2,354 research outputs found
Period-Color and Amplitude-Color Relations in Classical Cepheid Variables - VI. New Challenges for Pulsation Models
We present multiphase Period-Color/Amplitude-Color/Period-Luminosity
relations using OGLE III and Galactic Cepheid data and compare with state of
the art theoretical pulsation models. Using this new way to compare models and
observations, we find convincing evidence that both Period-Color and
Period-Luminosity Relations as a function of phase are dynamic and highly
nonlinear at certain pulsation phases. We extend this to a multiphase Wesenheit
function and find the same result. Hence our results cannot be due to reddening
errors. We present statistical tests and the urls of movies depicting the
Period-Color/Period Luminosity and Wesenheit relations as a function of phase
for the LMC OGLE III Cepheid data: these tests and movies clearly demonstrate
nonlinearity as a function of phase and offer a new window toward a deeper
understanding of stellar pulsation. When comparing with models, we find that
the models also predict this nonlinearity in both Period-Color and
Period-Luminosity planes. The models with (Z=0.004, Y=0.25) fare better in
mimicking the LMC Cepheid relations, particularly at longer periods, though the
models predict systematically higher amplitudes than the observations
Classical Cepheid Pulsation Models. XI. Effects of convection and chemical composition on the Period-Luminosity and Period-Wesenheit relations
In spite of the relevance of Classical Cepheids as primary distance
indicators, a general consensus on the dependence of the Period-Luminosity (PL)
relation on the Cepheid chemical composition has not been achieved yet. From
the theoretical point of view, our previous investigations were able to
reproduce some empirical tests for suitable assumptions on the helium to metal
relative enrichment, but those results relied on specific assumptions
concerning the Mass-Luminosity relation and the efficiency of the convective
transfer in the pulsating envelopes. In this paper, we investigate the effects
of the assumed value of the mixing length parameter l/Hp on the pulsation
properties and we release the assumption of a fixed Mass-Luminosity relation.
As a whole, we show that our pulsation relations appear fully consistent with
the observed properties of Galactic and Magellanic Cloud Cepheids, supporting
the predicted steepening and brightening of the PL relations when moving from
metal-rich to metal-poor variables. Moreover, we show that the distances
inferred by the predicted PW relations agree with recently measured
trigonometric parallaxes, whereas they suggest a correction to the values based
on the Infrared Surface Brightness technique, as already found from an
independent method. Finally, also the pulsation metal contents suggested by the
predicted PW relations appear in statistical agreement with spectroscopic
[Fe/H] measurements.Comment: 20 pages, 15 figure
Predicted properties of RR Lyrae stars in the SDSS photometric system
The luminosities and effective temperatures, as well as the whole bolometric
lightcurves of nonlinear convective RR Lyrae models with 0.0001<Z<0.006 are
transformed into the SDSS photometric system. The obtained ugriz lightcurves,
mean magnitudes and colors, pulsation amplitudes and color-color loops are
shown and analytical relations connecting pulsational to intrinsic stellar
parameters, similarly to the ones currently used in the Johnson-Cousins
filters, are derived. Finally the behaviour in the color-color planes is
compared with available observations in the literature and possible systematic
uncertainties affecting this comparison are discussed.Comment: accepted for publication in MNRA
Un terrain biographique sur le changement politique au Maroc. Suivre les traces d’Ahmed Benkirane
Insights into the Cepheid distance scale
We present an investigation of Cepheid distances using theory and
observations. Cepheid models indicate that the slope of the Period-Luminosity
(P-L) relation covering the entire period range (0.40<= logP <=2.0) becomes
steeper when moving from optical to NIR bands, and that the metallicity
dependence of the slope decreases from the B- to the K-band. We estimated V-
and I-band slopes for 87 Cepheid data sets belonging to 48 external galaxies
with nebular oxygen abundance 7.5<= 12+log (O/H) <=8.9. By using Cepheid
samples including more than 20 Cepheids, the chi^2 test indicates that the
hypothesis of a steepening of the P-L_{V,I} relations with increased
metallicity can be discarded at the 99% level. On the contrary, the observed
slopes agree with the metallicity trend predicted by pulsation models, i.e. the
slope is roughly constant for galaxies with 12+log (O/H) < 8.17 and becomes
shallower in the metal-rich regime, with a confidence level of 62% and 92%,
respectively. The chi^2 test concerning the hypothesis that the slope does not
depend on metallicity gives confidence levels either similar (P-L_V, 62%) or
smaller (P-L_I, 67%). We found that the slopes of optical and NIR
Period-Wesenheit (P-W) relations in external galaxies are similar to the slopes
of LMC. On this ground, the P-W relations provide robust distances relative to
the LMC, but theory and observations indicate that the metallicity dependence
of the zero-point in the different passbands has to be taken into account. We
compared the galaxy distances provided by Rizzi et al. (2007) using the TRGB
with our set of Cepheid distances based on the P-W relations. We found that the
metallicity correction on distances based on the P-WBV relation is
gamma_(B,V)=-0.52 mag dex^-1, whereas it is vanishing for the distances based
on the P-WVI and on the P-WJK relations. These findings fully support Cepheid
theoretical predictions.Comment: Paper accepted for publication on ApJ (21 pages, 16 figures)
How to boost clusters and regional change through cooperative social innovation
The aim of this paper is to illustrate how social innovation is promoted and spread by cooperative clusters in order to develop regional change. This paper focuses on the main drivers of the spreading and exaptation processes of social innovation. The cooperative cluster model, the exaptation concept, the top-down approach, the meso-institutions concept and the meso-level perspective are used to capture the strategic approach of spreading social innovation. The study analyses two successful clusters: Mondragon, made up of industrial SMEs, and Anecoop, an agricultural cooperative group, both leading clusters in their respective region. Qualitative methodology is used to compare both case studies. Among the findings, this paper is one of the first attempts to explain the territorial institutionalisation of social innovations by way of their exaptation. It presents adaptation and exaptation as distinct but partly sequential processes: the adaptation of social innovations in cooperative clusters paves the way for the subsequent leap via exaptation of these innovations in the whole of the territor
Optical and Near-Infrared UBVRIJHK Photometry for the RR Lyrae stars in the Nearby Globular Cluster M4 (NGC 6121)
We present optical and near-infrared UBVRIJHK photometry of stars in the
Galactic globular cluster M4 (NGC 6121) based upon a large corpus of
observations obtained mainly from public astronomical archives. We concentrate
on the RR Lyrae variable stars in the cluster, and make a particular effort to
accurately reidentify the previously discovered variables. We have also
discovered two new probable RR Lyrae variables in the M4 field: one of them by
its position on the sky and its photometric properties is a probable member of
the cluster, and the second is a probable background (bulge?) object. We
provide accurate equatorial coordinates for all 47 stars identified as RR
Lyraes, new photometric measurements for 46 of them, and new period estimates
for 45. We have also derived accurate positions and mean photometry for 34 more
stars previously identified as variable stars of other types, and for an
additional five non-RR Lyrae variable stars identified for the first time here.
