2,007 research outputs found
The Potassium abundance in the globular clusters NGC104, NGC6752 and NGC6809
We derived Potassium abundances in red giant branch stars in the Galactic
globular clusters NGC104 (144 stars), NGC6752 (134 stars) and NGC6809 (151
stars) using high-resolution spectra collected with FLAMES at the ESO - Very
Large Telescope. In the considered samples we do not find significant intrinsic
spreads in [K/Fe] (confirming the previous findings by Carretta et al.), at
variance with the cases of the massive clusters NGC2419 and NGC2808.
Additionally, marginally significant [K/Fe]-[O/Fe] anti-correlations are found
in NGC104 and NGC6809, and [K/Fe]-[Na/Fe] correlations are found in NGC104 and
NGC6752. No evidence of [K/Fe]-[Mg/Fe] anti-correlation are found. The results
of our analysis are consistent with a scenario in which the process leading to
the multi-populations in globular clusters implies also enrichment in the K
abundance, the amplitude of the associated [K/Fe] enhancement becoming
measurable only in stars showing the most extreme effects of O and Mg
depletion. Stars enhanced in [K/Fe] have been found so far only in clusters
harbouring some Mg-poor stars, while the other globulars, without a Mg-poor
sub-population, show small or null [K/Fe] spreads.Comment: 9 pages, 7 figures, 3 tables, accepted for publication in A&
The Red Giant Branch Tip and Bump of the Leo II dwarf spheroidal galaxy
We present V and I photometry of a 9.4' X 9.4' field centered on the dwarf
spheroidal galaxy Leo II. The Tip of the Red Giant Branch is identified at
I^{TRGB}=17.83 +/- 0.03 and adopting = -1.53 +/- 0.2 from the
comparison of RGB stars with Galactic templates, we obtain a distance modulus
(m-M)_0=21.84 +/- 0.13, corresponding to a distance D=233 +/- 15 Kpc. Two
significant bumps have been detected in the Luminosity Function of the Red
Giant Branch. The fainter bump (B1, at V=21.76 +/- 0.05) is the RGB bump of the
dominant stellar population, while the actual nature of the brightest one (B2,
at V=21.35 +/- 0.05) cannot be firmly assessed on the basis of the available
data, it can be due to the Asymptotic Giant Branch Clump of the main population
or it may be a secondary RGB bump. The luminosity of the main RGB bump (B1)
suggests that the majority of RGB stars in Leo II belongs to a population that
is ~4 gyr younger than the classical Galactic globular clusters. The stars
belonging to the He-burning Red Clump are shown to be significantly more
centrally concentrated than RR Lyrae and Blue Horizontal Branch stars, probing
the existence of an age/metallicity radial gradient in this remote dwarf
spheroidal.Comment: Accepted for publication by MNRAS. Latex, 10 pages, 8 .ps figure
Detection of a population gradient in the Sagittarius Stream
We present a quantitative comparison between the Horizontal Branch morphology
in the core of the Sagittarius dwarf spheroidal galaxy (Sgr) and in a wide
field sampling a portion of its tidal stream (Sgr Stream), located tens of kpc
away from the center of the parent galaxy. We find that the Blue Horizontal
Branch (BHB) stars in that part of the Stream are five times more abundant than
in the Sgr core, relative to Red Clump stars. The difference in the ratio of
BHB to RC stars between the two fields is significant at the 4.8 sigma level.
This indicates that the old and metal-poor population of Sgr was preferentially
stripped from the galaxy in past peri-Galactic passages with respect to the
intermediate-age metal rich population that presently dominates the bound core
of Sgr, probably due to a strong radial gradient that was settled within the
galaxy before its disruption. The technique adopted in the present study allows
to trace population gradients along the whole extension of the Stream.Comment: 4 pages, 3 .ps figures (fig. 1 at low resolution); Accepted for
publication by A&A Letter
Quantum field theory on quantum graphs and application to their conductance
We construct a bosonic quantum field on a general quantum graph. Consistency
of the construction leads to the calculation of the total scattering matrix of
the graph. This matrix is equivalent to the one already proposed using
generalized star product approach. We give several examples and show how they
generalize some of the scattering matrices computed in the mathematical or
condensed matter physics litterature.
Then, we apply the construction for the calculation of the conductance of
graphs, within a small distance approximation. The consistency of the
approximation is proved by direct comparison with the exact calculation for the
`tadpole' graph.Comment: 32 pages; misprints in tree graph corrected; proofs of consistency
and unitarity adde
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