Examinando por Autor "Lewis, J."

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Acceso Abierto
Detection of Reduced Sulfur on Vera Rubin Ridge by Quadratic Discriminant Analysis of Volatiles Observed During Evolved Gas Analysis.
(American Geophysical Union: Advancing Earth and Space Science, 2020-06-10) Wong, K. H.; Lewis, J.; Knudson, C. A.; Millan, M.; McAdam, A. C.; Eigenbrode, J. L.; Andrejkovičová, S.; Gómez, F.; Navarro González, R.; House, C. H.; Universidad Nacional Autónoma de México (UNAM); Navarro González, R. [0000-0002-6078-7621]; Knudson, C. A. [0000-0003-3875-2200]; Andrejkovicova, S. [0000-0001-8429-6926]; Gómez, F. [0000-0001-9977-7060]; McAdam, A. [0000-0001-9120-2991]; House, C. [0000-0002-4926-4985]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
The Mars Science Laboratory mission investigated Vera Rubin ridge, which bears spectral indications of elevated amounts of hematite and has been hypothesized as having a complex diagenetic history. Martian samples, including three drilled samples from the ridge, were analyzed by the Sample Analysis at Mars instrument suite via evolved gas analysis‐mass spectrometry (EGA‐MS). Here, we report new EGA‐MS data from Martian samples and describe laboratory analogue experiments. Analyses of laboratory analogues help determine the presence of reduced sulfur in Martian solid samples, which could have supported potential microbial life. We used evolved carbonyl sulfide (COS) and carbon disulfide (CS2) to identify Martian samples likely to contain reduced sulfur by applying a quadratic discriminant analysis. While we report results for 24 Martian samples, we focus on Vera Rubin ridge samples and select others for comparison. Our results suggest the presence of reduced sulfur in the Jura member of Vera Rubin ridge, which can support various diagenetic history models, including, as discussed in this work, diagenetic alteration initiated by a mildly reducing, sulfite‐containing groundwater.
Acceso Abierto
The Gaia -ESO Survey: A new approach to chemically characterising young open clusters: I. Stellar parameters, and iron-peak, α -, and proton-capture elements
(EDP Sciences, 2020-01-31) Baratella, M.; D´Orazi, V.; Carraro, G.; Desidera, S.; Randich, S.; Magrini, L.; Adibekyan, V.; Smiljanic, R.; Spina, L.; Tsantaki, M.; Tautvaisilenè, G.; Sousa, S. G.; Jofre, P.; Jiménez Esteban, F. M.; Delgado Mena, E.; Martell, S.; Van der Swaelmen, M.; Roccatagliata, V.; Gilmore, G.; Alfaro, Emilio J.; Bayo, A.; Bensby, T.; Bragaglia, A.; Franciosini, E.; Gonneau, A.; Heiter, U.; Hourihane, A.; Jeffries, R. D.; Koposov, S. E.; Morbidelli, L.; Prisinzano, L.; Sacco, G.; Sbordone, L.; Worley, Christopher; Zaggia, S.; Lewis, J.; European Commission (EC); Leverhulme Trust; Fundacao para a Ciencia e a Tecnologia (FCT); Agencia Estatal de Investigación (AEI); Jeffries, R. D. [0000-0001-5668-1288]; Magrini, L. [0000-0003-4486-6802]; Mena, E. D. [0000-0003-4434-2195]; Smiljanic, R. [0000-0003-0942-7855]; Koposov, S. [0000-0003-2644-135X]; Carraro, G. [0000-0002-0155-9434]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Context. Open clusters are recognised as excellent tracers of Galactic thin-disc properties. At variance with intermediate-age and old open clusters, for which a significant number of studies is now available, clusters younger than ≲ 150 Myr have been mostly overlooked in terms of their chemical composition until recently (with few exceptions). On the other hand, previous investigations seem to indicate an anomalous behaviour of young clusters, which includes (but is not limited to) slightly sub-solar iron (Fe) abundances and extreme, unexpectedly high barium (Ba) enhancements. Aims. In a series of papers, we plan to expand our understanding of this topic and investigate whether these chemical peculiarities are instead related to abundance analysis techniques. Methods. We present a new determination of the atmospheric parameters for 23 dwarf stars observed by the Gaia-ESO survey in five young open clusters (τ < 150 Myr) and one star-forming region (NGC 2264). We exploit a new method based on titanium (Ti) lines to derive the spectroscopic surface gravity, and most importantly, the microturbulence parameter. A combination of Ti and Fe lines is used to obtain effective temperatures. We also infer the abundances of Fe » I, Fe » II, Ti » I, Ti » II, Na » I, Mg » I, Al » I, Si » I, Ca » I, Cr » I, and Ni » I. Results. Our findings are in fair agreement with Gaia-ESO iDR5 results for effective temperatures and surface gravities, but suggest that for very young stars, the microturbulence parameter is over-estimated when Fe lines are employed. This affects the derived chemical composition and causes the metal content of very young clusters to be under-estimated. Conclusions. Our clusters display a metallicity [Fe/H] between +0.04 ± 0.01 and +0.12 ± 0.02; they are not more metal poor than the Sun. Although based on a relatively small sample size, our explorative study suggests that we may not need to call for ad hoc explanations to reconcile the chemical composition of young open clusters with Galactic chemical evolution models. © ESO 2020.
