Best-fit Age Research Articles

Multiwavelength Investigation of γ-Ray Source MGRO J1908+06 Emission Using Fermi-LAT, VERITAS and HAWC

This paper investigates the origin of the γ-ray emission from MGRO J1908+06 in the GeV–TeV energy band. By analyzing the data collected by the Fermi Large Area Telescope, the Very Energetic Radiation Imaging Telescope Array System, and High Altitude Water Cherenkov, with the addition of spectral data previously reported by LHAASO, a multiwavelength study of the morphological and spectral features of MGRO J1908+06 provides insight into the origin of the γ-ray emission. The mechanism behind the bright TeV emission is studied by constraining the magnetic field strength, the source age, and the distance through detailed broadband modeling. Both spectral shape and energy-dependent morphology support the scenario that inverse Compton emission of an evolved pulsar wind nebula associated with PSR J1907+0602 is responsible for the MGRO J1908+06 γ-ray emission with a best-fit true age of T = 22 ± 9 kyr and a magnetic field of B = 5.4 ± 0.8 μG, assuming the distance to the pulsar d PSR = 3.2 kpc.

Measuring the Chemodynamics and Ages of the M32 and M110 Dwarf Galaxies with APOGEE

We present a full-spectrum-fitting analysis of the central kinematics and chemistry of the Andromeda dwarf satellite galaxies M32 and M110. We use an Markov Chain Monte Carlo routine to fit high-resolution, near-infrared, integrated-light spectra from APOGEE with empirical simple stellar population templates constructed from individual APOGEE stellar spectra. This yields the best-fitting mean radial velocity, velocity dispersion, metallicity, α abundance, and age for each spectrum. In general, our results are consistent with literature values where available, and we explore possible reasons where offsets are measured. This study was presented in a poster at the 243rd meeting of the American Astronomical Society in 2024 January.

Geologic investigation of lobate scarps in the vicinity of Chandrayaan-3 landing site in the southern high latitudes of the moon

The Chandrayaan-3 primary landing site (PLS) is located in the southern high latitude region between 68–70° S and 31–33° E of the Moon. We have found two scarps (scarp #1 and #2) in the surrounding area of PLS. Since lobate scarps are one of the youngest tectonic structures on the Moon and they are seismically active recently, we have conducted a detailed morphological and topographic investigation of the scarps to examine their origin. Subsequently, chronological and seismic investigation of the inferred lobate thrust fault scarps in the PLS region was carried out to assess the safety and the possible hazards to the lander/rover of the Chandrayaan-3 mission. Our analysis reveals that out of the two scarps located in the PLS region, scarp #2 is a typical lobate thrust fault scarp, which is generally comparable in vergence direction, maximum relief, and maximum slope on the scarp face to the scarps found elsewhere on the Moon. Scarp #1 could be potentially a non-fault related scarp. The crater size-frequency distribution (CSFD) based best-fit ages derived for the scarp face, and hanging and footwalls of the scarp reveal that the scarp is a younger generation scarp (∼20–30 Ma). We have found evidence of fresh and faded boulder-fall trails on the rims and walls of multiple craters located around the scarp #2. The seismic measurements reveal potential shallow moonquakes induced by the lobate scarp #2 could have generated a moonquake of a cumulative or maximum possible moment magnitude of Mw 6.3. Based on our analysis of the potential ground shaking caused by the shallow moonquake, it appears that the landing site is safe from seismic hazards. Nevertheless, we propose that the Instrument for Lunar Seismic Activity (ILSA) onboard the Chandrayaan-3 lander could possibly detect recent Mw 4 shallow moonquakes, provided that they occur currently at a focal depth of <1 km.

