Near-Infrared Spectroscopy of Carbon-Enhanced Metal-Poor Stars. I. A SOAR/OSIRIS Pilot Study

We report on an abundance analysis for a pilot study of seven Carbon-Enhanced Metal-Poor (CEMP) stars, based on medium-resolution optical and near-infrared spectroscopy. The optical spectra are used to estimate [Fe/H], [C/Fe], [N/Fe], and [Ba/Fe] for our program stars. The near-infrared spectra, obtained during a limited early science run with the new SOAR 4.1m telescope and the Ohio State Infrared Imager and Spectrograph (OSIRIS), are used to obtain estimates of [O/Fe] and 12C/13C. The chemical abundances of CEMP stars are of importance for understanding the origin of CNO in the early Galaxy, as well as for placing constraints on the operation of the astrophysical s-process in very low-metallicity Asymptotic Giant Branch (AGB) stars. This pilot study includes a few stars with previously measured [Fe/H], [C/Fe], [N/Fe],[O/Fe], 12C/13C, and [Ba/Fe], based on high-resolution optical spectra obtained with large-aperture telescopes. Our analysis demonstrates that we are able to achieve reasonably accurate determinations of these quantities for CEMP stars from moderate-resolution optical and near-infrared spectra. This opens the pathway for the study of significantly larger samples of CEMP stars in the near future. Furthermore, the ability to measure [Ba/Fe] for (at least the cooler) CEMP stars should enable one to separate stars that are likely to be associated with s-process enhancements (the CEMP-s stars) from those that do not exhibit neutron-capture enhancements (the CEMP-no stars).Comment: 27 pages, including 5 tables, 6 figures, accepted for publication in The Astronomical Journa

A new study of 25^{25}Mg(α\alpha,n)28^{28}Si angular distributions at EαE_\alpha = 3 - 5 MeV

The observation of $^{26}$Al gives us the proof of active nucleosynthesis in the Milky Way. However the identification of the main producers of $^{26}$Al is still a matter of debate. Many sites have been proposed, but our poor knowledge of the nuclear processes involved introduces high uncertainties. In particular, the limited accuracy on the $^{25}$Mg($\alpha$,n)$^{28}$Si reaction cross section has been identified as the main source of nuclear uncertainty in the production of $^{26}$Al in C/Ne explosive burning in massive stars, which has been suggested to be the main source of $^{26}$Al in the Galaxy. We studied this reaction through neutron spectroscopy at the CN Van de Graaff accelerator of the Legnaro National Laboratories. Thanks to this technique we are able to discriminate the ($\alpha$,n) events from possible contamination arising from parasitic reactions. In particular, we measured the neutron angular distributions at 5 different beam energies (between 3 and 5 MeV) in the \ang{17.5}-\ang{106} laboratory system angular range. The presented results disagree with the assumptions introduced in the analysis of a previous experiment.Comment: 9 pages, 9 figures - accepted by EPJ

Drug resistance in B and non-B subtypes amongst subjects recently diagnosed as primary/recent or chronic HIV-infected over the period 2013–2016: Impact on susceptibility to first-line strategies including integrase strand-transfer inhibitors

Objectives To characterize the prevalence of transmitted drug resistance mutations (TDRMs) by plasma analysis of 750 patients at the time of HIV diagnosis from January 1, 2013 to November 16, 2016 in the Veneto region (Italy), where all drugs included in the recommended first line therapies were prescribed, included integrase strand transfer inhibitors (InNSTI). Methods TDRMs were defined according to the Stanford HIV database algorithm. Results Subtype B was the most prevalent HIV clade (67.3%). A total of 92 patients (12.3%) were expected to be resistant to one drug at least, most with a single class mutation (60/68–88.2% in subtype B infected subjectsand 23/24–95.8% in non-B subjects) and affecting mainly NNRTIs. No significant differences were observed between the prevalence rates of TDRMs involving one or more drugs, except for the presence of E138A quite only in patients with B subtype and other NNRTI in subjects with non-B infection. The diagnosis of primary/recent infection was made in 73 patients (9.7%): they had almost only TDRMs involving a single class. Resistance to InSTI was studied in 484 subjects (53 with primary-recent infection), one patient had 143C in 2016, a total of thirteen 157Q mutations were detected (only one in primary/recent infection). Conclusions Only one major InSTI-TDRM was identified but monitoring of TDRMs should continue in the light of continuing presence of NNRTI-related mutation amongst newly diagnosed subjects, sometime impacting also to modern NNRTI drugs recommended in first-line therapy

