Abundances of disk and bulge giants from high-resolution optical spectra -- IV. Zr, La, Ce, Eu

Stellar mass and metallicity are factors that affect the neutron-capture process. Due to this, the enrichment of the ISM and the abundance of neutron-capture elements vary with time, making them suitable probes for the Galactic chemical evolution. In this work we make a differential comparison of neutron-capture element abundances determined in the local disk(s) and the bulge, focusing on minimising possible systematic effects in the analysis, with the aim of finding possible differences/similarities between the populations. Abundances are determined for Zr, La, Ce and Eu in 45 bulge giants and 291 local disk giants, from high-resolution optical spectra. The abundances are determined by fitting synthetic spectra using the SME-code. The disk sample is separated into thin/thick disk components using a combination of abundances and kinematics. We find flat Zr, La, Ce trends in the bulge, with a $\sim 0.1$ dex higher La abundance compared with the disk, possibly indicating a higher s-process contribution for La in the bulge. [Eu/Fe] decreases with increasing [Fe/H], with a plateau at around [Fe/H] $\sim -0.4$, pointing at similar enrichment as $\alpha$-elements in all populations. We find that the r-process dominated the neutron-capture production at early times both in the disks and bulge. [La/Eu] for the bulge are systematically higher than the thick disk, pointing to either a) a different amount of SN II or b) a different contribution of the s-process in the two populations. Considering [(La+Ce)/Zr], the bulge and the thick disk follow each other closely, suggesting a similar ratio of high/low mass asymptotic giant branch-stars.Comment: 14 pages, 10 figures, accepted for publication in A&

Triaxial Superdeformation in 163 Lu

Abstract High-spin states in 163 Lu have been investigated using the Euroball spectrometer array. The previously known superdeformed band has been extended at low and high energies, and its connection to the normal-deformed states has been established. From its decay the mixing amplitude and interaction strength between superdeformed and normal states are derived. In addition, a new band with a similar dynamic moment of inertia has been found. The experimental results are compared to cranking calculations which suggest that the superdeformed bands in this mass region correspond to shapes with a pronounced triaxiality ( γ ≈±20°)

Is sulphur a typical alpha element?

Observationally, the galactic chemical evolution of sulphur shows a complex pattern. Some studies find no correlation between [S/Fe] and [Fe/H] at halo metallcities, which is typical for alpha -elements, others find [S/Fe] increasing towards lower metallicities, and still others find a combination of the two. Each scenario has different implications for the Galactic chemical evolution of sulphur. Here, we briefly summarise our results \citep{henrik:11,matrozis:13} from investigations where we derive stellar sulphur abundances from the [SI] lambda1082 nm line, a atomic transition which hardly shows any departures from local thermodynamic equilibrium, or LTE. Our results argue for a chemical evolution of sulphur that is typical for alpha -elements, contrary to some previous studies that have found high sulphur abundances ([S/Fe]gtrsim0 .6) for stars with -2.5<[Fe/H]<-1

Abundances of disk and bulge giants from high-resolution optical spectra : I. O, Mg, Ca, and Ti in the solar neighborhood and Kepler field samples

Context. The Galactic bulge is an intriguing and significant part of our Galaxy, but it is hard to observe because it is both distant and covered by dust in the disk. Therefore, there are not many high-resolution optical spectra of bulge stars with large wavelength coverage, whose determined abundances can be compared with nearby, similarly analyzed stellar samples.Aims. We aim to determine the diagnostically important alpha elements of a sample of bulge giants using high-resolution optical spectra with large wavelength coverage. The abundances found are compared to similarly derived abundances from similar spectra of similar stars in the local thin and thick disks. In this first paper we focus on the solar neighborhood reference sample.Methods. We used spectral synthesis to derive the stellar parameters as well as the elemental abundances of both the local and bulge samples of giants. We took special care to benchmark our method of determining stellar parameters against independent measurements of effective temperatures from angular diameter measurements and surface gravities from asteroseismology.Results. In this first paper we present the method used to determine the stellar parameters and elemental abundances, evaluate them, and present the results for our local disk sample of 291 giants.Conclusions. When comparing our determined spectroscopic temperatures to those derived from angular diameter measurements, we reproduce these with a systematic difference of +10 K and a standard deviation of 53 K. The spectroscopic gravities reproduce those determined from asteroseismology with a systematic offset of +0.10 dex and a standard deviation of 0.12 dex. When it comes to the abundance trends, our sample of local disk giants closely follows trends found in other works analyzing solar neighborhood dwarfs, showing that the much brighter giant stars are as good abundance probes as the often used dwarfs