Spectral age distribution for radio-loud active galaxies in the XMM-LSS field

ABSTRACT Jets of energetic particles, as seen in FR type-I and FR type-II sources, ejected from the centre of radio-loud AGN affect the sources surrounding the intracluster medium/intergalactic medium. Placing constraints on the age of such sources is important in order to measure the jet powers and determine the effects on feedback. To evaluate the age of these sources using spectral age models, we require high-resolution multiwavelength data. The new sensitive and high-resolution MIGHTEE survey of the XMM-LSS field, along with data from the Low Frequency Array (LOFAR) and the Giant Metrewave Radio Telescope (GMRT) provide data taken at different frequencies with similar resolution, which enables us to determine the spectral age distribution for radio-loud AGN in the survey field. In this study, we present a sample of 28 radio galaxies with their best-fitting spectral age distribution analysed using the Jaffe–Perola (JP) model on a pixel-by-pixel basis. Fits are generally good, and objects in our sample show maximum ages within the range of 2.8 to 115 Myr with a median of 8.71 Myr. High-resolution maps over a range of frequencies are required to observe detailed age distributions for small sources, and high-sensitivity maps will be needed in order to observe fainter extended emission. We do not observe any correlation between the total physical size of the sources and their age, and we speculate that both dynamical models and the approach to spectral age analysis may need some modification to account for our observations.

Factors associated with fruit and vegetable consumption among Burmese refugees.

The Burmese population is one of the fast-growing refugee populations in the USA. This study investigated behavioural and environmental factors associated with fruit and vegetable (FV) consumption among Burmese refugees. We conducted a cross-sectional interview survey in 2018-2019. The 24-h recall was used to assess dietary behaviour. Multivariable logistic regression models were constructed with meeting the daily FV consumption recommendation (two or more servings of fruits and three or more servings of vegetables) as the outcome variable. We selected socio-economics, nutritional knowledge, food shopping frequency, ethnicity of preferred food store owners, perceived neighbourhood food environment and network distance to preferred food stores as potential explanatory variables. Two Upstate New York counties. Burmese refugees (n 173) aged ≥18 years. Forty-five percentage of respondents met the daily FV consumption recommendation, and nearly all respondents identified ethnic (Burmese, Chinese/pan-Asian, or South Asian/halal) stores as their preferred stores to purchase FV. In the best-fit model, age (OR 1·08, 95 % CI (1·04, 1·12)) and shopping frequency (OR 1·51, 95 % CI (1·01, 2·26)) were positively associated, and network distance to preferred stores in kilometres (OR 0·81, 95 % CI (0·73, 0·90)) was negatively associated with meeting the daily FV consumption recommendation. No significant effect modifications by car ownership, poverty, length of stay in the USA and Supplemental Nutrition Assistance Program participation were detected. The findings suggested that having Asian ethnic food stores within a short, walkable distance from home and shopping at these stores often can promote healthy dietary behaviour among Burmese refugees.

The Age and Erosion Rate of Young Sedimentary Rock on Mars

The Medusae Fossae Formation (MFF) is an enigmatic sedimentary unit near the equator of Mars, with an uncertain formation process and absolute age. Due to the heavily wind-eroded surface, it is difficult to determine the absolute model age of the MFF using a one-parameter model based on the crater size–frequency distribution function with existing crater count data. We create a new two-parameter model that estimates both age and a constant erosion rate (β) by treating cratering as a random Poisson process. Our study uses new crater count data collected from Context Camera imagery for both the MFF and other young equatorial sedimentary rock. Based on our new model, the Central MFF formed >1.5 Gyr ago and had low erosion rates (<650 nm yr−1), whereas the East MFF, Far East MFF, and Zephyria Planum most likely formed <1.5 Gyr ago and had higher erosion rates (>740 nm yr−1). The top of Aeolis Mons (informally known as Mount Sharp) in Gale Crater and Eastern Candor have relatively young ages and low erosion rates. Based on the estimated erosion rates (since fast erosion permits metastable shallow ice), we also identify several sites, including Zephyria Planum, as plausible locations for shallow subsurface equatorial water ice that is detectable by gamma-ray spectroscopy or neutron spectroscopy. In addition to confirming <1.5 Gyr sedimentary rock formations on Mars, and distinguishing older and younger MFF sites, we find that fast-eroding locations have younger ages and MFF locations with slower erosion have older best-fit ages.