Influence of shower fluctuations and primary composition on studies of the shower longitudinal development

We study the influence of shower fluctuations, and the possible presence of different nuclear species in the primary cosmic ray spectrum, on the experimental determination of both shower energy and the proton air inelastic cross section from studies of the longitudinal development of atmospheric showers in fluorescence experiments. We investigate the potential of track length integral and shower size at maximum as estimators of shower energy. We find that at very high energy (~10^19-10^20 eV) the error of the total energy assignment is dominated by the dependence on the hadronic interaction model, and is of the order of 5%. At lower energy (~10^17-10^18 eV), the uncertainty of the energy determination due to the limited knowledge of the primary cosmic ray composition is more important. The distribution of depth of shower maximum is discussed as a measure of the proton-air cross section. Uncertainties in a possible experimental measurement of this cross section introduced by intrinsic shower fluctuations, the model of hadronic interactions, and the unknown mixture of primary nuclei in the cosmic radiation are numerically evaluated.Comment: 12 pages, 11 figures, 4 table

A new FSA approach for in situ γ\gamma-ray spectroscopy

An increasing demand of environmental radioactivity monitoring comes both from the scientific community and from the society. This requires accurate, reliable and fast response preferably from portable radiation detectors. Thanks to recent improvements in the technology, $\gamma$-spectroscopy with sodium iodide scintillators has been proved to be an excellent tool for in-situ measurements for the identification and quantitative determination of $\gamma$-ray emitting radioisotopes, reducing time and costs. Both for geological and civil purposes not only $^{40}$K, $^{238}$U, and $^{232}$Th have to be measured, but there is also a growing interest to determine the abundances of anthropic elements, like $^{137}$Cs and $^{131}$I, which are used to monitor the effect of nuclear accidents or other human activities. The Full Spectrum Analysis (FSA) approach has been chosen to analyze the $\gamma$-spectra. The Non Negative Least Square (NNLS) and the energy calibration adjustment have been implemented in this method for the first time in order to correct the intrinsic problem related with the $\chi ^2$ minimization which could lead to artifacts and non physical results in the analysis. A new calibration procedure has been developed for the FSA method by using in situ $\gamma$-spectra instead of calibration pad spectra. Finally, the new method has been validated by acquiring $\gamma$-spectra with a 10.16 cm x 10.16 cm sodium iodide detector in 80 different sites in the Ombrone basin, in Tuscany. The results from the FSA method have been compared with the laboratory measurements by using HPGe detectors on soil samples collected in the different sites, showing a satisfactory agreement between them. In particular, the $^{137}$Cs isotopes has been implemented in the analysis since it has been found not negligible during the in-situ measurements.Comment: accepted by Science of Total Environment: 8 pages, 10 figures, 3 table

Impact of a revised 25^{25}Mg(p,γ\gamma)26^{26}Al reaction rate on the operation of the Mg-Al cycle

Proton captures on Mg isotopes play an important role in the Mg-Al cycle active in stellar H-burning regions. In particular, low-energy nuclear resonances in the $^{25}$Mg(p,$\gamma$)$^{26}$Al reaction affect the production of radioactive $^{26}$Al$^{gs}$ as well as the resulting Mg/Al abundance ratio. Reliable estimations of these quantities require precise measurements of the strengths of low-energy resonances. Based on a new experimental study performed at LUNA, we provide revised rates of the $^{25}$Mg(p,$\gamma$)$^{26}$Al$^{gs}$ and the $^{25}$Mg(p,$\gamma$)$^{26}$Al$^{m}$ reactions with corresponding uncertainties. In the temperature range 50 to 150 MK, the new recommended rate of the $^{26}$Al$^{m}$ production is up to 5 times higher than previously assumed. In addition, at T$=100$ MK, the revised total reaction rate is a factor of 2 higher. Note that this is the range of temperature at which the Mg-Al cycle operates in an H-burning zone. The effects of this revision are discussed. Due to the significantly larger $^{25}$Mg(p,$\gamma$)$^{26}$Al$^{m}$ rate, the estimated production of $^{26}$Al$^{gs}$ in H-burning regions is less efficient than previously obtained. As a result, the new rates should imply a smaller contribution from Wolf-Rayet stars to the galactic $^{26}$Al budget. Similarly, we show that the AGB extra-mixing scenario does not appear able to explain the most extreme values of $^{26}$Al/$^{27}$Al, i.e. $>10^{-2}$, found in some O-rich presolar grains. Finally, the substantial increase of the total reaction rate makes the hypothesis of a self-pollution by massive AGBs a more robust explanation for the Mg-Al anticorrelation observed in Globular-Cluster stars

