334 research outputs found
Elevated r-process enrichment in Gaia Sausage and Sequoia
The Gaia Sausage and the Sequoia represent the major accretion events that formed the stellar halo of the Milky Way. A detailed chemical study of these main building blocks provides a pristine view of the early steps of the Galaxy's assembly. We present the results of the analysis of the UVES high-resolution spectroscopic observations at the 8.2m VLT of 9 Sausage/Sequoia members selected kinematically using Gaia DR2. We season this set of measurements with archival data from Nissen & Schuster (2011) and GALAH DR3 (2020). Here, we focus on the neutron-capture process by analysing Sr, Y, Ba and Eu behavior. We detect clear enhancement in Eu abundance ([Eu/Fe]~0.6-0.7) indicative of large prevalence of r-process in the stellar n-capture makeup. We are also able to trace the evolution of the heavy element production across a wide range of metallicity. Barium to europium ratio changes from a tight, flat sequence with [Ba/Eu]=-0.7 reflecting dominant core-collapse SNe contribution, to a clear upturn at higher iron abundances, betraying the onset of contamination from asymptotic giant branch (AGB) ejecta. Additionally, we discover two clear sequences in [Fe/H]-[Ba/Fe] plane likely caused by distinct levels of s-process pollution and mixing within the GS progenitor
The 3D kinematics of stellar substructures in the periphery of the Large Magellanic Cloud
We report the 3D kinematics of 27 Mira-like stars in the northern, eastern, and southern periphery of the Large Magellanic Cloud (LMC), based on Gaia proper motions and a dedicated spectroscopic follow-up. Low-resolution spectra were obtained for more than 40 Mira-like candidates, selected to trace known substructures in the LMC periphery. Radial velocities and stellar parameters were derived for all stars. Gaia data release 3 astrometry and photometry were used to discard outliers, derive periods for those stars with available light curves, and determine their photometric chemical types. The 3D motion of the stars in the reference frame of the LMC revealed that most of the stars, in all directions, have velocities consistent with being part of the LMC disc population, out of equilibrium in the radial and vertical directions. A suite of numerical simulations was used to constrain the most likely past interaction history between the Clouds given the phase-space distribution of our targets. Model realizations in which the Small Magellanic Cloud (SMC) had three pericentric passages around the LMC best resemble the observations. The interaction history of those model realizations has a recent SMC pericentric passage (∼320 Myr ago), preceded by an SMC crossing of the LMC disc at ∼0.97 Gyr ago, having a radial crossing distance of only ∼4.5 kpc. The previous disc crossing of the SMC was found to occur at ∼1.78 Gyr ago, with a similar radial crossing distance of ∼5.6 kpc
Tumor immune infiltration estimated from gene expression profiles predicts colorectal cancer relapse
A substantial fraction of patients with stage I-III colorectal adenocarcinoma (CRC) experience disease relapse after surgery with curative intent. However, biomarkers for predicting the likelihood of CRC relapse have not been fully explored. Therefore, we assessed the association between tumor infiltration by a broad array of innate and adaptive immune cell types and CRC relapse risk. We implemented a discovery-validation design including a discovery dataset from Moffitt Cancer Center (MCC; Tampa, FL) and three independent validation datasets: (1) GSE41258 (2) the Molecular Epidemiology of Colorectal Cancer (MECC) study, and (3) GSE39582. Infiltration by 22 immune cell types was inferred from tumor gene expression data, and the association between immune infiltration by each cell type and relapse-free survival was assessed using Cox proportional hazards regression. Within each of the four independent cohorts, CD4+ memory activated T cell (HR: 0.93, 95% CI: 0.90-0.96; FDR = 0.0001) infiltration was associated with longer time to disease relapse, independent of stage, microsatellite instability, and adjuvant therapy. Based on our meta-analysis across the four datasets, 10 innate and adaptive immune cell types associated with disease relapse of which 2 were internally validated using multiplex immunofluorescence. Moreover, immune cell type infiltration was a better predictors of disease relapse than Consensus Molecular Subtype (CMS) and other expression-based biomarkers (Immune-AICMCC:238.1-238.9; CMS-AICMCC: 241.0). These data suggest that transcriptome-derived immune profiles are prognostic indicators of CRC relapse and quantification of both innate and adaptive immune cell types may serve as candidate biomarkers for predicting prognosis and guiding frequency and modality of disease surveillance
Kondo effect in coupled quantum dots: a Non-crossing approximation study
The out-of-equilibrium transport properties of a double quantum dot system in
the Kondo regime are studied theoretically by means of a two-impurity Anderson
Hamiltonian with inter-impurity hopping. The Hamiltonian, formulated in
slave-boson language, is solved by means of a generalization of the
non-crossing approximation (NCA) to the present problem. We provide benchmark
calculations of the predictions of the NCA for the linear and nonlinear
transport properties of coupled quantum dots in the Kondo regime. We give a
series of predictions that can be observed experimentally in linear and
nonlinear transport measurements through coupled quantum dots. Importantly, it
is demonstrated that measurements of the differential conductance , for the appropriate values of voltages and inter-dot tunneling
couplings, can give a direct observation of the coherent superposition between
the many-body Kondo states of each dot. This coherence can be also detected in
the linear transport through the system: the curve linear conductance vs
temperature is non-monotonic, with a maximum at a temperature
characterizing quantum coherence between both Kondo states.Comment: 20 pages, 17 figure
The S2 Stream:the shreds of a primitive dwarf galaxy
We present a multi-instrument chemical analysis of the stars in the
metal-poor S2 halo stream using both high- and low-resolution spectroscopy,
complemented with a re-analysis of the archival data to give a total sample of
62 S2 members. Our high-resolution program provides alpha-elements (C, Mg, Si,
Ca and Ti), iron-peak elements (V, Cr, Mn, Fe, Ni), n-process elements (Sr, Ba)
and other elements such us Li, Na, Al, and Sc for a subsample of S2 objects. We
report coherent abundance patterns over a large metallicity spread (~1dex)
confirming that the S2 stream was produced by a disrupted dwarf galaxy. The
S2's alpha-elements display a mildly decreasing trend with increasing
metallicity which can be interpreted as a "knee" at [Fe/H]<-2. However, even at
the high end of [Fe/H], S2's [alpha/Fe] ratios do not climb down from the halo
plateau, signaling prehistoric enrichment pattern with minimal SN Ia
contribution. At the low metallicity end, the n-capture elements in S2 are
dominated by r-process production: several stars are Ba-enhanced but unusually
extremely poor in Sr. Moreover, some of the low-[Fe/H] stars appear to be
carbon-enhanced. We interpret the observed abundance patterns with the help of
chemical evolution models that demonstrate the need for modest star-formation
efficiency and low wind efficiency confirming that the progenitor of S2 was a
primitive dwarf galaxy.Comment: Submitted to MNRAS. Comments are welcome
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