Age Gradient Research Articles

Modeling and control strategy optimization of battery pack thermal management system considering aging and temperature inconsistency for fast charging

Maintaining the battery pack’s temperature in the desired range is crucial for fulfilling the thermal management requirements of a battery pack during fast charging. Furthermore, the temperature difference, temperature gradient, aging loss and energy consumption of the battery pack should be balanced to optimize its performance. This paper establishes the liquid cooling thermal management system model for an electric vehicle’s battery pack, which accurately characterizes the temperature distribution and electrical and aging characteristics of the battery pack. The discrepancies between the experimental and simulated results of battery’s fast charging-cooling suggest that maximum absolute temperature error is 2 °C, and the maximum relative voltage error is 1.5 %. Based on the non-dominated sorting genetic algorithm II algorithm, an optimization model with aging and temperature gradient of cells as objective functions is established. Three different thermal management strategies are created according to the optimization results. The comparison of these thermal management methods with the constant temperature cooling strategy demonstrates that the minimum temperature gradient strategy enhances the temperature consistency of the battery pack and reduces the maximum temperature gradient by 27 %. The minimum aging thermal management strategy depicts an aging loss of 0.091 %, reducing the charging time by 272 s and the maximum temperature gradient by 2.0 °C. The balanced thermal management strategy enables the battery pack to balance the temperature gradient and aging loss by optimizing the charging time, battery pack temperature difference, energy consumption and other indicators. The weight of each indicator is determined by its information entropy, which can be replaced according to the diverse needs to achieve different balanced thermal management strategies, providing a reference for the actual application of thermal management strategies.

Age-Related Blood Pressure Gradients Are Associated With Blood Pressure Control and Global Population Outcomes.

The strong relationship between blood pressure (BP) and age is well known. Limited evidence suggests that a steeper age-BP slope may be associated with an increased risk of adverse outcomes. The May Measurement Month campaign enables an investigation of geographic, socioeconomic, and sex differences in age-related BP gradients and their association with public-health outcomes. Cross-sectional, annual global BP May Measurement Month screening data were analyzed. Average systolic BP and age-related BP slopes across different age groups were calculated to assess regional, socioeconomic, and sex-stratified variations. The association of BP slopes derived from adjusted linear regression models with country-level health metrics was investigated. Age-related systolic BP gradients differed distinctly across global geographic regions, income levels, and between sexes. The steepest age gradients of BP were observed in populations from Africa and Europe. Women had lower BP levels than men at younger ages (20s and 30s) but subsequently experienced more pronounced age-related BP gradients. Geographically divergent age-related BP gradients were significantly associated with major national public health indicators. Globally, steeper age-related BP slopes were associated with poor BP control, increased disability-adjusted life years, and death rates. A steeper population age-BP slope of 1 mm Hg per 10 years was associated with a decrease in life expectancy of 3.3 years in this population (95% CI, -5.1 to -1.4; P=0.0007). Age-related BP gradients vary considerably across global populations and are associated with variability in BP-related risks and adverse outcomes across regions. Effective public health strategies may require region-specific targeting of adverse BP gradients to improve health outcomes.

Mismatches in Health: A Global Analysis of Discrepancies Between Self-Reported and Tested Mobility and Cognition

The health of individuals is frequently assessed based on self-reported information derived from surveys. However, self-reports are often inconsistent with their tested equivalents, indicating measurement issues. While discrepancies between self-reported and tested health indicators have been investigated for high-income countries in Europe, little comparative research has been conducted involving other low-income regions. This paper analyses discrepancies between self-reported and tested health limitations across 25 countries from six world regions with different income-levels, cultural backgrounds, institutional settings, and epidemiological trajectories. Using harmonised data from the Gateway to Global Aging, we match self-reported mobility and cognition with their tested equivalent to assess discrepancies at the individual level. Our results suggest that the consistency between these measures is strongly correlated with the Human Development Index, with lower scores of development showing higher discrepancies. Examining patterns by age reveals that self-reports do not accurately reflect the deterioration of health associated with aging – tested health exhibits a pronounced age gradient, whereas self-reported health varies little over the life course, particularly self-reported memory. We find no persistent gender differences in consistency. These discrepancies cast doubt on the reliability of mobility and cognitive self-reports, especially when comparing health across nations with differing development levels. * This article belongs to a special issue on “Levels and Trends of Health Expectancy: Understanding its Measurement and Estimation Sensitivity”.

