4,320 research outputs found
Chemical evolution of the Galactic bulge: different stellar populations and possible gradients
We compute the chemical evolution of the Galactic bulge to explain the
existence of two main stellar populations recently observed. After comparing
model results and observational data we suggest that the old more metal poor
stellar population formed very fast (on a timescale of 0.1-0.3 Gyr) by means of
an intense burst of star formation and an initial mass function flatter than in
the solar vicinity whereas the metal rich population formed on a longer
timescale (3 Gyr). We predict differences in the mean abundances of the two
populations (-0.52 dex for ) which can be interpreted as a metallicity
gradients. We also predict possible gradients for Fe, O, Mg, Si, S and Ba
between sub-populations inside the metal poor population itself (e.g. -0.145
dex for ). Finally, by means of a chemo-dynamical model following a
dissipational collapse, we predict a gradient inside 500 pc from the Galactic
center of -0.26 dex kpc^{-1} in Fe.Comment: 9 pages, 9 figures, accepted for publication in Section 5. of
Astronomy and Astrophysic
Peer effects on compliance with extortive requests
We conduct laboratory experiments to study peer effects on compliance with extortive requests. To this aim, we use an \u201cextortion game\u201d with multiple victims. In agreement with our hypothesis, our results show that when the information on peers\u2019 behavior is available, compliance with appropriative requests is triggered by conformism among victims rather than by punishment. Moreover, we find that extorted sums are rather small, requests are proportional to the victim\u2019s earnings, similar across victims, and are significantly lower when the extorter self-selects into this role. Punishment is rare, but effective. Finally, our results indicate that fairness concerns matter even in a context of extra-legal taxation, shaping both extorters\u2019 requests and victims\u2019 compliance
Chemical evolution of the bulge of M31: predictions about abundance ratios
We aim at reproducing the chemical evolution of the bulge of M31 by means of
a detailed chemical evolution model, including radial gas flows coming from the
disk. We study the impact of the initial mass function, the star formation rate
and the time scale for bulge formation on the metallicity distribution function
of stars. We compute several models of chemical evolution using the metallicity
distribution of dwarf stars as an observational constraint for the bulge of
M31. Then, by means of the model which best reproduces the metallicity
distribution function, we predict the [X/Fe] vs. [Fe/H] relations for several
chemical elements (O, Mg, Si, Ca, C, N). Our best model for the bulge of M31 is
obtained by means of a robust statistical method and assumes a Salpeter initial
mass function, a Schmidt-Kennicutt law for star formation with an exponent
k=1.5, an efficiency of star formation of , and an
infall timescale of Gyr. Our results suggest that the bulge
of M31 formed very quickly by means of an intense star formation rate and an
initial mass function flatter than in the solar vicinity but similar to that
inferred for the Milky Way bulge. The [/Fe] ratios in the stars of the
bulge of M31 should be high for most of the [Fe/H] range, as is observed in the
Milky Way bulge. These predictions await future data to be proven.Comment: Accepted for publication by MNRA
Monitoring and ming bio-physical parameters for hypoxia hazard in a coastal sand pit
Management of coastal areas requires monitoring and modeling of the anthropogenic drivers and the bio-physical processes affecting water quality. To assess the range of hydrographic conditions controlling oxygen distribution in the bottom layers of sand pits, a multi-year oceanographic survey has been conducted in a coastal area with several extraction pits. Hydrographic data including profiles of temperature, salinity and oxygen were collected and related to local wind conditions and circulation. Moreover, 1D and 3D high-resolution non-hydrostatic ocean models were used to describe turbulent mixing regimes and to obtain the range of wind speeds for which the critical anoxic conditions may occur. It is shown that wind speed appears to control the dynamics of oxygen concentrations, with oxygen depleted zones developing in a short time in low wind speed conditions. Moreover, the depth and the shape of the extraction pit contribute to decrease the mixing of the bottom layers and increase the water retention in the hole increasing the output and the persistence of oxygen depleted zones in the excavated area. The results of the numerical simulations show that the risk of hypoxia at the bottom of the sand pits is associated with higher temperatures and wind speed lower than 5 m/s, which is not infrequent during the summer season. However, the number of consecutive days of oxygen depletion can be considered lower than the danger threshold level assumed in the literature
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