Abundances Of Argon Research Articles

Spectral study of the planetary nebula NGC 2452

We provide a detailed study for the Galactic planetary nebula (PN) NGC 2452, which has long been suspected to be a member of the Galactic cluster NGC2453. The present study uses integral field unit (IFU) spectroscopic observations of the PN to explore its physical conditions, chemical abundances, kinematical characteristics, and morphological features. The strength of the singly ionized helium (HeII λ4686) line reveals that the PN is of high excitation class. The presence of the neutral lines of [OI] and [NI] a long with the value of the flux ratio F([Nii]λ6583)/F(Hα) indicates that the object is slightly optically thick. We compute the nebular density and temperature from a large number of diagnostic line ratios. The ionic and total abundances of helium (He) and carbon (C) are derived from their optical recombination lines (ORLs), while the abundances of nitrogen (N), oxygen (O), neon (Ne), argon (Ar), sulphur (S), and chlorine (Cl) are derived from their collisionlly-excitation lines (CELs). Faint lines like Krypton (Kr), Manganese (Mn), and Chromium (Cr), which are known to be products of the slow-process (s-process), are also seen in the PN spectrum. To illustrate the morphology and excitation structures of the PN, we generate a gallery of emission-line maps using the nebular data cubes. We find that the PN has an overall elliptical shape with a few interior clumps. In terms of physical and chemical properties, we find no significant differences between the entire PN and its accompanying clumps, considering the uncertainties associated with these parameters. Both the astronomical data from Gaia and the inferred radial velocity suggest that the PN belongs to the Galactic thin-disk.

The survey of planetary nebulae in Andromeda (M31)

Context. The Andromeda (M31) galaxy presents evidence of recent substantial mass accretion. This is unlike what has happened in the Milky Way, which has experienced a rather quiescent evolution. Aims. We use oxygen and argon abundances for planetary nebulae (PNe) with low internal extinction (progenitor ages of > 4.5 Gyr) and high extinction (progenitor ages < 2.5 Gyr), as well as those of the HII regions, to constrain the chemical enrichment and star formation efficiency in the thin and thicker discs of M31. Methods. The argon element is produced in larger fractions by Type Ia supernovae compared to oxygen. We find that the mean log(O/Ar) values of PNe as a function of their argon abundances, 12 + log(Ar/H), trace the interstellar medium (ISM) conditions at the time of birth of the M31 disc PN progenitors. Thus, the chemical enrichment and star formation efficiency information encoded in the [α/Fe] versus [Fe/H] distribution of stars is also imprinted in the oxygen-to-argon abundance ratio log(O/Ar) versus argon abundance for the nebular emissions of the different stellar evolution phases. We propose using the log(O/Ar) versus (12 + log(Ar/H)) distribution of PNe with different ages to constrain the star formation histories of the parent stellar populations in the thin and thicker M31 discs. Results. For the inner M31 disc (RGC < 14 kpc), the chemical evolution model that reproduces the mean log(O/Ar) values as a function of argon abundance for the high- and low-extinction PNe requires a second infall of metal-poorer gas during a gas-rich (wet) satellite merger. This wet merger triggered the burst of star formation seen by the PHAT survey in the M31 disc, ∼3 Gyr ago. A strong starburst is ongoing in the intermediate radial range (14 ≤ RGC ≤ 18 kpc). In the outer M31 disc (RGC > 18 kpc), the log(O/Ar) versus argon abundance distribution of the younger high-extinction PNe indicates that they too were formed in a burst, though mostly from the metal-poorer gas. Present-day HII regions show a range of oxygen-to-argon ratios, which is indicative of spatial variations and consistent with a present-day rainfall of metal-poorer gas onto the disc with different degrees of mixing with the previously enriched ISM. Conclusions. We implement the use of the log(O/Ar) versus argon abundance distribution for emission nebulae as a complement to the [α/Fe] versus [Fe/H] diagram for stars, and use it to constrain the star formation efficiency in the thin and thicker discs of M31. Diagrams for M31 PNe in different age ranges reveal that a secondary infall of gas affected the chemical evolution of the M31 thin disc. In M31, the thin disc is younger and less radially extended, formed stars at a higher star formation efficiency, and had a faster chemical enrichment timescale than the more extended thicker disc. Both the thin and thicker discs in M31 reach similar high argon abundances (12 + log(Ar/H)) ≃ 6.7. The chemical and structural properties of the thin and thicker discs in M31 are thus remarkably different from those determined for the Milky Way thin and thick discs.

