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NASA NTRS1982

Nuclear constraints on the age of the universe

A review is made of how one can use nuclear physics to put rather stringent limits on the age of the universe and thus the cosmic distance scale. The age can be estimated to a fair degree of accuracy. No single measurement of the time since the Big Bang gives a specific, unambiguous age. There are several methods that together fix the age with surprising precision. In particular, there are three totally independent techniques for estimating an age and a fourth technique which involves finding consistency of the other three in the framework of the standard Big Bang cosmological model. The three independent methods are: cosmological dynamics, the age of the oldest stars, and radioactive dating. This paper concentrates on the third of the three methods, and the consistency technique.

Schramm, D. N.↗

NASA NTRS1983

Nuclear constraints on the age of the universe

Schramm, D. N.↗

NASA NTRS2020

An Impact Crater Origin for the InSight Landing Site at Homestead Hollow, Mars: Implications for Near Surface Stratigraphy, Surface Processes, and Erosion Rates

The InSight mission to Mars landed within Homestead hollow on an Early Amazonian lavaplain. The hollow is a 27‐m‐diameter, 0.3‐m‐deep quasi‐circular depression that shares morphologic and sedimentologic characteristics to degraded impact craters. Unlike the intercrater plains outside of the hollow, the interior lacks cobbles and is dominated by loose sand, granules, and pebbles. Fresher craters near the landing site exhibit meter‐scale bedforms in their ejecta and on their floors due to sediment trapping.The sedimentology of the interior fill of Homestead hollow suggests similar trapping. The hollow falls along amorphologic continuum that requires low rates of rim degradation and fill. Crater degradation rates (rim erosion plus filling) in the landing site decline nonlinearly through time from 10−2to 10−4m/Myr as craters evolve to a hollow‐like form. Rim erosion rates are lower initially, at 10−3m/Myr, but converge with degradation rates to 10−4m/Myr. This implies that while filling plays an important role soon after crater formation, it is limited in later stages. Crater statistics indicate that the bulk of the fill occurred in the first~50 Myr for Homestead hollow. The estimated maximum age of the hollow is ~400 to 700 Myr. This requires near‐zero fill aggradation and long‐term soil stability for the bulk of the crater's history. Fill stability manifests in Homestead hollow as a ~5‐to 10‐cm‐thick duricrust, formed by exchanges of atmospheric water vapor with soil. The estimated degradation in the hollow requires ~2 to 3 m of sedimentary fill beneath the lander.

Maria Elaine Banks↗

NASA NTRS1997

Analysis of strontium metabolism in humans on the basis of the Techa river data

Age and sex features of strontium metabolism have been analyzed on studies of the population residing on the banks of the Techa river which was contaminated by fission products during the years 1949-1956. Measurements of 90Sr body burden have been performed since 1974 using a whole-body counter, and these have made it possible to estimate age-specific long-term retention and elimination rates for men and women. Regarding the retention that correlated with the respective maturation ages, distinct sex differences have been observed for adolescents, whereas only postmenopausal women showed a sharp increase of their elimination rates. There were no differences concerning the reproductive ages. Our experimental findings have a clear physiological interpretation and can be used to develop metabolic models for bone-seeking radionuclides.

NASA Discipline Radiation Health↗

DOE OSTI2018

Fundamental Properties of Co-moving Stars Observed by Gaia

We have estimated fundamental parameters for a sample of co-moving stars observed by Gaia and identified by Oh et al. We matched the Gaia observations to the 2MASS and Wide-Field Infrared Survey Explorer catalogs and fit MIST isochrones to the data, deriving estimates of the mass, radius, [Fe/H], age, distance, and extinction to 9754 stars in the original sample of 10606 stars. We verify these estimates by comparing our new results to previous analyses of nearby stars, examining fiducial cluster properties, and estimating the power-law slope of the local present-day mass function. A comparison to previous studies suggests that our mass estimates are robust, while metallicity and age estimates are increasingly uncertain. We use our calculated masses to examine the properties of binaries in the sample and show that separation of the pairs dominates the observed binding energies and expected lifetimes.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

