Browsing by Author "Koch, A."
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- ItemA new algorithm for optimizing the wavelength coverage for spectroscopic studies: Spectral Wavelength Optimization Code (SWOC)(OXFORD UNIV PRESS, 2016) Ruchti, G. R.; Feltzing, S.; Lind, K.; Caffau, E.; Korn, A. J.; Schnurr, O.; Hansen, C. J.; Koch, A.; Sbordone, L.; de Jong, R. S.The past decade and a half has seen the design and execution of several ground-based spectroscopic surveys, both Galactic and Extragalactic. Additionally, new surveys are being designed that extend the boundaries of current surveys. In this context, many important considerations must be done when designing a spectrograph for the future. Among these is the determination of the optimum wavelength coverage. In this work, we present a new code for determining the wavelength ranges that provide the optimal amount of information to achieve the required science goals for a given survey. In its first mode, it utilizes a user-defined list of spectral features to compute a figure-of-merit for different spectral configurations. The second mode utilizes a set of flux-calibrated spectra, determining the spectral regions that show the largest differences among the spectra. Our algorithm is easily adaptable for any set of science requirements and any spectrograph design. We apply the algorithm to several examples, including 4MOST, showing the method yields important design constraints to the wavelength regions.
- ItemA study of rotating globular clusters : the case of the old metal-poor globular cluster NGC 4372(2014) Kacharov, N.; Bianchini, P.; Koch, A.; Frank, M. J.; Martin, N. F.; Ven G., van de; Puzia, Thomas H.; McDonald, I.; Johnson, C. I.; Zijlstra, A. A.
- ItemComparison of q-Space Reconstruction Methods for Undersampled Diffusion Spectrum Imaging Data(2020) Varela Mattatall, Gabriel Enrique; Koch, A.; Stirnberg, R.; Chabert, S.; Uribe Arancibia, Sergio A.; Tejos Núñez, Cristián Andrés; Stöcker, T.; Irarrázaval Mena, Pablo
- ItemGalactic evolution of sulphur as traced by globular clusters(EDP SCIENCES S A, 2015) Kacharov, N.; Koch, A.; Caffau, E.; Sbordone, L.Context. Sulphur is an important volatile a element, but its role in the Galactic chemical evolution is still uncertain, and more observations constraining the sulphur abundance in stellar photospheres are required.
- ItemMAPL1 : q-space reconstruction usingl1-regularized mean apparent propagator(2020) Varela Mattatall, Gabriel Enrique; Castillo Passi, C.; Koch, A.; Mura, J.; Stirnberg, R.; Uribe Arancibia, Sergio A.; Tejos Núñez, Cristián Andrés; Stocker, T.; Irarrázaval Mena, Pablo
- ItemThe Gaia-ESO Survey: Detailed abundances in the metal-poor globular cluster NGC 4372(EDP SCIENCES S A, 2015) San Roman, I.; Munoz, C.; Geisler, D.; Villanova, S.; Kacharov, N.; Koch, A.; Carraro, G.; Tautvaisiene, G.; Vallenari, A.; Alfaro, E. J.; Bensby, T.; Flaccomio, E.; Francois, P.; Korn, A. J.; Pancino, E.; Recio Blanco, A.; Smiljanic, R.; Bergemann, M.; Costado, M. T.; Damiani, F.; Heiter, U.; Hourihane, A.; Jofre, P.; Lardo, C.; de Laverny, P.; Masseron, T.; Morbidelli, L.; Sbordone, L.; Sousa, S. G.; Worley, C. C.; Zaggia, S.We present the abundance analysis for a sample of 7 red giant branch stars in the metal-poor globular cluster NGC 4372 based on UVES spectra acquired as part of the Gaia-ESO Survey. This is the first extensive study of this cluster from high-resolution spectroscopy. We derive abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, Fe, Cr, Ni, Y, Ba, and La. We find a metallicity of [Fe/H] = -2.19 +/- 0.03 and find no evidence of any metallicity spread. This metallicity makes NGC 4372 one of the most metal-poor Galactic globular clusters. We also find an a-enhancement typical of halo globular clusters at this metallicity. Significant spreads are observed in the abundances of light elements. In particular, we find a Na-O anticorrelation. Abundances of O are relatively high compared with other globular clusters. This could indicate that NGC 4372 was formed in an environment with high O for its metallicity. A Mg-Al spread is also present that spans a range of more than 0.5 dex in Al abundances. Na is correlated with Al and Mg abundances at a lower significance level. This pattern suggests that the Mg-Al burning cycle is active. This behavior can also be seen in giant stars of other massive, metal-poor clusters. A relation between light and heavy s-process elements has been identified.
- ItemThe Gaia-ESO Survey: Galactic evolution of sulphur and zinc(EDP SCIENCES S A, 2017) Duffau, S.; Caffau, E.; Sbordone, L.; Bonifacio, P.; Andrievsky, S.; Korotin, S.; Babusiaux, C.; Salvadori, S.; Monaco, L.; Francois, P.; Skuladottir, A.; Bragaglia, A.; Donati, P.; Spina, L.; Gallagher, A. J.; Ludwig, H. G.; Christlieb, N.; Hansen, C. J.; Mott, A.; Steffen, M.; Zaggia, S.; Blanco Cuaresma, S.; Calura, F.; Friel, E.; Jimenez Esteban, F. M.; Koch, A.; Magrini, L.; Pancino, E.; Tang, B.; Tautvaisiene, G.; Vallenari, A.; Hawkins, K.; Gilmore, G.; Randich, S.; Feltzing, S.; Bensby, T.; Flaccomio, E.; Smiljanic, R.; Bayo, A.; Carraro, G.; Casey, A. R.; Costado, M. T.; Damiani, F.; Franciosini, E.; Hourihane, A.; Jofre, P.; Lardo, C.; Lewis, J.; Morbidelli, L.; Sousa, S. G.; Worley, C. C.Context. Due to their volatile nature, when sulphur and zinc are observed in external galaxies, their determined abundances represent the gas-phase abundances in the interstellar medium. This implies that they can be used as tracers of the chemical enrichment of matter in the Universe at high redshift. Comparable observations in stars are more difficult and, until recently, plagued by small number statistics.
- ItemTOPoS II. On the bimodality of carbon abundance in CEMP stars Implications on the early chemical evolution of galaxies(EDP SCIENCES S A, 2015) Bonifacio, P.; Caffau, E.; Spite, M.; Limongi, M.; Chieffi, A.; Klessen, R. S.; Francois, P.; Molaro, P.; Ludwig, H. G.; Zaggia, S.; Spite, F.; Plez, B.; Cayrel, R.; Christlieb, N.; Clark, P. C.; Glover, S. C. O.; Hammer, F.; Koch, A.; Monaco, L.; Sbordone, L.; Steffen, M.Context. In the course of the Turn Off Primordial Stars (TOPoS) survey, aimed at discovering the lowest metallicity stars, we have found several carbon-enhanced metal-poor (CEMP) stars. These stars are very common among the stars of extremely low metallicity and provide important clues to the star formation processes. We here present our analysis of six CEMP stars.