101 research outputs found
Near-Infrared Time-Series Photometry in the Field of Cygnus OB2 Association I - Rotational Scenario For Candidate Members
In the last decades, the early pre main sequence stellar rotational evolution
picture has been constrained by studies targeting different young regions at a
variety of ages. Observational studies suggest a mass-rotation dependence, and
for some mass ranges a connection between rotation and the presence of a
circumstellar disk. Not still fully explored, though, is the role of
environmental conditions on the rotational regulation.
We investigate the rotational properties of candidate members of the young
massive association Cygnus OB2. The Stetson variability index, Lomb-Scargle
periodogram, Saunders statistics, string/rope length method, and visual
verification of folded light curves were applied to select 1224 periodic
variable stars. Completeness and contamination of the periodic sample was
derived from Monte Carlo simulations, out of which 894 periods were considered
reliable. Our study was considered reasonably complete for periods from 2 to 30
days.
The general rotational scenario seen in other young regions is confirmed by
Cygnus OB2 period distributions, with disked stars rotating on average slower
than non-disked stars. A mass-rotation dependence was also verified, but as in
NGC 6530, lower mass stars are rotating on average slower than higher mass
stars, with an excess of slow rotators among the lower mass population. The
effect of the environment on the rotational properties of the association was
investigated by re-analysing the results while taking into account the incident
UV radiation arising from O stars in the association. Results compatible with
the disk-locking scenario were verified for stars with low UV incidence, but no
statistical significant relation between rotation and disk presence was
verified for stars with high UV incidence suggesting that massive stars can
have an important role on regulating the rotation of nearby low mass stars.Comment: Submitted on December 23, 201
Near-infrared time-series photometry in the field of Cygnus OB2 association II. Mapping the variability of candidate members
We present the results of a J, H, and K photometric variability survey of the
central 0.78 square degrees of the young OB association Cygnus OB2. We used
data observed with the Wide-Field CAMera at the United Kingdom Infrared
Telescope in 2007 (spanning 217 days) to investigate the light curves of 5083
low mass candidate members in the association and explore the occurrence and
main characteristics of their near-infrared variability. We identified 2529
stars (50 of the sample) with significant variability with
time-scales ranging from days to months. We classified the variable stars into
the following three groups according to their light curve morphology: periodic
variability (1697 stars), occultation variability (124 stars), and other types
of variability (726 stars). We verified that the disk-bearing stars in our
sample are significantly more variable in the near-infrared than diskless
stars, with a steep increase in the disk-fraction among stars with higher
variability amplitude. We investigated the trajectories described by variable
stars in the color-space and measured slopes for 335 stars describing linear
trajectories. Based on the trajectories in the color-space, we inferred that
the sample analyzed is composed of a mix of young stars presenting variability
due to hot and cold spots, extinction by circumstellar material, and changes in
the disk emission in the near-infrared. We contemplated using the use of
near-infrared variability to identify disk-bearing stars and verified that
53.4 of the known disk-bearing stars in our sample could have been
identified as such based solely on their variability. We present 18 newly
identified disk-bearing stars and 14 eclipsing binary candidates among CygOB2
lower-mass members.Comment: 19 pages, 21 Figure
A Cauchy-Dirac delta function
The Dirac delta function has solid roots in 19th century work in Fourier
analysis and singular integrals by Cauchy and others, anticipating Dirac's
discovery by over a century, and illuminating the nature of Cauchy's
infinitesimals and his infinitesimal definition of delta.Comment: 24 pages, 2 figures; Foundations of Science, 201
Stevin numbers and reality
We explore the potential of Simon Stevin's numbers, obscured by shifting
foundational biases and by 19th century developments in the arithmetisation of
analysis.Comment: 22 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1104.0375, arXiv:1108.2885, arXiv:1108.420
The VVV Templates Project. Towards an Automated Classification of VVV Light-Curves. I. Building a database of stellar variability in the near-infrared
Context. The Vista Variables in the V\'ia L\'actea (VVV) ESO Public Survey is
a variability survey of the Milky Way bulge and an adjacent section of the disk
carried out from 2010 on ESO Visible and Infrared Survey Telescope for
Astronomy (VISTA). VVV will eventually deliver a deep near-IR atlas with
photometry and positions in five passbands (ZYJHK_S) and a catalogue of 1-10
million variable point sources - mostly unknown - which require
classifications. Aims. The main goal of the VVV Templates Project, that we
introduce in this work, is to develop and test the machine-learning algorithms
for the automated classification of the VVV light-curves. As VVV is the first
massive, multi-epoch survey of stellar variability in the near-infrared, the
template light-curves that are required for training the classification
algorithms are not available. In the first paper of the series we describe the
construction of this comprehensive database of infrared stellar variability.