The survey of planetary nebulae in Andromeda (M31) – IV. Radial oxygen and argon abundance gradients of the thin and thicker disc

ABSTRACT We obtain a magnitude-limited sample of Andromeda (M 31) disc PNe with chemical abundance estimated through the direct detection of the [O iii] 4363 Å line. This leads to 205 and 200 PNe with oxygen and argon abundances, respectively. We find that high- and low-extinction M 31 disc PNe have statistically distinct argon and oxygen abundance distributions. In the radial range of 2−30 kpc, the older low-extinction disc PNe are metal-poorer on average with a slightly positive radial oxygen abundance gradient (0.006 ± 0.003 dex kpc−1) and slightly negative for argon (−0.005 ± 0.003 dex kpc−1), while the younger high-extinction disc PNe are metal-richer on average with steeper radial abundance gradients for both oxygen (−0.013 ± 0.006 dex kpc−1) and argon (−0.018 ± 0.006 dex kpc−1), similar to the gradients computed for the M 31 H ii regions. The M 31 disc abundance gradients are consistent with values computed from major merger simulations, with the majority of the low-extinction PNe being the older pre-merger disc stars in the thicker disc, and the majority of the high-extinction PNe being younger stars in the thin disc, formed during and after the merger event. The chemical abundance of the M 31 thicker disc has been radially homogenized because of the major merger. Accounting for disc scale lengths, the positive radial oxygen abundance gradient of the M 31 thicker disc is in sharp contrast to the negative one of the MW thick disc. However, the thin discs of the MW and M 31 have remarkably similar negative oxygen abundance gradients.

Chemical abundances in Seyfert galaxies – VIII. Argon abundance estimates

ABSTRACT For the first time, the argon abundance relative to hydrogen abundance (Ar/H) in the narrow line region of a sample of Seyfert 2 nuclei has been derived. In view of this, optical narrow emission line intensities of a sample of 64 local Seyfert 2 nuclei (z < 0.25) taken from Sloan Digital Sky Survey DR7 and measured by the MPA/JHU group were considered. We adopted the Te-method for AGNs, which is based on direct determination of the electron temperature, together with a grid of photoionization model results, built with the cloudy code, to obtain a method for the derivation of the Ar/H abundance. We find that for a metallicity range of $\rm 0.2 \: \lesssim \: (\mathit{ Z}/{\rm Z_{\odot }}) \: \lesssim \: 2.0$, Seyfert 2 nuclei present Ar/H abundance ranging from ∼0.1 to ∼3 times the argon solar value, adopting $\rm log(O/H)_{\odot }=-3.31$ and $\rm log(Ar/H)_{\odot }=-5.60$. These range of values correspond to $\rm 8.0 \: \lesssim \: (12+log(O/H) \: \lesssim \: 9.0$ and $\rm 5.4 \: \lesssim \: (12+log(Ar/H) \: \lesssim \: 6.9$, respectively. The range of Ar/H and Ar/O abundance values obtained from our sample are in consonance with estimations from extrapolations of the radial abundance gradients to the central parts of the disc for four spiral galaxies. We combined our abundance results with estimates obtained from a sample of H ii galaxies, which were taken from the literature, and found that the Ar/O abundance ratio decreases slightly as the O/H abundance increases.

Ionization correction factors and dust depletion patterns in giant H ii regions

ABSTRACT We provide new ionization correction factors (ICFs) for carbon, nitrogen, neon, sulfur, chlorine, and argon in giant H ii regions. The ICFs were computed using the most representative photoionization models from a large initial grid. The models were selected using an observational sample of 985 giant H ii regions (GHR) in spiral galaxies and blue compact galaxies (BCG). The observational sample was also used to assign a weight to each model describing how well it agrees with observations in the [O iii]/H β versus [N ii]/H α diagram. In addition to the ICFs we provide, for the first time, analytical expressions for their formal uncertainties. We use our ICFs to compute the abundances of nitrogen, neon, sulfur, and argon in our samples. Our abundances are robust within the adopted framework, but may require revision in the case of important changes in atomic data or in the spectral energy distribution of the ionizing radiation in H ii regions. Considering the abundance patterns we obtained for the BCG sample (abundances for the GHR sample are less reliable) we find that oxygen is depleted into dust grains at a rate increasing with metallicity and reaching 0.12 dex at solar abundances. The discussion of possible depletion of sulfur and argon requires considering recent Type Ia Supernova yields, which are still uncertain.