A Tanks-in-Series Approach to Estimate Parameters for Lithium-Ion Battery Models

Advanced Battery Management Systems (BMS) play a vital role in monitoring, predicting, and controlling the performance of lithium-ion batteries. BMS employing sophisticated electrochemical models can help increase battery cycle life and minimize charging time. However, in order to realize the full potential of electrochemical model-based BMS, it is critical to ensure accurate predictions and proper model parameterization. The accuracy of the predictions of an electrochemical model is dependent on the accuracy of its parameters, the values of which might change with battery cycling and aging. Parameter estimation for an electrochemical model is generally challenging due to the nonlinear nature and computational complexity of the model equations. To this end, this work utilizes the recently proposed Tanks-in-Series model for Li-ion batteries (J.Electrochem. Soc., 167, 013534 (2020)) to perform parameter estimation. The Tanks-in-Series approach allows for substantially faster parameter estimation compared to the original pseudo two-dimensional (p2D) model. The objective of this work is thus to demonstrate the gain in computational efficiency from the Tanks-in-Series approach. A sensitivity analysis of model parameters is also performed to benchmark the fidelity of the Tanks-in-Series model.

25 ENERGY STORAGE↗

DOE OSTI2023

Evidence for ground-state electron capture of K 40

Potassium-40 is a widespread, naturally occurring isotope whose radioactivity impacts estimated geological ages spanning billions of years, nuclear structure theory, and subatomic rare-event searches—including those for dark matter and neutrinoless double-beta decay. The decays of this long-lived isotope must be precisely known for its use as a geochronometer, and to account for its presence in low-background experiments. There are several known decay modes for potassium-40, but a predicted electron-capture decay directly to the ground state of argon-40 has never been observed. The existence of this decay mode impacts several fields, while theoretical predictions span an order of magnitude. Here we report on the first, successful observation of this rare decay mode, obtained by the KDK (potassium decay) Collaboration using a novel combination of a low-threshold x-ray detector surrounded by a tonne-scale, high-efficiency γ -ray tagger at Oak Ridge National Laboratory. A blinded analysis reveals a distinctly nonzero ratio of intensities of ground-state electron-captures ( I EC 0 ) over excited-state ones ( I EC * ) of I EC 0 / I EC * = 0.0095 ± stat 0.0022 ± sys 0.0010 (68% CL), with the null hypothesis rejected at 4 σ [Stukel et al. , Phys. Rev. Lett. 131 , 052503 (2023) ]. In terms of branching ratio, this unambiguous signal yields I EC 0 = 0.098 % ± stat 0.023 % ± sys 0.010 % , roughly half of the commonly used prediction. This first observation of a third-forbidden unique electron capture improves our understanding of low-energy backgrounds in dark-matter searches and has implications for nuclear-structure calculations. For example, a shell-model based theoretical estimate for the neutrinoless double-beta decay half-life of calcium-48 is increased by a factor of 7 - 2 + 3 . Our nonzero measurement shifts geochronological ages by up to a percent; implications are illustrated for Earth and solar system chronologies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

NASA NTRS1976

On the calculation of cosmic-ray exposure ages of stone meteorites

Abundances of cosmic ray-produced noble gases and Al-26, including some new measurements, have been compiled for some 23 stone meteorites with exposure ages less than 3,000,000 yr. Concentrations of cosmogenic He, Ne, and Ar in these meteorites have been corrected for differences in target element abundances by normalization to L-chondrite chemistry. Combined noble gas measurements in depth samples of the Keyes and St. Severin chondrites are utilized to derive equations for normalizing the production rates of cosmogenic He-3, Ne-21, and Ar-38 in chondrites to an adopted 'average' shielding. The measured unsaturated AL-26 concentrations and the calculated equilibrium Al-26 for these meteorites are combined to estimate exposure ages. These exposure ages are statistically compared with chemistry- and shielding-corrected concentrations of cosmogenic He, Ne, and Ar to derive absolute production rates for these nuclides, which are found to be roughly 25% higher than production rates used in the past. From these production rates and relative chemical correction factors, production rates for other classes of stone meteorites are derived.

