Browsing by Author "Monaco, L."

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    Detailed characterization of electron sources yielding first demonstration of European x-ray free-electron laser beam quality
    (College Park, Md. : APS, 2010) Stephan, F.; Boulware, C.H.; Krasilnikov, M.; Bähr, J.; Asova, G.; Donat, A.; Gensch, U.; Grabosch, H.J.; Hänel, M.; Hakobyan, L.; Henschel, H.; Ivanisenko, Y.; Jachmann, L.; Khodyachykh, S.; Khojoyan, M.; Kohler, W.; Korepanov, S.; Koss, G.; Kretzschmann, A.; Leich, H.; Ludecke, H.; Meissner, A.; Oppelt, A.; Petrosyan, B.; Pohl, M.; Riemann, S.; Rimjaem, S.; Sachwitz, M.; Schoneich, B.; Scholz, T.; Schulze, H.; Schultze, J.; Schwendicke, U.; Shapovalov, A.; Spesyvtsev, R.; Staykov, L.; Tonisch, F.; Walter, T.; Weisse, S.; Wenndorff, R.; Winde, M.; Vu, L.V.; Durr, H.; Kamps, T.; Richter, D.; Sperling, M.; Ovsyannikov, R.; Vollmer, A.; Knobloch, J.; Jaeschke, E.; Boster, J.; Brinkmann, R.; Choroba, S.; Flechsenhar, K.; Flottmann, K.; Gerdau, W.; Katalev, V.; Koprek, W.; Lederer, S.; Martens, C.; Pucyk, P.; Schreiber, S.; Simrock, S.; Vogel, E.; Vogel, V.; Rosbach, K.; Bonev, I.; Tsakov, I.; Michelato, P.; Monaco, L.; Pagani, C.; Sertore, D.; Garvey, T.; Will, I.; Templin, I.; Sandner, W.; Ackermann, W.; Arévalo, E.; Gjonaj, E.; Muller, W.F.O.; Schnepp, S.; Weiland, T.; Wolfheimer, F.; Ronsch, J.; Rossbach, J.
    The photoinjector test facility at DESY, Zeuthen site (PITZ), was built to develop and optimize photoelectron sources for superconducting linacs for high-brilliance, short-wavelength free-electron laser (FEL) applications like the free-electron laser in Hamburg (FLASH) and the European x-ray free-electron laser (XFEL). In this paper, the detailed characterization of two laser-driven rf guns with different operating conditions is described. One experimental optimization of the beam parameters was performed at an accelerating gradient of about 43 MV/m at the photocathode and the other at about 60 MV/m. In both cases, electron beams with very high phase-space density have been demonstrated at a bunch charge of 1 nC and are compared with corresponding simulations. The rf gun optimized for the lower gradient has surpassed all the FLASH requirements on beam quality and rf parameters (gradient, rf pulse length, repetition rate) and serves as a spare gun for this facility. The rf gun studied with increased accelerating gradient at the cathode produced beams with even higher brightness, yielding the first demonstration of the beam quality required for driving the European XFEL: The geometric mean of the normalized projected rms emittance in the two transverse directions was measured to be 1.260±13 mmmrad for a 1-nC electron bunch. When a 10% charge cut is applied excluding electrons from those phase-space regions where the measured phase-space density is below a certain level and which are not expected to contribute to the lasing process, the normalized projected rms emittance is about 0.9 mmmrad. © 2010 The American Physical Society.
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    The Gaia -ESO Survey: Lithium measurements and new curves of growth
    (Les Ulis : EDP Sciences, 2022) Franciosini, E.; Randich, S.; de Laverny, P.; Biazzo, K.; Feuillet, D.K.; Frasca, A.; Lind, K.; Prisinzano, L.; Tautvaišiene, G.; Lanzafame, A.C.; Smiljanic, R.; Gonneau, A.; Magrini, L.; Pancino, E.; Guiglion, G.; Sacco, G.G.; Sanna, N.; Gilmore, G.; Bonifacio, P.; Jeffries, R.D.; Micela, G.; Prusti, T.; Alfaro, E.J.; Bensby, T.; Bragaglia, A.; François, P.; Korn, A.J.; Van Eck, S.; Bayo, A.; Bergemann, M.; Carraro, G.; Heiter, U.; Hourihane, A.; Jofré, P.; Lewis, J.; Martayan, C.; Monaco, L.; Morbidelli, L.; Worley, C.C.; Zaggia, S.
