Nitrogen Abundances Research Articles

Effects of nitrogen source and N/P on growth and photosynthesis in the invasive marine macroalga Chaetomorpha valida.

The invasive marine macroalga Chaetomorpha valida blooms frequently in Apostichopus japonicus culture ponds in North China, resulting in negative environmental consequences. The factors driving this algal overgrowth are unclear. Previous studies observed that eutrophication strongly influences abnormal growth of nuisance macrophytes, but relatively few studies have addressed the types and abundance of nitrogen in A. japonicus culture ponds during the seasonal progression of a C. valida bloom and the effects of nitrogen source and N/P on C. valida growth and photosynthesis. In this study, we describe the structural features of nitrogen abundance and the seasonal progression of a C. valida bloom and uncover a relationship between nitrogen enrichment and C. valida growth. Common garden experiments demonstrated that C. valida can utilize different forms of nitrogen in the environment for rapid growth. Growth rate and photosynthesis capacity were related to the nitrogen source and N/P ratio. This study will provide a reference for maintenance of ecological balance and healthy aquaculture in A. japonicus culture ponds.

Dissimilatory nitrate reduction to ammonium dominates soil nitrate retention capacity in subtropical forests

The abundance, community composition and activity of key nitrogen (N)-cycling functional guilds were monitored at a site where coniferous Cunninghamia lanceolate and broadleaved Mytilaria laosensis were planted in 1993. Leaf cellulose, litter C/N ratio, leaf dry matter content, soil inorganic N content were significantly higher under C. lanceolata, while specific leaf area, litter production, litter magnesium, soil C and soil C/NO3− ratio were higher under M. laosensis. The 15N tracing experiment together with quantitative PCR revealed that autotrophic nitrification rates, as well as the abundances of ammonia-oxidizing archaea and comammox Nitrospira were significantly higher under C. lanceolate than M. laosensis. However, M. laosensis exhibited substantially higher nitrate retention capacity via dissimilatory nitrate reduction to ammonium (DNRA), accompanied by a significantly higher abundance of nrfA gene than C. lanceolate. The Illumina sequencing indicated that tree species markedly affected soil bacterial community composition regardless of the soil layers. Redundancy analysis suggested that litter C/N ratio was the most influential factor explaining functional gene abundances and bacterial communities. Taken together, our findings showed that M. laosensis improved soil N retention capacity mainly through inhibiting autotrophic nitrification while enhancing DNRA activity. This study highlights the importance of tree species identity in influencing the microbially-mediated N cycling and bacterial community composition.

When Does the Onset of Multiple Stellar Populations in Star Clusters Occur? III. No Evidence of Significant Chemical Variations in Main-sequence Stars of NGC 419

Abstract Recent studies have revealed that the onset age for the presence of multiple stellar populations (MPs) in star clusters seems to correspond to the disappearance of the extended main-sequence turnoff in young clusters, a pattern associated with stellar rotations. A speculative suggestion is that MPs might be caused by the magnetic brake, a stellar evolutionary effect linked to rotation. In this work, we use the young massive cluster NGC 419 as a testbed. We examined if its magnetically baked MS stars would exhibit MPs. Using the deep ultraviolet and visible images observed through the Hubble Space Telescope, combined with a specific color index that is sensitive to the nitrogen (N) abundance, we examined if its late G- and K-type MS stars are affected by N variation. Our analysis reports that the morphology of its GK-type MS is most likely a simple stellar population, and only a negligible probability, which indicates a N variation up to 0.4 dex is present. We therefore conclude that there is no significant N variation among its GK-type MS stars. The absence of a significant chemical variation among the late-type MS stars indicates that MPs might not be a specific pattern of magnetically braked stars.

