Heavy Element Enrichment Research Articles

Effect of the surface temperature on surface morphology, deuterium retention and erosion of EUROFER steel exposed to low-energy, high-flux deuterium plasma

Samples of EUFROFER, a reduced activation ferritic martensitic steel, were exposed in the linear plasma device Pilot-PSI to a deuterium (D) plasma with incident ion energy of ∼40eV and incident D flux of 2–6×1023D/m2s to fluences up to 1027D/m2 at surface temperatures ranging from 400K to 950K. The main focus of the study lays on the surface morphology changes dependent on the surface temperature and the surface composition evolution, e.g., the enrichment in tungsten; but also the erosion and the D retention are studied. The created surface morphology varies strongly with surface temperature from needle-like to corral-like structures. The visible lateral length scale of the formed structures is in the range of tens of nanometres to above 1µm and exhibits two thermal activated regimes below and above ∼770K with activation energies of 0.2eV and 1.3eV, respectively. The lateral variation of the enrichment of heavy elements on the surface is correlated to this surface morphology at least in the high temperature regime, independent of the origin of the enrichment (intrinsic from the sample or deposited by the plasma). Also the erosion exhibits temperature dependence at least above ∼770K as well as a fluence dependence. The amount of deuterium retained in the top 500nm is almost independent of the exposure temperature and is of the order of 1018D/m2, which would correspond to a sub-monolayer D coverage on the surface. The retained D in the volume summing up over the complete samples exceeds the D retained close to the surface by one order of magnitude.

Four Sub-Saturns with Dissimilar Densities: Windows into Planetary Cores and Envelopes

Abstract We present results from a Keck/HIRES radial velocity campaign to study four sub-Saturn-sized planets, K2-27b, K2-32b, K2-39b, and K2-108b, with the goal of understanding their masses, orbits, and heavy-element enrichment. The planets have similar sizes ( = 4.5–5.5 ), but have dissimilar masses ( = 16–60 ), implying a diversity in their core and envelope masses. K2-32b is the least massive ( ) and orbits in close proximity to two sub-Neptunes near a 3:2:1 period commensurability. K2-27b and K2-39b are significantly more massive at and , respectively, and show no signs of additional planets. K2-108b is the most massive at , implying a large reservoir of heavy elements of about ≈50 . Sub-Saturns as a population have a large diversity in planet mass at a given size. They exhibit remarkably little correlation between mass and size; sub-Saturns range from ≈6–60 , regardless of size. We find a strong correlation between planet mass and host star metallicity, suggesting that metal-rich disks form more massive planet cores. The most massive sub-Saturns tend to lack detected companions and have moderately eccentric orbits, perhaps as a result of a previous epoch of dynamical instability. Finally, we observe only a weak correlation between the planet envelope fraction and present-day equilibrium temperature, suggesting that photo-evaporation does not play a dominant role in determining the amount of gas sub-Saturns accrete from their protoplanetary disks.

A Chemical Composition Survey of the Iron-complex Globular Cluster NGC 6273 (M19)*

Abstract Recent observations have shown that a growing number of the most massive Galactic globular clusters contain multiple populations of stars with different [Fe/H] and neutron-capture element abundances. NGC 6273 has only recently been recognized as a member of this “iron-complex” cluster class, and we provide here a chemical and kinematic analysis of >300 red giant branch and asymptotic giant branch member stars using high-resolution spectra obtained with the Magellan–M2FS and VLT–FLAMES instruments. Multiple lines of evidence indicate that NGC 6273 possesses an intrinsic metallicity spread that ranges from about [Fe/H] = −2 to −1 dex, and may include at least three populations with different [Fe/H] values. The three populations identified here contain separate first (Na/Al-poor) and second (Na/Al-rich) generation stars, but a Mg–Al anti-correlation may only be present in stars with [Fe/H] ≳ −1.65. The strong correlation between [La/Eu] and [Fe/H] suggests that the s-process must have dominated the heavy element enrichment at higher metallicities. A small group of stars with low [α/Fe] is identified and may have been accreted from a former surrounding field star population. The cluster’s large abundance variations are coupled with a complex, extended, and multimodal blue horizontal branch (HB). The HB morphology and chemical abundances suggest that NGC 6273 may have an origin that is similar to ω Cen and M54.

