LBE). LBE may reduce the number of paths to be
explored up to exponentially. Within this framework, we also investigate
symbolic representations: for representing abstract states, in addition to
conjunctions as used in SBE, we investigate the use of arbitrary Boolean
formulas; for computing abstract-successor states, in addition to Cartesian
predicate abstraction as used in SBE, we investigate the use of Boolean
predicate abstraction. The new encoding leverages the efficiency of
state-of-the-art SMT solvers, which can symbolically compute abstract
large-block successors. Our experiments on benchmark C programs show that the
large-block encoding outperforms the single-block encoding.Comment: 13 pages (11 without cover), 4 figures, 5 table
Photometry and astrometry with JWST -- II. NIRCam distortion correction
In preparation to make the most of our own planned James Webb Space Telescope
investigations, we take advantage of publicly available calibration and
early-science observations to independently derive and test a
geometric-distortion solution for NIRCam detectors. Our solution is able to
correct the distortion to better than ~0.2 mas. Current data indicate that the
solution is stable and constant over the investigated filters, temporal
coverage, and even over the available filter combinations. We successfully
tested our geometric-distortion solution in three cases: (i) field-object
decontamination of M 92 field; (ii) estimate of internal proper motions of M
92; and (iii) measurement of the internal proper motions of the Large
Magellanic Cloud system. To our knowledge, the here-derived
geometric-distortion solution for NIRCam is the best available and we publicly
release it, as many other investigations could potentially benefit from it.
Along with our geometric-distortion solution, we also release a Python tool to
convert the raw-pixels coordinates of each detector into distortion-free
positions, and also to put all the ten detectors of NIRCam into a common
reference system.Comment: 13 pages, 12 figures (6 in low resolution), 3 tables. Accepted for
publication on February 21st, 2023, by Astronomische Nachrichten
(Astronomical Notes). Distortion correction software available at
https://web.oapd.inaf.it/bedin/files/PAPERs_eMATERIALs/JWST/Paper_02/Python
Familiarity effects on fish behaviour are disrupted in shoals that contain also unfamiliar individuals
Research on several social fishes has revealed that shoals constituted by familiar individuals behave remarkably differently compared to shoals formed by unfamiliar individuals. However, whether these behavioural changes may arise also in shoals composed by a mixture of familiar and unfamiliar individuals, a situation that may commonly occur in nature, is not clear. Here, we observed the behaviour of Mediterranean killifish (Aphanius fasciatus) shoals that were composed by both familiar and unfamiliar individuals (i.e. individuals were familiar to each other in pairs) and compared it with shoals entirely made by either unfamiliar or familiar individuals. Shoals formed by familiar individuals took longer to emerge from a refuge and swam more cohesively compared to shoals formed by unfamiliar fish. Shoals formed by a mixture of familiar and unfamiliar individuals behaved as shoals formed by unfamiliar individuals. Moreover, mixed shoals did not segregate in pairs according to their familiarity. This study suggests that mixed shoals do not show the behavioural effects of familiarity. Significance statement Laboratory studies have compared the behaviour of shoals formed by familiar fish versus shoals formed by unfamiliar fish, finding notable advantages in the former ones, such as improved antipredator and foraging behaviour. However, comparing these two opposite shoal types may not provide information on the natural situation, because in nature, shoals often change composition. We investigated how shoals formed by a mixture of familiar and unfamiliar fish behaved. We analysed shoals' preference for open environment versus covers and shoals' swimming cohesion. Results showed that shoals formed by both familiar and unfamiliar individuals mostly behave like shoals entirely formed by unfamiliar individuals. This suggests that the advantages of social groups formed by familiar fish might be hardly seen in nature for species in which shoal composition changes frequently
The broadening of the main sequence in the open cluster M38
Our recent multi-band photometric study of the colour width of the lower main
sequence of the open cluster M37 has revealed the presence of a sizeable
initial chemical composition spread in the cluster. If initial chemical
composition spreads are common amongst open clusters, this would have major
implications for cluster formation models and the foundation of the chemical
tagging technique. Here we present a study of the unevolved main sequence of
the open cluster M38, employing Gaia DR3 photometry and astrometry, together
with newly acquired Sloan photometry. We have analysed the distribution of the
cluster's lower main sequence stars with a differential colour-colour diagram
made of combinations of Gaia and Sloan magnitudes, like in the study of M37. We
employed synthetic stellar populations to reproduce the observed trend of M38
stars in this diagram, and found that the observed colour spreads can be
explained simply by the combined effect of differential reddening across the
face of the cluster and the presence of unresolved binaries. There is no need
to include in the synthetic sample a spread of initial chemical composition as
instead necessary to explain the main sequence of M37. Further photometric
investigations like ours, as well as accurate differential spectroscopic
