Aims. Our goal is to study the different morphologies associated to the interaction of the stellar winds of AGB stars and red supergiants with the interstellar medium (ISM) to follow the fate of the ...circumstellar matter injected into the interstellar medium. Methods. Far-infrared Herschel/PACS images at 70 and 160 μm of a sample of 78 Galactic evolved stars are used to study the (dust) emission structures developing out of stellar wind-ISM interaction. In addition, two-fluid hydrodynamical simulations of the coupled gas and dust in wind-ISM interactions are used for comparison with the observations. Results. Four distinct classes of wind-ISM interaction (i.e. “fermata”, “eyes”, “irregular”, and “rings”) are identified, and basic parameters affecting the morphology are discussed. We detect bow shocks for ~40% of the sample and detached rings for ~20%. The total dust and gas mass inferred from the observed infrared emission is similar to the stellar mass loss over a period of a few thousand years, while in most cases it is less than the total ISM mass potentially swept-up by the wind-ISM interaction. De-projected stand-off distances (R0) – defined as the distance between the central star and the nearest point of the interaction region – of the detected bow shocks (“fermata” and “eyes”) are derived from the PACS images and compared to previous results, model predictions, and the simulations. All observed bow shocks have stand-off distances smaller than 1 pc. Observed and theoretical stand-off distances are used together to independently derive the local ISM density. Conclusions. Both theoretical (analytical) models and hydrodynamical simulations give stand-off distances for adopted stellar properties that are in good agreement with the measured de-projected stand-off distance of wind-ISM bow shocks. The possible detection of a bow shock – for the distance-limited sample – appears to be governed by its physical size as set roughly by the stand-off distance. In particular the star’s peculiar space velocity and the density of the ISM appear decisive in detecting emission from bow shocks or detached rings. In most cases the derived ISM densities concur with those typical of the warm neutral and ionised gas in the Galaxy, though some cases point towards the presence of cold diffuse clouds. Tentatively, the “eyes” class objects are associated to (visual) binaries, while the “rings” generally do not appear to occur for M-type stars, only for C or S-type objects that have experienced a thermal pulse.
Many palaeoclimate studies have quantified pre-anthropogenic climate change to calculate climate sensitivity (equilibrium temperature change in response to radiative forcing change), but a lack of ...consistent methodologies produces a wide range of estimates and hinders comparability of results. Here we present a stricter approach, to improve intercomparison of palaeoclimate sensitivity estimates in a manner compatible with equilibrium projections for future climate change. Over the past 65 million years, this reveals a climate sensitivity (in K W(-1) m(2)) of 0.3-1.9 or 0.6-1.3 at 95% or 68% probability, respectively. The latter implies a warming of 2.2-4.8 K per doubling of atmospheric CO(2), which agrees with IPCC estimates.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract Background Practitioners and researchers are interested in assessing children's dietary intake and physical activity together to maximize resources and minimize subject burden. Objective Our ...aim was to investigate differences in dietary and/or physical activity recall accuracy by content (diet only; physical activity only; diet and physical activity), retention interval (same-day recalls in the afternoon; previous-day recalls in the morning), and grade (third; fifth). Design Children (n=144; 66% African American, 13% white, 12% Hispanic, 9% other; 50% girls) from four schools were randomly selected for interviews about one of three contents. Each content group was equally divided by retention interval, each equally divided by grade, each equally divided by sex. Information concerning diet and physical activity at school was validated with school-provided breakfast and lunch observations, and accelerometry, respectively. Dietary accuracy measures were food-item omission and intrusion rates, and kilocalorie correspondence rate and inflation ratio. Physical activity accuracy measures were absolute and arithmetic differences for moderate to vigorous physical activity minutes. Statistical analyses performed For each accuracy measure, linear models determined effects of content, retention interval, grade, and their two-way and three-way interactions; ethnicity and sex were control variables. Results Content was significant within four interactions: intrusion rate (content×retention-interval×grade; P =0.0004), correspondence rate (content×grade; P =0.0004), inflation ratio (content×grade; P =0.0104), and arithmetic difference (content×retention-interval×grade; P =0.0070). Retention interval was significant for correspondence rate ( P =0.0004), inflation ratio ( P =0.0014), and three interactions: omission rate (retention-interval×grade; P =0.0095), intrusion rate, and arithmetic difference (both already mentioned). Grade was significant for absolute difference ( P= 0.0233) and five interactions mentioned. Content effects depended on other factors. Grade effects were mixed. Dietary accuracy was better with same-day than previous-day retention interval. Conclusions Results do not support integrating dietary intake and physical activity in children's recalls, but do support using shorter rather than longer retention intervals to yield more accurate dietary recalls. Additional validation studies need to clarify age effects and identify evidence-based practices to improve children's accuracy for recalling dietary intake and/or physical activity.