Discovery of an asteroid family linked to (22) Kalliope and its moon Linus

Aims. According to adaptive-optics observations, (22) Kalliope is a 150-km-wide, dense, and differentiated body. Here, we interpret (22) Kalliope in the context of the bodies in its surroundings. While there is a known moon, Linus, with a 5:1 size ratio, no family has been reported in the literature, which is in contradiction with the existence of the moon. Methods. Using the hierarchical clustering method along with physical data, we identified the Kalliope family. It had previously been associated with (7481) San Marcello. We then used various models (N-body, Monte Carlo, and SPH) of its orbital and collisional evolution, including the breakup of the parent body, to estimate the dynamical age of the family and address its link to Linus. Results. The best-fit age is (900 ± 100) Myr according to our collisional model; this is in agreement with the position of (22) Kalliope, which was modified by chaotic diffusion due to 4–1–1 three-body resonance with Jupiter and Saturn. It seems possible that Linus and the Kalliope family were created at the same time, although our SPH simulations show a variety of outcomes for both satellite size and the family size-frequency distribution. The shape of (22) Kalliope itself was most likely affected by the gravitational re-accumulation of ‘streams’, which creates the characteristic hills observed on its surface. If the body was differentiated, its internal structure is most likely asymmetric.

Constraints on the uncertainty, timing, and magnitude of potential Mars oceans from topographic deformation models

Proposed ocean paleoshorelines on Mars have faced criticism over their genetic interpretation and because they deviate significantly from an expected equipotential surface (by many kilometers). Multiple geophysical deformation models have been proposed to explain this large topographic range and deviation including true polar wander and direct Tharsis-induced deformation. Yet, the application of these models is potentially flawed as there exists no consensus on exactly where these proposed paleoshorelines are located. Here, we apply these models to proposed maps and mappings of the putative martian ocean shorelines and show that even when considering deformation due to the rise of Tharsis and its associated true polar wander, the observed deviation within each Arabia level's paleotopography precludes them as past equipotential surfaces. Additionally, we compute best-fit ages for all proposed paleoshorelines relative to the rise of Tharsis and the ages span nearly the entire period of Tharsis construction. Assessment of the paleoelevations of open basin deltas and valley network termini also suggests disagreement with the timing of such features with a paleoocean. Overall, we find that these geophysical deformation models are unable to explain the large elevation ranges observed in the putative shoreline data and that the long-wavelength trends may simply be the result of mismapped features along the topographic dichotomy which itself may have been modified by Tharsis and/or true polar wander.

A new Bayesian approach toward improved regression of low-count U[sbnd]Pb geochronology data generated by LA-ICPMS

UPb dating of hydrogenic and fossil material can be a significant challenge because samples often contain low U levels and variable amounts of non-radiogenic Pb. Line scans using LA-ICPMS provide the widest range of ratios available for defining the radiogenic to common Pb mixing line, hence the best age estimate, but extracting this information requires processing many low-count data. Conventional least-squares regression of ratios based on such data can give inconsistent results. A new approach is introduced where data are regressed as count rates in a 3D space rather than ratios on a 2D plot. This is a maximum likelihood approach in that mixing planes covering a range of ages and common 207Pb/206Pb ratios (PbC) are compared to the data set and used to determine a relative probability density surface whose maximum should fix the best-fit age and common 207Pb/206Pb ratio. 95% confidence errors are determined from T and PbC values that cut off 2.5% of the area to the left and right of 2D plots generated by integration of the 3D plot over PbC and age, respectively. Results from a rugose coral fossil show that this approach gives age results similar to regressions of concordia data and more accurate than Tera-Wasserburg regressions on data from natural samples. Tests on randomly generated synthetic data do not show significant discrepancy between Isoplot ages but they do between values of PbC. The 3D approach is the only one that gives accurate results for both age and PbC.

Backtracing persistent biomarker shifts to the age of onset: A novel procedure applied to men’s and women’s white blood cell counts in post-traumatic stress disorder