Cressy, P. J., Jr.↗

DOE OSTI2017

Using 81 Kr and noble gases to characterize and date groundwater and brines in the Baltic Artesian Basin on the one-million-year timescale

Analyses for 81 Kr and noble gases on groundwater from the deepest aquifer system of the Baltic Artesian Basin (BAB) were performed to determine groundwater ages and uncover the flow dynamics of the system on a timescale of several hundred thousand years. We find that the system is controlled by mixing of three distinct water masses: Interglacial or recent meteoric water (δ 18 O ≈ –10.4‰) with a poorly evolved chemical and noble gas signature, glacial meltwater (δ 18 O ≤ –18‰) with elevated noble gas concentrations, and an old, high-salinity brine component (δ 18 O ≥ –4.5‰, ≥ 90 g Cl – /L) with strongly depleted atmospheric noble gas concentrations. The 81 Kr measurements are interpreted within this mixing framework to estimate the age of the end-members. Deconvoluted 81 Kr ages range from 300 ka to 1.3 Ma for interglacial or recent meteoric water and glacial meltwater. For the brine component, ages exceed the dating range of the ATTA-3 instrument of 1.3 Ma. The radiogenic noble gas components 4 He* and 40 Ar* are less conclusive but also support an age of > 1 Ma for the brine. Based on the chemical and noble gas concentrations and the dating results, we conclude that the brine originates from evaporated seawater that has been modified by later water–rock interaction. Furthermore, as the obtained tracer ages cover several glacial cycles, we discuss the impact of the glacial cycles on flow patterns in the studied aquifer system.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2022

Disentangling Alzheimer’s disease neurodegeneration from typical brain ageing using machine learning

Abstract Neuroimaging biomarkers that distinguish between changes due to typical brain ageing and Alzheimer’s disease are valuable for determining how much each contributes to cognitive decline. Supervised machine learning models can derive multivariate patterns of brain change related to the two processes, including the Spatial Patterns of Atrophy for Recognition of Alzheimer’s Disease (SPARE-AD) and of Brain Aging (SPARE-BA) scores investigated herein. However, the substantial overlap between brain regions affected in the two processes confounds measuring them independently. We present a methodology, and associated results, towards disentangling the two. T1-weighted MRI scans of 4054 participants (48–95 years) with Alzheimer’s disease, mild cognitive impairment (MCI), or cognitively normal (CN) diagnoses from the Imaging-based coordinate SysTem for AGIng and NeurodeGenerative diseases (iSTAGING) consortium were analysed. Multiple sets of SPARE scores were investigated, in order to probe imaging signatures of certain clinically or molecularly defined sub-cohorts. First, a subset of clinical Alzheimer’s disease patients (n = 718) and age- and sex-matched CN adults (n = 718) were selected based purely on clinical diagnoses to train SPARE-BA1 (regression of age using CN individuals) and SPARE-AD1 (classification of CN versus Alzheimer’s disease) models. Second, analogous groups were selected based on clinical and molecular markers to train SPARE-BA2 and SPARE-AD2 models: amyloid-positive Alzheimer’s disease continuum group (n = 718; consisting of amyloid-positive Alzheimer’s disease, amyloid-positive MCI, amyloid- and tau-positive CN individuals) and amyloid-negative CN group (n = 718). Finally, the combined group of the Alzheimer’s disease continuum and amyloid-negative CN individuals was used to train SPARE-BA3 model, with the intention to estimate brain age regardless of Alzheimer’s disease-related brain changes. The disentangled SPARE models, SPARE-AD2 and SPARE-BA3, derived brain patterns that were more specific to the two types of brain changes. The correlation between the SPARE-BA Gap (SPARE-BA minus chronological age) and SPARE-AD was significantly reduced after the decoupling (r = 0.56–0.06). The correlation of disentangled SPARE-AD was non-inferior to amyloid- and tau-related measurements and to the number of APOE ε4 alleles but was lower to Alzheimer’s disease-related psychometric test scores, suggesting the contribution of advanced brain ageing to the latter. The disentangled SPARE-BA was consistently less correlated with Alzheimer’s disease-related clinical, molecular and genetic variables. By employing conservative molecular diagnoses and introducing Alzheimer’s disease continuum cases to the SPARE-BA model training, we achieved more dissociable neuroanatomical biomarkers of typical brain ageing and Alzheimer’s disease.