Nitrogen and noble gases reveal a complex history of metasomatism in the Siberian lithospheric mantle

The Siberian flood basalts (SFB) erupted at the end of the Permian period (∼250 Ma) in response to a deep-rooted mantle plume beneath the Siberian Sub-Continental Lithospheric Mantle (SCLM). Plume-lithosphere interaction can lead to significant changes in the structure and chemistry of the SCLM and trigger the release of metasomatic material that was previously stored within the stable craton. Here, we investigate the nature of the Siberian-SCLM (S-SCLM) by measuring nitrogen abundances and isotopes (δ15N) in 11 samples of two petrologically-distinct suites of peridotitic xenoliths recovered from kimberlites which bracket the eruption of the SFB: the 360 Myr old Udachnaya and 160 Myr old Obnazhennaya pipes. Nitrogen isotope (δ15N) values range from -5.85 ± 1.29‰ to +3.94 ± 0.63‰, which encompasses the entire range between depleted Mid-Ocean Ridge Basalt (MORB) mantle (DMM; -5 ± 2‰) and plume-derived (+3 ± 2‰) endmembers. In addition, we present neon (n=7) and argon (n=8) abundance and isotope results for the same two suites of samples. The 20Ne/22Ne and 21Ne/22Ne range from atmospheric-like values of 9.88 up to 11.35 and from 0.0303 to 0.0385, respectively, suggesting an admixture of DMM and plume-derived components. Argon isotopes (40Ar/36Ar) range from 336.7 to 1122 and correlate positively with 40Ar contents. We show that volatile systematics of Siberian xenoliths: (1) exhibit evidence of ancient metasomatic and/or recycled signatures, and (2) show evidence of subsequent plume-like re-fertilization, which we attribute to the emplacement of the SFB. Metasomatic fluids are highly enriched in radiogenic gases and have elevated Br/Cl and I/Cl values, consistent with an ancient subducted crustal component. The metasomatic component is marked by light N isotope signatures, suggesting it may be derived from an anoxic Archean subducted source. Taken together, these N2-Ne-Ar isotope results suggest that mantle plume impingement has profoundly modified the S-SCLM, and that N, Ne and Ar isotopes are sensitive tracers of metasomatism in the S-SCLM. Metasomatic fluids that permeate the S-SCLM act to archive a “subduction-fingerprint” that can be used to probe relative volatile-element recycling efficiencies and thus provide insight into volatile transport between the surface and mantle reservoirs over Earth history.

Comparison between photon detection efficiency and tetraphenyl-butadiene coating stability of photomultiplier tubes immersed in liquid argon

Liquid argon detectors are an interesting option for neutrino experiments. The high density of liquid argon allows using it directly as target for neutrino interactions. The relatively large abundance of argon in the atmosphere makes it a cost-effective medium, allowing the construction of detectors of several hundred tons, such as ICARUS, and even several kton detectors are foreseen for the next generation of experiments, such as DUNE . Besides being suitable to act as the target, liquid argon also serves as the detection medium for the charged particles coming out of the interaction vertex. The interaction time, t0, can be determined by detecting the photons which are produced together with the electrons in the ionization process. To detect them, the integration of an efficient photon detection system into the liquid argon detector is necessary. One difficulty here is related to the fact that the emitted photons have a wavelength in the VUV range (128 nm). The classical approach for the photon detection system is, therefore, the usage of photomultiplier tubes coated with tetraphenyl-butadiene which shifts the VUV photons to about 430 nm, a wavelength to which the photomultiplier tubes are directly sensitive to. While the basic concept is well established and has been used in several experiments such as ICARUS, ArDM and DarkSide, some aspects of the coating are not well understood such as the preparation of the photomultiplier tube surface which can be either polished or sandblasted. To better understand the effect on the overall photon detection efficiency on one hand and the tetraphenyl-butadiene stability during the cooling down, on the other hand, the quantum efficiencies of sandblasted and polished photomultiplier tubes, coated following the same procedure, were measured with a setup at the Istituto Nazionale di Fisica Nucleare (INFN), in Pavia. In addition, the immersion of the photomultiplier tubes with different soak timings was tested, showing a significantly different behavior for fast and slow immersion for the polished photomultiplier tubes.