• Some biomarkers in mental disorders retain shifted levels long time after the onset. • A backtrace procedure for persistent shifts in cross-sectional data is presented. • It is demonstrated on leukocyte counts in post-traumatic stress disorder. • Neutrophil, lymphocyte and eosinophil counts showed the most impressive results. • The procedure opens new avenues for biomarker research in large epidemiological studies. Traumatic experiences tend to be preserved in altered biomarker profiles. These profiles can be traced back from cross-sectional data regarding the age of exposure. Consequently, the change across developmental stages, e.g. from childhood to adulthood, can also be reconstructed. This study introduces a backtrace procedure that is illustrated using white blood cell (WBC) counts in full / partial post-traumatic stress disorder (PTSD). The procedure was applied separately on men's and women's data to provide a replication of the analysis based on different subsamples. The analysis was carried out with data from the CoLaus|PsyCoLaus study (N = 5111, 2370 men and 2741 women, age range 35–88 years). It was restricted to traumatic experiences that occurred until the age of 35, i.e., the lower age limit of the sample. The WBC counts from up to two assessments were standardized, pooled and assigned to the reported age of trauma exposure. This resulted in age series for each marker, whereas the reference values were based on subjects who did not experience any trauma exposure. The backtrace procedure ascertained the peaks and troughs of the age series and determined the best-fitting critical age range surrounding each peak or trough based on the best p-value from simple t-tests. In CoLaus|PsyCoLaus, 750 participants reported trauma exposure until the age of 35, and 86 (out of 329) men and 187 (out of 421) women thereof were coded with a full or partial PTSD. Full / partial PTSD after trauma exposure in childhood was characterized by increased WBC counts (lymphocytes, eosinophils – in women also neutrophils). This pattern was partly retained during adolescence, in men due to eosinophils counts and in women due to lymphocyte counts. For exposure in young adulthood, the deviations were in the negative direction – in men with decreased basophils, in women with decreased lymphocytes and monocytes. Summarizing, the backtrace approach revealed WBC profiles in PTSD that were specific to particular developmental age stages. The strongest persistent upregulation of the immune system related to trauma exposure was traceable to childhood / early adolescence both in men and in women. Further research will show which biomarkers are similarly suitable for backtracing as WBC counts. As in PTSD, the backtrace approach could also be applied to identifying persistent biomarker profiles in other mental disorders, as well as autoimmune and other chronic diseases.

Extensive glaciation in the Erebus Montes region of Mars

Lobate debris apron (LDA) in the Mars' mid-latitudes substantiate extensive glaciation during the Late Amazonian. Detailed investigation of these landforms is imperative because different areas distributed at different latitudes, distinct geologic settings and varied regional topography may have responded to climate in different ways. In this study, mapping of LDA deposits in Erebus Montes region in the flat, low-lying plains of the northern mid-latitudes has been undertaken and examined at a detail previously not attempted to infer new insights on the history of extensive glaciation. LDA deposits show convex-up, steep terminus profiles consistent with typical down-gradient flow characteristics, and integrated flow patterns akin to the glacial landforms reported along the dichotomy boundary. Evidence for a broad piedmont-like lobe, down-gradient flow within a possible oblique-impact crater, and infilled craters, suggest focused localized flow and glaciation. Lobate flows emanating from small alcoves and superposed on the main LDA are not observed, which likely suggests that there is a lack of multi-stage glaciation facilitated by the alcove microclimatic conditions in the region. Linear-curvilinear ridges on the LDA deposits could be the remnant of the internal flow lineations, and are most likely produced by the sublimation of debris-rich ice. Brain-terrain textures, polygonal cracks and ring-mold craters are ubiquitous on the upper surface of LDA deposits, which provides the morphological evidence for the past accumulation of LDM in the region. Hitherto, radar-based investigations do not provide substantial evidence for the presence of extant water ice beneath LDA deposits. We find that the LDA deposits examined here are more consistent with the cold-based glacial behavior - morphological observations supports existence of the sublimation process in the region. We suggest that the derived best-fit age of ~30 Ma for the LDA deposits indicates age of the debris apron that has been mantled and the mapped LDA deposits in our study should be better represented by a broad age range of ~10–100 Ma. Together, our findings add another well-documented case to support the rapidly accumulating evidences for widespread extensive debris-covered glacial landsystems in the northern mid-latitudes of Mars in the Late Amazonian geological history.

Revised Best Estimates for the Age and Mass of the Methuselah Star HD 140283 Using MESA and Interferometry and Implications for 1D Convection

Abstract In light of recently revised observational measurements of the radius and spectroscopic parameters of the extremely old and metal-poor Gaia benchmark star HD 140283—also known as the Methuselah star due to prior suggestions that its age is in tension with the age of the universe—we present new, best estimates for the star’s mass and age from stellar modeling. These are derived using 1D stellar evolutionary tracks computed with MESA and the most up-to-date measurements from CHARA interferometry. Excluding modeling variance from the uncertainties, we report a mass of 0.809 ± 0.001 M ⊙ and an age of 12.01 ± 0.05 Gyr (1σ). When dominant sources of modeling uncertainty are taken into account, we report 0.81 ± 0.05 M ⊙ and 12 ± 0.5 Gyr, respectively. These results are consistent with recent literature, and the best-fitting age is not in conflict with the currently accepted age of the universe (13.5 Gyr).