The 3D non-LTE solar nitrogen abundance from atomic lines

Nitrogen is an important element in various fields of stellar and Galactic astronomy, and the solar nitrogen abundance is crucial as a yardstick for comparing different objects in the cosmos. In order to obtain a precise and accurate value for this abundance, we carried out N I line formation calculations in a 3D radiative-hydrodynamic STAGGER model solar atmosphere in full 3D non-local thermodynamic equilibrium (non-LTE). We used a model atom that includes physically motivated descriptions for the inelastic collisions of N I with free electrons and with neutral hydrogen. We selected five N I lines of high excitation energy to study in detail, based on their strengths and on their being relatively free of blends. We found that these lines are slightly strengthened from non-LTE photon losses and from 3D granulation effects, resulting in negative abundance corrections of around − 0.01 dex and − 0.04 dex, respectively. Our advocated solar nitrogen abundance is log ɛN = 7.77, with the systematic 1σ uncertainty estimated to be 0.05 dex. This result is consistent with earlier studies after correcting for differences in line selections and equivalent widths.

The [C ii]/[N ii] ratio in 3 < z < 6 sub-millimetre galaxies from the South Pole Telescope survey

ABSTRACT We present Atacama Compact Array and Atacama Pathfinder Experiment observations of the [N ii] 205 μm fine-structure line in 40 sub-millimetre galaxies lying at redshifts z = 3–6, drawn from the 2500 deg2 South Pole Telescope survey. This represents the largest uniformly selected sample of high-redshift [N ii] 205 μm measurements to date. 29 sources also have [C ii] 158 μm line observations allowing a characterization of the distribution of the [C ii] to [N ii] luminosity ratio for the first time at high redshift. The sample exhibits a median L$_{{\rm{[C\,{\small II}]}}}$/L$_{{\rm{[N\,{\small II}]}}}$ ≈ 11.0 and interquartile range of 5.0 –24.7. These ratios are similar to those observed in local (Ultra)luminous infrared galaxies (LIRGs), possibly indicating similarities in their interstellar medium. At the extremes, we find individual sub-millimetre galaxies with L$_{{\rm{[C\,{\small II}]}}}$/L$_{{\rm{[N\,{\small II}]}}}$ low enough to suggest a smaller contribution from neutral gas than ionized gas to the [C ii] flux and high enough to suggest strongly photon or X-ray region dominated flux. These results highlight a large range in this line luminosity ratio for sub-millimetre galaxies, which may be caused by variations in gas density, the relative abundances of carbon and nitrogen, ionization parameter, metallicity, and a variation in the fractional abundance of ionized and neutral interstellar medium.

Cassava/peanut intercropping improves soil quality via rhizospheric microbes increased available nitrogen contents

BackgroundIntercropping, an essential cultivation pattern in modern agricultural systems, increases crop yields and soil quality. Cassava and peanut intercropping systems exhibit advantages in solar utilization and cadmium absorption, etc. However, the inner mechanisms need to be elucidated. In this study, Illumina MiSeq platform was used to reveal the rhizospheric microbes and soil quality in cassava/peanut intercropping systems, and the results provided a reference for the application of this method in studying other intercropping systems.ResultsBoth intercropping cassava/peanut (IP) and intercropping peanut/cassava (IC) systems significantly increased available N, available K, pH value, and urease activity, comparing with that in monocropping cassava (MC) and monocropping peanut (MP) system. However, there were few effects on the total N, total P, total K, available P, organic matter, protease activity, catalase activity, sucrase activity, and acid phosphatase activity. Both IP and MP soils contained more bacteria and fungi than those in the IC and MC soils, which were mainly made of Proteobacteria and Actinobacteria. Intercropping remarkably increased the number of Nitrospirae in IP and IC soils comparing those in MC and MP soils. Redundancy analysis (RDA) revealed that the abundances of DA101, Pilimelia, and Ramlibacter were positively correlated to the soil quality. These results suggest that intercropping enhances the available nitrogen content of soil through increasing the quantity of rhizospheric microbes, especially that of DA101 and Pilimelia.ConclusionsThe cassava/peanut intercropping system improves soil quality through increasing the available nitrogen content and abundance of DA101, Pilimelia, and Ramlibacter in the soil.

