191 research outputs found
Physical parameters and the projection factor of the classical Cepheid in the binary system OGLE-LMC-CEP-0227
A novel method of analysis of double-lined eclipsing binaries containing a
radially pulsating star is presented. The combined pulsating-eclipsing light
curve is built up from a purely eclipsing light curve grid created using an
existing modeling tool. For every pulsation phase the instantaneous radius and
surface brightness are taken into account, being calculated from the
disentangled radial velocity curve of the pulsating star and from its
out-of-eclipse pulsational light curve and the light ratio of the components,
respectively. The best model is found using the Markov Chain Monte Carlo
method.
The method is applied to the eclipsing binary Cepheid OGLE-LMC-CEP-0227
(P_puls = 3.80 d, P_orb = 309 d). We analyze a set of new spectroscopic and
photometric observations for this binary, simultaneously fitting OGLE V-band,
I-band and Spitzer 3.6 {\mu}m photometry. We derive a set of fundamental
parameters of the system significantly improving the precision comparing to the
previous results obtained by our group. The Cepheid mass and radius are M_1 =
4.165 +/- 0.032 M_solar and R_1 = 34.92 +/- 0.34 R_solar, respectively.
For the first time a direct, geometrical and distance-independent
determination of the Cepheid projection factor is presented. The value p = 1.21
+/- 0.03(stat.) +/- 0.04(syst.) is consistent with theoretical expectations for
a short period Cepheid and interferometric measurements for {\delta} Cep. We
also find a very high value of the optical limb darkening coefficients for the
Cepheid component, in strong disagreement with theoretical predictions for
static atmospheres at a given surface temperature and gravity.Comment: 16 pages, 17 figures, accepted for publication in MNRA
Tropically convex constraint satisfaction
A semilinear relation S is max-closed if it is preserved by taking the
componentwise maximum. The constraint satisfaction problem for max-closed
semilinear constraints is at least as hard as determining the winner in Mean
Payoff Games, a notorious problem of open computational complexity. Mean Payoff
Games are known to be in the intersection of NP and co-NP, which is not known
for max-closed semilinear constraints. Semilinear relations that are max-closed
and additionally closed under translations have been called tropically convex
in the literature. One of our main results is a new duality for open tropically
convex relations, which puts the CSP for tropically convex semilinaer
constraints in general into NP intersected co-NP. This extends the
corresponding complexity result for scheduling under and-or precedence
constraints, or equivalently the max-atoms problem. To this end, we present a
characterization of max-closed semilinear relations in terms of syntactically
restricted first-order logic, and another characterization in terms of a finite
set of relations L that allow primitive positive definitions of all other
relations in the class. We also present a subclass of max-closed constraints
where the CSP is in P; this class generalizes the class of max-closed
constraints over finite domains, and the feasibility problem for max-closed
linear inequalities. Finally, we show that the class of max-closed semilinear
constraints is maximal in the sense that as soon as a single relation that is
not max-closed is added to L, the CSP becomes NP-hard.Comment: 29 pages, 2 figure
A large-scale survey for variable stars in M33
We have started a survey of M 33 in order to find variable stars and Cepheids
in particular. We have obtained more than 30 epochs of g'r'i' data with the
CFHT and the one-square-degree camera MegaCam. We present first results from
this survey, including the search for variable objects and a basic
characterization of the various groups of variable stars.Comment: To appear in the proceedings of the "Nonlinear stellar
hydrodynamics", conference in honor of Robert Buchler's 65th birthday, July
2007, Pari
New Baade-Wesselink distances and radii for four metal-rich Galactic Cepheids
We provided accurate estimates of distances, radii and iron abundances for
four metal-rich Cepheids, namely V340 Ara, UZ Sct, AV Sgr and VY Sgr. The main
aim of this investigation is to constrain their pulsation properties and their
location across the Galactic inner disk. We adopted new accurate NIR (J,H,K)
light curves and new radial velocity measurements for the target Cepheids to
determinate their distances and radii using the Baade-Wesselink technique. In
particular, we adopted the most recent calibration of the IR surface brightness
relation and of the projection factor. Moreover, we also provided accurate
measurements of the iron abundance of the target Cepheids. Current distance
estimates agree within one sigma with similar distances based either on
empirical or on theoretical NIR Period-Luminosity relations. However, the
uncertainties of the Baade-Wesselink distances are on average a factor of 3-4
smaller when compared with errors affecting other distance determinations. Mean
Baade-Wesselink radii also agree at one sigma level with Cepheid radii based
either on empirical or on theoretical Period-Radius relations. Iron abundances
are, within one sigma, similar to the iron contents provided by Andrievsky and
collaborators, thus confirming the super metal-rich nature of the target
Cepheids. We also found that the luminosity amplitudes of classical Cepheids,
at odds with RR Lyrae stars, do not show a clear correlation with the