Variations in plant–microbe–soil C:N:P stoichiometry along a 900-year age gradient in Torreya grandis ‘Merrillii’ plantations in Southeast China

Researches on the ecological stoichiometry of forest vegetation at different growth stages under long-term human management activities and its driving factors will help to clarify how the limited nutrient resources are allocated at different growth stages of forests, providing a basis and suggestions for scientific cultivation of artificial forests. In subtropical China, the C:N:P stoichiometry of an ancient Torreya grandis ‘Merrillii’ community was measured in leaves, twigs, roots, soils, and soil microbes with age gradients of 0–50, 50–100, 100–300, 300–500, and more than 500 years. The results showed that the nutrient use varied with tree ages. The N and P concentrations in the leaves, twigs, and roots of T. grandis had the similar increasing trends with the increasing tree age, and the N concentrations in leaves in 0-50-year-old forests were significantly lower than those forests of other ages. Particularly, the N:P ratio of different organs was always below 10, reflecting limited N supply of plants. The soil C content increased with the increasing T. grandis forest ages while the soil microbe C showed a fluctuated trend. There was a higher correlation among the C, N and P contents and their ratios in leaves, twigs and roots of 0-50-year-old forests than that in soil microbes, but inversely at more than 500-year-old forests. The homeostasis analysis results showed that the roots and soil microbes are more indicative of soil nutrient availability. The results of redundancy analysis showed that acid phosphatase activity had the highest impact on soil microbes in 0–10 and 10–20 cm soil layers, confirming that the decomposition and transformation of P in soils is very active. Moreover, soil enzyme activity mediates the influence of soil microbes on soil N and P limitation. In summary, tree age can effect the plant–microbe–soil C:N:P stoichiometry of T. grandis forests. The growth of T. grandis is mainly restricted by N, and reasonable application of N fertilizer is needed to promote its growth.

Age and metal gradients in massive quiescent galaxies at 0.6 ≲ z ≲ 1.0: implications for quenching and assembly histories

ABSTRACT We present spatially resolved, simple stellar population equivalent ages, stellar metallicities, and abundance ratios for 456 massive ($10.3\lesssim \log (\mathrm{M}_*/\mathrm{M}_\odot)\lesssim 11.8$) quiescent galaxies at $0.6\lesssim z\lesssim 1.0$ from the Large Early Galaxy Astrophysics Census, derived using full-spectrum models. Typically, we find flat age and [Mg/Fe] gradients, and negative [Fe/H] gradients, implying iron-rich cores. We also estimate intrinsic [Fe/H] gradients via forward modelling. We examine the observed gradients in three age bins. Younger quiescent galaxies typically have negative [Fe/H] gradients and positive age gradients, possibly indicating a recent central starburst. Additionally, this finding suggests that photometrically measured flat colour gradients in young quiescent galaxies are the result of the positive age and negative metallicity gradients cancelling each other. For older quiescent galaxies, the age gradients become flat and [Fe/H] gradients weaken, though remain negative. Thus, negative colour gradients at older ages are likely driven by metallicity gradients. The diminishing age gradient may result from the starburst fading. Furthermore, the persistence of the [Fe/H] gradients may suggest that the outskirts are simultaneously built up by mergers with lower metallicity satellites. On the other hand, the gradients could be inherited from the star-forming phase, in which case mergers may not be needed to explain our findings. This work illustrates the need for resolved spectroscopy, instead of just photometry, to measure stellar population gradients. Extending these measurements to higher redshift is imperative for understanding how stellar populations in quiescent galaxies are assembled over cosmic time.