Hwang, Gyujoon↗

DOE OSTI2019

Simulations of high-velocity impacts on metal in preparation for the Psyche mission

In 2026, the NASA Discovery mission Psyche will orbit the asteroid (16) Psyche, the largest known metal-rich asteroid in the main belt. To estimate relative ages of the surface, identify re-surfacing events and better constrain Psyche's history, impact craters will be counted and characterized. No spacecraft has ever visited a metal-rich small body; therefore, laboratory-scale impact experiments and numerical simulations will play an important role in the interpretation of the mission's data. However, the planetary applications of high-velocity impacts have so far mostly been studied for silicate targets. Limited attention has been drawn to planetary objects predominantly made of metal, and more laboratory experiments and numerical calibrations are needed. As part of this effort, we present a suite of numerical simulations using an adaptative smoothed particles hydrodynamics numerical code (ASPH) reproducing a high-velocity impact experiment conducted on a steel target. This work primarily focuses on the influence of the chosen equation of state and initial distribution of flaws in the material on the estimated crater dimensions, damage and temperature. Additionally, we find that changing the EOS and initial flaw distribution affects the crater dimensions, though for a vast majority of cases the dimensions remain within 20% of the experimental values. The target is in most cases only locally weakened but not fully damaged, independently from the EOS chosen. Finally, temperatures at the impact point and around the forming crater can reach values above the melting point of iron at <100 GPa, which is in agreement with experimental observations. These results allow us to speculate on the differences expected between the surfaces of visited silicate-rich asteroids and that of the metal-rich target of the Psyche mission.

36 MATERIALS SCIENCE↗

DOE OSTI2017

GASP. III. JO36: A Case of Multiple Environmental Effects at Play?

The so-called jellyfish galaxies are objects exhibiting disturbed morphology, mostly in the form of tails of gas stripped from the main body of the galaxy. Several works have strongly suggested ram pressure stripping to be the mechanism driving this phenomenon. Here, we focus on one of these objects, drawn from a sample of optically selected jellyfish galaxies, and use it to validate sinopsis, the spectral fitting code that will be used for the analysis of the GASP (GAs Stripping Phenomena in galaxies with MUSE) survey, and study the spatial distribution and physical properties of the gas and stellar populations in this galaxy. We compare the model spectra to those obtained with gandalf, a code with similar features widely used to interpret the kinematics of stars and gas in galaxies from IFU data. We find that sinopsis can reproduce the pixel-by-pixel spectra of this galaxy at least as well as gandalf does, providing reliable estimates of the underlying stellar absorption to properly correct the nebular gas emission. Using these results, we find strong evidences of a double effect of ram pressure exerted by the intracluster medium onto the gas of the galaxy. A moderate burst of star formation, dating between 20 and 500 Myr ago and involving the outer parts of the galaxy more strongly than the inner regions, was likely induced by a first interaction of the galaxy with the intracluster medium. Stripping by ram pressure, plus probable gas depletion due to star formation, contributed to create a truncated ionized gas disk. The presence of an extended stellar tail on only one side of the disk points instead to another kind of process, likely gravitational interaction by a fly-by or a close encounter with another galaxy in the cluster.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

The evolution of the Cappadocia Geothermal Province, Anatolia (Turkey): geochemical and geochronological evidence

Cappadocia Geothermal Province (CGP), central Turkey, consists of nine individual geothermal regions controlled by active regional fault systems. This paper examines the age dating of alteration minerals and the geochemistry (trace elements and isotopes) of the alteration minerals and geothermal waters, to assess the evolution of CGP in relation to regional tectonics. Ar–Ar age data of jarosite and alunite show that the host rocks were exposed to oxidizing conditions near the Earth’s surface at about 5.30 Ma. Based on the δ{sup 18}O–δD relationhip, water samples had a high altitude meteoric origin. The δ{sup 34}S values of jarosite and alunite indicate that water samples from the southern part of the study area reached the surface after circulation through volcanic rocks, while northern samples had traveled to the surface after interacting with evaporates at greater depths. REY (rare earth elements and yttrium) diagrams of alteration minerals (especially illite, jarosite and alunite) from rock samples, taken from the same locations as the water samples, display a similar REY pattern to water samples. This suggests that thermal fluids, which reached the surface along a fault zone and caused the mineral alteration in the past, had similar chemical composition to the current geothermal water. The geothermal conceptual model, which defines a volcanically heated reservoir and cap rocks, suggests there are no structural drawbacks to the use of the CGP geothermal system as a resource. However, fluid is insufficient to drive the geothermal system as a result of scanty supply of meteoric water due to evaporation significantly exceeding rainfall.

