4,927 research outputs found
Young and embedded clusters in Cygnus-X: evidence for building up the IMF?
We provide a new view on the Cygnus-X north complex by accessing for the
first time the low mass content of young stellar populations in the region.
CFHT/WIRCam camera was used to perform a deep near-IR survey of this complex,
sampling stellar masses down to ~0.1 M. Several analysis tools,
including a extinction treatment developed in this work, were employed to
identify and uniformly characterise a dozen unstudied young star clusters in
the area. Investigation of their mass distributions in low-mass domain revealed
a relatively uniform log-normal IMF with a characteristic mass of 0.320.08
M and mass dispersion of 0.400.06. In the high mass regime, their
derived slopes showed that while the youngest clusters (age < 4 Myr) presented
slightly shallower values with respect to the Salpeter's, our older clusters (4
Myr < age < 18 Myr) showed IMF compliant values and a slightly denser stellar
population. Although possibly evidencing a deviation from an 'universal' IMF,
these results also supports a scenario where these gas dominated young clusters
gradually 'build up' their IMF by accreting low-mass stars formed in their
vicinity during their first ~3 Myr, before the gas expulsion phase, emerging at
the age of ~4 Myr with a fully fledged IMF. Finally, the derived distances to
these clusters confirmed the existence of at least 3 different star forming
regions throughout Cygnus-X north complex, at distances of 500-900 pc, 1.4-1.7
kpc and 3.0 kpc, and revealed evidence of a possible interaction between some
of these stellar populations and the Cygnus-OB2 association.Comment: 20 pages, 19 figures. Contains an appendix with 10 extra figure
Mass distribution and structural parameters of Small Magellanic Cloud star clusters
In this work we estimate, for the first time, the total masses and mass
function slopes of a sample of 29 young and intermediate-age SMC clusters from
CCD Washington photometry. We also derive age, interstellar reddening and
structural parameters for most of the studied clusters by employing a
statistical method to remove the unavoidable field star contamination. Only
these 29 clusters out of 68 originally analysed cluster candidates present
stellar overdensities and coherent distribution in their colour-magnitude
diagrams compatible with the existence of a genuine star cluster. We employed
simple stellar population models to derive general equations for estimating the
cluster mass based only on its age and integrated light in the B, V, I, C and
T1 filter. These equations were tested against mass values computed from
luminosity functions, showing an excellent agreement. The sample contains
clusters with ages between 60 Myr and 3 Gyr and masses between 300 and 3000 Mo
distributed between ~0.5 deg. and ~2 deg. from the SMC optical centre. We
determined mass function slopes for 24 clusters, of which 19 have slopes
compatible with that of Kroupa IMF (2.3 +/- 0.7), considering the
uncertainties. The remaining clusters - H86-188, H86-190, K47, K63 and NGC242 -
showed flatter MFs. Additionally, only clusters with masses lower than ~1000 Mo
and flatter MF were found within ~0.6 deg. from the SMC rotational centre.Comment: 12 pages, 19 figures. Includes another 29 full-page figures of
supplementary material. Accepted for publication in the MNRA
Incomplete Transition Complexity of Basic Operations on Finite Languages
The state complexity of basic operations on finite languages (considering
complete DFAs) has been in studied the literature. In this paper we study the
incomplete (deterministic) state and transition complexity on finite languages
of boolean operations, concatenation, star, and reversal. For all operations we
give tight upper bounds for both description measures. We correct the published
state complexity of concatenation for complete DFAs and provide a tight upper
bound for the case when the right automaton is larger than the left one. For
all binary operations the tightness is proved using family languages with a
variable alphabet size. In general the operational complexities depend not only
on the complexities of the operands but also on other refined measures.Comment: 13 page
The Seyfert Population in the Local Universe
The magnitude-limited catalog of the Southern Sky Redshift Survey (SSRS2), is
used to characterize the properties of galaxies hosting Active Galactic Nuclei.