Starspots and Undetected Binary Stars Have Distinct Signatures in Young Stellar Associations

Young stars form in associations, meaning that young stellar associations provide an ideal environment to measure the age of a nominally coeval population. Isochrone fitting, which is the typical method for measuring the age of a coeval population, can be impacted by observational biases that obscure the physical properties of a population. One feature in isochrone fits of star-forming regions is an apparent mass-dependent age gradient, where lower-mass stars appear systematically younger than higher-mass stars. Starspots and stellar multiplicity are proposed mechanisms for producing the mass-dependent age gradient, but the relative importance of starspots versus multiplicity remains unclear. We performed a synthetic red optical low-resolution spectroscopic survey of a simulated analog to a 10 Myr stellar association including mass-dependent multiplicity statistics and age-dependent starspot coverage fractions. We found that undetected starspots alone do not produce an apparent mass-dependent age gradient, but instead uniformly reduce the average measured age of the population. We also found that binaries continue to produce an apparent mass-dependent age gradient and introduce more scatter in the age measurement than spots, but are easily removed from the population as long as there are good distance measurements to each target. We conclude that it is crucial to incorporate treatments of both starspots and undetected stellar multiplicity into isochrone fits of young stellar associations to attain reliable ages.

Getting the right tail right: Modeling tails of health expenditure distributions

Health expenditure data almost always include extreme values, implying that the underlying distribution has heavy tails. This may result in infinite variances as well as higher-order moments and bias the commonly used least squares methods. To accommodate extreme values, we propose an estimation method that recovers the right tail of health expenditure distributions. It extends the popular two-part model to develop a novel three-part model. We apply the proposed method to claims data from one of the biggest German private health insurers. Our findings show that the estimated age gradient in health care spending differs substantially from the standard least squares method.

Mechanisms behind high N2O emissions from livestock enclosures in Kenya revealed by dual-isotope and functional gene analyses

Livestock manure contributes to global warming due to greenhouse gas (GHG) emissions, especially nitrous oxide (N2O) and methane (CH4). In the arid and semi-arid lands of Sub-Saharan Africa (SSA), extensive pastoral grazing systems are common, with cattle grazing in the savanna during the day and kept in enclosures (called bomas in Kenya) during the night. Manure is usually not removed from bomas but left to accumulate, leading to excessive local nitrogen loads, making these bomas an overlooked N2O emission hotspot in SSA that is currently not accounted for in national and regional GHG budgets. Here, we present the first in-situ isotope measurements of N2O fluxes from 37 cattle bomas along an age gradient ranging from 0 to 5 years after boma abandonment in Kenya along with functional gene analysis of soil and manure samples. The isotopic composition of the emitted N2O from bomas suggests that on average 91 ± 8% N2O was produced via bacterial denitrification and/or nitrifier denitrification, with little variation across boma age class. We also found high levels of N2O reduction to N2 across all sample sites (81 ± 9%), indicating high levels of N2O consumption. The abundances of denitrification-related genes (nirK and narG) were significantly higher than those of nitrification-related genes (amoA: AOA and AOB) in the cattle manure samples taken from the bomas, corroborating N2O emissions largely being attributed to denitrification. Significant abundance of the reduction-related gene (nosZ) also corroborated the high potential for microbial N2O reduction in bomas. Thus, by combining dual-isotope and functional gene analysis, we were able to identify source processes that govern N2O emissions from these systems. More generally, making use of the manure by spreading it in the vicinity of the bomas or on dedicated forage plots could provide a win-win by enhancing savanna productivity while simultaneously mitigating GHG emissions.

Revegetating Mine Soils with Different Tree Species Influences Molecular Characteristics of Soil Organic Matter

ABSTRACT Although molecular characterization of soil organic carbon is crucial for understanding its dynamics, studies on reclaimed coal mine soil are comparatively limited. Therefore, the primary objective of this study was to ascertain the influence of tree species on the soil organic carbon content and molecular characteristics of soil organic carbon in a chronosequence of reclaimed coal mine soil. To investigate the effects of reclamation time on soil organic carbon characteristics, a chronosequence of three coal mine soil was used, each exhibiting different ages of reclamation: 8, 14, and 25 years. Along a re-vegetation age gradient of 8 to 25 years, the total soil organic carbon content increased. Within the 25 years of restored soil, the FTIR absorption intensities were lowest within the range of 2,920 and 2,850 cm−1, while they were highest within the range of 1,685, 1,425, and 1,285 cm−1which indicates presence of aromatic C=C. This shows that aromatic compounds contributed more significantly to the composition of soil organic carbon compared to aliphatic structures. Based on molecular characteristics, it is suggested that the soil organic carbon in 25-year old revegetated coal mine soil consists of aromatic and recalcitrant carbon. Among three tree species Dalbergia sissoo can be used for reclamation as quality and quantity of carbon found was higher under this tree species. In conclusion, the results indicated that the molecular properties of soil organic carbon were extremely important for understanding the dynamics of soil organic carbon in a restored coal mine soil chronosequence.

