Villanueva G.L.,NASA |
Villanueva G.L.,Catholic University of America |
Mumma M.J.,NASA |
Novak R.E.,The College of New Rochelle |
And 6 more authors.
Science | Year: 2015
We measured maps of atmospheric water (H2O) and its deuterated form (HDO) across the martian globe, showing strong isotopic anomalies and a significant high deuterium/hydrogen (D/H) enrichment indicative of great water loss. The maps sample the evolution of sublimation from the north polar cap, revealing that the released water has a representative D/H value enriched by a factor of about 7 relative to Earth's ocean [Vienna standard mean ocean water (VSMOW)]. Certain basins and orographic depressions show even higher enrichment, whereas high-altitude regions show much lower values (1 to 3 VSMOW). Our atmospheric maps indicate that water ice in the polar reservoirs is enriched in deuterium to at least 8 VSMOW, which would mean that early Mars (4.5 billion years ago) had a global equivalent water layer at least 137 meters deep. © 2015, American Association for the Advancement of Science. All rights reserved.
Mouradian Z.,Observatoire de Paris Meudon
Solar Physics | Year: 2013
This article proposes a unified observational model of solar activity based on sunspot number and the solar global activity in the rotation of the structures, both per 11-year cycle. The rotation rates show a variation of a half-century period and the same period is also associated to the sunspot amplitude variation. The global solar rotation interweaves with the observed global organisation of solar activity. An important role for this assembly is played by the Grand Cycle formed by the merging of five sunspot cycles: a forgotten discovery by R. Wolf. On the basis of these elements, the nature of the Dalton Minimum, the Maunder Minimum, the Gleissberg Cycle, and the Grand Minima are presented. © 2012 Springer Science+Business Media Dordrecht.
Barbuy B.,University of Sao Paulo |
Hill V.,University of Nice Sophia Antipolis |
Zoccali M.,University of Santiago de Chile |
Minniti D.,University of Santiago de Chile |
And 5 more authors.
Astronomy and Astrophysics | Year: 2013
Context. Manganese is mainly produced in type II SNe during explosive silicon burning, in incomplete Si-burning regions, and depends on several nucleosynthesis environment conditions, such as mass cut between the matter ejected and falling back onto the remnant, electron and neutron excesses, mixing fallback, and explosion energy. Manganese is also produced in type Ia SNe. Aims. The aim of this work is the study of abundances of the iron-peak element Mn in 56 bulge giants, among which 13 are red clump stars. Four bulge fields along the minor axis are inspected. The study of abundances of Mn-over-Fe as a function of metallicity in the Galactic bulge may shed light on its production mechanisms. Methods. High-resolution spectra were obtained using the FLAMES+UVES spectrograph on the Very Large Telescope. The spectra were obtained within a program to observe 800 stars using the GIRAFFE spectrograph, together with the present UVES spectra. Results. We aim at identifying the chemical evolution of manganese, as a function of metallicity, in the Galactic bulge. We find [Mn/Fe] ~-0.7 at [Fe/H] ~-1.3, increasing to a solar value at metallicities close to solar, and showing a spread around-0.7 ≤ [Fe/H] ≤-0.2, in good agreement with other work on Mn in bulge stars. There is also good agreement with chemical evolution models. We find no clear difference in the behaviour of the four bulge fields. Whereas [Mn/Fe] vs. [Fe/H] could be identified with the behaviour of the thick disc stars, [Mn/O] vs. [O/H] has a behaviour running parallel, at higher metallicities, compared to thick disc stars, indicating that the bulge enrichment might have proceeded differently from that of the thick disc. © 2013 ESO.
Simic Z.,Astronomical Observatory |
Simic Z.,Isaac Newton Institute of Chile |
Dimitrijevic M.S.,Astronomical Observatory |
Dimitrijevic M.S.,Isaac Newton Institute of Chile |
Sahal-Brechot S.,Observatoire de Paris Meudon
Monthly Notices of the Royal Astronomical Society | Year: 2013
New Stark broadening parameters of interest for the astrophysical, laboratory and technological plasma modelling, investigations and analysis for nine resonant Cr II multiplets have been determined within the semiclassical perturbation approach. In order to demonstrate one possibility for their usage in astrophysical plasma research, obtained results have been applied to the analysis of the Stark broadening influence on stellar spectral line shapes. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
Iwata I.,Japan National Astronomical Observatory |
Chamaraux P.,Observatoire de Paris Meudon
Astronomy and Astrophysics | Year: 2011
Context. According to models of evolution in the hierarchical structure formation scenarios, voids of galaxies are expected to expand. The Local Void (LV) is the closest large void, and it provides a unique opportunity to test observationally such an expansion. It has been found that the Local Group, which is on the border of the LV, is running away from the void center at ~260 km ∼ s-1. Aims. In this study we investigate the motion of the galaxies at the far-side border of the LV to examine the presence of a possible expansion. Methods. We selected late-type, edge-on spiral galaxies with radial velocities between 3000 km ∼ s-1 and 5000 km ∼ s -1, and carried out HI 21 cm line and H-band imaging observations. The near-infrared Tully-Fisher relation was calibrated with a large sample of galaxies and carefully corrected for Malmquist bias. It was used to compute the distances and the peculiar velocities of the LV sample galaxies. Among the 36 sample LV galaxies with good quality HI line width measurements, only 15 galaxies were selected for measuring their distances and peculiar velocities, in order to avoid the effect of Malmquist bias. Results. The average peculiar velocity of these 15 galaxies is found to be-419+208-251 km ∼ s-1, which is not significantly different from zero. Conclusions. Due to the intrinsically large scatter of Tully-Fisher relation, we cannot conclude whether there is a systematic motion against the center of the LV for the galaxies at the far-side boundary of the void. However, our result is consistent with the hypothesis that those galaxies at the far-side boundary have an average velocity of ~260 km ∼ s-1 equivalent to what is found at the position of the Local Group. © 2011 ESO.