Posts Tagged abundance

Recent Postings from abundance

Bent by baryons: the low mass galaxy-halo relation

The relation between galaxies and dark matter halos is of vital importance for evaluating theoretical predictions of structure formation and galaxy formation physics. We show that the widely used method of abundance matching based on dark matter only simulations fails at the low mass end because two of its underlying assumptions are broken: only a small fraction of low mass (below 10^9.5 solar masses) halos host a visible galaxy, and halos grow at a lower rate due to the effect of baryons. In this regime, reliance on dark matter only simulations for abundance matching is neither accurate nor self-consistent. We find that the reported discrepancy between observational estimates of the halo masses of dwarf galaxies and the values predicted by abundance matching does not point to a failure of LCDM, but simply to a failure to account for baryonic effects. Our results also imply that the Local Group contains only a few hundred observable galaxies in contrast with the thousands of faint dwarfs that abundance matching would suggest. We show how relations derived from abundance matching can be corrected, so that they can be used self-consistently to calibrate models of galaxy formation.

General limit on the relation between abundances of D and $^7$Li in big bang nucleosynthesis with nucleon injections

The injections of energetic hadrons could have occurred in the early universe by decays of hypothetical long-lived exotic particles. The injections induce the showers of nonthermal hadrons via nuclear scattering. Neutrons generated at these events can react with $^7$Be nuclei and reduce $^7$Be abundance solving a problem of the primordial $^7$Li abundance. We suggest that thermal neutron injection is a way to derive a model independent conservative limit on the relation between abundances of D and $^7$Li in a hadronic energy injection model. We emphasize that an uncertainty in cross sections of inelastic $n+p$ scattering affects the total number of induced neutrons, which determines final abundances of D and $^7$Li. In addition, the annihilations of antinucleons with $^4$He result in higher D abundance and trigger nonthermal $^6$Li production. It is concluded that a reduction of $^7$Li abundance from a value in the standard big bang nucleosynthesis (BBN) model down to an observational two $\sigma$ upper limit is necessarily accompanied by an undesirable increase of D abundance up to at least an observational 12 $\sigma$ upper limit from observations of quasi-stellar object absorption line systems. The effects of antinucleons and secondary particles produced in the hadronic showers always lead to a severer constraint. The BBN models involving any injections of extra neutrons are thus unlikely to reproduce a small $^7$Li abundance consistent with observations.

General limit on the relation between abundances of D and $^7$Li in big bang nucleosynthesis with nucleon injections [Cross-Listing]

The injections of energetic hadrons could have occurred in the early universe by decays of hypothetical long-lived exotic particles. The injections induce the showers of nonthermal hadrons via nuclear scattering. Neutrons generated at these events can react with $^7$Be nuclei and reduce $^7$Be abundance solving a problem of the primordial $^7$Li abundance. We suggest that thermal neutron injection is a way to derive a model independent conservative limit on the relation between abundances of D and $^7$Li in a hadronic energy injection model. We emphasize that an uncertainty in cross sections of inelastic $n+p$ scattering affects the total number of induced neutrons, which determines final abundances of D and $^7$Li. In addition, the annihilations of antinucleons with $^4$He result in higher D abundance and trigger nonthermal $^6$Li production. It is concluded that a reduction of $^7$Li abundance from a value in the standard big bang nucleosynthesis (BBN) model down to an observational two $\sigma$ upper limit is necessarily accompanied by an undesirable increase of D abundance up to at least an observational 12 $\sigma$ upper limit from observations of quasi-stellar object absorption line systems. The effects of antinucleons and secondary particles produced in the hadronic showers always lead to a severer constraint. The BBN models involving any injections of extra neutrons are thus unlikely to reproduce a small $^7$Li abundance consistent with observations.

The lithium abundances for a large sample of red giants

The lithium abundances for 378 G/K giants are derived with non-LTE correction considered. Among these, there are 23 stars that host planetary systems. The lithium abundance is investigated, as a function of metallicity, effective temperature, and rotational velocity, as well as the impact of a giant planet on G/K giants. The results show that the lithium abundance is a function of metallicity and effective temperature. The lithium abundance has no correlation with rotational velocity at vsini $<$ 10 km s$^{-1}$. Giants with planets present lower lithium abundance and slow rotational velocity (vsini $<$ 4 km s$^{-1}$). Our sample includes three Li-rich G/K giants, 36 Li-normal stars and 339 Li-depleted stars. The fraction of Li-rich stars in this sample agrees with the general rate of less than 1$\%$ in literature, and the stars that show normal amounts of Li are supposed to possess the same abundance at the current interstellar medium. For the Li-depleted giants, Li deficiency may have already taken place at the main sequence stage for many intermediate-mass (1.5-5 M$_{\odot}$) G/K giants. Finally, we present the lithium abundance and kinematic parameters for an enlarged sample of 565 giants using a compilation of literature, and confirm that the lithium abundance is a function of metallicity and effective temperature. With the enlarged sample, we investigate the differences between the lithium abundance in thin-/thick-disk giants, which indicate that the lithium abundance in thick-disk giants is more depleted than that in thin-disk giants.

The Hamburg/ESO R-process Enhanced Star survey (HERES) IX. Constraining pure r-process Ba/Eu abundance ratio from observations of r-II stars

The oldest stars born before the onset of the main s-process are expected to reveal a pure r-process Ba/Eu abundance ratio. We revised barium and europium abundances of selected very metal-poor (VMP) and strongly r-process enhanced (r-II) stars to evaluate an empirical r-process Ba/Eu ratio. Our calculations were based on non-local thermodynamic equilibrium (NLTE) line formation for Ba II and Eu II in the classical 1D MARCS model atmospheres. Homogeneous stellar abundances were determined from the Ba II subordinate and resonance lines by applying a common Ba isotope mixture. We used high-quality VLT/UVES spectra and observational material from the literature. For most investigated stars, NLTE leads to a lower Ba, but a higher Eu abundance. The resulting elemental ratio of the NLTE abundances amounts, on average, log(Ba/Eu) = 0.78+-0.06. This is a new constraint to pure r-process production of Ba and Eu. The obtained Ba/Eu abundance ratio of the r-II stars supports the corresponding Solar System r-process ratio as predicted by recent Galactic chemical evolution calculations of Bisterzo, Travaglio, Gallino, Wiescher, and Kappeler. We present the NLTE abundance corrections for lines of Ba II and Eu II in the grid of VMP model atmospheres.