Impact of the pandemic on leisure physical activity and alcohol consumption

BackgroundThe COVID-19 pandemic precipitated heightened morbidity and elevated mortality attributed to the SARS-CoV-2 infection. The pandemic also influenced health behaviors such as physical activity (PA) and alcohol consumption. The aim of this study was to examine changes in leisure PA and alcohol consumption in Sweden during the pandemic, and elucidate potential discrepancies in changes across demographic strata and socioeconomic status (SES).MethodsData were retrieved from two waves of the longitudinal cohort study Life conditions, Stress and Health (LSH) (n = 2,523). Two measures of change were used; longitudinal change relative to baseline (2012–2015) and reported change compared to before the pandemic. For these two change measures, differences between sex, age group and SES were analyzed using multinomial logistic regression.ResultsRegardless of the change measure, the proportion of individuals with diminished PA was notably higher among females compared to males. Furthermore, relative to baseline, females were less likely to have increased their PA, however according to the reported change they were more likely to have increased PA. Longitudinal change in PA compared to baseline followed a reversed age gradient, while, according to reported change, a decrease in PA during the pandemic was most prevalent in respondents 45 years of age at baseline (OR = 1.8, CI: 1.2–2.5) and respondents 50 years of age at baseline (OR = 1.7, CI: 1.2–2.4). High SES was associated with a greater variability in PA. Alcohol consumption was generally reduced during the pandemic. However, individuals aged 40 or 45 years at baseline were more likely than others to have initiated risky alcohol consumption.ConclusionsFemales exhibited a greater propensity to alter their PA levels during the pandemic, with the most profound decreases observed among individuals of working ages. Despite a general downturn in alcohol consumption, individuals aged 40 and 45 had a heightened likelihood of having initiated risky alcohol consumption compared to individuals in other age cohorts. In conclusion, societal restrictions during a pandemic render a dual impact on PA levels. While posing a risk for decreased PA among individuals in working ages, the restrictions also present a potential window of opportunity to increase PA, particularly among females.

Computed tomographic age estimation from the iliac crest and ischial tuberosity in an Indian population using supervised machine learning approaches.

Within the pelvis the iliac crest and ischial tuberosity display delayed ossification and fusion, thus, presenting as reliable maturity indicators. Amongst the different iliac crest and ischial tuberosity age estimation methods, the modified Kreitner-Kellinghaus stages constitute one of the more promising methods. The present study was directed towards establishing the applicability of the modified Kreitner-Kellinghaus method using five supervised machine learning approaches. Clinical CT scans of consenting individuals were collected and scored using the modified Kreitner-Kellinghaus method for the iliac crest and ischial tuberosity, independently. Age was subsequently estimated using different machine learning models. Cumulative scores computed from both markers were additionally employed for age estimation using machine learning. For iliac crest age estimation, Random Forest and Gradient Boosting Regression furnished lowest mean absolute error (2.42 years) and root mean square error (3.06 years). For ischial tuberosity age estimation, Gradient Boosting Regression garnered the lowest computations of mean absolute error (2.60 years) and root mean square error (3.09 years). For cumulative score based age estimation, Support Vector Regression and Gradient Boosting Regression yielded lowest mean absolute error (2.48 years) and root mean square error (3.07 years). Obtained error computations indicate that the iliac crest is a more accurate age marker in comparison to the ischial tuberosity. Additionally, cumulative score-based approaches garnered similar/ marginally more precise results in comparison to the iliac crest with all five models. This marginal improvement is not sufficient to justify employing the relatively more complicated cumulative score-based approach for age estimation. Hence, whenever available, the iliac crest should be preferred over the ischial tuberosity/ cumulative score-based approaches for age estimation.

