ﻻ يوجد ملخص باللغة العربية
We investigate the origin of the abundance ratios and scatter of $alpha$- and neutron-capture elements of old, metal-poor stars, using cosmological, hydrodynamical simulations of galaxy formation. For this, we implement a novel treatment for the production and distribution of chemical products of Type II supernovae, which considers the effects of the rotation of massive stars on the chemical yields and the effects of the different life-times of stars that are progenitors of this type of supernovae. We focus on the stellar halo of a Milky Way-mass galaxy, studying the abundances and scatter of [O/Fe], [Mg/Fe], [Si/Fe], [Sr/Fe], [Eu/Fe] and [Ba/Fe]. Our model is able, for the first time in a cosmological simulation, to describe at the same time the low scatter in the abundances of $alpha$-elements and the higher scatter associated to neutron-capture elements in the halo stars, as suggested by observations of the Milky Way. We also reproduce the scatter observed in the [Sr/Ba] ratio, which results from the treatment of the fast-rotating stars and the dependence of the chemical yields on the metallicity, mass and rotational velocities. Our simulations show that such scatter patterns appear naturally if the different ejection times associated to stars of different mass are properly described, without the need to invoke for additional mixing mechanisms or a distinct treatment of the alpha- and neutron-capture elements. Simulations of this type will help characterizing and identifying the past accretion debris as well as the pristine in-situ populations in the Galaxy unveiled by Gaia and spectroscopic data.
Determining the properties of old stellar populations (those with age >1 Gyr) has long involved the comparison of their integrated light, either in the form of photometry or spectroscopic indexes, with empirical or synthetic templates. Here we reeval
We identified 8 additional stars as members of the Helmi stream (HStr) in the combined GALAH+ DR3 and $Gaia$ EDR3 catalog. By consistently reevaluating claimed members from the literature, we consolidate a sample of 22 HStr stars with parameters dete
We present a direct comparison of the Pan-Andromeda Archaeological Survey (PAndAS) observations of the stellar halo of M31 with the stellar halos of 6 galaxies from the Auriga simulations. We process the simulated halos through the Auriga2PAndAS pipe
We combine Gaia data release 1 astrometry with Sloan Digital Sky Survey (SDSS) images taken some ~10-15 years earlier, to measure proper motions of stars in the halo of our Galaxy. The SDSS-Gaia proper motions have typical statistical errors of 2 mas
In this work we present chemical abundances of heavy elements (Z$>$28) for a homogeneous sample of 1059 stars from HARPS planet search program. We also derive ages using parallaxes from Hipparcos and Gaia DR1 to compare the results. We study the [X/F