1,050 research outputs found
Sobre la vegetación de la alianza Cistion laurifolii en los alrededores de Valencia
Se da a conocer la presencia, en la provincia de Valencia y zonas limítrofes, de comunidades fruticosas silicícolas pertenecientes a la alianza Cistion laurifolii; las cuales quedan encuadradas en tres asociaciones, una de ellas ya conocida de áreas cercanas: Erico scopariae-Cistetum populifolii, y otras dos nuevas: Thymo leplophylli-Cistetum ladaniferi y Erico scopariae-Arctostaphylletum crassifoliae.The presence of shrubyacidophilous communities, in Valencia region, belonging to the phytosociological alliance Cistion laurifolii, is studied. The are aranged in three associations: Erico scopariae-Arctostaphylletum crassifoliae, the two last of them are [email protected] ; carjua(a)uv.e
Homogeneous Photometry VI: Variable Stars in the Leo I Dwarf Spheroidal Galaxy
We have characterized the pulsation properties of 164 candidate RR Lyrae
variables (RRLs) and 55 candidate Anomalous and/or short-period Cepheids in Leo
I dwarf spheroidal galaxy. On the basis of its RRLs Leo I is confirmed to be an
Oosterhoff-intermediate type galaxy, like several other dwarfs. We show that in
their pulsation properties, the RRLs representing the oldest stellar population
in the galaxy are not significantly different from those of five other nearby,
isolated dwarf spheroidal galaxies. A similar result is obtained when comparing
them to RR Lyrae stars in recently discovered ultra-faint dwarf galaxies. We
are able to compare the period distributions and period-amplitude relations for
a statistically significant sample of ab type RR Lyrae stars in dwarf galaxies
(~1300stars) with those in the Galactic halo field (~14,000stars) and globular
clusters (~1000stars). Field RRLs show a significant change in their period
distribution when moving from the inner (dG14kpc)
halo regions. This suggests that the halo formed from (at least) two dissimilar
progenitors or types of progenitor. Considered together, the RRLs in classical
dwarf spheroidal and ultra-faint dwarf galaxies-as observed today-do not appear
to follow the well defined pulsation properties shown by those in either the
inner or the outer Galactic halo, nor do they have the same properties as RRLs
in globular clusters. In particular, the samples of fundamental-mode RRLs in
dwarfs seem to lack High Amplitudes and Short Periods ("HASP":AV>1.0mag and P
<0.48d) when compared with those observed in the Galactic halo field and
globular clusters. The observed properties of RRLs do not support the idea that
currently existing classical dwarf spheroidal and ultra-faint dwarf galaxies
are surviving representative examples of the original building blocks of the
Galactic halo.Comment: 49 pages in referee format, 12 figure
Bounded Delay and Concurrency for Earliest Query Answering
International audienceEarliest query answering is needed for streaming XML processing with optimal memory management. We study the feasibility of earliest query answering for node selection queries. Tractable queries are distinguished by a bounded number of concurrently alive answer candidates at every time point, and a bounded delay for node selection. We show that both properties are decidable in polynomial time for queries defined by deterministic automata for unranked trees. Our results are obtained by reduction to the bounded valuedness problem for recognizable relations between unranked trees
The ACS LCID project. IX. Imprints of the early Universe in the radial variation of the star formation history of dwarf galaxies
Based on Hubble Space Telescope observations from the Local Cosmology from
Isolated Dwarfs project, we present the star formation histories, as a function
of galactocentric radius, of four isolated Local Group dwarf galaxies: two dSph
galaxies, Cetus and Tucana, and two transition galaxies (dTrs), LGS-3 and
Phoenix. The oldest stellar populations of the dSphs and dTrs are, within the
uncertainties, coeval () at all galactocentric radii. We find that
there are no significative differences between the four galaxies in the
fundamental properties (such as the normalized star formation rate or
age-metallicity relation) of their outer regions (radii greater than four
exponential scale lengths); at large radii, these galaxies consist exclusively
of old () metal-poor stars. The duration of star formation in
the inner regions vary from galaxy to galaxy, and the extended central star
formation in the dTrs produces the dichotomy between dSph and dTr galaxy types.
The dTr galaxies show prominent radial stellar population gradients: the
centers of these galaxies host young () populations while the age
of the last formation event increases smoothly with increasing radius. This
contrasts with the two dSph galaxies. Tucana shows a similar, but milder,
gradient, but no gradient in age is detected Cetus. For the three galaxies with
significant stellar population gradients, the exponential scale length
decreases with time. These results are in agreement with outside-in scenarios
of dwarf galaxy evolution, in which a quenching of the star formation toward
the center occurs as the galaxy runs out of gas in the outskirts.Comment: Accepted to be published in Ap
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