Mineralogy, geochemistry and genesis of clays interlayered coal seams succession in the Neogene lacustrine Seyitömer coal deposit, Kütahya, western Turkey

The Seyitömer coal deposit is an important source of energy in Turkey. This study aims to determine mineralogical, geochemical characteristics, and genesis of clays associated with coal seams in order to identify their precipitation environment. The Late Miocene-Pliocene units comprise organic-rich shale, organic-rich marl, marl, coal seam, siltstone and sandstone deposited in a fluvial and lacustrine environment, with associated tuff and tuffite in the Seyitömer coal deposit. Serpentinite, sandstone, organic-rich shale and tuffaceous host rocks of the coal deposit are partly to completely argillized and partially carbonate cemented having also stockwork type silica in-fill fissures. Smectite, illite, and kaolinite are associated with quartz, feldspar, olivine, gypsum and pyrite. Oriented flaky illite with irregular outlined kaolinite, and smectite flakes edging and coating relict feldspar and volcanic glass grains developed by a dissolution-precipitation mechanism in an alkaline micro-environment during deposition and diagenetic process. The occurrence of subrounded microorganisms on resorbed feldspar and the coexistence of smectite/illite flakes with organic matter, pyrite, and siderite indicates that degradation of feldspar and devitrification of volcanic glass is biologically mediated. The slight enrichment of heavy rare earth elements (HREE) compared to light rare earth elements (LREE) with a positive Eu and Ce anomalies reflects fractional crystallization of feldspar and amphibole. Alteration of feldspar, biotite, serpentine and volcanic glass resulted in the concentration of Al, Fe, Mg, and K in a stagnant environment and precipitation of beidellitic smectite and illite in an alkaline environment. Kaolinite precipitated in an acidic open hydrological system. An increase in Ni/Co and V/(V+Ni) ratios in altered units also suggest anoxic and anoxic to dysoxic conditions. Occurrence of Pityosporites microalatus (Pinus), Laevigatosporites haardti, Pityosporites spp., Polyvestibulopollenites verus (Alnus), Compositae and Graminae in the Seyitömer coal deposit suggest subtropical to warm-temperature humid climate during Late Oligocene-Middle Miocene period. Association of argillization and silicification with coal, microorganisms, pyrite, and gypsum indicates a swampy environment and partial hydrothermal processes. This interpretation is corroborated by the calculated formation temperatures from stable isotope analysis of 30–463°C for smectite and 140–156°C for illite. The high δ34S isotope values (16.8–33.3‰) indicate a mixed diagenetic and hydrothermal origin for the sulphide and sulfate minerals.

EVOLUTIONARY ANALYSIS OF GASEOUS SUB-NEPTUNE-MASS PLANETS WITH MESA

ABSTRACT Sub-Neptune-sized exoplanets represent the most common types of planets in the Milky Way, yet many of their properties are unknown. Here, we present a prescription to adapt the capabilities of the stellar evolution toolkit Modules for Experiments in Stellar Astrophysics to model sub-Neptune-mass planets with H/He envelopes. With the addition of routines treating the planet core luminosity, heavy-element enrichment, atmospheric boundary condition, and mass-loss due to hydrodynamic winds, the evolutionary pathways of planets with diverse starting conditions are more accurately constrained. Using these dynamical models, we construct mass-composition relationships of planets from 1–400 M ⊕ and investigate how mass-loss impacts their composition and evolution history. We demonstrate that planet radii are typically insensitive to the evolution pathway that brought the planet to its instantaneous mass, composition and age, with variations from hysteresis . We find that planet envelope mass-loss timescales, , vary non-monotonically with H/He envelope mass fractions (at fixed planet mass). In our simulations of young (100 Myr) low-mass ( ) planets with rocky cores, is maximized at to 3%. The resulting convergent mass-loss evolution could potentially imprint itself on the close-in planet population as a preferred H/He mass fraction of . Looking ahead, we anticipate that this numerical code will see widespread applications complementing both 3D models and observational exoplanet surveys.

