The Origin of Fluorine: Abundances in AGB Carbon Stars Revisited

Revised spectroscopic parameters for the HF molecule and a new CN line list in the 2.3 mu region have been recently available, allowing a revision of the F content in AGB stars. AGB carbon stars are the only observationally confirmed sources of fluorine. Nowadays there is not a consensus on the relevance of AGB stars in its Galactic chemical evolution. The aim of this article is to better constrain the contribution of these stars with a more accurate estimate of their fluorine abundances. Using new spectroscopic tools and LTE spectral synthesis, we redetermine fluorine abundances from several HF lines in the K-band in a sample of Galactic and extragalactic AGB carbon stars of spectral types N, J and SC spanning a wide range of metallicities. On average, the new derived fluorine abundances are systematically lower by 0.33 dex with respect to previous determinations. This may derive from a combination of the lower excitation energies of the HF lines and the larger macroturbulence parameters used here as well as from the new adopted CN line list. Yet, theoretical nucleosynthesis models in AGB stars agree with the new fluorine determinations at solar metallicities. At low metallicities, an agreement between theory and observations can be found by handling in a different way the radiative/convective interface at the base of the convective envelope. New fluorine spectroscopic measurements agree with theoretical models at low and at solar metallicity. Despite this, complementary sources are needed to explain its observed abundance in the solar neighbourhood.Comment: 9 pages, 4 figures, accepted in A&

BCG vaccination and leprosy protection: review of current evidence and status of BCG in leprosy control.

The bacillus Calmette-Guérin (BCG) vaccine, initially developed to provide protection against TB, also protects against leprosy; and the magnitude of this effect varies. Previous meta-analyses did not provide a summary estimate of the efficacy due to the heterogeneity of the results. We conducted a meta-analysis of published data including recently published studies (up to June 2009) to determine the efficacy of BCG protection on leprosy and to investigate whether age at vaccination, clinical form, number of doses, type of study, the latitude of study area and year of publication influence the degree of efficacy and explain the variation. In the light of the results, we argue for more emphasis on the role of BCG vaccination in leprosy control and research

Spin-polarized transport in ferromagnetic multilayered semiconductor nanostructures

The occurrence of inhomogeneous spin-density distribution in multilayered ferromagnetic diluted magnetic semiconductor nanostructures leads to strong dependence of the spin-polarized transport properties on these systems. The spin-dependent mobility, conductivity and resistivity in (Ga,Mn)As/GaAs,(Ga,Mn)N/GaN, and (Si,Mn)/Si multilayers are calculated as a function of temperature, scaled by the average magnetization of the diluted magnetic semiconductor layers. An increase of the resistivity near the transition temperature is obtained. We observed that the spin-polarized transport properties changes strongly among the three materials.Comment: 3 pages, 4 figure

Is Λ\LambdaCDM an effective CCDM cosmology?

We show that a cosmology driven by gravitationally induced particle production of all non-relativistic species existing in the present Universe mimics exactly the observed flat accelerating $\Lambda$CDM cosmology with just one dynamical free parameter. This kind of scenario includes the creation cold dark matter (CCDM) model [Lima, Jesus & Oliveira, JCAP 011(2010)027] as a particular case and also provides a natural reduction of the dark sector since the vacuum component is not needed to accelerate the Universe. The new cosmic scenario is equivalent to $\Lambda$CDM both at the background and perturbative levels and the associated creation process is also in agreement with the universality of the gravitational interaction and equivalence principle. Implicitly, it also suggests that the present day astronomical observations cannot be considered the ultimate proof of cosmic vacuum effects in the evolved Universe because $\Lambda$CDM may be only an effective cosmology.Comment: 6 pages, 2 figures, changes in the abstract, introduction, new references and typo correction

Fluorine in a Carbon-Enhanced Metal-Poor Star

The fluorine abundance of the Carbon-Enhanced Metal-Poor (CEMP) star HE 1305+0132 has been derived by analysis of the molecular HF (1-0) R9 line at 2.3357 microns in a high-resolution (R = 50,000) spectrum obtained with the Phoenix spectrometer and Gemini-South telescope. Our abundance analysis makes use of a CNO-enhanced ATLAS12 model atmosphere characterized by a metallicity and CNO enhancements determined utilizing medium-resolution (R = 3,000) optical and near-IR spectra. The effective iron abundance is found to be [Fe/H] = -2.5, making HE 1305+0132 the most Fe-deficient star, by more than an order of magnitude, for which the abundance of fluorine has been measured. Using spectral synthesis, we derive a super-solar fluorine abundance of A(19F) = 4.96 +/- 0.21, corresponding to a relative abundance of [F/Fe] = 2.90. A single line of the Phillips C_2 system is identified in our Phoenix spectrum, and along with multiple lines of the first-overtone vibration-rotation CO (3-1) band head, C and O abundances of A(12C) = 8.57 +/- 0.11 and A(16O) = 7.04 +/- 0.14 are derived. We consider the striking fluorine overabundance in the framework of the nucleosynthetic processes thought to be responsible for the C-enhancement of CEMP stars and conclude that the atmosphere of HE 1305+0132 was polluted via mass transfer by a primary companion during its asymptotic giant branch phase. This is the first study of fluorine in a CEMP star, and it demonstrates that this rare nuclide can be a key diagnostic of nucleosynthetic processes in the early Galaxy.Comment: 13 pages, 3 figures; Accepted for publication in ApJ Letter