    Context. The Gaia-ESO Survey (GES) is a large public spectroscopic survey that was carried out using the multi-object FLAMES spectrograph at the Very Large Telescope. The survey provides accurate radial velocities, stellar parameters, and elemental abundances for ~115 000 stars in all Milky Way components. Aims. In this paper, we describe the method adopted in the final data release to derive lithium equivalent widths (EWs) and abundances. Methods. Lithium EWs were measured using two different approaches for FGK and M-type stars, to account for the intrinsic differences in the spectra. For FGK stars, we fitted the lithium line using Gaussian components, while direct integration over a predefined interval was adopted for M-type stars. Care was taken to ensure continuity between the two regimes. Abundances were derived using a new set of homogeneous curves of growth that were derived specifically for GES, and which were measured on a synthetic spectral grid consistently with the way the EWs were measured. The derived abundances were validated by comparison with those measured by other analysis groups using different methods. Results. Lithium EWs were measured for ~40 000 stars, and abundances could be derived for ~38 000 of them. The vast majority of the measures (80%) have been obtained for stars in open cluster fields. The remaining objects are stars in globular clusters, or field stars in the Milky Way disc, bulge, and halo. Conclusions. The GES dataset of homogeneous lithium abundances described here will be valuable for our understanding of several processes, from stellar evolution and internal mixing in stars at different evolutionary stages to Galactic evolution.
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    MINCE: I. Presentation of the project and of the first year sample
    (Les Ulis : EDP Sciences, 2022) Cescutti, G.; Bonifacio, P.; Caffau, E.; Monaco, L.; Franchini, M.; Lombardo, L.; Matas Pinto, A. M.; Lucertini, F.; François, P.; Spitoni, E.; Lallement, R.; Sbordone, L.; Mucciarelli, A.; Spite, M.; Hansen, C.J.; Di Marcantonio, P.; Kučinskas, A.; Dobrovolskas, V.; Korn, A.J.; Valentini, M.; Magrini, L.; Cristallo, S.; Matteucci, F.
    Context. In recent years, Galactic archaeology has become a particularly vibrant field of astronomy, with its main focus set on the oldest stars of our Galaxy. In most cases, these stars have been identified as the most metal-poor. However, the struggle to find these ancient fossils has produced an important bias in the observations - in particular, the intermediate metal-poor stars (-2.5 < [Fe/H] <-1.5) have been frequently overlooked. The missing information has consequences for the precise study of the chemical enrichment of our Galaxy, in particular for what concerns neutron capture elements and it will be only partially covered by future multi object spectroscopic surveys such as WEAVE and 4MOST. Aims. Measuring at Intermediate Metallicity Neutron Capture Elements (MINCE) is gathering the first high-quality spectra (high signal-to-noise ratio, S/N, and high resolution) for several hundreds of bright and metal-poor stars, mainly located in our Galactic halo. Methods. We compiled our selection mainly on the basis of Gaia data and determined the stellar atmospheres of our sample and the chemical abundances of each star. Results. In this paper, we present the first sample of 59 spectra of 46 stars. We measured the radial velocities and computed the Galactic orbits for all stars. We found that 8 stars belong to the thin disc, 15 to disrupted satellites, and the remaining cannot be associated to the mentioned structures, and we call them halo stars. For 33 of these stars, we provide abundances for the elements up to zinc. We also show the chemical evolution results for eleven chemical elements, based on recent models. Conclusions. Our observational strategy of using multiple telescopes and spectrographs to acquire high S/N and high-resolution spectra for intermediate-metallicity stars has proven to be very efficient, since the present sample was acquired over only about one year of observations. Finally, our target selection strategy, after an initial adjustment, proved satisfactory for our purposes.