860 research outputs found
Measuring mean densities of delta Scuti stars with asteroseismology. Theoretical properties of large separations using TOUCAN
We aim at studying the theoretical properties of the regular spacings found
in the oscillation spectra of delta Scuti stars. We performed a multi-variable
analysis covering a wide range of stellar structure and seismic properties and
model parameters representative of intermediate-mass, main sequence stars. The
work-flow is entirely done using a new Virtual Observatory tool: TOUCAN (the VO
gateway for asteroseismic models), which is presented in this paper. A linear
relation between the large separation and the mean density is predicted to be
found in the low frequency frequency domain (i.e. radial orders spanning from 1
to 8, approximately) of the main-sequence, delta Scuti stars' oscillation
spectrum. We found that such a linear behavior stands whatever the mass,
metallicity, mixing length, and overshooting parameters considered in this
work. The intrinsic error of the method is discussed. This includes the
uncertainty in the large separation determination and the role of rotation. The
validity of the relation found is only guaranteed for stars rotating up to 40
percent of their break-up velocity. Finally, we applied the diagnostic method
presented in this work to five stars for which regular patterns have been
found. Our estimates for the mean density and the frequency of the fundamental
radial mode match with those given in the literature within a 20 percent of
deviation. Asteroseismology has thus revealed an independent direct measure of
the average density of delta Scuti stars, analogous to that of the Sun. This
places tight constraints on the mode identification and hence on the stellar
internal structure and dynamics, and allows a determination the radius of
planets orbiting around delta Scuti stars with unprecedented precision. This
opens the way for studying the evolution of regular patterns in pulsating
stars, and its relation with stellar structure and evolution.Comment: 11 pages, 6 figures, A&A in pres
Sensitivity of the g-mode frequencies to pulsation codes and their parameters
From the recent work of the Evolution and Seismic Tools Activity (ESTA,
Lebreton et al. 2006; Monteiro et al. 2008), whose Task 2 is devoted to compare
pulsational frequencies computed using most of the pulsational codes available
in the asteroseismic community, the dependence of the theoretical frequencies
with non-physical choices is now quite well fixed. To ensure that the accuracy
of the computed frequencies is of the same order of magnitude or better than
the observational errors, some requirements in the equilibrium models and the
numerical resolutions of the pulsational equations must be followed. In
particular, we have verified the numerical accuracy obtained with the Saclay
seismic model, which is used to study the solar g-mode region (60 to
140Hz). We have compared the results coming from the Aarhus adiabatic
pulsation code (ADIPLS), with the frequencies computed with the Granada Code
(GraCo) taking into account several possible choices. We have concluded that
the present equilibrium models and the use of the Richardson extrapolation
ensure an accuracy of the order of in the determination of the
frequencies, which is quite enough for our purposes.Comment: 10 pages, 5 figures, accepted in Solar Physic
The burn severity and plant recovery relationship affect the biological and chemical soil properties of Pinus halepensis Mill. stands in the short and midterms after wildfire
In the Mediterranean Basin, changes in climate and fire regime (increased recurrence and severity) reduce
ecosystem services after wildfires by increasing soil degradation and losses in plant diversity. Our study was a
biological approach to relate soil properties to vegetation recovery and burn severity. We focused our study on
the natural recovery of the soil-plant interphase in Pinus halepensis Mill. forests located in the SE of Iberian
Peninsula, a semiarid climate. We included some chemical properties 3 years after fire (available phosphorus (P)
and soil organic carbon (Corg), among others), and biological soil indicators 3 and 5 years after fire (i.e. basal
soil respiration (BSR), microbial biomass carbon (Cmic), carbon mineralization coefficient (Cmineral), metabolic
quotient (qCO2) and microbial quotient (Cmic:Corg)). We analyzed the activity of three different enzymes: urease
(UR), phosphatase (PHP) and β-glucosidase (GLU).