High-resolution abundance analysis of very metal-poor r-I stars

Moderately r-process-enriched stars (r-I) are at least four times as common as those that are greatly enriched in r-process elements (r-II), and the abundances in their atmospheres are important tools for obtaining a better understanding of the nucleosynthesis processes responsible for the origin of the elements beyond the iron peak. The main aim of this work is to derive abundances for a sample of seven metal-poor stars with classified as r-I stars, to understand the role of these stars for constraining the astrophysical nucleosynthesis event(s) that is(are) responsible for the production of the r-process, and to investigate whether they differ, in any significant way, from the r-II stars. We carried out a detailed abundance analysis based on high-resolution spectra obtained with the VLT/UVES spectrograph. The OSMARCS LTE 1D model atmosphere grid was employed, along with the spectrum synthesis code Turbospectrum. We have derived abundances of light elements Li, C, and N, alpha-elements, odd-Z elements, iron-peak elements, and the trans-iron elements from the first peak, the second peak, the third peak, and the actinides regions. The results are compared with values for these elements for r-II and normal very and extremely metal-poor stars reported in the literature, ages based on radioactive chronometry are explored using different models, and a number of conclusions about the r-process and the r-I stars are presented. Hydrodynamical models were used for some elements, and general behaviors for the 3D corrections were presented.

Explaining the Ba, Y, Sr, and Eu abundance scatter in metal-poor halo stars: constraints to the r-process

Context. Thanks to the heroic observational campaigns carried out in recent years we now have large samples of metal-poor stars for which measurements of detailed abundances exist. [...] These data hold important clues on the nature of the contribution of the first stellar generations to the enrichment of our Galaxy. Aims. We aim to explain the scatter in Sr, Ba, Y, and Eu abundance ratio diagrams unveiled by the metal-poor halo stars. Methods. We computed inhomogeneous chemical evolution models for the Galactic halo assuming different scenarios for the r-process site: the electron-capture supernovae (EC) and the magnetorotationally driven (MRD) supernovae scenario. We also considered models with and without the contribution of fast-rotating massive stars (spinstars) to an early enrichment by the s-process. A detailed comparison with the now large sample of stars with measured abundances of Sr, Ba, Y, Eu, and Fe is provided (both in terms of scatter plots and number distributions for several abundance ratios). Results. The scatter observed in these abundance ratios of the very metal-poor stars (with [Fe/H] < -2.5) can be explained by combining the s-process production in spinstars, and the r-process contribution coming from massive stars. For the r-process we have developed models for both the EC and the MRD scenario that match the observations. Conclusions. With the present observational and theoretical constraints we cannot distinguish between the EC and the MRD scenario in the Galactic halo. Independently of the r-process scenarios adopted, the production of elements by an s-process in spinstars is needed to reproduce the spread in abundances of the light neutron capture elements (Sr and Y) over heavy neutron capture elements (Ba and Eu). We provide a way to test our suggestions by means of the distribution of the Ba isotopic ratios in a [Ba/Fe] or [Sr/Ba] vs. [Fe/H] diagram.

Measuring Jupiter's water abundance by Juno: the link between interior and formation models

The JUNO mission to Jupiter is planned to measure the water abundance in Jupiter’s atmosphere below the cloud layer. This measurement is important because it can be used to reveal valuable information on Jupiter’s origin and its composition. In this paper we discuss the importance of this measurement, the challenges in its interpretation, and address how it can be connected to interior and formation models of Jupiter.

Measuring Jupiter's water abundance by Juno: the link between interior and formation models [Replacement]

The JUNO mission to Jupiter is planned to measure the water abundance in Jupiter’s atmosphere below the cloud layer. This measurement is important because it can be used to reveal valuable information on Jupiter’s origin and its composition. In this paper we discuss the importance of this measurement, the challenges in its interpretation, and address how it can be connected to interior and formation models of Jupiter.

The Trace of the CNO Cycle in the Ring Nebula NGC6888

We present new results on the chemical composition of the Galactic ring nebula NGC6888 surrounding the WN6(h) star WR136. The data are based on deep spectroscopical observations taken with the High Dispersion Spectrograph at the 8.2m Subaru Telescope. The spectra cover the optical range from 3700 to 7400 A. The effect of the CNO cycle is well identified in the abundances of He, N, and O, while elements not involved in the synthesis such as Ar, S, and Fe present values consistent with the solar vicinity and the ambient gas. The major achievement of this work is the first detection of the faint CII 4267 recombination line in a Wolf-Rayet nebula. This allows to estimate the C abundance in NGC6888 and therefore investigate for the first time the trace of the CNO cycle in a ring nebula around a Wolf-Rayet star. Although the detection of the CII line has a low signal-to-noise ratio, the C abundance seems to be higher than the predictions of recent stellar evolution models of massive stars. The Ne abundance also show a puzzling pattern with an abundance of about 0.5 dex lower than the solar vicinity, which may be related to the action of the NeNa cycle. Attending to the constraints imposed by the dynamical timescale and the He/H and N/O ratios of the nebula, the comparison with stellar evolution models indicates that the initial mass of the stellar progenitor of NGC6888 is between 25 Msun and 40 Msun.

Molecular ions in the protostellar shock L1157-B1

We perform a complete census of molecular ions with an abundance larger than 1e-10 in the protostellar shock L1157-B1 by means of an unbiased high-sensitivity survey obtained with the IRAM-30m and Herschel/HIFI. By means of an LVG radiative transfer code the gas physical conditions and fractional abundances of molecular ions are derived. The latter are compared with estimates of steady-state abundances in the cloud and their evolution in the shock calculated with the chemical model Astrochem. We detect emission from HCO+, H13CO+, N2H+, HCS+, and, for the first time in a shock, from HOCO+, and SO+. The bulk of the emission peaks at blueshifted velocity, ~ 0.5-3 km/s with respect to systemic, has a width of ~ 4-8 km/s, and is associated with the outflow cavities (T_kin ~ 20-70 K, n(H2) ~ 1e5 cm-3). Observed HCO+ and N2H+ abundances are in agreement with steady-state abundances in the cloud and with their evolution in the compressed and heated gas in the shock for cosmic rays ionization rate Z = 3e-16 s-1. HOCO+, SO+, and HCS+ observed abundances, instead, are 1-2 orders of magnitude larger than predicted in the cloud; on the other hand they are strongly enhanced on timescales shorter than the shock age (~2000 years) if CO2, S or H2S, and OCS are sputtered off the dust grains in the shock. The performed analysis indicates that HCO+ and N2H+ are a fossil record of pre-shock gas in the outflow cavity, while HOCO+, SO+, and HCS+ are effective shock tracers and can be used to infer the amount of CO2 and sulphur-bearing species released from dust mantles in the shock. The observed HCS+ (and CS) abundance indicates that OCS should be one of the main sulphur carrier on grain mantles. However, the OCS abundance required to fit the observations is 1-2 orders of magnitude larger than observed. Further studies are required to fully understand the chemistry of sulphur-bearing species.