A nested alignment graph kernel through the dynamic time warping framework

In this paper, we propose a novel nested alignment graph kernel drawing on depth-based complexity traces and the dynamic time warping framework. Specifically, for a pair of graphs, we commence by computing the depth-based complexity traces rooted at the centroid vertices. The resulting kernel for the graphs is defined by measuring the global alignment kernel, which is developed through the dynamic time warping framework, between the complexity traces. We show that the proposed kernel simultaneously considers the local and global graph characteristics in terms of the complexity traces, but also provides richer statistic measures by incorporating the whole spectrum of alignment costs between these traces. Our experiments demonstrate the effectiveness and efficiency of the proposed kernel

Activation measurement of the 3He(alpha,gamma)7Be cross section at low energy

The nuclear physics input from the 3He(alpha,gamma)7Be cross section is a major uncertainty in the fluxes of 7Be and 8B neutrinos from the Sun predicted by solar models and in the 7Li abundance obtained in big-bang nucleosynthesis calculations. The present work reports on a new precision experiment using the activation technique at energies directly relevant to big-bang nucleosynthesis. Previously such low energies had been reached experimentally only by the prompt-gamma technique and with inferior precision. Using a windowless gas target, high beam intensity and low background gamma-counting facilities, the 3He(alpha,gamma)7Be cross section has been determined at 127, 148 and 169 keV center-of-mass energy with a total uncertainty of 4%. The sources of systematic uncertainty are discussed in detail. The present data can be used in big-bang nucleosynthesis calculations and to constrain the extrapolation of the 3He(alpha,gamma)7Be astrophysical S-factor to solar energies

πNN\pi NN coupling determined beyond the chiral limit

Within the conventional QCD sum rules, we calculate the $\pi NN$ coupling constant, $g_{\pi N}$, beyond the chiral limit using two-point correlation function with a pion. We consider the Dirac structure, $i\gamma_5$, at $m_\pi^2$ order, which has clear dependence on the PS and PV coupling schemes for the pion-nucleon interactions. For a consistent treatment of the sum rule, we include the linear terms in quark mass as they constitute the same chiral order as $m_\pi^2$. Using the PS coupling scheme for the pion-nucleon interaction, we obtain $g_{\pi N}=13.3\pm 1.2$, which is very close to the empirical $\pi NN$ coupling. This demonstrates that going beyond the chiral limit is crucial in determining the coupling and the pseudoscalar coupling scheme is preferable from the QCD point of view.Comment: 8 pages, revtex, some errors are corrected, substantially revise

Neutron-induced background by an alpha-beam incident on a deuterium gas target and its implications for the study of the 2H(alpha,gamma)6Li reaction at LUNA

The production of the stable isotope Li-6 in standard Big Bang nucleosynthesis has recently attracted much interest. Recent observations in metal-poor stars suggest that a cosmological Li-6 plateau may exist. If true, this plateau would come in addition to the well-known Spite plateau of Li-7 abundances and would point to a predominantly primordial origin of Li-6, contrary to the results of standard Big Bang nucleosynthesis calculations. Therefore, the nuclear physics underlying Big Bang Li-6 production must be revisited. The main production channel for Li-6 in the Big Bang is the 2H(alpha,gamma)6Li reaction. The present work reports on neutron-induced effects in a high-purity germanium detector that were encountered in a new study of this reaction. In the experiment, an {\alpha}-beam from the underground accelerator LUNA in Gran Sasso, Italy, and a windowless deuterium gas target are used. A low neutron flux is induced by energetic deuterons from elastic scattering and, subsequently, the 2H(d,n)3He reaction. Due to the ultra-low laboratory neutron background at LUNA, the effect of this weak flux of 2-3 MeV neutrons on well-shielded high-purity germanium detectors has been studied in detail. Data have been taken at 280 and 400 keV alpha-beam energy and for comparison also using an americium-beryllium neutron source.Comment: Submitted to EPJA; 13 pages, 8 figure