Hydrogen fluence in Genesis collectors: Implications for acceleration of solar wind and for solar metallicity.

NASA's Genesis mission was flown to capture samples of the solar wind and return them to the Earth for measurement. The purpose of the mission was to determine the chemical and isotopic composition of the Sun with significantly better precision than known before. Abundance data are now available for noble gases, magnesium, sodium, calcium, potassium, aluminum, chromium, iron, and other elements. Here, we report abundance data for hydrogen in four solar wind regimes collected by the Genesis mission (bulk solar wind, interstream low-energy wind, coronal hole high-energy wind, and coronal mass ejections). The mission was not designed to collect hydrogen, and in order to measure it, we had to overcome a variety of technical problems, as described herein. The relative hydrogen fluences among the four regimes should be accurate to better than ±5-6%, and the absolute fluences should be accurate to ±10%. We use the data to investigate elemental fractionations due to the first ionization potential during acceleration of the solar wind. We also use our data, combined with regime data for neon and argon, to estimate the solar neon and argon abundances, elements that cannot be measured spectroscopically in the solar photosphere.

16O(p,α)13N makes explosive oxygen burning sensitive to the metallicity of the progenitors of type Ia supernovae

Even though the main nucleosynthetic products of type Ia supernovae belong to the iron-group, intermediate-mass alpha-nuclei (silicon, sulfur, argon, and calcium) stand out in their spectra up to several weeks past maximum brightness. Recent measurements of the abundances of calcium, argon, and sulfur in type Ia supernova remnants have been interpreted in terms of metallicity-dependent oxygen burning, in accordance with previous theoretical predictions. It is known that α-rich oxygen burning results from 16O→12C followed by efficient 12C+12C fusion reaction, as compared to oxygen consumption by 16O fusion reactions, but the precise mechanism of dependence on the progenitor metallicity has remained unidentified so far. I show that the chain 16O(p,α)13N(γ,p)12C boosts α-rich oxygen burning when the proton abundance is large, increasing the synthesis of argon and calcium with respect to sulfur and silicon. For high-metallicity progenitors, the presence of free neutrons leads to a drop in the proton abundance and the above chain is not efficient. Although the rate of 16O(p,α)13N can be found in astrophysical reaction rate libraries, its uncertainty is unconstrained. Assuming that all reaction rates other than 16O(p,α)13N retain their standard values, an increase by a factor of approximately seven of the 16O(p,α)13N rate at temperatures in the order 3−5 × 109 K is enough to explain the whole range of calcium-to-sulfur mass ratios measured in Milky Way and LMC supernova remnants. These same measurements provide a lower limit to the 16O(p,α)13N rate in the mentioned temperature range, on the order of a factor of 0.5 with respect to the rate reported in widely used literature tabulations.

Comparison on Rare Gas Geochemical Characteristics and Gas Originations of Kuche and Southwestern Depressions in Tarim Basin, China