Sensitivity of ocean circulation to warming during the Early Eocene greenhouse

Multiple abrupt warming events ("hyperthermals") punctuated the Early Eocene and were associated with deep-sea temperature increases of 2 to 4 °C, seafloor carbonate dissolution, and negative carbon isotope (δ13C) excursions. Whether hyperthermals were associated with changes in the global ocean overturning circulation is important for understanding their driving mechanisms and feedbacks and for gaining insight into the circulation's sensitivity to climatic warming. Here, we present high-resolution benthic foraminiferal stable isotope records (δ13C and δ18O) throughout the Early Eocene Climate Optimum (~53.26 to 49.14 Ma) from the deep equatorial and North Atlantic. Combined with existing records from the South Atlantic and Pacific, these indicate consistently amplified δ13C excursion sizes during hyperthermals in the deep equatorial Atlantic. We compare these observations with results from an intermediate complexity Earth system model to demonstrate that this spatial pattern of δ13C excursion size is a predictable consequence of global warming-induced changes in ocean overturning circulation. In our model, transient warming drives the weakening of Southern Ocean-sourced overturning circulation, strengthens Atlantic meridional water mass aging gradients, and amplifies the magnitude of negative δ13C excursions in the equatorial to North Atlantic. Based on model-data consistency, we conclude that Eocene hyperthermals coincided with repeated weakening of the global overturning circulation. Not accounting for ocean circulation impacts on δ13C excursions will lead to incorrect estimates of the magnitude of carbon release driving hyperthermals. Our finding of weakening overturning in response to past transient climatic warming is consistent with predictions of declining Atlantic Ocean overturning strength in our warm future.

Is Everyone “Looking for Love?” Trends in Romantic Relationship Interest Among Singles During COVID-19

Using data from the Dynamics of Social Life During COVID-19 Survey (DSL-COVID), we examine dating and romantic relationship interest among singles amid a global pandemic and loneliness epidemic. This study provides a gendered life course perspective to understanding the heterogeneity of singles’ low romantic interest. We find larger gender differences among the previously married than never married singles. In addition, we document a stronger age gradient for single women than men in low romantic interest. We demonstrate that previously married single men’s romantic interest may be more responsive to loneliness than that of single women. These results suggest that lonely single men express the strongest desires to seek romance, net of controls, while single women express lower romantic interest. Overall, we argue for the possibility that a non-trivial segment of singles may exhibit low romantic interest, and their inclusion is important for social science research on union and family formation.

Impacts of Deep-Rooted Apple Tree on Soil Water Balance in the Semi-Arid Loess Plateau, China

Partitioning soil water balance (SWB) is an effective approach for deciphering the impacts of vegetation change on soil hydrological processes. Growing apple trees on the Loess Plateau, China, leads to a substantial deep soil water deficit, posing a serious threat to the sustainable development of apple production. However, the impact of deep-rooted apple trees on SWB remains poorly understood. In this study, we conducted a “Paired Plot” experiment to achieve this objective by decoupling SWB components using water stable isotopes, tritium, and soil water contents from deep soil cores (up to 25 m) under apple orchards with a stand age gradient of 8–23 years. The results showed that deep soil water storage under apple orchards was notably reduced compared to nearby farmland, showing a stand age-related pattern of deep soil water deficit (R2 = 0.91). By analyzing the changing patterns of SWB components, we found that the main factor driving this deficit is the water uptake process controlled by the deep root system. This process is triggered by the increased transpiration demand of apple trees and short-term water scarcity. These findings have implications for understanding soil water dynamics, sustainable agroforestry management, and soil water resources’ protection in this region and other similar water-limited areas.

Genotype-specific development of MEN 2 constituent components in 683 RET carriers.