Mass loss in main-sequence B stars

We calculate radiatively driven wind models of main-sequence B stars and provide the wind mass-loss rates and terminal velocities. The main-sequence mass-loss rate strongly depends on the stellar effective temperature. For the hottest B stars the mass-loss rate amounts to $10^{-9}\,\text{M}_\odot\,\text{year}^{-1}$, while for the cooler ones the mass-loss rate is by more than three orders of magnitude lower. Main sequence B stars with solar abundance and effective temperatures lower than about $15\,000\,\text{K}$ (later than the spectral type B5) do not have any homogeneous line-driven wind. We predict the wind mass-loss rates for the solar chemical composition and for modified abundance of heavier elements to study the winds of chemically peculiar stars. The mass-loss rate may both increase or decrease with increasing abundance depending on the importance of the induced emergent flux redistribution. Stars with overabundant silicon may have homogeneous winds even below the solar abundance wind limit at $15\,000\,\text{K}$. The winds of main-sequence B stars lie below the static limit, i.e., a static atmosphere solution is also possible. This points to an important problem of initiation of these winds. We discuss the implications of our models for the rotational braking, filling the magnetosphere of Bp stars and for chemically peculiar stars.

Discovery of secular variations in the atmospheric abundances of magnetic Ap stars

The stars of the middle main sequence have relatively quiescent outer layers, and unusual chemical abundance patterns may develop in their atmospheres. The presence of chemical peculiarities reveal the action of such subsurface phenomena as gravitational settling and radiatively driven levitation of trace elements, and their competition with mixing processes such as turbulent diffusion. We want to establish whether abundance peculiarities change as stars evolve on the main sequence, and provide observational constraints to diffusion theory. We have performed spectral analysis of 15 magnetic Bp stars that are members of open clusters (and thus have well-known ages), with masses between about 3 and 4 M_sun. For each star, we measured the abundances of He, O, Mg, Si, Ti, Cr, Fe, Pr and Nd. We have discovered the systematic time evolution of trace elements through the main-sequence lifetime of magnetic chemically peculiar stars as their atmospheres cool and evolve toward lower gravity. During the main sequence lifetime, we observe clear and systematic variations in the atmospheric abundances of He, Ti, Cr, Fe, Pr and Nd. For all these elements, except He, the atmospheric abundances decrease with age. The abundances of Fe-peak elements converge toward solar values, while the rare-earth elements converge toward values at least 100 times more abundant than in the Sun. Helium is always underabundant compared to the Sun, evolving from about 1% up to 10% of the solar He abundance. We have attempted to interpret the observed abundance variations in the context of radiatively driven diffusion theory, which appears to provide a framework to understand some, but not all, of the observed anomalous abundance levels and variations.

MyGIsFOS: an automated code for parameter determination and detailed abundance analysis in cool stars

The current and planned high-resolution, high-multiplexity stellar spectroscopic surveys, as well as the swelling amount of under-utilized data present in public archives have led to an increasing number of efforts to automate the crucial but slow process to retrieve stellar parameters and chemical abundances from spectra. We present MyGIsFOS, a code designed to derive atmospheric parameters and detailed stellar abundances from medium – high resolution spectra of cool (FGK) stars. We describe the general structure and workings of the code, present analyses of a number of well studied stars representative of the parameter space MyGIsFOS is designed to cover, and examples of the exploitation of MyGIsFOS very fast analysis to assess uncertainties through Montecarlo tests. MyGIsFOS aims to reproduce a “traditional” manual analysis by fitting spectral features for different elements against a precomputed grid of synthetic spectra. Fe I and Fe II lines can be employed to determine temperature, gravity, microturbulence, and metallicity by iteratively minimizing the dependence of Fe I abundance from line lower energy and equivalent width, and imposing Fe I – Fe II ionization equilibrium. Once parameters are retrieved, detailed chemical abundances are measured from lines of other elements. MyGIsFOS replicates closely the results obtained in similar analyses on a set of well known stars. It is also quite fast, performing a full parameter determination and detailed abundance analysis in about two minutes per star on a mainstream desktop computer. Currently, its preferred field of application are high-resolution and/or large spectral coverage data (e.g UVES, X-Shooter, HARPS, Sophie).

Constraining Non-thermal and Thermal properties of Dark Matter [Cross-Listing]

The observed dark matter (DM) abundance can be created from a thermal bath after the interaction rate which keeps the DM particles in thermal equilibrium falls below the expansion rate of the Universe. DM can also be excited directly from the inflaton or moduli decay, along with the excitation of the Standard Model degrees of freedom. Here we discuss the evolution of the DM abundance from the very onset of its creation from the inflaton decay. Based on the initial conditions such as the inflaton mass and its decay branching ratio to the DM, the reheating temperature, and the mass and interaction rate of the DM with the thermal bath, the DM particles can either thermalize or remain non-thermal throughout their evolution history. In the thermal case, the final abundance can be set by the standard freeze-out mechanism for large annihilation rates, irrespective of the initial condition. For smaller annihilation rates, it can be set by the freeze-in mechanism, also independent of the initial abundance, provided it is small to begin with. For even smaller interaction rates, the DM becomes non-thermal, and the relic abundance will be essentially set by the initial condition. Also depending on its mass and interaction rate, the DM could remain relativistic, thus acting like a dark radiation, or could behave as a warm or cold relic. We put model-independent constraints on the DM mass and annihilation rate from over-abundance, and compare with complementary constraints derived from indirect search experiments, Big Bang Nucleosynthesis, Cosmic Microwave Background, Planck measurements, and theoretical constraints from the unitarity of the scattering matrix. For the non-thermal DM scenario, we also show the allowed parameter space in terms of the inflaton and DM masses for a given reheating temperature, and compute the comoving free-streaming length to identify the hot, warm and cold DM regimes.

Revisited fluorine abundances in the globular cluster M22 (NGC 6656)

Fluorine is a fairly good tracer of formation histories of multiple stellar populations in globular clusters as already revealed by several studies. Large variations in fluorine abundance in red giant stars of the globular cluster M22 have been recently reported by two different groups. Futhermore, one of these studies claims that the abundance of fluorine is anti-correlated with sodium abundances in this cluster, leading to strong conclusions on the chemical history of M22. To validate this important finding, we re-examine the F abundance determinations of some of the previously studied stars. We have thus reanalysed some high-resolution VLT/CRIRES spectra of RGB stars found in M22 in order to re-estimate their fluorine abundance from the spectral synthesis of the HF line at 2.336microns. Unlike what has been previously estimated, we show that only upper limits or doubtful fluorine abundances with large uncertainties in M22 RGB stars can be derived. This is probably caused by an incorrect identification of continuum fluctuations as the HF signature combined with a wrong correction of the stellar radial velocity. Such continuum fluctuations could be the consequences of telluric residuals that are still present in the analysed spectra. Therefore, no definitive conclusions on the chemical pollution caused by the M22 first stellar generation can presently be drawn from the fluorine content of this cluster.