Earth system climate sensitivity (ESS) is the long‐term (>103 year) response of global surface temperature to doubled CO2 that integrates fast and slow climate feedbacks. ESS has energy policy ...implications because global temperatures are not expected to decline appreciably for at least 103 year, even if anthropogenic greenhouse gas emissions drop to zero. We report provisional ESS estimates of 3 °C or higher for some of the Cretaceous and Cenozoic based on paleo‐reconstructions of CO2 and temperature. These estimates are generally higher than climate sensitivities simulated from global climate models for the same ancient periods (approximately 3 °C). Climate models probably do not capture the full suite of positive climate feedbacks that amplify global temperatures during some globally warm periods, as well as other characteristic features of warm climates such as low meridional temperature gradients. These absent feedbacks may be related to clouds, trace greenhouse gases (GHGs), seasonal snow cover, and/or vegetation, especially in polar regions. Better characterization and quantification of these feedbacks is a priority given the current accumulation of atmospheric GHGs.
We summarize the first results from the Gould Belt Survey, obtained toward the Aquila rift and Polaris Flare regions during the science demonstration phase of Herschel. Our 70–500 μm images taken in ...parallel mode with the SPIRE and PACS cameras reveal a wealth of filamentary structure, as well as numerous dense cores embedded in the filaments. Between ~350 and 500 prestellar cores and ~45–60 Class 0 protostars can be identified in the Aquila field, while ~300 unbound starless cores and no protostars are observed in the Polaris field. The prestellar core mass function (CMF) derived for the Aquila region bears a strong resemblance to the stellar initial mass function (IMF), already confirming the close connection between the CMF and the IMF with much better statistics than earlier studies. Comparing and contrasting our Herschel results in Aquila and Polaris, we propose an observationally-driven scenario for core formation according to which complex networks of long, thin filaments form first within molecular clouds, and then the densest filaments fragment into a number of prestellar cores via gravitational instability.
The long-term carbon cycle depends on many feedbacks. Silicate weathering consumes atmospheric CO2, but is also enhanced by the increased temperatures brought about by this important greenhouse gas. ...The long-term sensitivity ... of climate to CO...-doubling modulates the strength of this negative feedback. We update the model-experiment of Royer and others (2007) by estimating an empirical probability-density function (PDF) of ... for the Phanerozoic by using an improved GEOCARBSULF carbon-cycle model to predict a larger, recalibrated set of proxy-CO2 measurements from the present-day to 420 Ma. The new GEOCARBSULF parameterizes the rapid weathering of volcanic rocks, relative to plutonic rocks. Updates to the carbon-cycle model and the proxy-CO... data set induce opposing model responses. As a result, our experiment maintains an agreement with ... estimates based on numerical climate models and late Cenozoic paleoclimate. For a climate sensitivity ... that is uniform throughout the Phanerozoic, the most probable value is 3... to 4 ...C. GEOCARBSULF fits the proxy-CO2 data equally well, and with far more parameter choices, if ... is amplified by at least a factor of two during the glacial intervals of the Paleozoic (260-340 Ma) and Cenozoic (0-40 Ma), relative to non-glacial intervals of Earth history. For glacial amplification of two, the empirical PDFs for glacial climate sensitivity predict ... with ~99 percent probability, ... with ~95 percent probability, and ... with ~90 percent probability. The most probable values are ... to 8 ...C. This result supports the notion that the response of Earth's present-day surface temperature will be amplified by the millennial and longer-term waxing and waning of ice sheets. (ProQuest: ... denotes formulae/symbols omitted.)