Statistical Fitting of Evolutionary Models to Rotation Rates of Sun-like Stars

Abstract We apply for the first time a two-dimensional fitting statistic, τ 2, to rotational-evolution models (REMs) of stars (0.1–1.3 M ⊙) on the period–mass plane. The τ 2 statistic simultaneously considers all cluster rotation data to return a goodness of fit, allowing for data-driven improvement of REMs. We construct data sets for Upper Sco, the Pleiades, and Praesepe, to which we tune our REMs. We use consistently determined stellar masses (calculated by matching K s magnitudes to isochrones) and literature rotation periods. As a first demonstration of the τ 2 statistic, we find the best-fitting gyrochronology age for Praesepe, which is in good agreement with the literature. We then systematically vary three parameters that determine the dependence of our stellar wind torque law on the Rossby number in the saturated and unsaturated regimes, and the location of the transition between the two. By minimizing τ 2, we find best-fit values for each parameter. These values vary slightly between clusters, mass determinations, and initial conditions, highlighting the precision of τ 2 and its potential for constraining REMs, gyrochronology, and our understanding of stellar physics. Our resulting REMs, which implement the best-possible fitting form of a broken-power-law torque, are statistically improved on previous REMs using similar formulations, but still do not simultaneously describe the observed rotation distributions of the lowest masses, which have both slow and fast rotators by the Praesepe age, and the shape of the converged sequence for higher masses. Further complexity in the REMs is thus required to accurately describe the data.

Late Cretaceous-Cenozoic cooling of the southern Lower Yangtze River area: A response to subduction of the Izanagi and Pacific plates

Late Cretaceous-Cenozoic large-scale extension in the eastern South China Block (SCB) has been widely studied. While the exact timing is not well constrained and the geodynamics is inconclusive. Here, we studied the cooling and uplifting history of the southern Lower Yangtze River area (LYRA) in the northeastern SCB using the fission track chronology. The apatite fission track (AFT) single grain ages are decomposed into two best-fit age peaks during 80–50.2 Ma and 43.7–34.5 Ma, respectively. The thermal history modeling of apatite reveals that there exists a rapid cooling process during ca. 80–50 Ma, a slow cooling process during ca. 50–35 Ma and another rapid cooling process during ca. 35–12 Ma. The 80–50.2 Ma age peak corresponds to the rapid cooling process during ca. 80–50 Ma, and the 43.7–34.5 Ma age peaks roughly correspond to the slow cooling process during ca. 50–35 Ma. The tectonic analysis shows that the rapid cooling stage during ca. 80–50 Ma, linked to the rapid rifting in the southern LYRA and coeval strong rifting in the northern LYRA, has resulted from flat subduction of young oceanic crust of the Izanagi Plate. The slow cooling stage during ca. 50–35 Ma is linked to the subduction of the Izanagi-Pacific spreading ridge. The another rapid cooling stage during ca. 35–12 Ma corresponds to a rapid uplifting of the southern LYRA, resulted from the regional compression and tectonic inversion in East China.

On the precision of full-spectrum fitting of simple stellar populations – II. The dependence on star cluster mass in the wavelength range 0.3–5.0 µm

ABSTRACT In this second paper of a series on the accuracy and precision of the determination of age and metallicity of simple stellar populations (SSPs) by means of the full-spectrum fitting technique, we study the influence of star cluster mass through stochastic fluctuations of the number of stars near the top of the stellar mass function, which dominate the flux in certain wavelength regimes depending on the age. We consider SSP models based on the Padova isochrones, spanning the age range $7.0 \le \mbox{log(age/yr}) \le 10.1$. Simulated spectra of star clusters in the mass range 104 ≤ M/M⊙ &amp;lt; 106 are compared with SSP model spectra to determine best-fitting ages and metallicities using a full-spectrum fitting routine in four wavelength regimes: the blue optical (0.35–0.70 µm), the red optical (0.6–1.0 µm), the near-infrared (near-IR; 1.0–2.5 µm), and the mid-IR (2.5–5.0 µm). We compare the power of each wavelength regime in terms of both the overall precision of age and metallicity determination and its dependence on cluster mass. We also study the relevance of spectral resolution in this context by utilizing two different spectral libraries (BaSeL and BT-Settl). We highlight the power of the mid-IR regime in terms of identifying young massive clusters in dusty star-forming regions in distant galaxies. The spectra of the simulated star clusters and SSPs are made available online to enable follow-up studies by the community.