The CHESS survey of the L1157-B1 bow-shock: high and low excitation water vapor

Molecular outflows powered by young protostars strongly affect the kinematics and chemistry of the natal molecular cloud through strong shocks resulting in substantial modifications of the abundance of several species. As part of the "Chemical Herschel Surveys of Star forming regions" guaranteed time key program, we aim at investigating the physical and chemical conditions of H20 in the brightest shock region B1 of the L1157 molecular outflow. We observed several ortho- and para-H2O transitions using HIFI and PACS instruments on board Herschel, providing a detailed picture of the kinematics and spatial distribution of the gas. We performed a LVG analysis to derive the physical conditions of H2O shocked material, and ultimately obtain its abundance. We detected 13 H2O lines probing a wide range of excitation conditions. PACS maps reveal that H2O traces weak and extended emission associated with the outflow identified also with HIFI in the o-H2O line at 556.9 GHz, and a compact (~10") bright, higher-excitation region. The LVG analysis of H2O lines in the bow-shock show the presence of two gas components with different excitation conditions: a warm (Tkin~200-300 K) and dense (n(H2)~(1-3)x10^6 cm-3) component with an assumed extent of 10" and a compact (~2"-5") and hot, tenuous (Tkin~900-1400 K, n(H2)~10^3-10^4 cm-3) gas component, which is needed to account for the line fluxes of high Eu transitions. The fractional abundance of the warm and hot H2O gas components is estimated to be (0.7-2)x10^{-6} and (1-3)x10^{-4}, respectively. Finally, we identified an additional component in absorption in the HIFI spectra of H2O lines connecting with the ground state level, probably arising from the photodesorption of icy mantles of a water-enriched layer at the edges of the cloud.

Radiative Levitation of Silicon in the Atmospheres of Two Hyades DA White Dwarfs

The presence of silicon at the surface of the two Hyades DA white dwarfs WD 0421+162 and WD 0431+126 requires mechanisms that counteract the effects of the downward diffusion. Radiative levitation calculations indicate that the silicon abundance observed in WD 0431+126 corresponds to the abundance supported by radiative levitation. Detailed time-dependent diffusion calculations that take into account radiative levitation and accretion indicate that accretion with rates of dM/dt(Si) < 1.00E4 g/s could also be present without disrupting the abundance supported by radiative levitation. In the case of WD 0421+162, accretion with a rate of dM/dt(Si) = 1.25E5 g/s must be invoked, because its observed silicon abundance is larger than the abundance supported by radiative levitation. This accretion rate is lower than the accretion rate given by the accretion-diffusion model, because the radiative levitation slows down the downward diffusion of silicon. The silicon abundances observed in the two Hyades white dwarfs cannot be interpreted solely in terms of accretion. The interpretation of the silicon abundances must take into account the interplay between radiative levitation and accretion.

The Morphology and Dynamics of Jet-Driven Supernova Remnants: the Case of W49B

The circumstellar medium (CSM) of a massive star is modified by its winds before a supernova (SN) explosion occurs, and thus the evolution of the resulting supernova remnant (SNR) is influenced by both the geometry of the explosion as well as the complex structure of the CSM. Motivated by recent work suggesting the SNR W49B was a jet-driven SN expanding in a complex CSM, we explore how the dynamics and the metal distributions in a jet-driven explosion are modified by the interaction with the surrounding environment. In particular, we perform hydrodynamical calculations to study the dynamics and explosive nucleosynthesis of a jet-driven SN triggered by the collapse of a 25 solar masses Wolf-Rayet star and its subsequent interaction with the CSM up to several hundred years following the explosion. We find that although the CSM has small-scale effects on the structure of the SNR, the overall morphology and abundance patterns are reflective of the initial asymmetry of the SN explosion. Thus, we predict that jet-driven SNRs, such as W49B, should be identifiable based on morphology and abundance patterns at ages up to several hundred years, even if they expand into a complex CSM environment.

The polluted atmosphere of the white dwarf NLTT 25792 and the diversity of circumstellar environments

We present an analysis of X-Shooter spectra of the polluted, hydrogen-rich white dwarf NLTT 25792. The spectra show strong lines of calcium (Ca H&K, near-infrared calcium triplet, and Ca I 4226 and numerous lines of iron along with magnesium and aluminum lines from which we draw the abundance pattern. Moreover, the photospheric Ca H&K lines are possibly blended with a circumstellar component shifted by -20 km/s relative to the photosphere. A comparison with a sample of four white dwarfs with similar parameters show considerable variations in their abundance patterns, particularly in the calcium to magnesium abundance ratio that varies by a factor of five within this sample. The observed variations, even after accounting for diffusion effects, imply similar variations in the putative accretion source. Also, we find that silicon and sodium are significantly underabundant in the atmosphere of NLTT 25792, a fact that may offer some clues on the nature of the accretion source.

Abundance Profiling of Extremely Metal-Poor Stars and Supernova Properties in the Early Universe

The first metal enrichment in the universe was made by a supernova (SN) explosion of a population (Pop) III star and chemical evolution of the universe is recorded in abundance patterns of extremely metal-poor (EMP) stars. Increasing number of the EMP stars are now being discovered. This allows us to statistically constrain properties of SNe of Pop III stars (Pop III SNe). We investigate the properties of Pop III SNe by comparing their nucleosynthetic yields with the abundance patterns of the EMP stars. We focus on the most metal-poor stars with [Fe/H] $\lsim-3.5$ and present Pop III SN models that reproduce well their individual abundance patterns. From these models we derive relations between abundance ratios and properties of Pop III SNe: [(C+N)/Fe] vs. an ejected Fe mass, and [(C+N)/Mg] vs. a remnant mass. Using fitting formulae, distribution of the abundance ratios of EMP stars is converted to those of the properties of Pop III SNe, which can be compared with SNe in the present day. Large samples of EMP stars obtained by ongoing and planning EMP star surveys and subsequent high-dispersion spectroscopic observations will give a clue to confining properties of Pop III SNe in the early universe.

A Systematic Retrieval Analysis of Secondary Eclipse Spectra III: Diagnosing Chemical Disequilibrium in Planetary Atmospheres

Chemical disequilibrium has recently become a relevant topic in the study of the atmospheres of of transiting extrasolar planets, brown dwarfs, and directly imaged exoplanets. We present a new way of assessing whether or not a Jovian-like atmosphere is in chemical disequilibrium from observations of detectable or inferred gases such as H$_2$O, CH$_4$, CO, and H$_2$. Our hypothesis, based on previous kinetic modeling studies, is that cooler atmospheres will show stronger signs of disequilibrium than hotter atmospheres. We verify this with chemistry-transport models and show that planets with temperatures less than $\sim$1200 K are likely to show the strongest signs of disequilibrium due to the vertical quenching of CO, and that our new approach is able to capture this process. We also find that in certain instances a planetary composition may appear in equilibrium when it actually is not due to the degeneracy in the shape of the vertical mixing ratio profiles. We determine the state of disequilibrium in eight exoplanets using the results from secondary eclipse temperature and abundance retrievals. We find that all of the planets in our sample are consistent with thermochemical equilibrium to within 3-sigma. Future observations are needed to further constrain the abundances in order to definitively identify disequilibrium in exoplanet atmospheres.

