2,429 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&
Stable self similar blow up dynamics for slightly L^2 supercritical NLS equations
We consider the focusing nonlinear Schr\"odinger equations in dimension and for slightly
supercritical nonlinearities p_c
with and 0<\e\ll 1. We prove the existence and stability in the energy space of a self similar finite time blow up dynamics and provide a qualitative description of the singularity formation near the blow up tim
General Conditions for Lepton Flavour Violation at Tree- and 1-Loop Level
In this work, we compile the necessary and sufficient conditions a theory has
to fulfill in order to ensure general lepton flavour conservation, in the
spirit of the Glashow-Weinberg criteria for the absence of flavour-changing
neutral currents. At tree-level, interactions involving electrically neutral
and doubly charged bosons are investigated. We also investigate flavour changes
at 1-loop level. In all cases we find that the essential theoretical
requirements can be reduced to a few basic conditions on the particle content
and the coupling matrices. For 1-loop diagrams, we also investigate how exactly
a GIM-suppression can occur that will strongly reduce the rates of lepton
flavour violating effects even if they are in principle present in a certain
theory. In all chapters, we apply our criteria to several models which can in
general induce lepton flavour violation, e.g. LR-symmetric models or the MSSM.
In the end we give a summarizing table of the obtained results, thereby
demonstrating the applicability of our criteria to a large class of models
beyond the Standard Model.Comment: 31 pages, 2 figure
Spectroscopic binaries among AGB stars from HERMES/Mercator: the case of V Hya
We report on our search for spectroscopic binaries among a sample of AGB
stars. Observations were carried out in the framework of the monitoring of
radial velocities of (candidate) binary stars performed at the Mercator 1.2m
telescope, using the HERMES spectrograph. We found evidence for duplicity in UV
Cam, TU Tau, BL Ori, VZ Per, T Dra, and V Hya. This short communication focus
on V Hya, found to behave like RV Tau of the b subtype, which are binaries
surrounded by a disc.Comment: Poster presented at IAU Symp. 343 "Why Galaxies Care About AGB
Stars", Vienna, august 201
IP Eri: A surprising long-period binary system hosting a He white dwarf
We determine the orbital elements for the K0 IV + white dwarf (WD) system IP
Eri, which appears to have a surprisingly long period of 1071 d and a
significant eccentricity of 0.25. Previous spectroscopic analyses of the WD,
based on a distance of 101 pc inferred from its Hipparcos parallax, yielded a
mass of only 0.43 M, implying it to be a helium-core WD. The orbital
properties of IP Eri are similar to those of the newly discovered long-period
subdwarf B star (sdB) binaries, which involve stars with He-burning cores
surrounded by extremely thin H envelopes, and are therefore close relatives to
He WDs. We performed a spectroscopic analysis of high-resolution spectra from
the HERMES/Mercator spectrograph and concluded that the atmospheric parameters
of the K0 component are K, , [Fe/H] = 0.09
and km/s. The detailed abundance analysis focuses on C, N, O
abundances, carbon isotopic ratio, light (Na, Mg, Al, Si, Ca, Ti) and s-process
(Sr, Y, Zr, Ba, La, Ce, Nd) elements. We conclude that IP Eri abundances agree
with those of normal field stars of the same metallicity. The long period and
non-null eccentricity indicate that this system cannot be the end product of a
common-envelope phase; it calls instead for another less catastrophic
binary-evolution channel presented in detail in a companion paper (Siess et al.
2014).Comment: 14 pages, 10 figures, 4 tables, accepted for publication in A&A
(Update of Table 3, Fig. 8 and text in Sect. 5.1, 5.3 and 6 due to minor
corrections on N and Y II
Potassium: a new actor on the globular cluster chemical evolution stage. The case of NGC 2808
We derive [K/Fe] abundance ratios for 119 stars in the globular cluster NGC
2808, all of them having O, Na, Mg and Al abundances homogeneously measured in
previous works. We detect an intrinsic star-to-star spread in the Potassium
abundance. Moreover [K/Fe] abundance ratios display statistically significant
correlations with [Na/Fe] and [Al/Fe], and anti-correlations with [O/Fe] and
[Mg/Fe]. All the four Mg deficient stars ([Mg/Fe]<0.0) discovered so far in NGC
2808 are enriched in K by ~0.3 dex with respect to those with normal [Mg/Fe].
NGC 2808 is the second globular cluster, after NGC 2419, where a clear Mg-K
anti-correlation is detected, albeit of weaker amplitude. The simultaneous
correlation/anti-correlation of [K/Fe] with all the light elements usually
involved in the chemical anomalies observed in globular cluster stars, strongly
support the idea that these abundance patterns are due to the same
self-enrichment mechanism that produces Na-O and Mg-Al anti-correlations. This
finding suggests that detectable spreads in K abundances may be typical in the
massive globular clusters where the self-enrichment processes are observed to
produce their most extreme manifestations.Comment: Accepted for publication by ApJ, 5 pages, 3 figure
Renormalization and blow up for charge one equivariant critical wave maps
We prove the existence of equivariant finite time blow up solutions for the
wave map problem from 2+1 dimensions into the 2-sphere. These solutions are the
sum of a dynamically rescaled ground-state harmonic map plus a radiation term.
The local energy of the latter tends to zero as time approaches blow up time.
This is accomplished by first "renormalizing" the rescaled ground state
harmonic map profile by solving an elliptic equation, followed by a
perturbative analysis
Tomography of the red supergiant star {\mu} Cep
A tomographic method, aiming at probing velocity fields at depth in stellar
atmospheres, is applied to the red supergiant star {\mu} Cep and to snapshots
of 3D radiative-hydrodynamics simulation in order to constrain atmospheric
motions and relate them to photometric variability.Comment: 2 pages, 2 figures, accepted as Proceedings of IAU Symposium No. 343,
201
Improved Limit on theta_{13} and Implications for Neutrino Masses in Neutrino-less Double Beta Decay and Cosmology
We analyze the impact of a measurement, or of an improved bound, on
theta_{13} for the determination of the effective neutrino mass in
neutrino-less double beta decay and cosmology. In particular, we discuss how an
improved limit on (or a specific value of) theta_{13} can influence the
determination of the neutrino mass spectrum via neutrino-less double beta
decay. We also discuss the interplay with improved cosmological neutrino mass
searches.Comment: 22 pages, 5 figures. Minor corrections, matches version in PR
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