Element geochemical characteristics of a soil profile developed on dolostone in central Guizhou, southern China: implications for parent materials

This study presents bulk chemical compositions of the Tongmuling soil profile, which developed on dolostone, and the overlying strata covering the bedrock in the central Guizhou province (southern China). The chemical weathering characteristics of the studied profile were investigated and the inheritance relationships between the terra rossa and overlying strata were discussed. The results show that there is no remarkable variation in the major elements and weathering indices from the rock–soil interface to the topsoil, indicating that the studied profile was not typical for in situ crustal chemical weathering. The terra rossa were mainly composed of SiO2, Al2O3 and Fe2O3. Compared with the insoluble residues and overlying strata, the terra rossa are characterized by an enrichment of Y and Cs and depletion of Ba and Sr. The subsoil shows a notable Ce negative anomaly, characterized by heavy rare earth element enrichment (L/H = 1.55–3.74), whereas the topsoil shows a positive Ce anomaly with light rare earth element enrichment (L/H = 5.93–9.14). According to Laterite-forming capacity estimates, the terra rossa could not have only been formed from acid-insoluble residues from the bedrock; Al2O3 versus Fe2O3 and Nb plotted against Ta show significant positive correlations between the terra rossa and overlying strata. The Eu/Eu* versus GdN/YbN and ternary diagrams for Sc, Th, Zr, and Ta suggest that the overlying strata could also provide parent materials for the genesis of terra rossa.

Possible Population III remnants at redshift 3.5

Abstract The first stars, known as Population III (PopIII), produced the first heavy elements, thereby enriching their surrounding pristine gas. Previous detections of metals in intergalactic gas clouds, however, find a heavy element enrichment larger than 1/1000 times that of the solar environment, higher than expected for PopIII remnants. In this letter, we report the discovery of a Lyman limit system (LLS) at z = 3.53 with the lowest metallicity seen in gas with discernable metals, 10−3.41±0.26 times the solar value, at a level expected for PopIII remnants. We make the first relative abundance measurement in such low metallicity gas: the carbon-to-silicon ratio is 10−0.26±0.17 times the solar value. This is consistent with models of gas enrichment by a PopIII star formation event early in the Universe, but also consistent with later, Population II enrichment. The metals in all three components comprising the LLS, which has a velocity width of 400 km s−1, are offset in velocity by ∼+6 km s−1 from the bulk of the hydrogen, suggesting the LLS was enriched by a single event. Relative abundance measurements in this near-pristine regime open a new avenue for testing models of early gas enrichment and metal mixing.

Signatures of volatiles in the lunar proton albedo

We find evidence for hydrated material in the lunar regolith using “albedo protons” measured with the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on the Lunar Reconnaissance Orbiter (LRO). Fluxes of these albedo protons, which are emitted from the regolith due to steady bombardment by high energy radiation (Galactic Cosmic Rays), are observed to peak near the poles, and are inconsistent with the latitude trends of heavy element enrichment (e.g., enhanced Fe abundance). The latitudinal distribution of albedo protons anti-correlates with that of epithermal or high energy neutrons. The high latitude enhancement may be due to the conversion of upward directed secondary neutrons from the lunar regolith into tertiary protons due to neutron–proton collisions in hydrated regolith that is more prevalent near the poles. The CRaTER instrument may thus provide important measurements of volatile distributions within regolith at the Moon and potentially, with similar sensors and observations, at other bodies within the Solar System.