The Kuche Depression is considered as the most important gas resource potential and gas exploring area with great gas resource potential and prospect in the Tarim Basin. Based on geochemical experimental analyses and comprehensive geological studies, the general geochemical characteristics of molecular and isotope compositions of rare gases as well as hydrocarbon gases and nonhydrocarbon gases are comparatively studied in the Kuche and Southwestern Depressions. Then, their genetic types are separately identified and gas originations are comprehensively discussed. The main results are as follows. (1) Gas fields in the Kuche Depression have a higher methane abundance, accompanied with low N2and CO2abundances, but the Akemomu gas field in the Southwestern Depression has a relatively lower average methane abundance, accompanied with high average N2and CO2abundances. The helium abundance of natural gases in gas fields from the Kuche Depression general has 1 order of magnitude higher than the air value. Comparatively, it has more than 2 orders of magnitude higher than the atmospheric value in the Akemomu gas field from the Southwestern Depression. The neon, argon, krypton, and xenon abundances in both Kuche and Southwestern Depressions are lower than the corresponding air values. (2) Natural gases from gas fields in the Kuche Depression and the Southwestern Depressions are generally typical coal-formed gases. The rare gases in the Kuche Depression have typical crustal genesis, mainly deriving from the radioactive decay of elements in the crust, while in the Akemomu gas field from the Southwestern Depression, the rare gases have main crustal genesis with a proportion of 92.5%, probably accompanied with a little mantled genetic contribution. (3) Natural gases in the Kuche Depression are generally derived from coal measure source rocks of Jurassic and Triassic, which principally originated from Jurassic in strata period and coals in source rock types. The Jurassic source rocks account for 55%-75% and the Triassic source rocks account for 25%-45% approximately, while coals occupy 68% and mudstones occupy 32% separately. Natural gases from the Akemomu gas field in the Southwestern Depression mainly originated from humic mudstones of marine and continental transitional source rocks of Carboniferous to Permian.

Excited states of Ca39 and their significance in nova nucleosynthesis

Background: Discrepancies exist between the observed abundances of argon and calcium in oxygen-neon nova ejecta and those predicted by nova models. An improved characterization of the $^{38}\mathrm{K}(p,\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{39}\mathrm{Ca}$ reaction rate over the nova temperature regime ($\ensuremath{\sim}0.1--0.4$ GK), and thus the nuclear structure of $^{39}\mathrm{Ca}$ above the proton threshold [5770.92(63) keV], is necessary to resolve these contradictions.Purpose: The present study was performed to search for low-spin proton resonances in the $^{38}\mathrm{K}+p$ system, and to improve the uncertainties in energies of the known astrophysically significant proton resonances in $^{39}\mathrm{Ca}$.Methods: The level structure of $^{39}\mathrm{Ca}$ was investigated via high-resolution charged-particle spectroscopy with an Enge split-pole spectrograph using the $^{40}\mathrm{Ca}(^{3}\mathrm{He},\ensuremath{\alpha})\phantom{\rule{0.16em}{0ex}}^{39}\mathrm{Ca}$ reaction. Differential cross sections were measured over six laboratory angles at 21 MeV. Distorted-wave Born approximation calculations were performed to constrain the spin-parity assignments of observed levels with special attention to those significant in determination of the $^{38}\mathrm{K}(p,\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{39}\mathrm{Ca}$ reaction rate over the nova temperature regime.Results: The resonance energies corresponding to two out of three astrophysically important states at 6154(5) and 6472.2(24) keV are measured with better precision than previous charged-particle spectroscopy measurements. A tentatively new state is discovered at 5908(3) keV. The spin-parity assignments of a few of the astrophysically important resonances are determined.Conclusions: The present $^{38}\mathrm{K}(p,\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{39}\mathrm{Ca}$ upper limit thermonuclear reaction rate at 0.1--0.4 GK is higher than that determined by Christian et al. [Phys. Rev. C 97, 025802 (2018)] by at most a factor of 1.4 at 0.1 GK.

The ultrafast outflow of WKK 4438: Suzaku and NuSTAR X-ray spectral analysis

Previous X-ray spectral analysis has revealed an increasing number of AGNs with high accretion rates where an outflow with a mildly relativistic velocity originates from the inner accretion disk. Here we report the detection of a new ultra-fast outflow (UFO) with a velocity of $v_{\rm out}=0.319^{+0.005}_{-0.008}c$ in addition to a relativistic disk reflection component in a poorly studied NLS1 WKK~4438, based on archival \nustar and \suzaku observations. The spectra of both \suzaku and \nustar observations show an Fe~\textsc{xxvi} absorption feature and the \suzaku data also show evidence for an Ar~\textsc{xviii} with the same blueshift. A super-solar argon abundance ($Z^{\prime}_{\rm Ar}>6Z_{\odot}$) and a slight iron over-abundance ($Z^{\prime}_{\rm Fe}=2.6^{+1.9}_{-2.0}Z_{\odot}$) are found in our spectral modelling. Based on Monte-Carlo simulations, the detection of the UFO is estimated to be around at 3$\sigma$ significance. The fast wind most likely arises from a radius of $\geq20r_g$ away from the central black hole. The disk is accreting at a high Eddington ratio ($L_{\rm bol}=0.4-0.7L_{\rm Edd}$). The mass outflow rate of the UFO is comparable with the disk mass inflow rate ($\dot M_{\rm out}>30\%\dot M_{\rm in}$), assuming a maximum covering factor. The kinetic power of the wind might not be high enough to have influence in AGN feedback ($\dot E_{\rm wind}/L_{\rm bol}\approx 3-5\%$) due to a relatively small column density ($12^{+9}_{-4}\times10^{22}$~cm$^{-2}$). However note that both the inferred velocity and the column density could be lower limits owing to the low viewing angle ($i=23^{+3}_{-2}$$^{\circ}$).