The RAVE harvest: from the relation between abundances and kinematic of the Milky Way stars to tools for the abundance analysis of the spectra

RAVE is a spectroscopic survey of the Milky Way which collected more than 500,000 stellar spectra of nearby stars in the Galaxy. The RAVE consortium analysed these spectra to obtain radial velocities, stellar parameters and chemical abundances. These data, together with spatial and kinematic information like positions, proper motions, and distance estimations, make the RAVE database a rich source for galactic archaeology. I present recent investigations on the chemo-kinematic relations and chemical gradients in the Milky Way disk by using RAVE data and compare our results with the Besancon models. I also present the code SPACE, an evolution of the RAVE chemical pipeline, which integrates the measurements of stellar parameters and chemical abundances in one single process.

Constraints on Majorana Dark Matter from a Fourth Lepton Family [Cross-Listing]

We study the possibility of dark matter in the form of heavy neutrinos from a fourth lepton family with helicity suppressed couplings such that dark matter is produced thermally via annihilations in the early Universe. We present all possible constraints for this scenario coming from LHC and collider physics, underground direct detectors, neutrino telescopes, and indirect astrophysical searches. Although we embed the WIMP candidate within a model of composite dynamics, the majority of our results are model independent and applicable to all models where heavy neutrinos with suppressed couplings account for the dark matter abundance.

Carbon and Oxygen Abundances in Cool Metal-rich Exoplanet Hosts: A Case Study of the C/O Ratio of 55 Cancri

The super-Earth exoplanet 55 Cnc e, the smallest member of a five-planet system, has recently been observed to transit its host star. The radius estimates from transit observations, coupled with spectroscopic determinations of mass, provide constraints on its interior composition. The composition of exoplanetary interiors and atmospheres are particularly sensitive to elemental C/O ratio, which to first order can be estimated from the host stars. Results from a recent spectroscopic study analyzing the 6300A [O I] line and two C I lines suggest that 55 Cnc has a carbon-rich composition (C/O=1.12+/-0.09). However oxygen abundances derived using the 6300A [O I] line are highly sensitive to a Ni I blend, particularly in metal-rich stars such as 55 Cnc ([Fe/H]=0.34+/-0.18). Here, we further investigate 55 Cnc’s composition by deriving the carbon and oxygen abundances from these and additional C and O absorption features. We find that the measured C/O ratio depends on the oxygen lines used. The C/O ratio that we derive based on the 6300A [O I] line alone is consistent with the previous value. Yet, our investigation of additional abundance indicators results in a mean C/O ratio of 0.78+/-0.08. The lower C/O ratio of 55 Cnc determined here may place this system at the sensitive boundary between protoplanetary disk compositions giving rise to planets with high (>0.8) versus low (<0.8) C/O ratios. This study illustrates the caution that must applied when determining planet host star C/O ratios, particularly in cool, metal-rich stars.

Mixed axion/neutralino dark matter in the SUSY DFSZ axion model [Cross-Listing]

We examine mixed axion/neutralino cold dark matter production in the SUSY DFSZ axion model where an axion superfield couples to Higgs superfields. We calculate a wide array of axino and saxion decay modes along with their decay temperatures, and thermal and non-thermal production rates. For a SUSY benchmark model with a standard underabundance (SUA) of Higgsino-like dark matter (DM), we find for the PQ scale f_a< 10^{12} GeV that the DM abundance is mainly comprised of axions as the saxion/axino decay occurs before the standard neutralino freeze-out and thus its abundance remains suppressed. For 10^{12}<~ f_a<~ 10^{14} GeV, the saxion/axino decays occur after neutralino freeze-out so that the neutralino abundance is enhanced by the production via decay and subsequent re-annihilation. For f_a>~ 10^{14} GeV, both neutralino dark matter and dark radiation are typically overproduced. For judicious parameter choices, these can be suppressed and the combined neutralino/axion abundance brought into accord with measured values. A SUSY benchmark model with a standard overabundance (SOA) of bino DM is also examined and typically remains excluded due at least to too great a neutralino DM abundance for f_a<~ 10^{15} GeV. For f_a>~ 10^{15} GeV and lower saxion masses, large entropy production from saxion decay can dilute all relics and the SOA model can be allowed by all constraints.

Baryogenesis, dark matter and inflation in the Next-to-Minimal Supersymmetric Standard Model [Replacement]

Explaining baryon asymmetry, dark matter and inflation are important elements of a successful theory that extends beyond the Standard Model of particle physics. In this paper we explore these issues within the Next-to-Minimal Supersymmetric Standard Model (NMSSM), by studying the conditions for a strongly first order electroweak phase transition, the abundance of the lightest supersymmetric particle (LSP), and inflation driven by a gauge invariant flat direction of MSSM made up of right handed squarks. We present the regions of parameter space which can yield successful predictions for cosmic microwave background (CMB) radiation, the observed relic density for the neutralino LSP, and successful baryogenesis constrained by collider measurements, such as the recent Higgs mass bound, branching ratios of rare, flavour violating decays, and the invisible Z decay width. We also explore where dark matter interactions with xenon nuclei would fall within current bounds of XENON100 and the projected limits for the XENON1T and LUX experiments.

Cross-Section Measurements of the 86Kr(g,n) Reaction to Probe the s-Process Branching at 85Kr

We have carried out photodisintegration cross-section measurements on 86Kr using monoenergetic photon beams ranging from the neutron separation energy, S_n = 9.86 MeV, to 13 MeV. We combine our experimental 86Kr(g,n)85Kr cross section with results from our recent 86Kr(g,g’) measurement below the neutron separation energy to obtain the complete nuclear dipole response of 86Kr. The new experimental information is used to predict the neutron capture cross section of 85Kr, an important branching point nucleus on the abundance flow path during s-process nucleosynthesis. Our new and more precise 85Kr(n,g)86Kr cross section allows to produce more precise predictions of the 86Kr abundance from s-process models. In particular, we find that the models of the s-process in asymptotic giant branch stars of mass < 1.5 Msun, where the 13C neutron source burns convectively rather than radiatively, represent a possible solution for the highest 86Kr/82Kr ratios observed in meteoritic stardust SiC grains.

Early Disc Accretion as the Origin of Abundance Anomalies in Globular Clusters

Globular clusters (GCs), once thought to be well approximated as simple stellar populations (i.e. all stars having the same age and chemical abundance), are now known to host a variety of anomalies, such as multiple discrete (or spreads in) populations in colour-magnitude diagrams and abundance variations in light elements (e.g., Na, O, Al). Multiple models have been put forward to explain the observed anomalies, although all have serious shortcomings (e.g., requiring a non-standard initial mass function of stars and GCs to have been initially 10-100 times more massive than observed today). These models also do not agree with observations of massive stellar clusters forming today, which do not display significant age spreads nor have gas/dust within the cluster. Here we present a model for the formation of GCs, where low mass pre-main sequence (PMS) stars accrete enriched material released from interacting massive binary and rapidly rotating stars onto their circumstellar discs, and ultimately onto the young stars. As was shown in previous studies, the accreted material matches the unusual abundances and patterns observed in GCs. The proposed model does not require multiple generations of star-formation, conforms to known properties of massive clusters forming today, and solves the "mass budget problem" without requiring GCs to have been significantly more massive at birth. Potential caveats to the model as well as model predictions are discussed.