Cooperative research for small-scale biomass fired boilers for Ecodesign Directive

Nytillverkade småskaliga biobränslepannor måste uppfylla ekodesignkraven senast år 2020. I en marknadsundersökning från 2014 klarade ingen av 11 testade pelletspannor alla ställda krav, vilket tydligt visar på ett utvecklingsbehov. Föreliggande projekt har haft som syfte att panntillverkare och forskningsinstitut branschgemensamt ska bemöta de förbränningstekniska utmaningar som tillverkarna står inför. För pelletspannor är den största utmaningen med ekodesigndirektivet att prestanda till största delen beräknas från drift vid partiell last (låg last). Tidigare har prestanda bara fastställts vid nominell last och designen optimerats därefter. I detta projekt har tester körts med två moderna pelletspannor som har olika typer av pelletsbrännare: en med horisontellt brännarrör och en med undermatad brännarkopp. Resultaten visar att tillräckligt god förbränning kunde upprätthållas vid partiell last med båda brännartyperna. Dock uppvisade rörbrännaren betydligt lägre emissioner vid partiell last, troligtvis beroende på att förbränningszonen i denna brännare är skyddad från värmestrålningsutbyte med kylande pannväggar. Ett ganska omfattande arbete lades ned på att förse koppbrännaren med en skyddande krage som skulle skydda förbränningszonen. Det resulterade dock inte in någon betydande förbättring, antagligen beroende på att tillförseln av sekundärluft inte blev optimal. Ett mer omfattande arbete krävs för att utveckla en optimal brännardesign av denna typ. För vedpannor är det en utmaning att klara ekodesigndirektivets NOx-krav på 200 mg/Nm³. En mängd temperaturmätningar i en vedpanna för villabruk resulterade i att termisk NOx-bildning kunde uteslutas. Pannan förseddes med ett system för rökgasåterföring, men det minskade inte NOx-emissionen. Därefter provades olika vedsorter. NOx-emissionen kunde minskas till att klara gränsvärdet med avbarkad björkved. Kemiska analyser visade att björkbarken innehöll 0,49% kväve jämfört med 0,09% i stamveden. Även granved gav låga NOx-emissioner, men det bränslet medförde ökade emissioner av CO och OGC. För att vedpannor ska klara kraven på CO, OGC och stoft krävs optimering med avseende på vedens slutförbränningsfas. I det skedet är emissionerna som högst, vilket beror på att värmeeffekten avtar och luftflödet tenderar att kyla ned rökgasen innan de brännbara gaserna brunnit ut. Den optiska partikelmätningen visade tydlig korrelation mellan stoft och CO i rökgasen. Om pannan uppfyller gränsvärdet för CO så finns goda chanser att även kravet på partiklar uppfylls. Verkningsgraden som anges i ekodesigndirektivet beräknas utgående från bränslets övre värmevärde. Dessutom subtraheras vissa förlustfaktorer. Detta innebär att pannan inte får ha några onödigt stora värmeförluster eller omotiverat hög elförbrukning för att klara satta krav. Mätningar visade att den största förlusten sker via värmen i rökgasen. Den näst största förlustposten är värmetransport från pannkroppen. För verkningsgraden ökar betydelsen av en välisolerad pannkropp vid partiell last. De två pelletspannor som användes inom projektet låg väl till för att kunna uppfylla ekodesigndirektivets krav på verkningsgrad.New domestic biofuel boilers must meet the Ecodesign Directive by 2020. In a market survey from 2014, none of 11 tested pellet boilers did meet all requirements, clearly indicating a developmental need. In the present project boiler manufacturers and research institutes have collaborated in response to the combustion engineering challenges. For pellet boilers, the biggest challenge with the Ecodesign Directive is that performance is largely calculated from partial load operation (low load). Previously, performance has only been determined at nominal load and the design has been optimized accordingly. In this project, tests have been run with two modern pellet boilers that have different types of pellet burner: one with horizontal burner tube and one with an underfeed burner cup. The results