4,071 research outputs found
Evidence of the inhomogeneity of the stellar population in the differentially reddened globular cluster NGC 3201
We report on evidence of the inhomogeneity (multiplicity) of the stellar
population in the Galactic globular cluster (GC) NGC 3201, which is irregularly
reddened across its face. We carried out a more detailed and careful analysis
of our recently published new multi-color photometry in a wide field of the
cluster with particular emphasis on the U band. Using the photometric data
corrected for differential reddening, we found for the first time two key signs
of the inhomogeneity in the cluster's stellar population and of its radial
variation in the GC. These are (1) an obvious trend in the color-position
diagram, based on the (U-B) color-index, of red giant branch (RGB) stars, which
shows that the farther from the cluster's center, the bluer on average the
(U-B) color of the stars is; and (2) the dependence of the radial distribution
of sub-giant branch (SGB) stars in the cluster on their U magnitude, where
brighter stars are less centrally concentrated than their fainter counterparts
at a confidence level varying between 99.2% and 99.9% depending on the
color-index used to select the stars. The same effects were recently found by
us in the GC NGC 1261. However, contrary to NGC 1261, we are not able to
unambiguously suggest which of the sub-populations of SGB/RGB stars can be the
progenitor of blue and red horizontal branch stars of the cluster. Apart from
M4, NGC 3201 is another GC very probably with an inhomogeneous stellar
population, which has essentially lower mass than the most massive Galactic GCs
where multiple stellar populations were unambiguously detected for the first
timeComment: 5 pages, 4 figure
One-point statistics and intermittency of induced electric field in the solar wind
The interplanetary induced electric field e=vxb is studied, using solar wind
time series. The probability distribution functions (PDFs) of the electric
field components are measured from the data and their non-gaussianity is
discussed. Moreover, for the first time we show that the electric field
turbulence is characterized by intermittency. This point is addressed by
studying, as usual, the scaling of the PDFs of field increments, which allows a
quantitative characterization of intermittency.Comment: Accepted for publication on Europhysics Letters, April 22th, 200
Galactic globular cluster 47 Tucanae: new ties between the chemical and dynamical evolution of globular clusters?
It is generally accepted today that Galactic globular clusters (GGCs) consist
of at least two generations of stars that are different in their chemical
composition and perhaps age. However, knowledge about the kinematical
properties of these stellar generations, which may provide important
information for constraining evolutionary scenarios of the GGCs, is still
limited. We therefore study the connections between chemical and kinematical
properties of different stellar generations in the Galactic globular cluster 47
Tuc. To achieve this goal, we used abundances of Li, O, and Na determined in
101 main sequence turn-off (TO) stars with the aid of 3D hydrodynamical model
atmospheres and NLTE abundance analysis methodology. We divided our sample TO
stars into three groups according to their position in the [Li/Na]-[Na/O] plane
to study their spatial distribution and kinematical properties. We find that
there are statistically significant radial dependencies of lithium and oxygen
abundances, A(Li) and A(O), as well as that of [Li/Na] abundance ratio. Our
results show that first-generation stars are less centrally concentrated and
dynamically hotter than stars belonging to subsequent generations. We also find
a significant correlation between the velocity dispersion and O and Na
abundance, and between the velocity dispersion and the [Na/O] abundance ratio.Comment: 4 pages, 6 figures, accepted for publication in A&
Rotational splitting as a function of mode frequency for six Sun-like stars
Asteroseismology offers the prospect of constraining differential rotation in
Sun-like stars. Here we have identified six high signal-to-noise main-sequence
Sun-like stars in the Kepler field, which all have visible signs of rotational
splitting of their p-mode frequencies. For each star, we extract the rotational
frequency splitting and inclination angle from separate mode sets (adjacent
modes with l=2, 0, and 1) spanning the p-mode envelope. We use a Markov chain
Monte Carlo method to obtain the best fit and errors associated with each
parameter. We are able to make independent measurements of rotational
splittings of ~8 radial orders for each star. For all six stars, the measured
splittings are consistent with uniform rotation, allowing us to exclude large
radial differential rotation. This work opens the possibility of constraining
internal rotation of Sun-like stars.Comment: Published in Astronomy and Astrophysics. 4 pages, 3 figure
Constraints on mass loss and self-enrichment scenarios for the globular clusters of the Fornax dSph
Recently, high-dispersion spectroscopy has demonstrated conclusively that
four of the five globular clusters (GCs) in the Fornax dwarf spheroidal galaxy
are very metal-poor with [Fe/H]<-2. The remaining cluster, Fornax 4, has
[Fe/H]=-1.4. This is in stark contrast to the field star metallicity
distribution which shows a broad peak around [Fe/H]=-1 with only a few percent
of the stars having [Fe/H]<-2. If we only consider stars and clusters with
[Fe/H]<-2 we thus find an extremely high GC specific frequency, SN=400,
implying by far the highest ratio of GCs to field stars known anywhere. We
estimate that about 1/5-1/4 of all stars in the Fornax dSph with [Fe/H]<-2
belong to the four most metal-poor GCs. These GCs could, therefore, at most
have been a factor of 4-5 more massive initially. Yet, the Fornax GCs appear to
share the same anomalous chemical abundance patterns known from Milky Way GCs,
commonly attributed to the presence of multiple stellar generations within the
clusters. The extreme ratio of metal-poor GC- versus field stars in the Fornax
dSph is difficult to reconcile with scenarios for self-enrichment and early
evolution of GCs in which a large fraction (90%-95%) of the first-generation
stars have been lost. It also suggests that the GCs may not have formed as part
of a larger population of now disrupted clusters with an initial power-law mass
distribution. The Fornax dSph may be a rosetta stone for constraining theories
of the formation, self-enrichment and early dynamical evolution of star
clusters.Comment: 4 pages, 2 figures, accepted for A&A Letter
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