analyses on large samples of open clusters, are necessary to understand whether
chemical abundance spreads are common among the open cluster population.Comment: 8 pages, 10 figures. Accepted for publication in MNRAS on 2023, June
0
Signature of a chemical spread in the open cluster M37
Recent Gaia photometry of the open cluster M37 have disclosed the existence
of an extended main-sequence turn off -- like in Magellanic clusters younger
than about 2 Gyr -- and a main sequence that is broadened in colour beyond what
is expected from the photometric errors, at magnitudes well below the region of
the extended turn off, where neither age differences nor rotation rates (the
candidates to explain the extended turn off phenomenon) are expected to play a
role. Moreover, not even the contribution of unresolved binaries can fully
explain the observed broadening. We investigated the reasons behind this
broadening by making use of synthetic stellar populations and differential
colour-colour diagrams using a combination of Gaia and Sloan filters. From our
analysis we have concluded that the observed colour spread in the Gaia
colour-magnitude diagram can be reproduced by a combination of either a
metallicity spread Delta[Fe/H] ~ 0.15 plus a differential reddening across the
face of the cluster spanning a total range DeltaE (B - V) ~ 0.06, or a spread
of the initial helium mass fraction DeltaY ~ 0.10 plus a smaller range of
reddening DeltaE (B - V) ~ 0.03. High-resolution differential abundance
determinations of a sizeable sample of cluster stars are necessary to confirm
or exclude the presence of a metal abundance spread. Our results raise the
possibility that also individual open clusters, like globular clusters and
massive star clusters, host stars born with different initial chemical
compositions.Comment: 10 pages, 10 figures. Accepted for publication in MNRAS on 2022,
August 31, manuscript ID. MN-22-2637-M
Photometry and astrometry with JWST -- III. A NIRCam-Gaia DR3 analysis of the open cluster NGC 2506
In the third paper of this series aimed at developing the tools for analysing
resolved stellar populations using the cameras on board of the James Webb Space
Telescope (JWST), we present a detailed multi-band study of the 2 Gyr Galactic
open cluster NGC 2506. We employ public calibration data-sets collected in
multiple filters to: (i) derive improved effective Point Spread Functions
(ePSFs) for ten NIRCam filters; (ii) extract high-precision photometry and
astrometry for stars in the cluster, approaching the main-sequence (MS) lower
mass of ~0.1 Msun; and (iii) take advantage of the synergy between JWST and
Gaia DR3 to perform a comprehensive analysis of the cluster's global and local
properties. We derived a MS binary fraction of ~57.5 %, extending the Gaia
limit (~0.8 Msun) to lower masses (~0.4 Msun) with JWST. We conducted a study
on the mass functions (MFs) of NGC 2506, mapping the mass segregation with Gaia
data, and extending MFs to lower masses with the JWST field. We also combined
information on the derived MFs to infer an estimate of the cluster present-day
total mass. Lastly, we investigated the presence of white dwarfs (WDs) and
identified a strong candidate. However, to firmly establish its cluster
membership, as well as that of four other WD candidates and of the majority of
faint low-mass MS stars, further JWST equally deep observations will be
required. We make publicly available catalogues, atlases, and the improved
ePSFs.Comment: 20 pages, 17 figures (5 in low resolution), 4 tables. Accepted for
publication in MNRAS on August 5, 2023. PSF models, catalogs and stacked
images are publicly available at
https://web.oapd.inaf.it/bedin/files/PAPERs_eMATERIALs/JWST/Paper_03
Exploring the origin of the extended main sequence turn off in M37 through the white dwarf cooling sequence
We use new observations from the Canada-France-Hawaii Telescope to study the
white dwarf cooling sequence of the open cluster M37, a cluster that displays
an extended main sequence turn-off and, according to a recent photometric
analysis, also a spread of initial chemical composition. By taking advantage of
a first epoch collected in 1999 with the same telescope, we have been able to
calculate proper motions for sources as faint as g ~ 26 (about ~ 6 magnitudes
fainter than the Gaia limit), allowing us to separate cluster members from
field stars. This has enabled us to isolate a sample of the white dwarf
population of M37, reaching the end of the cooling sequence (at g ~ 23.5). The
here-derived atlas and calibrated catalogue of the sources in the field of view
is publicly released as supplementary on-line material. Finally, we present an
exhaustive comparison of the white dwarf luminosity function with theoretical
models, which has allowed us to exclude the age-spread scenario as the main
responsible for the extended turnoff seen in the cluster
colour-magnitude-diagram.Comment: 10 pages, 13 figures. Accepted for publication in MNRAS on 2023, June
1
Astrometric star-cluster membership probability: application to the case of M 37 with Gaia EDR3
In this work, starting from the well-accepted relations in literature, we introduce a new formalism to compute the astrometric membership probabilities for sources in star clusters, and we provide an application to the case of the open cluster M 37. The novelty of our approach is a refined - and magnitude-dependent - modelling of the parallax distribution of the field stars. We employ the here-derived list of members to estimate the cluster's mean systemic astrometric parameters, which are based on the most recent Gaia's catalogue (EDR3)
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