show that sufficient combustion performance could be maintained at partial load with both burner types. However, the tube burner exhibited significantly lower emissions at partial loads, probably due to the combustion zone in this burner being protected from heat radiation exchange with cooling boiler walls. A rather extensive work was laid down to provide the cup burner with a protective collar that would protect the combustion zone. However, it did not result in any significant improvement, probably because the supply of secondary air did not become optimal. A more extensive work is required to develop an optimal burner design of this type. For wood log boilers, it is a challenge to comply with the NOx requirements of the Ecodesign Directive of 200 mg / Nm³. A variety of temperature measurements in a wood log boiler resulted in the exclusion of thermal NOx formation. The boiler was fitted with a flue gas recirculation system, but it did not reduce the NOx emission. Then different varieties of wood fuels were tested. The NOx emission could be reduced to meet the requirement using barked birch wood. Chemical analyzes showed that the birch bark contained 0.49% nitrogen compared to 0.09% in the stock. Spruce logs also gave low NOx emissions, but that fuel resulted in increased CO and OGC emissions. For wood log boilers to meet the requirements for CO, OGC and dust, optimization is required under the wood's final combustion phase. At this stage, emissions are at its highest, due to the decreasing heat output while the airflow tends to cool down the flue gas faster than the combustible gases burn out. The optical particle measurement showed a clear correlation between dust and CO in the flue gas. If the boiler meets the CO limit, there are good chances that the requirement for particles also will be met. The efficiency specified in the Ecodesign Directive is calculated based on the fuel's higher heating value. In addition, some loss factors are subtracted. This implies that the boiler must not have unnecessarily large heat losses or excessive electricity consumption to meet the requirements. Measurements showed that the biggest loss occurs with the heat in the flue gas. The second largest loss is heat from the boiler body. For the efficiency, the importance of a well-insulated boiler body increases in the case of partial loads. The two pellet boilers used in the project were well suited to meet the eco-directive directive's efficiency requirements.Detta arbete har finansierats av Energimyndigheten inom Bränsleprogrammet omvandling och samfinansierats av de medverkande industriparterna Ariterm Sweden AB, Nibe AB och Värmebaronen AB.</p

Evidence against Anomalous Compositions for Giants in the Galactic Nuclear Star Cluster

Very strong Sc I lines have recently been found in cool M giants in the Nuclear Star Cluster (NSC) in the Galactic center. Interpreting these as anomalously high scandium abundances in the Galactic center would imply a unique enhancement signature and chemical evolution history for NSCs, and a potential test for models of chemical enrichment in these objects. We present high resolution K-band spectra (NIRSPEC/Keck II) of cool M giants situated in the solar neighborhood and compare them with spectra of M giants in the NSC. We clearly identify strong Sc I lines in our solar neighborhood sample as well as in the NSC sample. The strong Sc I lines in M giants are therefore not unique to stars in the NSC and we argue that the strong lines are a property of the line formation process that currently escapes accurate theoretical modeling. We further conclude that for giant stars with effective temperatures below approximately 3800 K these Sc I lines should not be used for deriving the scandium abundances in any astrophysical environment until we better understand how these lines are formed. We also discuss the lines of vanadium, titanium, and yttrium identified in the spectra, which demonstrate a similar striking increase in strength below 3500 K effective temperature