Weaning and stunting affect nitrogen and carbon stable isotope natural abundances in the hair of young children

Natural abundances of stable nitrogen and carbon isotopes (δ15N and δ13C) can vary with both dietary intake and metabolic (specifically catabolic) state. In low-income countries, weaning is a period of dietary transition from milk to plant-based foods and a high-risk period for malnutrition. We explored how diet and malnutrition impact hair δ15N and δ13C in young children by an observational, cross-sectional study in Cox’s Bazar District, Bangladesh [255 children, 6–59 months with 19.6% wasted (7.1% severely) and 36% stunted (9.8% severely)]. Hair δ15N and δ13C exhibited exponential decreases with age, with the loss of one trophic level (3.3‰ and 0.8‰, respectively) from 6 to 48 months, which we associate with the shift from exclusive breastfeeding to complete weaning. After adjustment for age and breastfeeding status, hair isotopic values were unaffected by wasting but lower in severe stunting (−0.45‰ to −0.6‰, P < 0.01). In this population of young children, whose isotopic values in hair primarily depended on age, we failed to observe any effect of wasting, likely due to opposite, compensating effects between dietary and metabolic changes involved. In contrast, we evidenced low δ15N and δ13C values in severely stunted children that likely indicate chronic exposure to diets low in animal products.

Nitrogen storage regulation by PII protein: lessons learned from taxonomic outliers

The paper 'Interaction of N-acetyl-l-glutamate kinase with the PII signal transducer in the non-photosynthetic alga Polytomellaparva: Co-evolution towards a hetero-oligomeric enzyme' by Selim et al. highlights how the study of a true taxonomic oddity, the heterotrophic unicellular alga P.parva, has been instrumental in uncovering the large potential for adaptive variation in the signaling complex of PII with the enzyme N-acetylglutamate kinase (NAGK). This complex modifies the regulatory properties of NAGK, allowing nitrogen stockpiling as arginine. In P.parva, a stable PII-NAGK complex is formed which lacks regulation by canonical PII effectors but which exhibits novel adaptive responses to nitrogen abundance mediated by glutamine, a neo-effector of PII proteins of photosynthetic eukaryotes.

Aggregation index, carbon, nitrogen, and natural abundance of 13C and 15N in soil aggregates and bulk soil cultivated with onion under crop successions and rotations

Use of soil cover crops of different families in crop rotation or succession under no-tillage system (NTS) for onion production results in higher soil quality compared to land use systems with less plant diversity. The objective was to evaluate the effect of using different combinations of plant species from different botanical families in rotation and succession of soil cover crops in NTS for onion production on formation of macroaggregates, mesoaggregates, and microaggregates, and on total organic C (TOC) and N (TN) contents, including isotopic forms of C and N, in soil aggregates and bulk soil. The treatments (T) evaluated were maize/onion (NTS-T1); cover plants (winter)/onion (NTS-T2); maize/winter grasses/onion (NTS-T3); velvet bean/onion (NTS-T4); millet/cover plants (winter)/onion (NTS-T5); velvet bean/rye/onion (NTS-T6); maize/onion in conventional tillage system (CTS-T7); and intercrop cover plants (summer)/onion (NTS-T8). We evaluated macroaggregates (8.0–0.25 mm), microaggregates (&amp;lt;0.25 mm), and bulk soil (&amp;lt;2.0 mm) at depths of 0–5, 5–10, and 10–20 cm, in a nine-year field experiment. The greater plant diversity in T2–T6 and T8 resulted in higher geometric mean diameter (GMD) of aggregates compared to T1 and T7. The T8 was more efficient in increasing GMD in the 10–20 cm soil depth than the other treatments. The T1 was more efficient in improving the evaluated soil physical and chemical attributes than T7. The use of NTS with plants of the Poaceae and Fabaceae families in single or intercrop systems for onion production resulted in higher TOC and TN contents in the 0–5 and 5–10 cm soil depths compared to CTS. Isotope 15N measurements showed that C and N were more protected in microaggregates in all evaluated treatments and depths compared to macroaggregates and bulk soil. Macroaggregates had more TOC and TN than microaggregates.