metal-content. This circumstantial evidence appears to be the consequence of
the Hertzsprung progression together with the dependence of the topology of the
instability strip on metallicity, evolutionary effects and binaries.Comment: 9 pages, 7 figures, A&A accepte
On the distance of the globular cluster M4 (NGC 6121) using RR Lyrae stars: I. optical and near-infrared Period-Luminosity and Period-Wesenheit relations
We present new distance determinations to the nearby globular M4 (NGC~6121)
based on accurate optical and Near Infrared (NIR) mean magnitudes for
fundamental (FU) and first overtone (FO) RR Lyrae variables (RRLs), and new
empirical optical and NIR Period-Luminosity (PL) and Period-Wesenheit (PW)
relations. We have found that optical-NIR and NIR PL and PW relations are
affected by smaller standard deviations than optical relations. The difference
is the consequence of a steady decrease in the intrinsic spread of cluster RRL
apparent magnitudes at fixed period as longer wavelengths are considered. The
weighted mean visual apparent magnitude of 44 cluster RRLs is
\left=13.329\pm0.001 (standard error of the mean) 0.177
(weighted standard deviation) mag. Distances were estimated using RR Lyr itself
to fix the zero-point of the empirical PL and PW relations. Using the entire
sample (FUFO) we found weighted mean true distance moduli of
11.350.030.05 mag and 11.320.020.07 mag. Distances were
also evaluated using predicted metallicity dependent PLZ and PWZ relations. We
found weighted mean true distance moduli of 11.2830.0100.018 mag (NIR
PLZ) and 11.2720.0050.019 mag (optical--NIR and NIR PWZ). The above
weighted mean true distance moduli agree within 1. The same result is
found from distances based on PWZ relations in which the color index is
independent of the adopted magnitude (11.2720.0040.013 mag). These
distances agree quite well with the geometric distance provided by
\citep{kaluzny2013} based on three eclipsing binaries. The available evidence
indicates that this approach can provide distances to globulars hosting RRLs
with a precision better than 2--3\%.Comment: Accepted for publication on Ap
Young and Intermediate-age Distance Indicators
Distance measurements beyond geometrical and semi-geometrical methods, rely
mainly on standard candles. As the name suggests, these objects have known
luminosities by virtue of their intrinsic proprieties and play a major role in
our understanding of modern cosmology. The main caveats associated with
standard candles are their absolute calibration, contamination of the sample
from other sources and systematic uncertainties. The absolute calibration
mainly depends on their chemical composition and age. To understand the impact
of these effects on the distance scale, it is essential to develop methods
based on different sample of standard candles. Here we review the fundamental
properties of young and intermediate-age distance indicators such as Cepheids,
Mira variables and Red Clump stars and the recent developments in their
application as distance indicators.Comment: Review article, 63 pages (28 figures), Accepted for publication in
Space Science Reviews (Chapter 3 of a special collection resulting from the
May 2016 ISSI-BJ workshop on Astronomical Distance Determination in the Space
Age
The Large Magellanic Cloud and the Distance Scale
The Magellanic Clouds, especially the Large Magellanic Cloud, are places
where multiple distance indicators can be compared with each other in a
straight-forward manner at considerable precision. We here review the distances
derived from Cepheids, Red Variables, RR Lyraes, Red Clump Stars and Eclipsing
Binaries, and show that the results from these distance indicators generally
agree to within their errors, and the distance modulus to the Large Magellanic
Cloud appears to be defined to 3% with a mean value of 18.48 mag, corresponding
to 49.7 Kpc. The utility of the Magellanic Clouds in constructing and testing
the distance scale will remain as we move into the era of Gaia.Comment: 23 pages, accepted for publication in Astrophysics and Space Science.
From a presentation at the conference The Fundamental Cosmic Distance Scale:
State of the Art and the Gaia Perspective, Naples, May 201
Toward an internally consistent astronomical distance scale
Accurate astronomical distance determination is crucial for all fields in
astrophysics, from Galactic to cosmological scales. Despite, or perhaps because
of, significant efforts to determine accurate distances, using a wide range of
methods, tracers, and techniques, an internally consistent astronomical
distance framework has not yet been established. We review current efforts to
homogenize the Local Group's distance framework, with particular emphasis on
the potential of RR Lyrae stars as distance indicators, and attempt to extend
this in an internally consistent manner to cosmological distances. Calibration
based on Type Ia supernovae and distance determinations based on gravitational
lensing represent particularly promising approaches. We provide a positive
outlook to improvements to the status quo expected from future surveys,
missions, and facilities. Astronomical distance determination has clearly
reached maturity and near-consistency.Comment: Review article, 59 pages (4 figures); Space Science Reviews, in press
(chapter 8 of a special collection resulting from the May 2016 ISSI-BJ
workshop on Astronomical Distance Determination in the Space Age
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