Neon, sulphur, and argon abundances of planetary nebulae in the sub-solar metallicity Galactic anti-centre

Context.Spectra of planetary nebulae show numerous fine structure emission lines from ionic species, enabling us to study the overall abundances of the nebular material that is ejected into the interstellar medium. The abundances derived from planetary nebula emission show the presence of a metallicity gradient within the disk of the Milky Way up to Galactocentric distances of ~10 kpc, which are consistent with findings from studies of different types of sources, including H II regions and young B-type stars. The radial dependence of these abundances further from the Galactic centre is in dispute.Aims.We aim to derive the abundances of neon, sulphur and argon from a sample of planetary nebulae towards the Galactic anti-centre, which represent the abundances of the clouds from which they were formed, as they remain unchanged throughout the course of stellar evolution. We then aim to compare these values with similarly analysed data from elsewhere in the Milky Way in order to observe whether the abundance gradient continues in the outskirts of our Galaxy.Methods.We have observed 23 planetary nebulae at Galactocentric distances of 8–21 kpc withSpitzerIRS. The abundances were calculated from infrared emission lines, for which we observed the main ionisation states of neon, sulphur, and argon, which are little affected by extinction and uncertainties in temperature measurements or fluctuations within the planetary nebula. We have complemented these observations with others from optical studies in the literature, in order to reduce or avoid the need for ionisation correction factors in abundance calculations.Results.The overall abundances of our sample of planetary nebulae in the Galactic anti-centre are lower than those in the solar neighbourhood. The abundances of neon, sulphur, and argon from these stars are consistent with a metallicity gradient from the solar neighbourhood up to Galactocentric distances of ~20 kpc, albeit with varying degrees of dispersion within the data.

A FEROS Survey of Hot Subdwarf Stars

Abstract We have completed a survey of twenty-two ultraviolet-selected hot subdwarfs using the Fiber-fed Extended Range Optical Spectrograph (FEROS) and the 2.2-m telescope at La Silla. The sample includes apparently single objects as well as hot subdwarfs paired with a bright, unresolved companion. The sample was extracted from our GALEX catalogue of hot subdwarf stars. We identified three new short-period systems (P = 3.5 hours to 5 days) and determined the orbital parameters of a long-period (P = 62d.66) sdO plus G III system. This particular system should evolve into a close double degenerate system following a second common envelope phase.We also conducted a chemical abundance study of the subdwarfs: Some objects show nitrogen and argon abundance excess with respect to oxygen. We present key results of this programme.

Evolutionary status of the Of?p star HD 148937 and of its surrounding nebula NGC 6164/5