Deep-Learning-Based Approach for Estimation of Fractional Abundance of Nitrogen in Soil From Hyperspectral Data

One of the vital growth nutrient parameters of crops is soil Nitrogen (N) content. The ability to accurately grasp soil nutrient information is a prerequisite for scientific fertilization within the field of precision agriculture. Information pertaining to soil macronutrients, such as N, may be obtained quickly through hyperspectral imaging techniques. Objective of this research is to explore the use of a deep learning (DL) network to estimate the abundance of urea fertilizer mixed soils for spectroradiometer data. The proposed approach was tested for silt clay and loamy types of soils. Spectral regions of 1899.2 nm for urea and 2195.1 nm for soils were identified as optimum spectral absorption features. The accuracy evaluation was performed using a linear regression model between actual and estimated abundances. At 1899.2 nm, the coefficient of determination ( R 2) for mixed samples of urea and silt clay soil was found to be 0.945, while R 2 for urea mixed loamy soil were 0.954. Similarly, at 2195.1 nm, R 2 obtained 0.953 for urea mixed silt clay soil and 0.944 for urea mixed loamy soil. The results show that the estimated abundances obtained through the derivative analysis for spectral unmixing (DASU)-based DL network facilitated a greater accuracy in comparison to the sole use of DASU. These results were then verified through conventional chemical analysis methods. The outcome of this article determines the abundance of urea mixed soils. Therefore, it is inferred that the hyperspectral imaging technique may be utilized in-situ to assess the agricultural land's soil fertility status.

Nanofibrils of a CuII-Thiophenyltriazine-Based Porous Polymer: A Diverse Heterogeneous Nanocatalyst

Herein, we report knitting of a thiophenyltriazine-based porous organic polymer (TTPOP) with high surface area and high abundance of nitrogen and sulfur sites, synthesized through a simple one-step Friedel–Crafts reaction of 2,4,6-tri(thiophen-2-yl)-1,3,5-triazine and formaldehyde dimethyl acetal in the presence of anhydrous FeCl3, and thereafter grafting of Cu(OAc)2·H2O in the porous polymer framework to achieve the potential catalyst (CuII-TTPOP). TTPOP and CuII-TTPOP were characterized thoroughly utilizing solid-state 13C-CP MAS NMR, Fourier transform infrared, wide-angle powder X-ray diffraction, thermogravimetric analysis, and X-ray photoelectron spectroscopy and surface imaging by transmission electron microscopy and field emission scanning electron microscopy. The porosity of the nanomaterials was observed in the surface imaging and verified through conducting N2 gas adsorption techniques. Keeping in mind the tremendous importance of C-C and C-N coupling and cyclization processes, the newly synthesized CuII-TTPOP was employed successfully for a wide range of organic catalytic transformations under mild conditions to afford directly valuable diindolylmethanes and spiro-analogues, phthalimidines, propargyl amines, and their sugar-based chiral compounds with high yields using readily available substrates. The highly stable new heterogeneous catalyst showed outstanding sustainability, robustness, simple separation, and recyclability.

Lacustrine micro-ecosystem responses to the inflow discharge gradient of water diversion from Yangtze River to Lake Taihu.

