The effect of heavy element opacity on pre-main sequence Li depletion

Recent 3-D analysis of the solar spectrum data suggests a significant change of the solar chemical composition. This may affect the temporal evolution of the surface abundance of light elements since the extension of the convective envelope is largely affected by the internal opacity value. We analyse the influence of the adopted solar mixture on the opacity in the convective envelope of pre-main sequence (PMS) stars and thus on PMS lithium depletion. The surface Li abundance depends on the relative efficiency of several processes, some of them still not known with the required precision; this paper thus analyses one of the aspects of this ``puzzle''. Focusing on PMS evolution, where the largest amount of Li burning occurs, we computed stellar models for three selected masses (0.8, 1.0 and 1.2 Msun, with Z=0.013, Y=0.27, alpha=1.9) by varying the chemical mixture, that is the internal element distribution in Z. We analysed the contribution of the single elements to the opacity at the temperatures and densities of interest for Li depletion. Several mixtures were obtained by varying the abundance of the most important elements one at a time; we then calculated the corresponding PMS Li abundance evolution. We found that a mixture variation does change the Li abundance: at fixed total metallicity, the Li depletion increases when increasing the fraction of elements heavier than O.Comment: A&A accepted, 11 pages, 18 eps figure

Collecting data through high throughput in vitro early toxicity and off-target liability assays to rapidly identify limitations of novel thyromimetics

In order to rapidly identify the phenotypic profile and possible off-target liability effects of novel synthesized thyromimetics for selection of lead compounds for further optimization studies, we performed in vitro screening on a new small library of synthetic thyromimetics. A comprehensive panel of early toxicity assays comprising cytotoxicity on 4 different cell lines (osteosarcoma, U2OS; lung fibroblast, hTERT; human breast adenocarcinoma, MCF7; human embryonic kidney, HEK293), hERG liability, cytochrome P450 inhibition (CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A4 isoforms), and off-target liability against selected proteins (Aurora B kinase and phosphodiesterase PDE4C1) and epigenetic enzymes (HDAC4, HDAC6, HDAC8, HDAC9 & SIRT7). All the compounds were screened at 10 μM in at least triplicate using well-established in vitro assays with readouts in luminescence or fluorescence polarization mode. The raw data were processed using Microsoft Excel and the Z′ for each assay was calculated (acceptable Z' >0.40). The processed and normalized data were organized in tables and visualized using spider plots. The results which are reported in the present manuscript can be used in prediction studies of early toxicity and off-target liabilities of other thyromimetics using in silico methods. The data reported herein support our research article entitled “Design, synthesis and biological evaluation of novel TRβ selective agonists sustained by ADME-Toxicity analysis” by Runfola M., Sestito S., et al. [1

A New Fast Silicon Photomultiplier Photometer

The realization of low-cost instruments with high technical performance is a goal which deserves some efforts in an epoch of fast technological developments: indeed such instruments can be easily reproduced and therefore allow to open new research programs in several Observatories. We realized a fast optical photometer based on the SiPM technology, using commercially available modules. Using low-cost components we have developed a custom electronic chain to extract the signal produced by a commercial MPPC module produced by Hamamatsu, in order to obtain sub millisecond sampling of the light curve of astronomical sources, typically pulsars. In the early February 2011 we observed the Crab Pulsar at the Cassini telescope with our prototype photometer, deriving its period, power spectrum and shape of its light curve in very good agreement with the results obtained in the past with other instruments.Comment: Accepted for Publications of the Astronomical Society of Pacific (PASP), 8 pages, 8 figure

Open clusters as key tracers of Galactic chemical evolution. III. Element abundances in Berkeley 20, Berkeley 29, Collinder 261, and Melotte 66