We present optical and near-infrared color-magnitude diagrams for the cluster
and show the locations of the variable stars in them. We present the Bailey
(period-amplitude) diagrams and the period-frequency histogram for the RR Lyrae
stars in M4 and compare them to the corresponding diagrams for M5 (NGC 5904).
We conclude that the RR Lyrae populations in the two clusters are quite similar
in all the relevant properties that we have considered. The mean periods,
pulsation-mode ratios, and Bailey diagrams of these two clusters show support
for the recently proposed "Oosterhoff-neutral" classification.Comment: 33 pages, 16 figures, 7 table
Massive stellar systems: observational challenges and perspectives in the E-ELT era
We introduce the empirical framework concerning optical and near-infrared (NIR) photometry of crowded stellar fields. In particular, we address the impact that linear detectors and analytical PSF played in improving the accuracy and the precision of multi-band color-magnitude diagrams (CMDs). We focus our attention on recent findings based on deep NIR images collected with Adaptive Optics (AO) systems at the 8-10m class telescopes and discuss pros and cons of the different approaches. We also discuss the estimate of the absolute age of globular clusters using a well defined knee along the lower main sequence. We mention the role which the current AO-assisted instruments will have in addressing longstanding astrophysical problems of the Galactic center. Finally, we outline the role of first generation of E-ELT instruments upon photometry and spectroscopy of crowded stellar fields
On a new theoretical framework for RR Lyrae stars I: the metallicity dependence
We present new nonlinear, time-dependent convective hydrodynamical models of
RR Lyrae stars computed assuming a constant helium-to-metal enrichment ratio
and a broad range in metal abundances (Z=0.0001--0.02). The stellar masses and
luminosities adopted to construct the pulsation models were fixed according to
detailed central He burning Horizontal Branch evolutionary models. The
pulsation models cover a broad range in stellar luminosity and effective
temperatures and the modal stability is investigated for both fundamental and
first overtones. We predict the topology of the instability strip as a function
of the metal content and new analytical relations for the edges of the
instability strip in the observational plane. Moreover, a new analytical
relation to constrain the pulsation mass of double pulsators as a function of
the period ratio and the metal content is provided. We derive new
Period-Radius-Metallicity relations for fundamental and first-overtone
pulsators. They agree quite well with similar empirical and theoretical
relations in the literature. From the predicted bolometric light curves,
transformed into optical (UBVRI) and near-infrared (JHK) bands, we compute the
intensity-averaged mean magnitudes along the entire pulsation cycle and, in
turn, new and homogenous metal-dependent (RIJHK) Period-Luminosity relations.
Moreover, we compute new dual and triple band optical, optical--NIR and NIR
Period-Wesenheit-Metallicity relations. Interestingly, we find that the optical
Period-W(V,B-V) is independent of the metal content and that the accuracy of
individual distances is a balance between the adopted diagnostics and the
precision of photometric and spectroscopic datasets.Comment: 51 pages, 20 figures, 9 tables, accepted for publication on Ap
Performance analysis of the Level control with inverse response by using particle swarm optimization
Boiler is an important utility system to support operations in the industry. The control of water level in the steam drum is a complicated task due to the non-minimum phase (NMP), which possibly will cause instability to the controlled water level in the steam drum. Process identification and controller design are difficult tasks for the steam drum because of non-minimum phase. Following the previous literature, this paper proposed process identification to 3rd order transfer function and optimization of Proportional-Integral-Derivative (PID) tunings of the water level by using Particle Swarm Optimization (PSO). A Graphical User Interface (GUI) has been developed to provide a direct platform to deal with these tasks. The result of PSO is compared with other tuning methods in terms of performance indicator and index. An analysis of the performance curve in 3-dimension graphs is also presented to visualize the output performance of various proportional and integral gain settings. The study has concluded that PSO provided better PI tunings for the best control of the Heat Exchanger function in the LOOP-PRO software
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