Water diversion project is always taken as the emergency and effective engineering measure to deal with the cyanobacterial blooms in eutrophic lakes. The inflow discharge and duration are the critical parameters influencing the effects and costs of the water diversion activities. Due to the impacts of meteorological and hydrological factors such as precipitation and wind-wave currents, the environmental influence of water diversion on shallow eutrophic lakes is always unclear. To explore the quantitative relationships among inflow discharges, duration and ecological parameters in water-receiving lakes, the typical water diversion engineering-Water Diversion Project from Yangtze River to Lake Taihu was taken as an example and the mesocosm experiment modeling the micro-ecosystem of the water-receiving Meiliang Bay in Lake Taihu was conducted with five groups of inflow discharges according to the practical discharges of the main river channel-Wangyu River. Each micro-ecosystem had a volume of 15 L and was studied for a period of 30days (25days for the water diversion period and 5days for the stop period). The results showed that the inflow discharges had different extents of impact on the physicochemical and biological characteristics of the micro-ecosystems. The concentrations of total dissolved solids, total nitrogen, nitrate, active silicate and bacterial abundance in the experimental groups (inflow discharges > 100m3/s) were all decreased compared with the control group, with the lowest values in the period of 10-15 days. During the stop period, the concentrations of sensitive biotic and abiotic parameters were all recovered with different extents and different from the initial state of this experiment, which revealed that the effects of the short-term water diversion on lake ecosystems were resilient and durable. There were quantitative relationships among the inflow discharge, content interpolation and variation in water nutrients, with different relationships in different periods of the water diversion. The influence of water diversion on lake ecosystems was not only related to the direct impacts of allochthonous inputs, but also with the indirect effects of internal habitat variation in lakes.

Effects of nitrogen concentration on growth, biomass, and biochemical composition of Desmodesmus communis (E. Hegewald) E. Hegewald

Nitrogen, being one of the building blocks of biomacromolecules, is an important nutrient for microalgae growth. Nitrogen availability alters the growth and biochemical composition of microalgae. We investigated the effects of different nitrogen concentrations on specific growth rate (SGR), biomass productivity (BP), total protein and lipid content and amino acid and fatty acid composition of Desmodesmus communis. Nitrogen deficiency increased algal growth and changed the lipid amount and composition. The maximum growth and BP were detected in 75% N−medium. The highest total protein and lipid amount were detected in 50% N− and 75% N−media, respectively. Amino acid and fatty acid compositions of samples varied widely depending on the nutrient concentrations. The amount of unsaturated fatty acid (USFAs) was higher than saturated fatty acid (SFAs) and Linolenic acid percentage is higher than the limit of European standards in all media. The data reported here provide important contributions how nitrogen scarcity and abundance affect the growth and biochemical content of microalgae and this information can further be utilized in culture optimization in studies aimed at microalgae production for biofuels.

Jupiter formed as a pebble pile around the N2 ice line

Context. The region around the H2O ice line, due to its higher surface density, seems to be the ideal location to form planets. The core of Jupiter, as well as the cores of close-in gas giants are therefore thought to form in this region of the disk. Nevertheless, constraining the formation location of individual planets has proven to be difficult. Aims. We aim to use the nitrogen abundance in Jupiter, which is around four times solar, in combination with Juno constraints on the total mass of heavy elements in Jupiter to narrow down its formation scenario. Methods. Different pathways of enrichment of the atmosphere of Jupiter are considered, such as the accretion of enriched gas, pebbles, and planetesimals, and their implications for the oxygen abundance of Jupiter are discussed. Results. The super-solar nitrogen abundance in Jupiter necessitates the accretion of extra N2 from the proto-solar nebula. The only location of the disk where this can happen is outside or just inside the N2 ice line. These constraints favor a pebble accretion origin of Jupiter, from the perspective of composition and planet formation. We predict that Jupiter’s oxygen abundance is between 3.6 and 4.5 times solar.

The fungicide "fluopyram" promotes pepper growth by increasing the abundance of P-solubilizing and N-fixing bacteria.