Aims. The magnetic star HD148937 is the only Galactic Of?p star surrounded by a nebula. The structure of this nebula is particularly complex and is composed, from the center out outwards, of a close bipolar ejecta nebula (NGC6164/5), an ellipsoidal wind-blown shell, and a spherically symmetric Stromgren sphere. The exact formation process of this nebula and its precise relation to the star's evolution remain unknown. Methods. We analyzed infrared Spitzer IRS and far-infrared Herschel/PACS observations of the NGC6164/5 nebula. The Herschel imaging allowed us to constrain the global morphology of the nebula. We also combined the infrared spectra with optical spectra of the central star to constrain its evolutionary status. We used these data to derive the abundances in the ejected material. To relate this information to the evolutionary status of the star, we also determined the fundamental parameters of HD148937 using the CMFGEN atmosphere code. Results. The H$\alpha$ image displays a bipolar or "8"-shaped ionized nebula, whilst the infrared images show dust to be more concentrated around the central object. We determine nebular abundance ratios of N/O = 1.06 close to the star, and N/O = 1.54 in the bright lobe constituting NGC6164. Interestingly, the parts of the nebula located further from HD148937 appear more enriched in stellar material than the part located closer to the star. Evolutionary tracks suggest that these ejecta have occured $\sim$1.2-1.3 and $\sim$0.6 Myrs ago, respectively. In addition, we derive abundances of argon for the nebula compatible with the solar values and we find a depletion of neon and sulfur. The combined analyses of the known kinematics and of the new abundances of the nebula suggest either a helical morphology for the nebula, possibly linked to the magnetic geometry, or the occurrence of a binary merger.

A study of the shell of Nova V2659 Cyg

Results of a study of the shell of Nova V2659 Cyg based on spectrophotometric observations carried out over a year and a half after its eruption are presented. The physical conditions in the nova shell have been studied. The electron temperature (9000 K) and density (5 × 106 cm−3) in the nebular stage have been estimated, together with the abundances of helium, oxygen, nitrogen, neon, argon, and iron. The abundances of nitrogen, oxygen, neon, and argon are enhanced relative to the solar values. The relative abundances are [N/H] = 2.26 ± 0.25 dex, [O/H] = 1.66 ± 0.35 dex, [Ne/H] = 0.78 ± 0.25 dex, and [Ar/H] = 0.32 ± 0.38 dex. The estimated mass of oxygen and total mass of the emitting shell are ≈1 × 10−4 M ⊙ and ≈3 × 10−4 M ⊙, respectively. In the period of chaotic brightness oscillations, the maximum velocity of the shell expansion derived from the radial velocities of the absorption components of the HI and FeII line profiles increased by ≈400 km/s 41 days after the maximum, and by ≈200 km/s 101 days after the maximum, reaching 1600 km/s in both cases.

THE MYSTERIOUS CASE OF THE SOLAR ARGON ABUNDANCE NEAR SUNSPOTS IN FLARES

ABSTRACT Recently we discussed an enhancement of the abundance of Ar xiv relative to Ca xiv near a sunspot during a flare, observed in spectra recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft. The observed Ar xiv/Ca xiv ratio yields an argon/calcium abundance ratio seven times greater than expected from the photospheric abundance. Such a large abundance anomaly is unprecedented in the solar atmosphere. We interpreted this result as being due to an inverse first ionization potential (FIP) effect. In the published work, two lines of Ar xiv were observed, and one line was tentatively identified as an Ar xi line. In this paper, we report observing a similar enhancement in a full-CCD EIS flare spectrum in 13 argon lines that lie within the EIS wavelength ranges. The observed lines include two Ar xi lines, four Ar xiii lines, six Ar xiv lines, and one Ar xv line. The enhancement is far less than reported in Doschek et al. but exhibits similar morphology. The argon abundance is close to a photospheric abundance in the enhanced area, and the abundance could be photospheric. This enhancement occurs in association with a sunspot in a small area only a few arcseconds (1″ = about 700 km) in size. There is no enhancement effect observed in the normally high-FIP sulfur and oxygen line ratios relative to lines of low-FIP elements available to EIS. Calculations of path lengths in the strongest enhanced area in Doschek et al. indicate a depletion of low-FIP elements.

The absolute optical oscillator strengths of the 3p54 s and excitations of argon measured by the dipole (γ, γ) method

The optical oscillator strengths of the 3p54s and excitations of argon are of crucial importance in determining the elemental abundance of argon from astronomical observations. Substantial efforts have been made to determine the optical oscillator strengths of the 3p54s and transitions of argon, however, significant discrepancies among the reported values still exist. In this work, the absolute optical oscillator strengths of the 3p54s and transitions of argon have been measured by a newly developed high-resolution dipole (γ, γ) method. A comprehensive comparison with the previous experimental and theoretical data was then made as a cross-check.