Assessing matrix quality by Raman spectroscopy helps predict fracture toughness of human cortical bone

Developing clinical tools that assess bone matrix quality could improve the assessment of a person’s fracture risk. To determine whether Raman spectroscopy (RS) has such potential, we acquired Raman spectra from human cortical bone using microscope- and fiber optic probe-based Raman systems and tested whether correlations between RS and fracture toughness properties were statistically significant. Calculated directly from intensities at wavenumbers identified by second derivative analysis, Amide I sub-peak ratio I1670/I1640, not I1670/I1690, was negatively correlated with Kinit (N = 58; R2 = 32.4%) and J-integral (R2 = 47.4%) when assessed by Raman micro-spectroscopy. Area ratios (A1670/A1690) determined from sub-band fitting did not correlate with fracture toughness. There were fewer correlations between RS and fracture toughness when spectra were acquired by probe RS. Nonetheless, the I1670/I1640 sub-peak ratio again negatively correlated with Kinit (N = 56; R2 = 25.6%) and J-integral (R2 = 39.0%). In best-fit general linear models, I1670/I1640, age, and volumetric bone mineral density explained 50.2% (microscope) and 49.4% (probe) of the variance in Kinit. I1670/I1640 and v1PO4/Amide I (microscope) or just I1670/I1640 (probe) were negative predictors of J-integral (adjusted-R2 = 54.9% or 37.9%, respectively). While Raman-derived matrix properties appear useful to the assessment of fracture resistance of bone, the acquisition strategy to resolve the Amide I band needs to be identified.

The role of the Haiyuan Fault in accelerating incision rate of the Yellow River at the Mijia Shan Area, northeastern Tibetan Plateau, as revealed by in-situ 10Be dating

In this study, we employed cosmogenic nuclide 10Be analysis to determine the formation ages of the Yellow River terraces in the Mijia Shan and the Laolongwan Basin at the northeastern periphery of the Tibetan Plateau. The aim of this study is to determine local fluvial incision rates and the effect from tectonic activities. The two sets of terraces were surveyed in field and dated by cosmogenic 10Be exposure dating method. The results show that the best-fitting terrace ages in the Mijia Shan are respective 68.0-9.4+11.2 ka for T11 and 174.7-38.4+52 ka for T14. In addition, in the Laolongwan basin, sample S3 constrains an age of 123.9 ± 2.7 ka and S2 yields an age of 45.0 ± 1.8 ka. Combining the strath heights of the sampled terraces, the fluvial incision rates were determined. The results showed that the fluvial incision rate of the Yellow River is ∼1.94 mm/a in the Mijia Shan over the last 175 ka, while a much lower incision rate of ∼0.73 mm/a is yielded in the Laolongwan Basin since the last ∼120 ka. The incision rate in the Mijia Shan is almost twice more than that in the Laolongwan Basin. Considering the same climatic condition in both the Mijia Shan and the Laolongwan Basin, the difference between the two incision rates (∼1.21 mm/a) might be due to local tectonic deformation which is derived from the Haiyuan active strike-slip fault. Consequently, our results showed that the Haiyuan fault plays an important role in accelerating the incision rate in the Mijia Shan. Hence, it is suggested that the role of the main geological structures across the main river should also be considered when studying the evolution of terraces of big rivers.