Dynamical models and Galaxy surveys

Equilibrium dynamical models are essential tools for extracting science from surveys of our Galaxy. We show how models can be tested with data from a survey before the survey’s selection function has been determined. We illustrate the application of this method by presenting some results for the RAVE survey. We extend our published analytic distribution functions to include chemistry and fit the chosen functional form to a combination of the Geneva–Copenhagen survey (GCS) and a sample of G-dwarfs observed at z~1.75 kpc by the SEGUE survey. By including solid dynamics we are able to predict the contribution that the thick disc/halo stars surveyed by SEGUE should make to the GCS survey. We show that the measured [Fe/H] distribution from the GCS includes many fewer stars at [Fe/H]<-0.6 than are predicted. The problem is more likely to lie in discordant abundance scales than with incorrect dynamics.

Radial migration in a bar-dominated disk galaxy I: Impact on chemical evolution

We study radial migration and chemical evolution in a bar-dominated disk galaxy, by analyzing the results of a fully self-consistent, high resolution N-body+SPH simulation. We find different behaviours for gas and star particles. Gas within corotation is driven in the central regions by the bar, where it forms a pseudo-bulge (disky-bulge), but it undergoes negligible radial displacement outside the bar region. Stars undergo substantial radial migration at all times, caused first by transient spiral arms and later by the bar. Despite the important amount of radial migration occurring in our model, its impact on the chemical properties is limited. The reason is the relatively flat abundance profile, due to the rapid early evolution of the whole disk. We show that the implications of radial migration on chemical evolution can be studied to a good accuracy by post-processing the results of the N-body+SPH calculation with a simple chemical evolution model having detailed chemistry and a parametrized description of radial migration. We find that radial migration impacts on chemical evolution both directly (by moving around the long-lived agents of nucleosynthesis, like e.g. SNIa or AGB stars, and thus altering the abundance profiles of the gas) and indirectly (by moving around the long-lived tracers of chemical evolution and thus affecting stellar metallicity profiles, local age-metallicity relations and metallicity distributions of stars, etc.).

On Iron Monoxide Nanoparticles as a Carrier of the Mysterious 21 Micrometer Emission Feature in Post-Asymptotic Giant Branch Stars

A prominent, mysterious emission feature peaking at ~20.1 micrometer — historically known as the “21 micrometer’ feature — is seen in over two dozen Galactic and Magellanic Cloud carbon-rich post-asymptotic giant branch (post-AGB) stars. The nature of its carrier remains unknown since the first detection of the 21 micrometer feature in 1989. Over a dozen materials have been suggested as possible carrier candidates. However, none of them has been accepted: they either require too much material (compared to what is available in the circumstellar shells around these post-AGB stars), or exhibit additional emission features which are not seen in these 21 micrometer sources. Recently, iron monoxide (FeO) nanoparticles seem to be a promising carrier candidate as Fe is an abundant element and FeO emits exclusively at ~21 micrometer. In this work, using the proto-typical protoplanetary nebula HD 56126 as a test case, we examine FeO nanoparticles as a carrier for the 21 micrometer feature by modeling their infrared emission, with FeO being stochastically heated by single stellar photons. We find that FeO emits too broad a 21 micrometer feature to explain the observed one and the Fe abundance required to be locked up in FeO exceeds what is available in HD 56126. We therefore conclude that FeO nanoparticles are unlikely responsible for the 21 micrometer feature.

Galileogenesis: A new cosmophenomenological zip code for reheating through R-parity violating coupling [Cross-Listing]

In this paper we introduce an idea of leptogenesis scenario in higher derivative gravity induced DBI Galileon framework {\it aka Galileogenesis} in presence of one-loop R-parity violating couplings in the background of a low energy effective supergravity setup. We have studied extensively the detailed feature of reheating constraints and the cosmophenomenological consequences of thermal gravitino dark matter in light of PLANCK and PDG data. Finally we have also established a direct cosmological connection among dark matter relic abundance, reheating temperature and tensor-to-scalar ratio in the context of DBI Galileon inflation.

Nitrogen Abundances and the Distance Moduli of the Pleiades and Hyades

Recent reanalyses of HIPPARCOS parallax data confirm a previously noted discrepancy with the Pleiades distance modulus estimated from main-sequence fitting in the color-magnitude diagram. One proposed explanation of this distance modulus discrepancy is a Pleiades He abundance that is significantly larger than the Hyades value. We suggest that, based on our theoretical and observational understanding of Galactic chemical evolution, nitrogen abundances may serve as a proxy for helium abundances of disk stars. Utilizing high-resolution near-UV Keck/HIRES spectroscopy, we determine N abundances in the Pleiades and Hyades dwarfs from NH features in the 3330 Ang region. While our Hyades N abundances show a modest 0.2 dex trend over a 800 K Teff range, we find the Pleiades N abundance (by number) is 0.13+/-0.05 dex lower than in the Hyades for stars in a smaller overlapping Teff range around 6000 K; possible systematic errors in the lower Pleiades N abundance result are estimated to be at the <0.10 dex level. Our results indicate [N/Fe]=0 for both the Pleiades and Hyades, consistent with the ratios exhibited by local Galactic disk field stars in other studies. If N production is a reliable tracer of He production in the disk, then our results suggest the Pleiades He abundance is no larger than that in the Hyades. This finding is supported by the relative Pleiades-Hyades C, O, and Fe abundances interpreted in the current context of Galactic chemical evolution, and is resistant to the effects on our derived N abundances of a He abundance difference like that needed to explain the Pleiades distance modulus discrepancy. A physical explanation of the Pleiades distance modulus discrepancy does not appear to be related to He abundance.

Improved Ti II log(gf) Values and Abundance Determinations in the Photospheres of the Metal-Poor Star HD 84937

Atomic transition probability measurements for 364 lines of Ti II in the UV through near IR are reported. Branching fractions from data recorded using a Fourier transform spectrometer and a new echelle spectrometer are combined with published radiative lifetimes to determine these transition probabilities. The new results are in generally good agreement with previously reported FTS measurements. Use of the new echelle spectrometer, independent radiometric calibration methods, and independent data analysis routines enables a reduction of systematic errors and overall improvement in transition probability accuracy over previous measurements. The new Ti II data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to derive new, more accurate Ti abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. The Ti abundances derived using Ti II for these two stars match those derived using Ti I and support the relative Ti/Fe abundance ratio versus metallicity seen in previous studies.