Rare-earth, major, and trace element geochemistry of deep-sea sediments in the Indian Ocean: Implications for the potential distribution of REY-rich mud in the Indian Ocean

We analyzed 1338 deep-sea sediment samples from 19 Deep Sea Drilling Project/Ocean Drilling Program sites covering a large portion of the Indian Ocean, and constructed a new and comprehensive data set of their bulk chemical compositions, including rare-earth, major, and trace elements. The bulk-sediment rare-earth and yttrium (REY) composition of the REY-enriched samples, characterized by relatively small negative Ce anomalies, almost no Y anomalies, and enrichment in heavy rare-earth elements, can be interpreted as the superposition of the REY compositions of apatite and hydrogenous Fe-Mn oxides. Although the hydrothermal component is a key factor in the formation of REY-rich mud in the Pacific Ocean, it is less important in the Indian Ocean, probably because there is less hydrothermal input of Fe-oxyhydroxides from seafloor hydrothermal vents there. The relationships among Fe 2 O 3 , MnO, P 2 O 5 , Co, and total REY contents suggest that a primary factor controlling REY enrichment in deep-sea sediments is the sedimentation rate. A low sedimentation rate allows both fish debris apatite and hydrogenous Fe-Mn (oxyhydr)oxides to accumulate in the surface sediments. On the basis of these results, we identified two potential areas in the Indian Ocean where REY-rich mud may be present in surface sediments: the south-southeastern Wharton Basin and the southern Central Indian Ocean Basin. The resource potential of the latter area might be particularly high if the distributions of REY-rich mud and Fe-Mn nodule fields broadly overlap.

Rare earth elements and stable isotope geochemistry of carbonates from the mélange zone of Manipur ophiolitic Complex, Indo-Myanmar Orogenic Belt, Northeast India

Carbonates that occur in the melange zone of Manipur ophiolitic complex (MOC), Indo-Myanmar Orogenic Belt, Northeast India contain diverse fauna with dominance of foraminifera assemblages (planktonic and benthic) and calcareous nanofossils. Rare earth element (REE) contents (~51 ppm average value) in the MOC carbonates are high compared with the average value of typical marine carbonate (~28 ppm). The Post-Archean Australian Shale (PAAS)-normalized REE patterns of these carbonates exhibit seawater-like REE patterns with light rare earth elements (LREE) depletion and relative heavy rare earth elements (HREE) enrichment with negative Ce anomalies (Ce/Ce* = 0.28–0.69) and positive Eu anomalies (Eu/Eu* = 1.07–2.08). The carbonates show depleted values of δ13C ‰ (PDB) (0.89–2.74 ‰) which characterize marine precipitates while depletion in δ18O ‰ (PDB), reaching minimum values (−6.29 to −11.40 %). The negative anomalies of Ce in these carbonates suggest that they were deposited under oxygenated environment. The observed shale-normalized positive Eu anomalies and spread in negative δ18O values to a lesser extent of δ13C ‰ (PDB) values of these carbonates suggest their formation were altered by diagenesis in shallow marine environment. Field, petrographical studies in conjunction with REE and stable isotope characteristics suggest that these carbonates form part of the ophiolitic melange zone that emplaced during subduction and obduction processes of the Indian plate and Myanmar plate collision.

Comprehensive abundance analysis of red giants in the open clusters NGC 1342, 1662, 1912, 2354 and 2447

We have observed high-dispersion echelle spectra of red giant members in the five open clusters (OCs) NGC 1342, NGC 1662, NGC 1912, NGC 2354 and NGC 2447 and determined their radial velocities and chemical compositions. These are the first chemical abundance measurements for all but NGC 2447. We combined our clusters from this and previous papers with a sample drawn from the literature for which we remeasured the chemical abundances to establish a common abundance scale. With this homogeneous sample of OCs, we study the relative elemental abundances of stars in OCs in comparison with field stars as a function of age and metallicity. We find a range of mild enrichment of heavy (Ba–Eu) elements in young OC giants over field stars of the same metallicity. Our analysis supports that the youngest stellar generations in cluster might be underrepresented by the solar neighbourhood field stars.