The sizes and shapes (physiognomy) of fossil leaves are widely applied as proxies for paleoclimatic and paleoecological variables. However, significant improvements to leaf-margin analysis, used for ...nearly a century to reconstruct mean annual temperature (MAT), have been elusive; also, relationships between physiognomy and many leaf ecological variables have not been quantified. Using the recently developed technique of digital leaf physiognomy, correlations of leaf physiognomy to MAT, leaf mass per area, and nitrogen content are quantified for a set of test sites from North and Central America. Many physiognomic variables correlate significantly with MAT, indicating a coordinated, convergent evolutionary response of fewer teeth, smaller tooth area, and lower degree of blade dissection in warmer environments. In addition, tooth area correlates negatively with leaf mass per area and positively with nitrogen content. Multiple linear regressions based on a subset of variables produce more accurate MAT estimates than leaf-margin analysis (standard errors of ±2 vs. ±3°C); improvements are greatest at sites with shallow water tables that are analogous to many fossil sites. The multivariate regressions remain robust even when based on one leaf per species, and the model most applicable to fossils shows no more signal degradation from leaf fragmentation than leaf-margin analysis.
Abstract We present a JWST imaging survey of I Zw 18, the archetypal extremely metal-poor, star-forming (SF), blue compact dwarf galaxy. With an oxygen abundance of only ∼3% Z ⊙ , it is among the ...lowest-metallicity systems known in the local Universe, and is, therefore, an excellent accessible analog for the galactic building blocks which existed at early epochs of ionization and star formation. These JWST data provide a comprehensive infrared (IR) view of I Zw 18 with eight filters utilizing both Near Infrared Camera (F115W, F200W, F356W, and F444W) and Mid-Infrared Instrument (F770W, F1000W, F1500W, and F1800W) photometry, which we have used to identify key stellar populations that are bright in the near- and mid-IR. These data allow for a better understanding of the origins of dust and dust-production mechanisms in metal-poor environments by characterizing the population of massive, evolved stars in the red supergiant (RSG) and asymptotic giant branch (AGB) phases. In addition, it enables the identification of the brightest dust-enshrouded young stellar objects (YSOs), which provide insight into the formation of massive stars at extremely low metallicities typical of the very early Universe. This paper provides an overview of the observational strategy and data processing, and presents first science results, including identifications of dusty AGB, RSG, and bright YSO candidates. These first results assess the scientific quality of JWST data and provide a guide for obtaining and interpreting future observations of the dusty and evolved stars inhabiting compact dwarf SF galaxies in the local Universe.
Reading a CO2 Signal from Fossil Stomata Beerling, D. J.; Royer, D. L.
New phytologist,
March 2002, Letnik:
153, Številka:
3
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
The inverse relationship between atmospheric CO2 and the stomatal index (proportion of epidermal cells that are stomata) of vascular land plant leaves has led to the use of fossil plant cuticles for ...determining ancient levels of CO2. In contemporary plants the stomatal index repeatedly shows a lower sensitivity atmospheric CO2 levels above 340 ppm in the short term. These observations demonstrate that the phenotypic response is nonlinear and may place constraints on estimating higher-than-present palaeo- CO2 levels in this way. We review a range of evidence to investigate the nature of this nonlinearity. Our new data, from fossil Ginkgo cuticles, suggest that the genotypic response of fossil Ginkgo closely tracks the phenotypic response seen in CO2 enrichment experiments. Reconstructed atmospheric CO2 values from fossil Ginkgo cuticles compare well with the stomatal ratio method of obtaining a quantitative CO2 signal from extinct fossil plants, and independent geochemical modelling studies of the long-term carbon cycle. Although there is self-consistency between palaeobiological and geochemical CO2 estimates, it should be recognized that the nonlinear response is a limitation of the stomatal approach to estimating high palaeo- CO2 levels.
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