A Joint Model Of X-ray And Infrared Backgrounds. II. Compton-Thick AGN Abundance

We estimate the abundance of Compton-thick (CT) active galactic nuclei (AGN) based on our joint model of X-ray and infrared backgrounds. At L_{rest 2-10 keV} > 10^42 erg/s, the CT AGN density predicted by our model is a few 10^-4 Mpc^-3 from z=0 up to z=3. CT AGN with higher luminosity cuts (> 10^43, 10^44 & 10^45 erg/s) peak at higher z and show a rapid increase in the number density from z=0 to z~2-3. The CT to all AGN ratio appears to be low (2-5%) at f_{2-10keV} > 10^-15 erg/s/cm^2 but rises rapidly toward fainter flux levels. The CT AGN account for ~ 38% of the total accreted SMBH mass and contribute ~ 25% of the cosmic X-ray background spectrum at 20 keV. Our model predicts that the majority (90%) of luminous and bright CT AGN (L_{rest 2-10 keV} > 10^44 erg/s or f_{2-10keV} > 10^-15 erg/s/cm^2) have detectable hot dust 5-10 um emission which we associate with a dusty torus. The fraction drops for fainter objects, to around 30% at L_{rest 2-10 keV} > 10^42 erg/s or f_{2-10keV} > 10^-17 erg/s/cm^2. Our model confirms that heavily-obscured AGN (N_HI > 10^23 cm^-2) can be separated from unobscured and mildly-obscured ones (N_HI < 10^23 cm^-2) in the plane of observed-frame X-ray hardness vs. mid-IR/X-ray ratio.

The Dynamics of Galaxy Pairs in a Cosmological Setting

We use the Millennium Simulation, and an abundance-matching framework, to investigate the dynamical behaviour of galaxy pairs embedded in a cosmological context. Our main galaxy-pair sample, selected to have separations under 250 kpc/h, consists of over 1.3 million pairs at redshift z = 0, with stellar masses greater than 10^9 Msun, probing mass ratios down to 1:1000. We use dark matter halo membership and energy to classify our galaxy pairs. In terms of halo membership, central-satellite pairs tend to be in isolation (in relation to external more massive galaxies), are energetically- bound to each other, and are also weakly-bound to a neighbouring massive galaxy. Satellite-satellite pairs, instead, inhabit regions in close proximity to a more massive galaxy, are energetically-unbound, and are often bound to that neighbour. We find that 60% of our paired galaxies are bound to both their companion and to a third external object. Moreover, only 9% of our pairs resemble the kind of systems described by idealised binary merger simulations in complete isolation. In sum, we demonstrate the importance of properly connecting galaxy pairs to the rest of the Universe.

Noiseless Gravitational Lensing Simulations

The microphysical properties of the DM particle can, in principle, be constrained by the properties and abundance of substructures in DM halos, as measured through strong gravitational lensing. Unfortunately, there is a lack of accurate theoretical predictions for the lensing signal of substructures, mainly because of the discreteness noise inherent to N-body simulations. Here we present Recursive-TCM, a method that is able to provide lensing predictions with an arbitrarily low discreteness noise, without any free parameters or smoothing scale. This solution is based on a novel way of interpreting the results of N-body simulations, where particles simply trace the evolution and distortion of Lagrangian phase-space volume elements. We discuss the advantages of this method over the widely used cloud-in-cells and adaptive-kernel smoothing density estimators. Applying the new method to a cluster-sized DM halo simulated in warm and cold DM scenarios, we show how the expected differences in their substructure population translate into differences in the convergence and magnification maps. We anticipate that our method will provide the high-precision theoretical predictions required to interpret and fully exploit strong gravitational lensing observations.

Noiseless Gravitational Lensing Simulations [Replacement]

The microphysical properties of the DM particle can, in principle, be constrained by the properties and abundance of substructures in DM halos, as measured through strong gravitational lensing. Unfortunately, there is a lack of accurate theoretical predictions for the lensing signal of substructures, mainly because of the discreteness noise inherent to N-body simulations. Here we present Recursive-TCM, a method that is able to provide lensing predictions with an arbitrarily low discreteness noise, without any free parameters or smoothing scale. This solution is based on a novel way of interpreting the results of N-body simulations, where particles simply trace the evolution and distortion of Lagrangian phase-space volume elements. We discuss the advantages of this method over the widely used cloud-in-cells and adaptive-kernel smoothing density estimators. Applying the new method to a cluster-sized DM halo simulated in warm and cold DM scenarios, we show how the expected differences in their substructure population translate into differences in the convergence and magnification maps. We anticipate that our method will provide the high-precision theoretical predictions required to interpret and fully exploit strong gravitational lensing observations.

Luminous Infrared Galaxies With the Submillimeter Array. IV. 12CO J=6-5 Observations of VV 114

We present high-resolution (~2.5") observations of 12CO J=6-5 towards the luminous infrared galaxy VV 114 using the Submillimeter Array. We detect 12CO J=6-5 emission from the eastern nucleus of VV 114 but do not detect the western nucleus or the central region. We combine the new 12CO J=6-5 observations with previously published or archival low-J CO observations, that include 13CO J=1-0 Atacama Large Millimeter/submillimeter Array cycle 0 observations, to analyze the beam-averaged physical conditions of the molecular gas in the eastern nucleus. We use the radiative transfer code RADEX and a Bayesian likelihood code to constrain the temperature (T_kin), density (n(H2)) and column density (N(12CO)) of the molecular gas. We find that the most probable scenario for the eastern nucleus is a cold (T_kin = 38 K), moderately dense (n(H2) = 10^2.89 cm^-3) molecular gas component. We find the most probable 12CO to 13CO abundance ratio ([12CO]/[13CO]) is 229, roughly three times higher than the Milky Way value. This high abundance ratio may explain the observed high 12CO/ 13CO line ratio (> 25). The unusual 13CO J=2-1/J=1-0 line ratio of 0.6 is produced by a combination of moderate 13CO optical depths (tau = 0.4 – 1.1) and extremely subthermal excitation temperatures. We measure the CO-to-H2 conversion factor, alpha_co to be 0.5 M_sol (K km s^-1 pc^2)^-1, which agrees with the widely used factor for ultra luminous infrared galaxies of Downes & Solomon (1998; alpha_co =0.8 M_sol (K km s^-1 pc^2)^-1).

Two semi-automated computational approaches for spectroscopic analysis of stellar photospheres: detailed characterization at high resolution and abundance determination at medium resolution

We report on two distinct computational approaches to self-consistently measure photospheric properties of large samples of stars. Both procedures consist of a set of several semi-integrated tasks based on shell and Python scripts, which efficiently run either our own codes or open source software commonly adopted by the astronomical community. One approach aims to derive the main stellar photospheric parameters and abundances of a few elements by analysing high-resolution spectra from a given public library homogeneously constructed. The other one is applied to recover the abundance of a single element in stars with known photospheric parameters by using mid-resolution spectra from another open homogeneous database and calibrating derived abundances. Both semi-automated computational approaches provide homogeneity and objectivity to every step of the process and represent a fast way to reach partial and final results as well as to estimate measurement errors, making possible to systematically evaluate and improve the distinct steps.

Revision of the derivation of stellar rates from experiment and impact on Eu s-process contributions

A new, general formalism to include experimental data in revised stellar rates is discussed, containing revised uncertainties. Application to the s-process shows that the actual uncertainties in the neutron capture rates can be larger than would be expected from the experimental errors alone. As a specific example for how astrophysical conclusions can depend on the approach selected to derive stellar rates, the 151Eu/(151Eu+153Eu) abundance ratio from AGB star models is presented. Finally, a recommended workflow for the derivation of stellar rates from experiment is laid out.

