Early metal enrichment in high-redshift quasars

Quasars are powerful systems whose spectrum is rich of metal features that allow us to investigate the chemical evolution of galaxies at very high redshift, even close to the reionization epoch. I review the main observational constraints on the metallicity of quasars host galaxies at high redshift and discuss the implications and issues for models of galaxy evolution in the early universe.Comment: 8 pages, invited review at the workshop "Probing Stellar Populations out to the Distant Universe

Early results of fissurectomy and advancement flap for resistant chronic anal fissure without hypertonia of the internal anal sphincter

The aim of this study was to assess the efficacy of fissurectomy with skin advancement flap in healing chronic anal fissures without hypertonia of the internal anal sphincter. Twenty-six consecutive patients who failed healing after well-practiced topical medical therapy were enrolled. Anorectal manometry was performed preoperative and 6 months postoperatively. All patients were treated with fissurectomy and advancement flap through healthy skin tissue. All patients healed completely within 30 days from operation. The intensity and the duration of pain postdefecation was reduced significantly with respect to the preoperative values starting from the first defecation. One patient suffered urinary retention, two patients suffered infections, and two partial breakdowns were recorded. At 6 months the maximum resting pressure values were similar to those were detected preoperatively. One month after surgery, anal incontinence was reported in seven patients, four of whom complained about it preoperatively. At 12 months, only three subjects reported incontinence. No patients needed reoperation and no recurrences were detected. The fissurectomy, in combination with advancement flap, is a safe sphincter-saving procedure for the treatment of chronic anal fissures without hypertonia of internal anal sphincter that fails medical conservative treatment

Evolution of 3-9 Mo Stars for Z=0.001 - 0.03 and Metallicity Effects on Type Ia Supernovae

Recent observations have revealed that Type Ia supernovae (SNe Ia) are not perfect standard candles but show some variations in their absolute magnitudes, light curve shapes, and spectra. The C/O ratio in the SNe Ia progenitors (C-O white dwarfs) may be related to this variation. In this work, we systematically investigate the effects of stellar mass (M) and metallicity (Z) on the C/O ratio and its distribution in the C-O white dwarfs by calculating stellar evolution from the main-sequence through the end of the second dredge-up for M=3-9 Mo and Z=0.001-0.03. We find that the total carbon mass fraction just before SN Ia explosion varies in the range 0.36 -- 0.5. We also calculate the metallicity dependence of the main-sequence-mass range of the SN Ia progenitor white dwarfs. Our results show that the maximum main-sequence mass to form C-O white dwarfs decreases significantly toward lower metallicity, and the number of SN Ia progenitors may be underestimated if metallicity effectis neglected. We discuss the implications of these results on the variation of SNe Ia, determination of cosmological parameters, luminosity function of white dwarfs, and the galactic chemical evolution.Comment: Added references and corrected typos. To appear in the Astrophysical Journal 1999 March 10 issu

The CHilean Automatic Supernova sEarch (CHASE)

The CHASE project started in 2007 with the aim of providing young southern supernovae (SNe) to the Carnegie Supernova Project (CSP) and Millennium Center for Supernova Studies (MCSS) follow-up programs. So far CHASE has discovered 33 SNe with an average of more than 2.5 SNe per month in 2008. In addition to the search we are carrying out a follow-up program targeting bright SNe. Our fully automated data reduction allows us to follow the evolution on the light curve in real time, triggering further observations if something potentially interesting is detectedComment: 4 pages, 2 figures, conference proceedin

Galactic chemical evolution of heavy elements: from Barium to Europium

We follow the chemical evolution of the Galaxy for elements from Ba to Eu, using an evolutionary model suitable to reproduce a large set of Galactic (local and non local) and extragalactic constraints. Input stellar yields for neutron-rich nuclei have been separated into their s-process and r-process components. The production of s-process elements in thermally pulsing asymptotic giant branch stars of low mass proceeds from the combined operation of two neutron sources: the dominant reaction 13C(alpha,n)16O, which releases neutrons in radiative conditions during the interpulse phase, and the reaction 22Ne(alpha,n)25Mg, marginally activated during thermal instabilities. The resulting s-process distribution is strongly dependent on the stellar metallicity. For the standard model discussed in this paper, it shows a sharp production of the Ba-peak elements around Z = Z_sun/4. Concerning the r-process yields, we assume that the production of r-nuclei is a primary process occurring in stars near the lowest mass limit for Type II supernova progenitors. The r-contribution to each nucleus is computed as the difference between its solar abundance and its s-contribution given by the Galactic chemical evolution model at the epoch of the solar system formation. We compare our results with spectroscopic abundances of elements from Ba to Eu at various metallicities (mainly from F and G stars) showing that the observed trends can be understood in the light of the present knowledge of neutron capture nucleosynthesis. Finally, we discuss a number of emerging features that deserve further scrutiny.Comment: 34 pages, 13 figures. accepted by Ap