Physical properties and chemical composition of the cores in the California molecular cloud

Aims. We aim to reveal the physical properties and chemical composition of the cores in the California molecular cloud (CMC), so as to better understand the initial conditions of star formation. Methods. We made a high-resolution column density map (18.2′′) with Herschel data, and extracted a complete sample of the cores in the CMC with the fellwalker algorithm. We performed new single-pointing observations of molecular lines near 90 GHz with the IRAM 30m telescope along the main filament of the CMC. In addition, we also performed a numerical modeling of chemical evolution for the cores under the physical conditions. Results. We extracted 300 cores, of which 33 are protostellar and 267 are starless cores. About 51% (137 of 267) of the starless cores are prestellar cores. Three cores have the potential to evolve into high-mass stars. The prestellar core mass function (CMF) can be well fit by a log-normal form. The high-mass end of the prestellar CMF shows a power-law form with an index α = −0.9 ± 0.1 that is shallower than that of the Galactic field stellar mass function. Combining the mass transformation efficiency (ε) from the prestellar core to the star of 15 ± 1% and the core formation efficiency (CFE) of 5.5%, we suggest an overall star formation efficiency of about 1% in the CMC. In the single-pointing observations with the IRAM 30m telescope, we find that 6 cores show blue-skewed profile, while 4 cores show red-skewed profile. [HCO+]/[HNC] and [HCO+]/[N2H+] in protostellar cores are higher than those in prestellar cores; this can be used as chemical clocks. The best-fit chemical age of the cores with line observations is ~5 × 104 yr.

The GeMS/GSAOI Galactic Globular Cluster Survey (G4CS). I. A Pilot Study of the Stellar Populations in NGC 2298 and NGC 3201

Abstract We present the first results from the GeMS/GSAOI Galactic Globular Cluster Survey (G4CS) of the Milky Way globular clusters NGC 3201 and NGC 2298. Using the Gemini South Adaptive Optics Imager (GSAOI), in tandem with the Gemini Multi-conjugate adaptive optics System (GeMS) on the 8.1 m Gemini-South telescope, we collected deep near-IR observations of both clusters, resolving their constituent stellar populations down to K s ≃ 21 Vega mag. Point-spread function (PSF) photometry was performed on the data using spatially variable PSFs to generate JHK s photometric catalogs for both clusters. These catalogs were combined with Hubble Space Telescope (HST) data to augment the photometric wavelength coverage, yielding catalogs that span the near-UV to near-IR. We then applied 0.14 mas yr−1 accurate proper-motion cleaning and differential-reddening corrections and chose to anchor our isochrones using the lower main-sequence knee and the main-sequence turnoff prior to age determination. As a result of the data quality, we found that the K s versus F606W − K s and F336W versus F336W − K s color–magnitude diagrams were the most diagnostically powerful. We used these two color combinations to derive the stellar population ages, distances, and reddening values for both clusters. Following isochrone fitting using three different isochrone sets, we derived best-fit absolute ages of 12.2 ± 0.5 Gyr and 13.2 ± 0.4 Gyr for NGC 3201 and NGC 2298, respectively. This was done using a weighted average over the two aforementioned color combinations, following a pseudo-χ 2 determination of the best-fit isochrone set. Our derived parameters are in good agreement with recent age determinations of the two clusters, with our constraints on the ages being or ranking among the most statistically robust.

Gemini Spectra of Star Clusters in the Spiral Galaxy M101

Abstract We present low resolution, visible light spectra of 41 star clusters in the spiral galaxy M101, taken with the Gemini/GMOS instrument. We measure Lick indices for each cluster and compare with BaSTI models to estimate their ages and metallicities. We also measure the line-of-sight velocities. We find that 25 of the clusters are fairly young massive clusters (YMCs) with ages of hundreds of millions of years, and 16 appear to be older, globular clusters (GCs). There are at least four GCs with best-fit ages of ≈1–3 Gyr and eight with best-fit ages of ≈5–10 Gyr. The mean metallicity of the YMCs is [Fe/H] ≈ −0.1 and for the GCs is [Fe/H] ≈ −0.9. We find a near-continuous spread in both age and metallicity for our sample, which may indicate that M101 had a more-or-less continuous history of cluster and star formation. From the kinematics, we find that the YMCs rotate with the H i gas fairly well, while the GCs do not. We cannot definitively say whether the GCs sampled here lie in an inner halo, thick disk, or bulge/psuedobulge component, although given the very small bulge in M101, the last seems unlikely. The kinematics and ages of the YMCs suggest that M101 may have undergone heating of its disk or possibly a continuous merger/accretion history for the galaxy.