58 GEOSCIENCES↗

DOE OSTI2018

Application of multiple-isotope and groundwater-age data to identify factors affecting the extent of denitrification in a shallow aquifer near a river in South Korea

The extent of denitrification in a small agricultural area near a river in Yangpyeong, South Korea, was determined using multiple isotopes, groundwater age, and physicochemical data for groundwater. The shallow groundwater at one monitoring site had high concentrations of NO{sub 3}-N (74–83 mg L{sup −1}). The δ{sup 15}N-NO{sub 3} values for groundwater in the study area ranged between +9.1 and +24.6‰ in June 2014 and +12.2 to +21.6‰ in October 2014. High δ{sup 15}N-NO{sub 3} values (+10.7 to +12.5‰) in both sampling periods indicated that the high concentrations of nitrate in the groundwater originated from application of organic fertilizers and manure. In the northern part of the study area, some groundwater samples showed elevated δ{sup 15}N-NO{sub 3} and δ{sup 18}O-NO{sub 3} values, which suggest that nitrate was removed from the groundwater via denitrification, with N isotope enrichment factors ranging between −4.8 and −7.9‰ and O isotope enrichment factors varying between −3.8 and −4.9‰. Similar δD and δ{sup 18}O values of the surface water and groundwater in the south appear to indicate that groundwater in that area was affected by surface-water infiltration. The mean residence times (MRTs) of groundwater showed younger ages in the south (10–20 years) than in the north (20–30 years). Hence, it was concluded that denitrification processes under anaerobic conditions with longer groundwater MRT in the northern part of the study area removed considerable amounts of nitrate. This study demonstrates that multi-isotope data combined with physicochemical data and age-dating information can be effectively applied to characterize nitrate contaminant sources and attenuation processes.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2018

National and subnational mortality and disability-adjusted life years (DALYs) attributable to 17 occupational risk factors in Iran, 1990–2015

Highlights: • Mortality and morbidity from 17 occupational risks in Iran, 1990–2015 were estimated. • During 1990–2015, national DALYs from occupational risks increased by 65%. • During 1990–2015, the share of women in the attributable DALYs rose from 13% to 20%. • Proportion of YLLs in national DALYs due to occupational risks in 2015 was 23%. • Spatial inequality in the attributable DALY rate decreased from 1990 to 2015. We estimated age-sex specific and cause-specific mortality, years of life lost due to premature mortality (YLLs), years lived with disability (YLDs) and disability-adjusted life years (DALYs) attributable to 17 individual occupational risks in Iran at the national and subnational levels in 1990–2015 based on the Global Burden of Disease Study 2015 (GBD 2015). The burden of disease attributable to occupational risk factors was calculated using the comparative risk assessment methodology based on 10 outcomes and 21 risk-outcome pairs. The temporal changes in the attributable burden of disease were decomposed into the contribution of population growth, population ageing, risk-deleted DALY rate, and risk exposure. National DALYs attributable to occupational risks at the national level in 1990, 2005, and 2015 were 138,210 (95% uncertainty interval 64,429–223,028), 193,243 (91,645–310,281), and 228,310 (106,782–371,709), respectively indicating a total increase of 65% (65–67) during the study period. Between 1990 and 2015, the share of the attributable DALYs for women rose by 55% (51–58) from 13% (12–14) to 20% (19–21). The proportion of YLLs in national DALYs attributable to occupational risks during the study period slightly decreased from 24% in 1990 to 23% in 2015. The five occupational risks with the highest contributions in the national attributable DALYs in 2015 were ergonomic factors (107,490), noise (52,122), exposure to particulate matter, gases, and fumes (26,847), asthmagens (19,347), and exposure to asbestos (7842). From 1990 to 2015, the increase in total DALYs attributable to occupational carcinogens (112%) was higher than that for other occupational risks. During the study period, changes in risk deleted DALY rate and risk exposure led to decreases in total DALYs attributable to occupational risks by 14% and 30%, respectively. Based on the Gini coefficient, spatial inequality in DALY rate attributable to occupational risks at the provincial level decreased during 1990–2015. A comprehensive plan for management of exposure to occupational risks, especially occupational carcinogens can cause an important effect for control of the increasing trend of occupational health losses.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2018