Using emission-line ratios, we identify a total of 162 (3%) Seyfert galaxies
out of the parent sample with 5399 galaxies. The sample contains 121 Seyfert 2
galaxies and 41 Seyfert 1. The SSRS2 Seyfert galaxies are predominantly in
spirals of types Sb and earlier, or in galaxies with perturbed appearance as
the result of strong interactions or mergers. Seyfert galaxies in this sample
are twice as common in barred hosts than the non-Seyferts. By assigning
galaxies to groups using a percolation algorithm we find that the Seyfert
galaxies in the SSRS2 are more likely to be found in binary systems, when
compared to galaxies in the SSRS2 parent sample. However, there is no
statistically significant difference between the Seyfert and SSRS2 parent
sample when systems with more than 2 galaxies are considered. The analysis of
the present sample suggests that there is a stronger correlation between the
presence of the AGN phenomenon with internal properties of galaxies
(morphology, presence of bar, luminosity) than with environmental effects
(local galaxy density, group velocity dispersion, nearest neighbor distance).Comment: 35 pages, 13 figures, Accepted to be publised in Astronomical Journa
Coupled quintessence and vacuum decay
We discuss observational consequences of a class of cosmological models
characterized by the dilution of pressureless matter attenuated with respect to
the usual scaling due to the decay of vacuum energy. We carry out a
joint statistical analysis of observational data from the new \emph{gold}
sample of 182 SNe Ia, recent estimates of the CMB shift parameter, and BAO
measurements from the SDSS to show that such models favor the decay of vacuum
only into the dark matter sector, and that the separately conserved baryons
cannot be neglected. In order to explore ways to more fundamentally motivated
models, we also derive a coupled scalar field version for this general class of
vacuum decay scenarios.Comment: 6 pages, 3 figures, LaTe
GeMs/GSAOI observations of La Serena 94: an old and far open cluster inside the solar circle
Physical properties were derived for the candidate open cluster La Serena 94,
recently unveiled by the VVV collaboration. Thanks to the exquisite angular
resolution provided by GeMS/GSAOI, we could characterize this system in detail,
for the first time, with deep photometry in JHK - bands. Decontaminated
JHK diagrams reach about 5 mag below the cluster turnoff in H. The locus
of red clump giants in the colour - colour diagram, together with an extinction
law, was used to obtain an average extinction of . The
same stars were considered as standard - candles to derive the cluster
distance, kpc. Isochrones were matched to the cluster colour -
magnitude diagrams to determine its age, , and
metallicity, . A core radius of pc was
found by fitting King models to the radial density profile. By adding up the
visible stellar mass to an extrapolated mass function, the cluster mass was
estimated as M, consistent with an
integrated magnitude of and a tidal radius of
pc. The overall characteristics of La Serena 94 confirm that
it is an old open cluster located in the Crux spiral arm towards the fourth
Galactic quadrant and distant kpc from the Galactic centre. The
cluster distorted structure, mass segregation and age indicate that it is a
dynamically evolved stellar system.Comment: 16 pages, 24 figures, 2 Tables, accepted by MNRAS; corrected typo
Aromatic L-Aminoacid Decarboxylase Deficiency A Defect of the Neurotransmitter Metabolism with Severe Neurological Impairment
A descarboxilase dos L-aminoácidos aromáticos, um enzima piridoxina dependente, é responsável pela conversão da L-dopa em dopamina e do 5 hidroxitriptofano em serotonina. A deficiência desse enzima, um erro inato do metabolismo dos neurotransmissores, resulta numa doença autossómica recessiva com manifestações neurológicas graves.
Os dois casos apresentados de deficiência da descarboxilase dos L-aminoácidos aromáticos, entidade pela primeira vez descrita no nosso país, apresentam características clínicas semelhantes,
resultantes da disfunção do metabolismo aminérgico: hipotonia, distonia, atraso no desenvolvimento psicomotor, episódios de
movimentos oculógiros, irritabilidade e instabilidade vasomotora.
A tomografia computadorizada e a ressonância magnética cerebrais foram normais em ambos os casos. Os exames bioquímicos e o estudo da actividade enzimática permitiram fazer o diagnóstico
de deficiência da descarboxilase dos L-aminoácidos aromáticos.
O nosso objectivo é chamar a atenção para a necessidade de investigar os defeitos do metabolismo dos neurotransmilissores na
presença de Uma doença neurológica crónica sem etiologia conhecida. A importância de colocar este diagnóstico diferencial, o
mais precocemente possível, advém das possibilidades de terapêutica, aconselhamento genético adequado e diagnóstico pré-natal, já hoje existentes
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