Fluopyram, as a reasonably good fungicide and nematicide, is widely used to control agricultural pests worldwide. However, its effects on soil microbial communities and plant growth remain controversial. Therefore, in this study, we investigated the effects of three concentrations (0.5, 1.5, and 5.0 mg/kg) of the fluopyram (Lufuda 41.7% a.i., suspension concentrate, SC) on the pepper rhizosphere microorganisms and pepper seedlings growth in a plant growth room. Moreover, we also investigated the dissipation of fluopyram in the soil, pepper roots, and leaves across a time interval of 45 days. The results showed that fluopyram application increased the number of pepper rhizosphere phosphate (P)-solubilizing bacteria, the abundance of nitrogen (N)-fixing nifH genes, and the pepper seedling growth. The results of terminal restriction fragment length polymorphism (T-RFLP) analysis demonstrated that fluopyram did not alter rhizosphere bacterial community structure and diversity. However, fluopyram did increase the relative abundances of 138 bp and 400 bp T-RFs closely representing Bacillus and Rhizobium genera that were known as efficient plant growth promoting bacteria with P-solubilization and N-fixation properties. Corresponding to the increase of plant growth and beneficial microbes, the half-lives of fluopyram in soil and plant tissues also decreased that nevertheless suggested the role of plant-microbe interactions in the faster removal of fluopyram after application. Our results suggest that short-lived and easily degradable pesticides may have less toxicological effects on soil health while their judicious use may reshape plant-microbe interactions in favor of the plant growth.

Increased abundance of nitrogen transforming bacteria by higher C/N ratio reduces the total losses of N and C in chicken manure and corn stover mix composting.

The aim of this work was to investigate how the initial C/N ratio during composting of chicken manure/corn stover mix affected the succession of dominant bacteria in the mix which led to the reduction of the total losses of N and C in the composting process. 16S rDNA sequencing indicated that the succession of predominant bacteria was significantly affected by the temperature and the initial C/N ratio during composting. Redundancy analysis showed that higher C/N appeared to promote the relative abundance of nitrogen fixing bacteria Thermoactinomyces, Planifilum, Flavobacterium, Bacillaceae, Pseudomonas,Sphingobacterium, Paenibacillus, Bacillus and Thermobifida, while compressing the denitrifying bacteria Pusillimonas, Ignatzschineria, Alcanivorax, Cerasibacillus, Truepera and Erysipelothrix. C/N ratio of 30:1 yielded the least C/N losses in the composting process, indicating that adjustment to the initial C/N ratio could affect nitrogen transforming bacteria to reduce the total losses of N and C and improve compost quality.

Electron Densities and Nitrogen Abundances in Ionized Gas Derived Using [N ii] Fine-structure and Hydrogen Recombination Lines

Abstract We present a method for deriving the electron density of ionized gas using the ratio of the intensity of the [N ii] 205 μm line to that of hydrogen radio recombination lines (RRLs). We use this method to derive electron densities of 21 velocity components in 11 lines of sight through the Galaxy, including the Galactic center. We observed, at high spectral resolution, the [N ii] 205 μm with the Herschel/HIFI and SOFIA/GREAT instruments and the RRLs with the Green Bank Telescope and the NASA Deep Space Network Deep Space Station 43 (DSS-43) telescope. We find typical electron densities between 8 and 170 cm−3, which are consistent with those derived at low spectral resolution using the [N ii] 205 μm/122 μm ratio with Herschel/PACS on a larger sample of sight lines in the Galactic plane. By matching the electron densities derived from the [N ii] 205 μm/RRL intensity ratio and the [N ii] 122 μm/205 μm intensity ratio, we derive the nitrogen fractional abundance for most of the velocity components. We investigate the dependence of the N/H ratio on galactocentric distance in the inner Galaxy (R gal &lt; 6 kpc), which is inaccessible in optical studies owing to dust extinction. We find that the distribution of nitrogen abundances in the inner Galaxy derived from our data has a slope that is consistent with that found in the outer Galaxy in optical studies. This result is inconsistent with some suggestions of a flatter distribution of the nitrogen abundance in the inner Galaxy.