Evolution and Nucleosynthesis of Zero Metal Intermediate Mass Stars

New stellar models with mass ranging between 4 and 8 Mo, Z=0 and Y=0.23 are presented. The models have been evolved from the pre Main Sequence up to the Asymptotic Giant Branch (AGB). At variance with previous claims, we find that these updated stellar models do experience thermal pulses in the AGB phase. In particular we show that: a) in models with mass larger than 6 Mo, the second dredge up is able to raise the CNO abundance in the envelope enough to allow a "normal" AGB evolution, in the sense that the thermal pulses and the third dredge up settle on; b) in models of lower mass, the efficiency of the CNO cycle in the H-burning shell is controlled by the carbon produced locally via the 3alpha reactions. Nevertheless the He-burning shell becomes thermally unstable after the early AGB. The expansion of the overlying layers induced by these weak He-shell flashes is not sufficient by itself to allow a deep penetration of the convective envelope. However, immediately after that, the maximum luminosity of the He flash is attained and a convective shell systematically forms at the base of the H-rich envelope. The innermost part of this convective shell probably overlaps the underlying C-rich region left by the inter-shell convection during the thermal pulse, so that fresh carbon is dredged up in a "hot" H-rich environment and a H flash occurs. This flash favours the expansion of the outermost layers already started by the weak thermal pulse and a deeper penetration of the convective envelope takes place. Then, the carbon abundance in the envelope rises to a level high enough that the further evolution of these models closely resembles that of more metal rich AGB stars. These stars provide an important source of primary carbon and nitrogen.Comment: 28 pages, 5 tables and 17 figures. Accepted for publication in Ap

Solar analogues in open clusters: The case of M67

Solar analogues are fundamental targets for a better understanding of our Sun and our Solar System. Usually, this research is limited to field stars, which offer several advantages and limitations. In this work, we present the results of a research of solar twins performed for the first time in a open cluster, namely M67. Our analysis allowed us to find five solar twins and also to derive a solar colour of (B-V)0=0.649+/-0.016 and a cluster distance modulus of 9.63+/-0.08. This study encourages us to apply the same method to other open clusters, and to do further investigations for planet search in the solar twins we find.Comment: 4 pages, 2 figures; Proceedings of the conference "Probing Stellar Populations out to the Distant Universe", Cefalu' (Italy), September 7 - 19, 2008. To be published in the AIP Conf. Proc. Serie

Optical and infrared observations of the supernova SN 1999el

Optical and near-infrared light curves of the Type IIn supernova 1999el in NGC 6951 are presented. A period of 220 days (416 days in the near-infrared) is covered from the first observation obtained a few days before maximum light. Spectroscopic observations are also discussed. Using as a distance calibrator the Type Ia SN 2000E, which occurred some months later in the same galaxy, and fitting a blackbody law to the photometric data we obtain a maximum bolometric luminosity for SN 1999el of $\sim 10^{44}$ erg s$^{-1}$. In general, the photometric properties of SN 1999el are very similar to those of SN 1998S, a bright and well studied Type IIn SN, showing a fast decline in all observed bands similar to those of Type II-L SNe. The differences with SN 1998S are analyzed and ascribed to the differences in a pre-existing circumstellar envelope in which dust was already present at the moment of the SN outburst. We infer that light echoes may play a possibly significant role in affecting the observed properties of the light curves, although improved theoretical models are needed to account for the data. We conclude that mass loss in the progenitor RG stars is episodic and occurs in an asymmetric way. This implies that collapsing massive stars appear as normal Type II SN if this occurs far from major mass loss episodes, whereas they appear as Type IIn SNe if a large mass loss episode is in progress.Comment: 30 pages, 8 figures, figure 1 available as jpeg file, ApJ in pres

Measurement of the cross-section and charge asymmetry of WW bosons produced in proton-proton collisions at s=8\sqrt{s}=8 TeV with the ATLAS detector

This paper presents measurements of the $W^+ \rightarrow \mu^+\nu$ and $W^- \rightarrow \mu^-\nu$ cross-sections and the associated charge asymmetry as a function of the absolute pseudorapidity of the decay muon. The data were collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS experiment at the LHC and correspond to a total integrated luminosity of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the 1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured with an uncertainty between 0.002 and 0.003. The results are compared with predictions based on next-to-next-to-leading-order calculations with various parton distribution functions and have the sensitivity to discriminate between them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables, submitted to EPJC. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13