Contribution of climate and land cover changes to reduction in soil erosion rates within small cultivated catchments in the eastern part of the Russian Plain during the last 60 years

Highlights: • The soil erosion has decreased at least 2–3 times over the last 30 years at the RP. • The increase in winter air temperature is the key reason for the soil loss reduction. • The crop rotation changes is the factor of erosion rate reduction at the forest zone. The eastern part of the Russian Plain is an important agricultural region of European Russia with high proportion of cultivated lands in the steppe, forest-steppe and forest (southern part) landscape zones. Soil erosion is the main process of land degradation and surface water contamination there. Climate and land cover changes have been observed in this region during the last 30 years. However, field quantitative assessments of soil erosion rates are not available for the eastern part of European Russia due to the lack of monitoring data as well as the evaluation of erosion/deposition processes in cultivated catchments using other field methods. Three representative small cultivated catchments with high (> 80%) proportion of cultivated lands were selected in the forest (southern part), forest-steppe and steppe zones of the study region to evaluate sedimentation rates in dry valley bottoms of the catchments for two-time intervals (1963–1986 and 1987–2016) based on the application of the bomb-derived and Chernobyl-derived {sup 137}Cs isotope for sediment dating. The 3–4 depth {sup 137}Cs profiles were used to assess the sedimentation rates within the each investigated catchment. It was established that the sedimentation rates have considerably decreased (at least 2–3 times) over the last 30 years compared to 1963–1986 in all the investigated catchments. This is in agreement with results of erosion rate calculations using erosion models for the forest zone, however not consistent with erosion rates assessments for the forest-steppe and steppe zones. According to the model calculations, erosion rates show a slight decrease in the forest-steppe zone and increase in the steppe zone. The reduction in surface runoff during snowmelt period is one of the reasons for decrease in erosion rates within cultivated slopes for all the investigated catchments. The increase in proportion of perennial grasses in the regional crop rotation is another important reason for the decrease in erosion rates for the catchment located in the south of the forest zone. The importance of land cover changes in a major decrease of soil losses from the cultivated fields of the investigated catchments located in the forest-steppe and steppe zones cannot be identified due to the lack detailed information about crop rotation for those particular sites. However, available regional information about crop rotation changes for the two-time intervals (1960–1980 and 1996–2012) do not explain very high reduction in sedimentation rates in the dry valley bottoms after 1986.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2015

A preliminary study of paleotsunami deposit along the south coast of East Java: Pacitan-Banyuwangi

Along the southern coast of East Java Indonesia, at a number of localities, it can be identified and attempted to assign the age of tsunami deposit. Laboratory analyses were conducted also to support this study such as Granulometry, Paleontology and radiometric dating analysis. The presence of tsunami 1994 deposit in the area of Pancer, Lampon, Prigi and Grajagan was found, as a result of 7.8 Magnitude Banyuwangi Earthquake. The radiometric dating analysis also identified some paleotsunami deposit of about 1921 and 1930 in the area of Prigi and Teleng. This paleotsunami is assumed to have a correlation with an earthquake in the south of Java at the same time. An outcrop in the Prigi and Teleng strongly convinced the fact of an earthquake generated tsunami in the south of Java in the year of about 1921 and 1930.

58 GEOSCIENCES↗

DOE OSTI2015

Discovery of a faint outer halo milky way star cluster in the southern sky

We report the discovery of a new, low-luminosity star cluster in the outer halo of the Milky Way. High-quality gr photometry is presented, from which a color–magnitude diagram is constructed, and estimates of age, [Fe/H], [α/Fe], and distance are derived. The star cluster, which we designate as Kim 2, lies at a heliocentric distance of ∼105 kpc. With a half-light radius of ∼12.8 pc and ellipticity of ϵ ∼ 0.12, it shares the properties of outer halo globular clusters, except for at higher metallicity ([Fe/H] ∼ −1.0) and lower luminosity (M{sub V}∼−1.5). These parameters are similar to those for the globular cluster AM 4, which is considered to be associated with the Sagittarius dwarf spheroidal galaxy. We find evidence of dynamical mass segregation and the presence of extra-tidal stars that suggests that Kim 2 is most likely a star cluster. Spectroscopic observations for radial-velocity membership and chemical abundance measurements are needed to further understand the nature of the object.

79 ASTRONOMY AND ASTROPHYSICS↗