Carbon, nitrogen and oxygen abundance gradients in M101 and M31

Abstract We present deep spectrophotometry of 18 H ii regions in the nearby massive spiral galaxies M 101 and M 31. We have obtained direct determinations of electron temperature in all the nebulae. We detect the C ii 4267 Å line in several H ii regions, permitting to derive the radial gradient of C/H in both galaxies. We also determine the radial gradients of O/H, N/O, Ne/O, S/O, Cl/O and Ar/O ratios. As in other spiral galaxies, the C/H gradients are steeper than those of O/H producing negative slopes of the C/O gradient. The scatter of the abundances of O with respect to the gradient fittings do not support the presence of significant chemical inhomogeneities across the discs of the galaxies, especially in the case of M101. We find trends in the S/O, Cl/O and Ar/O ratios as a function of O/H in M101 that can be reduced using Te indicators different from the standard ones for calculating some ionic abundances. The distribution of the N/O ratio with respect to O/H is rather flat in M31, similarly to previous findings for the Milky Way. Using the disc effective radius – Re – as a normalization parameter for comparing gradients, we find that the latest estimates of Re for the Milky Way provide an excess of metallicity in apparent contradiction with the mass-metallicity relation; a value about two times larger might solve the problem. Finally, using different abundance ratios diagrams we find that the enrichment timescales of C and N result to be fairly similar despite their different nucleosynthetic origin.

Photospheric nitrogen abundances and carbon 12C/13C ratios of red giant stars

Abstract Nitrogen abundances and carbon isotope ratios (12C$/$13C) in the atmospheres of red giants are known to be influenced by dredge-up of H-burning products, and serve as useful probes to study the nature of evolution-induced envelope mixing. We determined the [N/Fe] and 12C$/$13C ratios for 239 late-G/early-K giant stars by applying the spectrum-fitting technique to the 12CN and 13CN lines in the ∼8002–8005 Å region, with the aim of investigating how these quantities are related to other similar mixing-affected indicators which were already reported in our previous work. It was confirmed that [N/Fe] values are generally supersolar (typically by several tenths of a dex, though widely differing from star to star), anti-correlated with [C/Fe], and correlated with [Na/Fe], as expected from theory. As seen from their dependence upon stellar parameters, it appears that mixing tends to be enhanced with an increase of stellar luminosity (or mass) and rotational velocity, which is also reasonable from the theoretical viewpoint. In contrast, the resulting 12C$/$13C ratios turned out to be considerably diversified in the range of ∼5–50 (with a peak around ∼20), without showing any systematic dependence upon C or N abundance anomalies caused by the mixing of CN-cycled material. It thus appears that our understanding of the photospheric 12C$/$13C ratios in red giants is still incomplete, requiring more observational studies.

Hubble Space Telescope Spectroscopy of a Planetary Nebula in an M31 Open Cluster: Hot-bottom Burning at 3.4 M⊙*

Abstract We use imaging and spectroscopy from the Hubble Space Telescope (HST) to examine the properties of a bright planetary nebula (PN) projected within M31's young open cluster B477-D075. We show that the probability of a chance superposition of the PN on the cluster is small, ≲2%. Moreover, the radial velocity of the PN is the same as that of the cluster within the measurement error of ∼10 km s−1. Given the expected ∼70 km s−1 velocity dispersion in this region, ∼8 kpc from M31's nucleus, the velocity data again make it extremely likely that the PN belongs to the cluster. Applying isochrone fitting to archival color–magnitude photometric data from the HST Advanced Camera for Surveys, we determine the cluster age and metallicity to be 290 Myr and Z = 0.0071, respectively, implying an initial mass of for any PN produced by the cluster. From HST’s Space Telescope Imaging Spectrograph observations and Cloudy photoionization modeling, we find that the PN is likely a Type I planetary, with a nitrogen abundance that is enhanced by ∼5–6 times over the solar value scaled to the cluster metallicity. If the PN is indeed a cluster member, these data present strong empirical evidence that hot-bottom burning occurs in asymptotic giant branch stars with initial masses as low as 3.4 M ⊙.