Methods. First we performed a systematic search in the literature and public
data archives, second, we coordinated a worldwide observational campaign, and
third we exploited the VVV variability database itself on (optically)
well-known stars to gather high-quality infrared light-curves of several
hundreds of variable stars. Results. We have now collected a significant (and
still increasing) number of infrared template light-curves. This database will
be used as a training-set for the machine-learning algorithms that will
automatically classify the light-curves produced by VVV. The results of such an
automated classification will be covered in forthcoming papers of the series.Comment: 12 pages, 16 figures, 3 tables, accepted for publication in A&A. Most
of the data are now accessible through http://www.vvvtemplates.org
"Vamos vencer o trĂĄfico": anĂĄlise verbo-visual da significação e do tema de uma palavra em uma capa da revista Ăpoca
A Burgessian critique of nominalistic tendencies in contemporary mathematics and its historiography
We analyze the developments in mathematical rigor from the viewpoint of a
Burgessian critique of nominalistic reconstructions. We apply such a critique
to the reconstruction of infinitesimal analysis accomplished through the
efforts of Cantor, Dedekind, and Weierstrass; to the reconstruction of Cauchy's
foundational work associated with the work of Boyer and Grabiner; and to
Bishop's constructivist reconstruction of classical analysis. We examine the
effects of a nominalist disposition on historiography, teaching, and research.Comment: 57 pages; 3 figures. Corrected misprint
Leibniz's Infinitesimals: Their Fictionality, Their Modern Implementations, And Their Foes From Berkeley To Russell And Beyond
Many historians of the calculus deny significant continuity between
infinitesimal calculus of the 17th century and 20th century developments such
as Robinson's theory. Robinson's hyperreals, while providing a consistent
theory of infinitesimals, require the resources of modern logic; thus many
commentators are comfortable denying a historical continuity. A notable
exception is Robinson himself, whose identification with the Leibnizian
tradition inspired Lakatos, Laugwitz, and others to consider the history of the
infinitesimal in a more favorable light. Inspite of his Leibnizian sympathies,
Robinson regards Berkeley's criticisms of the infinitesimal calculus as aptly
demonstrating the inconsistency of reasoning with historical infinitesimal
magnitudes. We argue that Robinson, among others, overestimates the force of
Berkeley's criticisms, by underestimating the mathematical and philosophical
resources available to Leibniz. Leibniz's infinitesimals are fictions, not
logical fictions, as Ishiguro proposed, but rather pure fictions, like
imaginaries, which are not eliminable by some syncategorematic paraphrase. We
argue that Leibniz's defense of infinitesimals is more firmly grounded than
Berkeley's criticism thereof. We show, moreover, that Leibniz's system for
differential calculus was free of logical fallacies. Our argument strengthens
the conception of modern infinitesimals as a development of Leibniz's strategy
of relating inassignable to assignable quantities by means of his
transcendental law of homogeneity.Comment: 69 pages, 3 figure
Ten Misconceptions from the History of Analysis and Their Debunking
The widespread idea that infinitesimals were "eliminated" by the "great
triumvirate" of Cantor, Dedekind, and Weierstrass is refuted by an
uninterrupted chain of work on infinitesimal-enriched number systems. The
elimination claim is an oversimplification created by triumvirate followers,
who tend to view the history of analysis as a pre-ordained march toward the
radiant future of Weierstrassian epsilontics. In the present text, we document
distortions of the history of analysis stemming from the triumvirate ideology
of ontological minimalism, which identified the continuum with a single number
system. Such anachronistic distortions characterize the received interpretation
of Stevin, Leibniz, d'Alembert, Cauchy, and others.Comment: 46 pages, 4 figures; Foundations of Science (2012). arXiv admin note:
text overlap with arXiv:1108.2885 and arXiv:1110.545
Open Problems on Central Simple Algebras
We provide a survey of past research and a list of open problems regarding
central simple algebras and the Brauer group over a field, intended both for
experts and for beginners.Comment: v2 has some small revisions to the text. Some items are re-numbered,
compared to v
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