Comparative Geochemical Study of the Tertiary and Quaternary Lavas of Western Senegal and the Cape Verde Islands: Geodynamic Implications

The western area of Senegal was the site of a basic volcanism in the Tertiary and Quaternary. That volcanism had caused the formation of alkaline olivine basalts, basanites and nephelinites from microlitic and porphyritic texture to dolerite texture. The geochemistry of major elements shows that the Quaternary basalts are more aluminous and more siliceous, but they contain less magnesium, less iron and less calcium than the Tertiary basalts. Two types of basalt occur here, based on the characteristics of the major elements in the Tertiary lavas: the highly undersaturated basalts of the Cape Verde Peninsula and the slightly undersaturated basalts of the Thiès Plateau. The characteristics of the trace elements reveal shallow interactions due to the contamination and/or assimilation, and to the fractional crystallization, but not due to the heterogeneity of the source. The strong enrichment in light rare earth elements (LREE) and the slight enrichment in heavy rare earth elements (HREE), the anomalies which are negative in K and Pb and positive in Nb, Ta and Eu of the Tertiary and Quaternary basalts of Western Senegal and similar anomalies of the same elements (Pb not analyzed) described in the Cape Verde islands, allow us to establish links between the petrogenetic mechanisms that had caused the formation of the basalts of this Islands and Western Senegal. Moreover, the volcanic activity in Western Senegal (of continental lntraplate type) and that of the Cape Verde Islands (oceanic intraplate type) are probably related to the hot spot located on the vertical of the Cape Verde.

Arthur Michael Wolfe

Arthur Michael Wolfe

Geochemistry and mineralogy of REY-rich mud in the eastern Indian Ocean

Deep-sea sediments in parts of the Pacific Ocean were recently found to contain remarkably high concentrations of rare-earth elements and yttrium (REY) of possible economic significance. Here we report similar REY-rich mud in a core section from Deep Sea Drilling Project Site 213 in the eastern Indian Ocean. The sediments consist mainly of siliceous ooze, with subordinate zeolitic clay that contains relatively high REY concentrations. The maximum and average total REY (ΣREY) contents of this material are 1113 and 629ppm, respectively, which are comparable to those reported from the Pacific Ocean. The REY-rich mud at Site 213 shows enrichment in heavy rare-earth elements, negative Ce anomalies, and relatively low Fe2O3/ΣREY ratios, similar to those in the Pacific Ocean. In addition, the major-element composition of the Indian Ocean REY-rich mud indicates slight enrichment in lithogenic components, which probably reflects a contribution from southern African eolian dust. A volcaniclastic component from neighboring mid-ocean ridges or intraplate volcanoes is also apparent. Elemental compositions and X-ray diffraction patterns for bulk sediment, and microscopic observation and elemental mapping of a polished thin section, demonstrate the presence of phillipsite and biogenic apatite, such as fish debris, in the REY-rich mud. The strong correlation between total REY content and apatite abundance implies that apatite plays an important role as a host phase of REY in the present deep-sea sediment column. However, positive correlations between ΣREY and elements not present in apatite (e.g., Fe2O3, MnO, and TiO2) imply that the REY-rich mud is not formed by a simple mixture of REY-enriched apatite and other components.

Investigating the abundance enrichment pattern of heavy elements in the only observed CEMP-r/s star J004441.04-732136.4 of the SMC

The post-AGB star J004441 is the first and the only one CEMP-r/s star found in SMC. Herein, we investigate the observed abundance pattern of the heavy elements using our parametric model. A consistent fitting results was obtained for the sample star. Based on the low r = 0.08, the s-process nucleosynthesis occurred in the interior is supposed to belong to the single neutron-exposure event. The median value of \(\tau _0 = 0.44\left( {\tfrac{{T_9 }} {{0.348}}} \right)^{1/2} mbarn^{ - 1}\) supports a higher efficiency of the s-process nucleosynthesis relative to J004441 than that of the solar system, however, the value is not sufficiently high to favor the formation of a lead star. Thus, J004441 does not belong to lead star group. The large Cs value of J004441 supports the intrinsic characteristic of the s-enrichment. The Cs value is similar with that found in halo CEMP-r/s stars, which indicates that the r-process contributions is critical during heavy element enrichment. This star has a metallicity of [Fe/H] = −1.34, which is larger than that of Galaxy halo CEMP-r/s stars. The reason may be because of the different history of metallicity enrichment between the SMC and the Galaxy halo.

