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- Ventura, P., et al.
(författare)
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Gas and dust from extremely metal-poor AGB stars
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 655
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Tidskriftsartikel (refereegranskat)abstract
- Context. The study of stars that evolve through the asymptotic giant branch (AGB) proves crucial in several astrophysical contexts because these objects provide important feedback to the host system in terms of the gas that is poured into the interstellar medium after being exposed to contamination from nucleosynthesis processes, and in terms of the dust that forms in their wind. Most of the studies conducted so far have been focused on AGB stars with solar and sub-solar chemical composition, whereas the extremely metal-poor domain has been poorly explored. Aims. We study the evolution of extremely metal-poor AGB stars with metallicities down to [Fe/H] = -5 to understand the main evolutionary properties and the efficiency of the processes able to alter their surface chemical composition, and to determine the gas and dust yields. Methods. We calculated two sets of evolutionary sequences of stars in the 1-7.5M(circle dot) mass range that evolved from the pre-main sequence to the end of the AGB phase. To explore the extremely metal-poor chemistries, we adopted the metallicities Z= 3 x 10(-5) and Z= 3 x 10(-7), which correspond to [Fe/H]= -3 and [Fe/H]= -5, respectively. The results from stellar evolution modelling were used to calculate the yields of the individual chemical species. We also modelled dust formation in the wind to determine the dust produced by these objects. Results. The evolution of AGB stars in the extremely metal-poor domain we explored proves highly sensitive to the initial mass of the star. M <= 2 M-circle dot stars experience several third-dredge-up events, which favour the gradual surface enrichment of C-12 and the formation of significant quantities of carbonaceous dust, similar to 0.01 M-circle dot. The C-13 and nitrogen yields are found to be significantly smaller than in previous explorations of low-mass metal-poor AGB stars because the proton ingestion episodes experienced during the initial AGB phases are weaker. M >= 5 M-circle dot stars experience hot bottom burning, and their surface chemistry reflects the equilibria of a very advanced proton-capture nucleosynthesis; little dust production takes place in their wind. Intermediate-mass stars experience both third dredge-up and hot bottom burning: they prove efficient producers of nitrogen, which is formed by proton captures on C-12 nuclei of primary origin dredged up from the internal regions.
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- Trevisan, Caterina, et al.
(författare)
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Judgment Capacity, Fear of Falling, and the Risk of Falls in Community-Dwelling Older Adults : The Progetto Veneto Anziani Longitudinal Study
- 2020
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Ingår i: Rejuvenation Research. - : Mary Ann Liebert Inc. - 1549-1684 .- 1557-8577. ; 23:3, s. 237-244
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Tidskriftsartikel (refereegranskat)abstract
- Little is known of the factors that transform fear of falling (FOF) from a normal adaptive to a maladaptive response that could alter its impact on fall risk. Focusing on judgment capacity, we investigated whether it is associated with FOF and FOF-related activity restriction (AR), and whether it modifies the influence of FOF on fall risk. Data came from 2625 community-dwelling older adults enrolled in the Progetto Veneto Anziani. Baseline FOF and AR were assessed through personal interviews, and judgment capacity-high, moderate, or poor-through situational tests. At follow-up after 4.4 years, self-reported falls during the previous year were recorded. The associations between judgment and FOF/AR, and between FOF and the risk of at least one fall or recurrent falls (two or more falls), stratified by judgment capacity, were evaluated using multinomial logistic regressions. Compared with high-judgment participants, lower judgment participants were 20% more likely to report FOF; moderate judgment participants were 54% more likely and poor judgment participants twice as likely to report AR. After adjusting for potential confounders, including physical activity and physical performance, FOF increased the reporting of at least one fall only in the poor judgment group. The association between FOF and recurrent falls was stronger in individuals with poor (odds ratio [OR] = 3.66, 95% confidence interval [CI]: 2.10-6.36) than with moderate (OR = 2.81, 95% CI: 2.22-3.55) or high (OR = 1.65, 95% CI: 1.48-1.83) judgment. Poor judgment capacity increases the probability of FOF and AR in older adults, and may exacerbate the effect of FOF in increasing fall risk.
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