Recycling of crustal material by the Iceland mantle plume: New evidence from nitrogen elemental and isotope systematics of subglacial basalts

We report new nitrogen (N2) abundance and isotope (δ15N) data for 43 subglacial basaltic glasses from the neovolcanic zones of Iceland, a key locality in studies of mantle plume geochemistry and crust–mantle processes. New helium and argon abundance and isotope data are also reported to supplement previous studies (Füri et al., 2010; Barry et al., 2014), allowing elemental ratios (e.g., N2/40Ar∗ where 40Ar∗=radiogenic 40Ar) to be calculated. Subglacial basaltic glasses with N2>2μcm3STP/g show a wide range in δ15N values, from −2.91 to +11.96‰ (vs. Air), with values >6‰ only observed at one locality in the Eastern Rift Zone. Elemental ratios involving N2, i.e., N2/3He, and N2/40Ar∗, span several orders of magnitude from 2.5×105 to 9.0×107, and 32.8 to 1.46×106, respectively. In contrast, argon isotope ratios (40Ar/36Ar) are limited, ranging from air-like (∼298.6) values up to 1330. Glasses exhibit a wide range in helium isotope ratios (8–26 RA), with clear distinctions between individual rift segments.A number of processes have extensively modified original mantle source N isotope and relative abundance compositions – most significantly air interaction, crustal contamination in some instances, and possibly degassing-induced fractionation. Under the assumption that the starting 4He/40Ar∗ production ratio of Iceland mantle is identical to the depleted MORB mantle (DMM), a filtering protocol for the entire N dataset, based upon 40Ar/36Ar and 4He/40Ar∗ ratios, was adopted to identify samples with unmodified δ15N values. Consequently, we identify 22 samples that define the Icelandic mantle N-isotope distribution (δ15N=−2.29 to +5.71‰). Using the filtered dataset, we investigate simple binary mixing scenarios involving N2/3He–N2/40Ar∗–δ15N variations to identify mantle end-member compositions. Mixing scenarios are consistent with a recycled component in the Iceland mantle source, defined by a high and heterogeneous δ15N end-member. Moreover, this end-member is coupled to the high 3He/4He signature, and is characterized by He depletion and/or the presence of excess N2. These features strongly suggest the presence of recycled crustal N-component(s) integrated into and/or entrained by the Iceland plume source.These new results reveal the highly heterogeneous nature of nitrogen in the hybrid Iceland plume source, consistent with models based on trace elements and radiogenic isotopes that advocate for significant heterogeneity of recycled crustal component(s) sampled by the Iceland plume. A relatively young age of the recycled crustal material (possibly Phanerozoic) is consistent with the association of positive δ15N values and high N2/40Ar∗ ratios with constraints from radiogenic isotopes (e.g., Pb), thus indicating a relatively short time-interval (∼108years) between subduction of crustal material and entrainment by the Iceland mantle plume.

CHEMICAL ABUNDANCES OF PLANETARY NEBULAE IN THE SUBSTRUCTURES OF M31

We present deep spectroscopy of planetary nebulae (PNe) that are associated with the substructures of the Andromeda Galaxy (M31). The spectra were obtained with the OSIRIS spectrograph on the 10.4 m GTC. Seven targets were selected for the observations, three in the Northern Spur and four associated with the Giant Stream. The most distant target in our sample, with a rectified galactocentric distance >100 kpc, was the first PN discovered in the outer streams of M31. The [O III] 4363 auroral line was well detected in the spectra of all targets, enabling electron temperature determination. Ionic abundances are derived based on the [O III] temperatures, and elemental abundances of helium, nitrogen, oxygen, neon, sulfur, and argon are estimated. The relatively low N/O and He/H ratios as well as abundance ratios of alpha-elements indicate that our target PNe might belong to populations as old as ~2 Gyr. Our PN sample, including the current seven and the previous three observed by Fang et al., have rather homogeneous oxygen abundances. The study of abundances and the spatial and kinematical properties of our sample leads to the tempting conclusion that their progenitors might belong to the same stellar population, which hints at a possibility that the Northern Spur and the Giant Stream have the same origin. This may be explained by the stellar orbit proposed by Merrett et al. Judging from the position and kinematics, we emphasize that M32 might be responsible for the two substructures. Deep spectroscopy of PNe in M32 will help to assess this hypothesis.