ABUNDANCE PROFILING OF EXTREMELY METAL-POOR STARS AND SUPERNOVA PROPERTIES IN THE EARLY UNIVERSE

After the Big Bang nucleosynthesis, the first heavy element enrichment in the Universe was made by a supernova (SN) explosion of a population (Pop) III star (Pop III SN). The abundance ratios of elements produced from Pop III SNe are recorded in abundance patterns of extremely metal-poor (EMP) stars. The observations of the increasing number of EMP stars have made it possible to statistically constrain the explosion properties of Pop III SNe. We present Pop III SN models whose nucleosynthesis yields well-reproduce individually the abundance patterns of 48 such metal-poor stars as [Fe/H] $\mathrel{\rlap{\lower 4pt \hbox{$\sim$}}\raise 1pt \hbox {$<$}}-3.5$. We then derive relations between the abundance ratios of EMP stars and certain explosion properties of Pop III SNe: the higher [(C+N)/Fe] and [(C+N)/Mg] ratios correspond to the smaller ejected Fe mass and the larger compact remnant mass, respectively. Using these relations, the distributions of the abundance ratios of EMP stars are converted to those of the explosion properties of Pop III SNe. Such distributions are compared with those of the explosion properties of present day SNe: The distribution of the ejected Fe mass of Pop III SNe has the same peak as that of the resent day SNe but shows an extended tail down to $\sim10^{-2}-10^{-5}M_\odot$, and the distribution of the mass of the compact remnant of Pop III SNe is as wide as that of the present day stellar-mass black holes. Our results demonstrate the importance of large samples of EMP stars obtained by ongoing and future EMP star surveys and subsequent high-dispersion spectroscopic observations in clarifying the nature of Pop III SNe in the early Universe.

English

Present paper deals with the petrogenesis of gabbros and pyroxenites of Bhavani complex, Tamil Nadu, Southern India. Studied gabbros are mainly composed of pyroxenes with minor plagioclase (An10-30) and amphibole minerals. Pyroxenites are composed of coarse-grained clinopyroxenes, orthopyroxenes and medium-grained hornblende minerals.&nbsp; Geochemically, in the total alkali vs. SiO2&nbsp;diagram studied samples are broadly classified as gabbros and their magma type is tholeiitic in nature, however, based on the TiO2, MnO, P2O5&nbsp;diagram most of the studied samples fall within the calc-alkaline basaltic (CAB) field. In chondrite-normalized rare earth element (REEs) patterns, pyroxenites show negative Eu anomaly with slight enrichment of heavy rare earth elements (HREEs). The negative Eu anomaly in these samples indicates fractionation of plagioclase. The flat chondrite-normalized REEs pattern of gabbros in association with low CaO, Al2O3, Sr content and absence of Eu anomaly suggest removal of plagioclase component from basic parental magma. In primitive mantle (PM) and mid-ocean ridge basalt (MORB) normalized incompatible trace element patterns studied samples have enrichment of large ion lithophile elements (LILEs) and light rare earth elements (LREEs). Tectonic setting discrimination diagrams, in addition to their geochemical characteristics such as Nb-Ta, Zr-Hf negative anomalies and low values of (La/Yb)cn and (La/Sm)cn, suggest volcanic arc tectonic setting. &nbsp; Key words:&nbsp;Bhavani, layered complex, Geochemistry, light rare earth elements (LREEs), large ion lithophile elements (LILEs), petrogenesis.