The changes in most chemical properties were ephemeral, but P and Corg showed higher values in burned
areas, and the highest were found for low-moderate severity. Plant recovery was the triggering factor for the
recovery of Corg and biological soil function. Burn severity and time after fire influenced Cmic and the
Cmic:Corg, which were higher for moderate-high severity 3 years later, but were below the unburned values 5
years after fire. The microbial activities of GLU and UR were recovered in burned areas 5 years after fire. The
PHP values lowered according to higher burn severity and time after fire. The soil ecological trends obtained by a
principal component analysis revealed a relationship linking GLU, BSR and qCO2 that explained soil response to
burn severity. PHP, Cmic and Cmic:Corg explained most of the variability related to time after fire.
Our results provide insights into how burn severity, in Mediterranean fire-prone Aleppo pine stands,
modulated the natural plant recovery linked to soil biochemical and microbiological response to fire. High burn
severity limited natural vegetation recovery, and both reduced biological soil functionality. This knowledge can
be implemented in post-fire planning to apply post-fire management (for mitigation and restoration) in which
the “no intervention” tool should be contemplated. These findings provide information to be applied in adaptive
forest management to improve the resilience of vulnerable ecosystems and to reduce burn severity in future fire
events.This study was supported by a research award provided by the Instituto Estudios Albacetenses (IEA2016-Daniel Moya) and funds provided to the Forest Ecology Research Group by the University Castilla-La Mancha.The authors also thank the Spanish Institute for Agricultural and Food Research and Technology (INIA) for the funding awarded through National Research Projects GEPRIF (RTA2014-00011-C06), POSTFIRE_CARE (CGL2016-75178-C2-1-R) financed by the Spanish Research Agency (AIE), and the European Union for European Funding for Regional Development (FEDER)
A Hartree-Bose mean-field approximation for IBM-3
A Hartree-Bose mean-field approximation for the IBM-3 is presented. A Hartree-Bose transformation from the spherical to the deformed bosons with charge-dependent parameters is proposed which allows bosonic pair correlations and includes higher angular momentum bosons. The formalism contains previously proposed IBM-2 and IBM-3 intrinsic states as particular limits.Dirección General de Investigación Científica y Técnica PB 95/0123, PB95-0533European Commission CI1*-CT94-007
Trebouxia lynnae sp. nov. (former Trebouxia sp. TR9): biology and biogeography of an epitome lichen symbiotic microalga
Two microalgal species, Trebouxia jamesii and Trebouxia sp. TR9, were detected as the main photobionts coexisting in the thalli of the lichen Ramalina farinacea. Trebouxia sp. TR9 emerged as anew taxon in lichen symbioses and was successfully isolated and propagated in in vitro culture andthoroughly investigated. Several years of research have confirmed the taxon Trebouxia sp. TR9 tobe a model/reference organism for studying mycobiont–photobiont association patterns in lichensymbioses. Trebouxia sp. TR9 is the first symbiotic, lichen-forming microalga for which an exhaustivecharacterization of cellular ultrastructure, physiological traits, genetic and genomic diversity is available.The cellular ultrastructure was studied by light, electron and confocal microscopy; physiologicaltraits were studied as responses to different abiotic stresses. The genetic diversity was previouslyanalyzed at both the nuclear and organelle levels by using chloroplast, mitochondrial, and nucleargenome data, and a multiplicity of phylogenetic analyses were carried out to study its intraspecificdiversity at a biogeographical level and its specificity association patterns with the mycobiont.Here, Trebouxia sp. TR9 is formally described by applying an integrative taxonomic approach and ispresented to science as Trebouxia lynnae, in honor of Lynn Margulis, who was the primary modernproponent for the significance of symbiosis in evolution. The complete set of analyses that werecarried out for its characterization is provided
Hartree-Bose mean-field approximation for the interacting boson model (IBM-3)
A Hartree-Bose mean-field approximation for the IBM-3 is presented. A Hartree-Bose transformation from spherical to deformed bosons with charge-dependent parameters is proposed which allows bosonic pair correlations and includes higher angular momentum bosons. The formalism contains previously proposed IBM-2 and IBM-3 intrinsic states as particular limits.DGICYT PB95/0123 PB95–0533Comisión Europea CI1*-CT94-007
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