363 research outputs found
A new, Gaia based, catalogue of blue straggler stars in open clusters
Blue straggler stars are exotic objects present in all stellar environments
whose nature and formation channels are still partially unclear. They seem to
be particularly abundant in open clusters (OCs), thus offering a unique chance
to tackle these problems statistically.We aim to build up a new and homogeneous
catalogue of blue straggler stars (BSS) in Galactic OCs using Gaia to provide a
more solid assessment of the membership of these stars. We also aim to explore
possible relationships of the straggler abundance with the parent cluster's
structural and dynamical parameters. As a by-product, we also search for
possible yellow straggler stars (YSS), which are believed to be stragglers in a
more advanced evolution stage. We employed photometry, proper motions, and
parallaxes extracted from Gaia DR2 for 408 Galactic star clusters and searched
for stragglers within them after performing a careful membership analysis. The
number of BBS emerging from our more stringent, selection criteria turns out to
be significantly smaller than in previous versions of this catalogue. OCs are
therefore not a preferable environment for these kinds of stars anymore. In
addition, we found that BSS start to appear in clusters with ages larger than
log(t) ~ 8.7 and are therefore absent in very young star clusters.The present
catalogue supersedes the previous ones in several ways: membership assessment,
number of stragglers found, and so forth. The new list includes 897 BSS and 77
YSS candidates in 408 OCs. We expect this catalogue to be the basis for a new
round of studies of BSS and YSS.Comment: 9 pages, 4 figures, accepted for publication in A&A Journal on
22/02/202
Chemical evolution of the metal poor Globular Cluster NGC 6809
We present the abundances analysis for a sample of 11 red giant branch stars
in the metal-poor globular cluster NGC 6809 based on high-resolution spectra.
Our main goals are to characterize its chemical composition and analyze this
cluster's behavior associated with the Multiple Population (MPs) phenomenon. In
our work we obtained the stellar parameters and chemical abundances of 24
elements (O, Na, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Sc, Ni, Cu, Zn, Y, Zr,
Ba, La, Ce, Eu, Nd and Dy). We found a radial velocity of 174.7 3.2 km
and a mean iron content of [Fe/H]=-2.01 0.02 in good agreement
with other studies. Moreover, we found a large spread in the abundances of the
light elements O, Na and Al confirming the presence of a Na-O anti-correlation
a Na-Al correlation. The Mg-Al anti-correlation is also present in our cluster.
The and iron-peak elements show good agreement with the halo field
star trend. The heavy elements are dominated by the r-process.Comment: 13 pages, 11 figures, 3 tables, accepted for publication in MNRA
The blue straggler population of the open clusters Trumpler 5, Trumpler 20, and NGC 2477
We present a study, based on Gaia DR2, of the population of blue straggler
stars (BSS) in the open clusters Trumpler 5, Trumpler 20, and NGC 2477. All
candidates were selected according to their position in the color-magnitude
diagram, to their proper motion components, and to their parallax. We also
looked for yellow stragglers, i.e., possible evolved blue stragglers. We found
that Trumpler 5 hosts a large BSS population, which allowed us to analyze their
radial distribution as a probe of the cluster's dynamical status. The BSS
distribution was compared with that of red giant branch stars (RGB) to evaluate
mass segregation. Our results indicate that blue straggler stars are not more
centrally concentrated than RGB stars in any of the clusters. The radial
distribution of BSS in Trumpler 5 is flat. Additionally, using a multi-epoch
radial velocity survey conducted with the high-resolution spectrograph
FLAMES/GIRAFFE at VLT, we measured the radial velocities of a sample of
stragglers, for the sake of comparison with the mean radial velocity and the
velocity dispersion of the clusters. Based on the radial velocity variations
for different epochs, we roughly classified these stars as possible close-or
long-period binaries.Comment: 20 pages, 5 figures, accepted for publication in A
Recovering 3D structural properties of galaxies from SDSS-like photometry
Because of the 3D nature of galaxies, an algorithm for constructing spatial
density distribution models of galaxies on the basis of galaxy images has many
advantages over surface density distribution approximations. We present a
method for deriving spatial structure and overall parameters of galaxies from
images and estimate its accuracy and derived parameter degeneracies on a sample
of idealised model galaxies. The test galaxies consist of a disc-like component
and a spheroidal component with varying proportions and properties. Both
components are assumed to be axially symmetric and coplanar. We simulate these
test galaxies as if observed in the SDSS project through ugriz filters, thus
gaining a set of realistically imperfect images of galaxies with known
intrinsic properties. These artificial SDSS galaxies were thereafter remodelled
by approximating the surface brightness distribution with a 2D projection of a
bulge+disc spatial distribution model and the restored parameters were compared
to the initial ones. Down to the r-band limiting magnitude 18, errors of the
restored integral luminosities and colour indices remain within 0.05 mag and
errors of the luminosities of individual components within 0.2 mag. Accuracy of
the restored bulge-to-disc ratios (B/D) is within 40% in most cases, and
becomes worse for galaxies with low B/D, but the general balance between bulges
and discs is not shifted systematically. Assuming that the intrinsic disc axial
ratio is < 0.3, the inclination angles can be estimated with errors < 5deg for
most of the galaxies with B/D < 2 and with errors < 15deg up to B/D = 6. Errors
of the recovered sizes of the galactic components are below 10% in most cases.