Rare earth elements geochemistry in surface floodplain sediments from the Xiangjiang River, middle reach of Changjiang River, China

The Xiangjiang River is one of the most important tributaries of the Changjiang River in southern China. In this study, floodplain sediments from the Xiangjiang River have been analyzed for sediment grain size, and trace and rare earth elements (REEs). The results have been used to characterize the sediments REE composition and distribution and to identify the sediment sources and the effects of industrial pollution. The total REE (ΣREE) concentrations of the river sediments show wide variations, ranging from 37.5 to 237.4 μg g−1, with an average of 145.6 μg g−1. The chondrite-normalized REE patterns can be differentiated into two groups, whereas the average upper continental crust (UCC)-normalized REE pattern can be classified four groups. ΣREE shows strong positive correlations with clay (%) (r = 0.91), and <30 μm (%) (r = 0.89) and strong negative correlations with sand (%) (r = 0.91), implying that the grain size is an important factor in controlling the REE abundance because REEs are preferentially enriched in clay minerals in fine sediments and diluted by quartz and carbonate minerals in coarse sediments. ΣREE yields strong positive correlations with Mn (r = 0.78) and Fe (r = 0.97), suggesting that the REE composition of Xiangjiang river sediments is controlled by clay mineral compositions. The reason is that Fe- and Mn- oxyhydroxides accumulate in fine-grained sediments and control the REE abundance. Two stations (XJ08 and XJ14) show different UCC- and chondrite-normalized REE distribution patterns with relative light rare earth element (LREE) depletion and heavy rare earth element (HREE) enrichment compared with other stations, suggesting they have been polluted by industrial effluents. Therefore, REEs can be effectively used to trace sediment provenance and pollution sources.

The atmospheric chemistry of the warm Neptune GJ 3470b: Influence of metallicity and temperature on the CH4/CO ratio

Current observation techniques are able to probe the atmosphere of some giant exoplanets and get some clues about their atmospheric composition. However, the chemical compositions derived from observations are not fully understood, as for instance in the case of the CH4/CO abundance ratio, which is often inferred different from what has been predicted by chemical models. Recently, the warm Neptune GJ3470b has been discovered and because of its close distance from us and high transit depth, it is a very promising candidate for follow up characterisation of its atmosphere. We study the atmospheric composition of GJ3470b in order to compare with the current observations of this planet, to prepare the future ones, but also as a typical case study to understand the chemical composition of warm (sub-)Neptunes. The metallicity of such atmospheres is totally uncertain, and vary probably to values up to 100x solar. We explore the space of unknown parameters to predict the range of possible atmospheric compositions. Within the parameter space explored we find that in most cases methane is the major carbon-bearing species. We however find that in some cases, typically for high metallicities with a sufficiently high temperature the CH4/CO abundance ratio can become lower than unity, as suggested by some multiwavelength photometric observations of other warm (sub-)Neptunes, such as GJ1214b and GJ436b. As for the emission spectrum of GJ3470b, brightness temperatures at infrared wavelengths may vary between 400 and 800K depending on the thermal profile and metallicity. Combined with a hot temperature profile, a substantial enrichment in heavy elements by a factor of 100 with respect to the solar composition can shift the carbon balance in favour of carbon monoxide at the expense of CH4. Nevertheless, current observations of this planet do not allow yet to determine which model is more accurate.

The glass mosaics tesserae of “Villa del Casale” (Piazza Armerina, Italy): a multi-technique archaeometric study

A wide selection of glass tesserae from mosaics of the Roman “Villa del Casale” (Piazza Armerina, Enna, Italy) were characterized from a chemical and textural perspective, with the aim of providing archaeometric information about the raw materials and manufacturing techniques utilized at this archaeological site of utmost importance. The studied samples are vitreous colored tesserae, both opaque and transparent. The textures and chemical compositions of the coloring and opacifying agents were determined through a multi-technique approach based on scanning electron microscopy, X-ray diffraction, electron microprobe analyses for major elements, and inductively coupled plasma mass spectrometry for trace elements. On the basis of major element contents, the samples can be classified as natron-based silica–lime glasses. As regards the opacifiers/coloring materials, a substantial use of Pb and Ca antimonates, and metallic copper was observed. A slight enrichment of heavy rare earth elements (REE) relative to light REE, and a number of positive correlations between high field-strength elements suggest that the raw materials used for the production of the Piazza Armerina tesserae included a mature sand, enriched in quartz and heavy mineral phases.