The age-specific development of the 3 constituent components of multiple endocrine neoplasia type 2 (MEN 2) is incompletely characterized for many of the >30 causative rearranged during transfection (RET) mutations, which this genetic association study aimed to specify. Included in the study were 683 carriers of heterogeneous RET germline mutations: 53 carriers with 1 highest-risk mutation (codon 918); 240 carriers with 8 different high-risk mutations (codon 634); 176 carriers with 16 different intermediate-risk mutations (codon 609, 611, 618, 620 or 630); and 214 carriers with 6 different low-risk mutations (codon 768, 790, 804 or 891). There was a strong genotype-specific development of MEN 2 constituent components, with distinct age gradients from C cell disease to node-negative MTC, from node-negative to node-positive MTC, from node-positive MTC to pheochromocytoma, and from pheochromocytoma to primary hyperparathyroidism. Primary hyperparathyroidism was not observed among the 53 MEN 2B patients who carried highest-risk mutations (age range 0.5-50 yrs.), of whom no more than 12 (23%) and 3 (6%) carriers were older than age 30 yrs. and 35 yrs., respectively. The age-specific development of MTC differed significantly between the 4 RET risk categories, whereas the age-specific development of pheochromocytoma differed significantly only between the 2 strongest RET risk categories. No significant differences were noted in the development of primary hyperparathyroidism. These findings delineate age-specific disease manifestation corridors for the 3 constituent components of MEN 2 by RET genotype. These corridors are useful for initial risk assessment and organ-specific surveillance of newly identified RET carriers going forward.

Aquatic Bird Species Richness and Distribution along an Age Gradient of Reservoirs in Tigray National Regional State, Northern Ethiopia

Aquatic Bird Species Richness and Distribution along an Age Gradient of Reservoirs in Tigray National Regional State, Northern Ethiopia

Porous asphalt mixture performance in cold regions: Case study of Chicago

Porous Asphalt Mixtures (PAMs) improve resilience of flexible pavements in the context of climate change. PAM application in coastal cities like Chicago is of interest; however severe winters compromise the durability of PAMs given their susceptibility to freeze-thaw. This work aimed to evaluate the to-date experience with PAMs in Chicago, exploring benefits and limitations to be considered for future projects in the Southern Lake Michigan region. Full-depth PAM cores were obtained from seven sections, constructed in different years. Tests were conducted to assess the evolution of surface texture, internal structure, and multi-scale material properties. Regarding surface texture, consistent change over time was observed, such as loss of the “channel” structure, and increase in mean profile parameters because of raveling. Also, binder content varies with time within different layer depths. An aging gradient in terms of stiffness from top to bottom within the layer does not necessarily occur. However, binder ductility shows drastic and consistent reduction throughout the layer as aging increases. Analysis of internal structure using a CT scan revealed that there is also a lack of homogeneity in the air void and particle size distributions. Finally, this study suggests that full-depth PAM viscoelastic behavior is sensitive to saturation level, and this is a relevant subject to be considered, since partial saturation may be a condition often observed in the field.

Non-linear response of Norway spruce to climate variation along elevational and age gradients in the Carpathians

Climate change, namely increased warming coupled with a rise in extreme events (e.g., droughts, storms, heatwaves), is negatively affecting forest ecosystems worldwide. In these ecosystems, growth dynamics and biomass accumulation are driven mainly by environmental constraints, inter-tree competition, and disturbance regimes. Usually, climate–growth relationships are assessed by linear correlation due to the simplicity and straightforwardness of modeling. However, applying this method may bias results, since the ecological and physiological responses of trees to environmental factors are non-linear, and usually bell-shaped.In the Eastern Carpathian, Norway spruce is at the southeasternmost edge of its natural occurrence; this region is thus potentially vulnerable to climate change. A non-linear assessment of climate–growth relationships using machine-learning techniques for Norway spruce in this area had not been conducted prior to this study. To address this knowledge gap, we analyzed a large tree-ring network from 158 stands, with over 3000 trees of varying age distributed along an elevational gradient. Our results showed that non-linearity in the growth-climate response of spruce was season-specific: temperatures from the previous autumn and current growing season, along with water availability during winter, induced a bell-shaped response. Moreover, we found that at low elevations, spruce growth was mainly limited by water availability in the growing season, while winter temperatures are likely to have had a slight influence along the entire elevational gradient. Furthermore, at elevations lower than 1400 m, spruce trees were also found to be sensitive to previous autumn water availability. Overall, our results shed new light on the response of Norway spruce to climate in the Carpathians, which may aid in management decisions.