Acceso Abierto
The Gaia-ESO Survey: Age spread in the star forming region NGC 6530 from the HR diagram and gravity indicators
(EDP Sciences, 2019-03-26) Prisinzano, L.; Damiani, F.; Kalari, V.; Jeffries, R. D.; Bonito, R.; Micela, G.; Wright, N. James; Jackson, R. J.; Tognelli, E.; Guarcello, M. G.; Vink, Jorick S.; Klutsch, A.; Jiménez Esteban, F. M.; Roccatagliata, V.; Tautvaisilenè, G.; Gilmore, G.; Randich, S.; Alfaro, Emilio J.; Flaccomio, E.; Koposov, S.; Lanzafame, A. C.; Pancino, E.; Bergemann, M.; Carraro, G.; Franciosini, E.; Frasca, A.; Gonneau, A.; Hourihane, A.; Jofre, P.; Lewis, J.; Magrini, L.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Worley, Charlotte C.; Zaggia, S.; European Commission (EC); Leverhulme Trust; Istituto Nazionale di Astrofisica (INAF); Ministero dell'Istruzione, dell'Università e della Ricerca (MIUR); Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Context. In very young clusters, stellar age distribution is empirical proof of the duration of star cluster formation and thus it gives indications of the physical mechanisms involved in the star formation process. Determining the amount of interstellar extinction and the correct reddening law are crucial steps to derive fundamental stellar parameters and in particular accurate ages from the Hertzsprung-Russell diagram. Aims. In this context, we seek to derive accurate stellar ages for NGC 6530, the young cluster associated with the Lagoon Nebula to infer the star formation history of this region. Methods. We used the Gaia-ESO survey observations of the Lagoon Nebula, together with photometric literature data and Gaia DR2 kinematics, to derive cluster membership and fundamental stellar parameters. Using spectroscopic effective temperatures, we analysed the reddening properties of all objects and derived accurate stellar ages for cluster members. Results. We identified 652 confirmed and 9 probable members. The reddening inferred for members and non-members allows us to distinguish foreground objects, mainly main-sequence stars, and background objects, mainly giants, and to trace the three-dimensional structure of the nebula. This classification is in agreement with the distances inferred from Gaia DR2 parallaxes for these objects. Finally, we derive stellar ages for 382 confirmed cluster members for which we obtained the individual reddening values. In addition, we find that the gravity-sensitive γ index distribution for the M-type stars is correlated with stellar age. Conclusions. For all members with Teff < 5500 K, the mean logarithmic age is 5.84 (units of years) with a dispersion of 0.36 dex. The age distribution of stars with accretion or discs, i.e. classical T Tauri stars with excess (CTTSe), is similar to that of stars without accretion and without discs, i.e. weak T Tauri stars with photospheric emission (WTTSp). We interpret this dispersion as evidence of a real age spread since the total uncertainties on age determinations, derived from Monte Carlo simulations, are significantly smaller than the observed spread. This conclusion is supported by evidence of the decrease of the gravity-sensitive γ index as a function of stellar ages. The presence of a small age spread is also supported by the spatial distribution and kinematics of old and young members. In particular, members with accretion or discs, formed in the last 1 Myr, show evidence of subclustering around the cluster centre, in the Hourglass Nebula and in the M8-E region, suggesting a possible triggering of star formation events by the O-type star ionization fronts.