Galactic open clusters are since long recognized as one of the best tools for investigating the radial distribution of iron and other metals. We employed FLAMES at VLT to collect UVES spectra of bright giant stars in a large sample of open clusters, spanning a wide range of Galactocentric distances, ages, and metallicities. We present here the results for four clusters: Berkeley 20 and Berkeley 29, the two most distant clusters in the sample; Collinder 261, the oldest and the one with the minimum Galactocentric distance; Melotte 66. Equivalent width analysis was carried out using the spectral code MOOG and Kurucz model atmospheres to derive abundances of Fe, Al, Mg, Si, Ca, Ti, Cr, Ni, Ba; non-LTE Na abundances were derived by direct line-profile fitting. We obtain subsolar metallicities for the two anticenter clusters Be 20 ([Fe/H]=-0.30, rms=0.02) and Be 29 ([Fe/H]=-0.31, rms=0.03), and for Mel 66 ([Fe/H]=-0.33, rms=0.03), located in the third Galactic quadrant, while Cr 261, located toward the Galactic center, has higher metallicity ([Fe/H]=+0.13, rms=0.05 dex). The alpha-elements Si, Ca and Ti, and the Fe-peak elements Cr and Ni are in general close to solar; the s-process element Ba is enhanced. Non-LTE computations of Na abundances indicate solar scaled values, suggesting that the enhancement in Na previously determined in giants in open clusters could be due to neglected non-LTE effects. Our results support the presence of a steep negative slope of the Fe radial gradient up to about 10-11 kpc from the Galactic center, while in the outer disk the [Fe/H] distribution seems flat. All the elemental ratios measured are in very good agreement with those found for disk stars of similar metallicity and no trend with Galactocentric distance seems to be present.Comment: Accepted for publication on A&

Element abundances in the metal rich open cluster NGC6253

We have carried out a big FLAMES survey of 10 Galactic open clusters aiming at different goals. One of them is the determination of chemical abundances, in order to put constraints on the radial metallicity gradient in the disk and its evolution. One of the sample clusters is the very metal rich NGC 6253. We have obtained UVES high resolution spectra of seven candidate cluster members (from the turn off up to the red clump) with the goal of determining the chemical composition of NGC 6253 and to investigate its origin and role in the interpretation of the radial metallicity gradient in the disk. Equivalent width analysis and spectral synthesis were performed using MOOG and Kurucz model atmospheres. We derived abundances of Fe, alpha- and Fe-peak elements, the light element Na and the s-process element Ba. Excluding two likely non-members and the clump giant, whose metallicity from equivalent widths is overestimated, we find an average [Fe/H]=+0.36+/-0.07 (rms) for the cluster. For most of the other elements we derive solar abundance ratios.Comment: accepted by A&A (02/01/2007), 21 pages, 11 ps figure

The evolution of the Galactic metallicity gradient from high-resolution spectroscopy of open clusters

Open clusters offer a unique possibility to study the time evolution of the radial metallicity gradients of several elements in our Galaxy, because they span large intervals in age and Galactocentric distance, and both quantities can be more accurately derived than for field stars. We re-address the issue of the Galactic metallicity gradient and its time evolution by comparing the empirical gradients traced by a sample of 45 open clusters with a chemical evolution model of the Galaxy. At variance with previous similar studies, we have collected from the literature only abundances derived from high--resolution spectra. The clusters have distances $7 < RGC<22$ kpc and ages from $\sim 30$ Myr to 11 Gyr. We also consider the $\alpha$-elements Si, Ca, Ti, and the iron-peak elements Cr and Ni. The data for iron-peak and $\alpha$-elements indicate a steep metallicity gradient for R_GC<12$kpc and a plateau at larger radii. The time evolution of the metallicity distribution is characterized by a uniform increase of the metallicity at all radii, preserving the shape of the gradient, with marginal evidence for a flattening of the gradient with time in the radial range 7-12 kpc. Our model is able to reproduce the main features of the metallicity gradient and its evolution with an infall law exponentially decreasing with radius and with a collapse time scale of the order of 8 Gyr at the solar radius. This results in a rapid collapse in the inner regions, i.e.$R_{\rm GC}\lesssim 12$ kpc (that we associate with an early phase of disk formation from the collapse of the halo) and in a slow inflow of material per unit area in the outer regions at a constant rate with time.Comment: 16 pages, 18 figures, A&A accepte

