Precision limits of the twin-beam multiband URSULA

URSULA is a multiband astronomical photoelectric photometer which minimizes errors introduced by the presence of the atmosphere. It operates with two identical channels, one for the star to be measured and the other for a reference star. After a technical description of the present version of the apparatus, some measurements of stellar sources of different brightness, and in different atmospheric conditions are presented. These measurements, based on observations made with the 91 cm Cassegrain telescope of the Catania Astrophysical Observatory, are used to check the photometer accuracy and compare its performance with that of standard photometers

Lithium Depletion Boundary in a Pre-Main Sequence Binary System

A lithium depletion boundary is detected in HIP 112312 (GJ 871.1 A and B), a \~12 Myr old pre-main sequence binary system. A strong (EW 300 mA) Li 6708 A absorption feature is seen at the secondary (~M4.5) while no Li 6708 A feature is detected from the primary (~M4). The physical companionship of the two stars is confirmed from common proper motions. Current theoretical pre-main sequence evolutionary models cannot simultaneously match the observed colors, brightnesses, and Li depletion patterns of this binary system. At the age upper limit of 20 Myr, contemporary theoretical evolutionary models predict too slow Li depletion. If true Li depletion is a faster process than predicted by theoretical models, ages of open clusters (Pleiades, alpha Persei, and IC 2391) estimated from the Li depletion boundary method are all overestimated. Because of the importance of the open cluster age scale, development of self-consistent theoretical models to match the HIP 112312 data is desirable.Comment: Accepted in ApJL. 5 pages total (3 tables, 3 figures

Metabolic syndrome and insulin resistance in pre-pubertal children with psoriasis

Psoriasis in adults is associated with an increased risk of metabolic disease. Various cardiometabolic comorbidities have been reported in childhood psoriasis, but only a few studies have analyzed the prevalence of metabolic syndrome. We performed a single-center prospective study investigating the prevalence of metabolic syndrome and insulin resistance in children with psoriasis. The prevalence of metabolic syndrome was evaluated in 60 pre-pubertal children with psoriasis (age: 3\u201310 years), accordingly to recently established criteria for the diagnosis of metabolic syndrome in children. Insulin resistance was considered altered when the homeostatic model assessment (HOMA-IR) for insulin resistance was 65 90th sex- and age-specific percentile and HOMA 2-IR was > 1.8. Eighteen (30%) children with psoriasis were found to have metabolic syndrome. Sixteen (27%) children were found to have insulin resistance. Conclusion: Our data underline the importance of assessing metabolic syndrome not only in adults and adolescents but also in young children with psoriasis.What is Known:\u2022 Psoriasis in adults is strongly associated with metabolic disease and insulin resistance.\u2022 Very limited data are available on the prevalence of metabolic syndrome and insulin resistance in pre-pubertal children with psoriasis.What is New:\u2022 This study reports that in pre-pubertal children with psoriasis, there is a high prevalence of metabolic syndrome and insulin resistance.\u2022 In children with psoriasis metabolic syndrome risk factors should be assessed

Determination of squalene by-products during model compound vulcanization studies by LC-ESI-MS using silver nitrate as a post-column reagent

High Performance Liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI-MS) using silvernitrate as a post-column reagent has been used for the determination of squalene by-products during model compound vulcanization studies. In this method, after all by-products were separated by reverse-phase liquid chromatography, analytes formed complexes with silver cation by mixing with a silver nitrate solution. The positive ion ESI mass spectra of squalene, squalene by-products and intermediates of vulcanization process showed [M+Ag]+ and/or [M+Ag+AgNO3]+ ions. The method described in this paper overcomes the ESI technique limitations related to the ionization of hydrocarbon. Furthermore, results obtained working with this methodology helped to gain more insight into the natural rubber accelerated vulcanization process. In this sense the identification of the different crosslink types was determined, proving that the elution time increases with the decrease of sulfur chain length inthe crosslink. Squalene with pendant group was also identified

Probabilistic Quantum Memories

Typical address-oriented computer memories cannot recognize incomplete or noisy information. Associative (content-addressable) memories solve this problem but suffer from severe capacity shortages. I propose a model of a quantum memory that solves both problems. The storage capacity is exponential in the number of qbits and thus optimal. The retrieval mechanism for incomplete or noisy inputs is probabilistic, with postselection of the measurement result. The output is determined by a probability distribution on the memory which is peaked around the stored patterns closest in Hamming distance to the input.Comment: Revised version to appear in Phys. Rev. Let

Self-Enrichment in Globular Clusters: Is There a Role for the Super-Asymptotic Giant Branch Stars?

In four globular clusters (GCs) a non negligible fraction of stars can be interpreted only as a very helium rich population. The evidence comes from the presence of a "blue" main sequence in $\omega$ Cen and NGC 2808, and from the the very peculiar horizontal branch morphology in NGC 6441 and NGC 6388. Although a general consensus is emerging on the fact that self--enrichment is a common feature among GCs, the helium content required for these stars is Y\simgt0.35, and it is difficult to understand how it can be produced without any --or, for $\omega$ Cen, without a considerable--associated metal enhancement. We examine the possible role of super--AGB stars, and show that they may provide the required high helium. However, the ejecta of the most massive super--AGBs show a global CNO enrichment by a factor of $\simeq$4, due to the dredge--out process occurring at the second dredge up stage. If these clusters show no evidence for this CNO enrichment, we can rule out that at least the most massive super--AGBs evolve into O--Ne white dwarfs and take part in the formation of the second generation stars. This latter hypothesis may help to explain the high number of neutron stars present in GCs. The most massive super--AGBs would in fact evolve into electron--capture supernovae. Their envelopes would be easily ejected out of the cluster, but the remnant neutron stars remain into the clusters, thanks to their small supernova natal kicks.Comment: version accepted for publication in The Astrophysical Journal Letter

The early evolution of Globular Clusters: the case of NGC 2808

Enhancement and spread of helium among globular cluster stars have been recently suggested as a way to explain the horizontal branch blue tails, in those clusters which show a primordial spread in the abundances of CNO and other elements involved in advanced CNO burning (D'Antona et al. 2002). In this paper we examine the implications of the hypothesis that, in many globular clusters, stars were born in two separate events: an initial burst (first generation), which gives origin to probably all high and intermediate mass stars and to a fraction of the cluster stars observed today, and a second, prolonged star formation phase (second generation) in which stars form directly from the ejecta of the intermediate mass stars of the first generation. In particular, we consider in detail the morphology of the horizontal branch in NGC 2808 and argue that it unveils the early cluster evolution, from the birth of the first star generation to the end of the second phase of star formation. This framework provides a feasible interpretation for the still unexplained dichotomy of NGC 2808 horizontal branch, attributing the lack of stars in the RR Lyr region to the gap in the helium content between the red clump, whose stars are considered to belong to the first stellar generation and have primordial helium, and the blue side of the horizontal branch, whose minimum helium content reflects the helium abundance in the smallest mass (~4Msun)contributing to the second stellar generation. This scenario provides constraints on the required Initial Mass Function, in a way that a great deal of remnant neutron stars and stellar mass black holes might have been produced.Comment: 23 pages, 7 figures, in press on The Astrophysical Journa