In general, models of disc components are more accurate than models of
spheroidal components for geometrical reasons.Comment: 15 pages, 13 figures, accepted for publication in RA
Two-tape finite automata with quantum and classical states
{\it Two-way finite automata with quantum and classical states} (2QCFA) were
introduced by Ambainis and Watrous, and {\it two-way two-tape deterministic
finite automata} (2TFA) were introduced by Rabin and Scott. In this paper we
study 2TFA and propose a new computing model called {\it two-way two-tape
finite automata with quantum and classical states} (2TQCFA). First, we give
efficient 2TFA algorithms for recognizing languages which can be recognized by
2QCFA. Second, we give efficient 2TQCFA algorithms to recognize several
languages whose status vis-a-vis 2QCFA have been posed as open questions, such
as . Third, we show that
can be recognized by {\it -tape
deterministic finite automata} (TFA). Finally, we introduce {\it
-tape automata with quantum and classical states} (TQCFA) and prove that
can be recognized by TQCFA.Comment: 25 page
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Space charge behaviour in epoxy laminates under high constant electric field
The development of space charge in insulating materials is one of the main causes of their electrical ageing. The pulsed electro-acoustic method is often used to determine space charge distribution, but the signal analysis in the case of laminate structures is much more complex to analyse. In this paper the authors describe and use a simulated signal in order to study laminates made of epoxy resin and fibre mat. The relatively large conductivity of the fibres compared with that of the resin seems to produce a rapid charge dissociation and recombination in the fibres. Under voltage the presence of fibres close to an electrode seems to promote charge injection
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Terahertz emission from the intrinsic Josephson junctions of high-symmetry thermally-managed Bi2Sr2CaCu2O8+ÎŽ microstrip antennas
We show for high-symmetry disk, square, or equilateral triangular thin microstrip antennas of any composition respectively obeying Câv, C4v, and C3v point group symmetries, that the transverse magnetic electromagnetic cavity mode wave functions are restricted in form to those that are one-dimensional representations of those point groups. Plots of the common nodal points of the ten lowest-energy non-radiating two-dimensional representations of each of these three symmetries are presented. For comparison with symmetry-broken disk intrinsic Josephson junction microstrip antennas constructed from the highly anisotropic layered superconductor Bi2 Sr2 CaCu2 O8+ÎŽ (BSCCO), we present plots of the ten lowest frequency orthonormal wave functions and of their emission power angular distributions. These results are compared with previous results for square and equilateral triangular thin microstrip antennas
A Study of the Blue Straggler Population of the Old Open Cluster Collinder 261
Blue stragglers (BSs) are stars located in an unexpected region of the colorâmagnitude diagram (CMD) of a stellar
population, as they appear bluer and more luminous than the stars in the turn-off region. They are ubiquitous, since
they have been found among Milky Way field stars, in open and globular clusters, and also in other galaxies of the
Local Group. Here we present a study on the BS population of the old and metal-rich open cluster Collinder 261,
based on Gaia DR2 data and on a multi-epoch radial velocity survey conducted with Fibre Large Array Multi
Element Spectrograph (FLAMES) at the Very Large Telescope (VLT). We also analyze the radial distribution of
the BS population to probe the dynamical status of the cluster. BS candidates were identified first with Gaia DR2,
according to their position on the CMD, proper motions, and parallaxes. Their radial distribution was compared
with those of main sequence, red giant, and red clump stars, to evaluate mass segregation. Additionally, their radial
velocities (and the associated uncertainties) were compared with the mean radial velocity and velocity dispersion of
the cluster. When possible, close binaries and long-period binaries were also identified, based on the radial velocity
variations for the different epochs. We also looked for yellow stragglers, i.e., possible evolved BSs. We found 53
BS members of Collinder 261, six of them were already identified in previous catalogs. Among the BS candidates
with radial velocity measurements, we found one long-period binary, five close-binary systems, three nonvariable
stars; we also identified one yellow stragglerIndexaciĂłn: Scopu
Periodic Emission from the Gamma-ray Binary 1FGL J1018.6-5856
Gamma-ray binaries are stellar systems containing a neutron star or black
hole with gamma-ray emission produced by an interaction between the components.
These systems are rare, even though binary evolution models predict dozens in
our Galaxy. A search for gamma-ray binaries with the Fermi Large Area Telescope
(LAT) shows that 1FGL J1018.6-5856 exhibits intensity and spectral modulation
with a 16.6 day period. We identified a variable X-ray counterpart, which shows
a sharp maximum coinciding with maximum gamma-ray emission, as well as an
O6V((f)) star optical counterpart and a radio counterpart that is also
apparently modulated on the orbital period. 1FGL J1018.6-5856 is thus a
gamma-ray binary, and its detection suggests the presence of other fainter
binaries in the Galaxy.Comment: Contact authors: R.H.D. Corbet, M. Kerr, C.C. Cheun
Rhomboid family member 2 regulates cytoskeletal stress-associated Keratin 16.
Keratin 16 (K16) is a cytoskeletal scaffolding protein highly expressed at pressure-bearing sites of the mammalian footpad. It can be induced in hyperproliferative states such as wound healing, inflammation and cancer. Here we show that the inactive rhomboid protease RHBDF2 (iRHOM2) regulates thickening of the footpad epidermis through its interaction with K16. K16 expression is absent in the thinned footpads of irhom2-/- mice compared with irhom2+/+mice, due to reduced keratinocyte proliferation. Gain-of-function mutations in iRHOM2 underlie Tylosis with oesophageal cancer (TOC), characterized by palmoplantar thickening, upregulate K16 with robust downregulation of its type II keratin binding partner, K6. By orchestrating the remodelling and turnover of K16, and uncoupling it from K6, iRHOM2 regulates the epithelial response to physical stress. These findings contribute to our understanding of the molecular mechanisms underlying hyperproliferation of the palmoplantar epidermis in both physiological and disease states, and how this 'stress' keratin is regulated
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