Young Metal-Rich Stars in the Halo of M82: a tidal dwarf galaxy?

Abstract We present Hubble Space Telescope Advanced Camera for Surveys photometry of an arc structure of stars in the southern halo of M82. The structure is located at a projected height of ≈5 kpc from the disk of M82 but its stellar content exhibits a younger mean age than that of typical halo stars. We measured the distance, mean age, and peak metallicity of the stars in the arc and used them to determine the structure’s origin. The arc color-magnitude diagram yields a tip of red giant branch (RGB) distance of 3.63 ± 0.08 Mpc, similar to that of M82, confirming its association with the galaxy. The color-magnitude diagram also reveals a population of predominantly young stars with a mean age of ≈100 - 160 Myr, which is similar to that of the young stars formed in the tidal debris between M81, M82, and NGC 3077. We derived the mean metallicity of the halo stars surrounding the arc to be [Fe/H] ≈ -1.0, similar to that of the RGB population of the halo of M81. The RGB stars in the arc, while they are slightly more metal-rich than the halo RGB, show no spatial correlation with the young stars, suggesting that the arc is consist of mainly young stellar population. Furthermore, the observed age gradient along the structure of the arc indicates that the arc began forming from the closer side to M82, then moving outward. Taken together, the results suggest that the formation of the young stars which gives rise to the arc structure could have been triggered by the interactions between M82’s southern outflow and the HI gas clouds surrounding it, representing a snapshot of a tidal dwarf galaxy in the process of forming.

A catalogue of asteroseismically calibrated ages for APOGEE DR17

Context. The formation history and evolution of the Milky Way through cosmological time is a complex field of research requiring the sampling of highly accurate stellar ages for all Galaxy components. Such highly reliable ages are starting to become available thanks to the synergy of asteroseismology, spectroscopy, stellar modelling, and machine learning analysis in the era of all-sky astronomical surveys.Aims. Our goal is to provide an accurate list of ages for the Main Red Star Sample of the APOGEE DR17 catalogue. In order to reach this goal, ages obtained under asteroseismic constraints are used to train a machine learning model.Methods. As our main objective is to obtain reliable age predictions without the need for asteroseismic parameters, the optimal choice of stellar non-asteroseismic parameters was investigated to obtain the best performances on the test set. The stellar parametersTeffand L, the abundances of [CI/N],[Mg/Ce], and [α/Fe], the U(LSR) velocity, and the vertical height from the Galactic plane ‘Z’ were used to predict ages with a categorical gradient boost decision trees model. The model was trained on two merged samples of the TESS Southern Continuous Viewing Zone and the Second APOKASC catalogue to avoid a data shift and to improve the reliability of the predictions. Finally, the model was tested on an independent data set of the K2 Galactic Archaeology Program.Results. A model with a median fractional age error of 20.8% is obtained. Its prediction variance between the validation and the training set is 4.77%. For stars older than 3 Gyr, the median fractional error in age ranges from 7% to 23%. For stars with ages ranging from 1 to 3 Gyr, the median fractional error in age ranges from 26% to 28%. For stars younger than 1 Gyr, the median fractional error is 43%. The optimised model applies to 125 445 stars from the Main Red Star Sample of the APOGEE DR17 catalogue. Our analysis of the ages confirms previous findings regarding the flaring of the young Galactic disc towards its outer regions. Additionally, we find an age gradient among the youngest stars within the Galactic plane. Finally, we identify two groups of a few metal-poor ([Fe/H] < −1 dex) young stars (Age < 2 Gyr) with similar peculiar chemical abundances and halo kinematics. These are likely the outcomes of the predicted third and latest episode of gas infall in the solar vicinity (~2.7 Gyr ago).Conclusions. We make a catalogue of asteroseismically calibrated ages for 125 445 red giants from the APOGEE DR17 catalogue available to the community. The analysis of the associated stellar parameters corroborates the predictions of different literature models.