Old open clusters as key tracers of Galactic chemical evolution. First results: NGC 3960

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Element abundances of unevolved stars in the open cluster M 67

We determined the metallicity ([Fe/H]), together with O, Na, Mg, Al, Si, Ca, Ti, Cr and Ni abundances for a sample of 10 unevolved or slightly evolved stars belonging to the open cluster M 67. We find an average metallicity [Fe/H]=0.03 +/- 0.01, in very good agreement with previous determinations. All the [X/Fe] abundance ratios are very close to solar. The star-to-star scatter in [Fe/H] and [X/Fe] ratios for all elements, including oxygen, is lower than 0.05 dex, implying that the large dispersion in lithium reported in previous studies is not due to differences in these element abundances. We also find that, when using a homogeneous scale, the abundance pattern of unevolved stars in our sample is very similar to that of evolved stars, suggesting that, at least in this cluster, RGB and clump stars have not undergone any chemical processing. Finally, our results show that M 67 has a chemical composition that is representative of the solar neighborhood.Comment: 18 pages, 5 figures, accepted for publication in A&

The spermidine analogue GC7 (N1-guanyl-1,7-diamineoheptane) induces autophagy through a mechanism not involving the hypusination of eIF5A

The exogenous administration of spermidine promotes longevity in many model organisms. It has been proposed that this anti-age activity of spermidine is related to this polyamine's ability to promote autophagy. Since spermidine is the substrate for the eIF5A post-translational modification by hypusination, we asked ourselves whether mature eIF5A may represent the link between spermidine and autophagy induction. To test this hypothesis, we inhibited the conversion of native eIF5A by a pharmacological approach, using the N1-guanyl-1,7-diamineoheptane (GC7), a spermidine analogue which competitively and reversibly inhibits deoxyhypusine synthase (DHS). In addition, we also employed genetic approaches by ablating both the eIF5A protein itself and DHS, the rate limiting enzyme catalyzing the conversion of lysine to hypusine. Collectively the data presented in this study demonstrate that the mature eIF5A (hypusinated form) is not involved in the autophagic pathway and that the inhibitor of DHS, GC7, produces off-target effect(s) resulting in marked induction of basal autophagy. These data are relevant in light of the fact that GC7 is considered a potent and selective inhibitor of DHS and is a potential candidate drug for cancer, diabetes and HIV therapy

Lithium evolution in intermediate age and old open clusters: NGC 752 revisited

We present new high resolution spectroscopic observations of the intermediate age (~2 Gyr) open cluster NGC 752. We investigate the Li vs. Teff distribution and we obtain a new accurate determination of the cluster metallicity. We compare the results for NGC 752 with other intermediate age and old clusters spanning the age range from the Hyades (~0.6 Gyr) to NGC 188 (~6-8 Gyr). We find that NGC 752 has a solar iron content ([Fe/H]=+0.01+/-0.04), at variance with early reports of sub-solar metallicity. We find that NGC 752 is only slightly more Li depleted than the younger Hyades and has a Li pattern almost identical to that observed in the ~2 Gyr old IC 4651 and NGC 3680. As for the latter clusters, we find that NGC 752 is characterized by a tight Li vs. Teff distribution for solar-type stars, with no evidence for a Li spread as large as the one observed in the solar age solar metallicity M 67. We discuss these results in the framework of mixing mechanisms and Li depletion on the main sequence (MS). We conclude that the development of a large scatter in Li abundances in old open clusters might be an exception rather than the rule (additional observations of old clusters are required), and that metallicity variations of the order of ~0.2 dex do not affect Li depletion after the age of the Hyades.Comment: A&A accepted, 10 pages, 5 ps figure