Observational nuclear astrophysics: neutron-capture element abundances in old, metal-poor stars

The chemical abundances of metal-poor stars provide a great deal of information regarding the individual nucleosynthetic processes that created the observed elements and the overall process of chemical enrichment of the galaxy since the formation of the first stars. Here we review the abundance patterns of the neutron-capture elements (Z > 38) in those metal-poor stars and our current understanding of the conditions and sites of their production at early times. We also review the relative contributions of these different processes to the build-up of these elements within the galaxy over time, and outline outstanding questions and uncertainties that complicate the interpretation of the abundance patterns observed in metal-poor stars. It is anticipated that future observations of large samples of metal-poor stars will help discriminate between different proposed neutron-capture element production sites and better trace the chemical evolution of the galaxy.

Broad N2H+ emission towards the protostellar shock L1157-B1

We present the first detection of N2H+ towards a low-mass protostellar outflow, namely the L1157-B1 shock, at about 0.1 pc from the protostellar cocoon. The detection was obtained with the IRAM 30-m antenna. We observed emission at 93 GHz due to the J = 1-0 hyperfine lines. The analysis of the emission coupled with the HIFI CHESS multiline CO observations leads to the conclusion that the observed N2H+(1-0) line originates from the dense (> 10^5 cm-3) gas associated with the large (20-25 arcsec) cavities opened by the protostellar wind. We find a N2H+ column density of few 10^12 cm-2 corresponding to an abundance of (2-8) 10^-9. The N2H+ abundance can be matched by a model of quiescent gas evolved for more than 10^4 yr, i.e. for more than the shock kinematical age (about 2000 yr). Modelling of C-shocks confirms that the abundance of N2H+ is not increased by the passage of the shock. In summary, N2H+ is a fossil record of the pre-shock gas, formed when the density of the gas was around 10^4 cm-3, and then further compressed and accelerated by the shock.

26Al in the Early Solar System: Not so Unusual After All

Recently acquired evidence shows that extrasolar asteroids exhibit over a factor of 100 variation in the iron to aluminum abundance ratio. This large range likely is a consequence of igneous differentiation that resulted from heating produced by radioactive decay of 26Al with an abundance comparable to that in the solar system’s protoplanetary disk at birth. If so, the conventional view that our solar system began with an unusually high amount of 26Al should be discarded.

A Low Metallicity Molecular Cloud In The Lower Galactic Halo

We find evidence for the impact of infalling, low-metallicity gas on the Galactic disk. This is based on FUV absorption line spectra, 21-cm emission line spectra, and FIR mapping to estimate the abundance and physical properties of IV21 (IVC135+54-45), a galactic intermediate-velocity molecular cloud (IVMC) that lies ~300 pc above the disk. The metallicity of IV21 was estimated using observations toward the sdB star PG1144+615, located at a projected distance of 16 pc from the cloud’s densest core, by measuring ion and HI column densities for comparison with known solar abundances. Despite the cloud’s bright FIR emission and large column densities of molecular gas as traced by CO, we find that it has a sub-solar metallicity of log(Z/Z_Sun)=-0.43 +/- 0.12dex. IV21 is thus the first known sub-solar metallicity cloud in the solar neighborhood. In contrast, most intermediate-velocity clouds (IVC) have near-solar metallicities and are believed to originate in the Galactic Fountain. The cloud’s low metallicity is also atypical for Galactic molecular clouds, especially in the light of the bright FIR emission which suggest a substantial dust content. The measured I_100mu/N(HI) ratio is a factor of three below the average found in high latitude \HI clouds within the solar neighborhood. We argue that IV21 represents the impact of an infalling, low-metallicity high-velocity cloud (HVC) that is mixing with disk gas in the lower Galactic halo.

Deuterated molecules in Orion KL from Herschel/HIFI

We present a comprehensive study of the deuterated molecules detected in the fullband HIFI survey of the Orion KL region. Ammonia, formaldehyde, and methanol and their singly deuterated isotopologues are each detected through numerous transitions in this survey with a wide range in optical depths and excitation conditions. In conjunction with a recent study of the abundance of HDO and H$_2$O in Orion KL, this study yields the best constraints on deuterium fractionation in an interstellar molecular cloud to date. As previous studies have found, both the Hot Core and Compact Ridge regions within Orion KL contain significant abundances of deuterated molecules, suggesting an origin in cold grain mantles. In the Hot Core, we find that ammonia is roughly a factor of 2 more fractionated than water. In the Compact Ridge, meanwhile, we find similar deuterium fractionation in water, formaldehyde, and methanol, with D/H ratios of (2—8) $\times$ $10^{-3}$. The [CH$_2$DOH]/[CH$_3$OD] ratio in the Compact Ridge is found to be $1.2 \pm 0.3$. The Hot Core generally has lower deuterium fractionation than the Compact Ridge, suggesting a slightly warmer origin, or a greater contribution from warm gas phase chemistry.

A comprehensive near and far ultraviolet spectroscopic study of the hot DA white dwarf G191-B2B

We present a detailed spectroscopic analysis of the hot DA white dwarf G191-B2B, using the best signal to noise, high resolution near and far UV spectrum obtained to date. This is constructed from co-added \textit{HST} STIS E140H, E230H, and \textit{FUSE} observations, covering the spectral ranges of 1150-3145\AA\, and 910-1185\AA\, respectively. With the aid of recently published atomic data, we have been able to identify previously undetected absorption features down to equivalent widths of only a few m\AA. In total, 976 absorption features have been detected to $3\sigma$ confidence or greater, with 947 of these lines now possessing an identification, the majority of which are attributed to Fe and Ni transitions. In our survey, we have also potentially identified an additional source of circumstellar material originating from Si {\sc iii}. While we confirm the presence of Ge detected by \citet{vennes05a}, we do not detect any other species. Furthermore, we have calculated updated abundances for C, N, O, Si, P, S, Fe, and Ni, while also calculating, for the first time, an NLTE abundance for Al, deriving Al {\sc iii}/H=$1.60_{-0.08}^{+0.07}\times{10}^{-7}$. Our analysis constitutes what is the most complete spectroscopic survey of any white dwarf. All observed absorption features in the \textit{FUSE} spectrum have now been identified, and relatively few remain elusive in the STIS spectrum.

The Hamburg/ESO R-process Enhanced Star survey (HERES) VIII. The r+s star HE 1405 0822

Aims.The aim of this study is a detailed abundance analysis of the newly discovered r-rich star HE 1405 0822, which has [Fe=H]=-2.40. This star shows enhancements of both r- and s-elements, [Ba/Fe]= +1.95 and [Eu/Fe]=1.54, for which reason it is called r+s star. Methods.Stellar parameters and element abundances were determined by analying high-quality VLT/UVES spectra. We used Fe I line excitation equilibria to derive the e?ective temperature. The surface gravity was calculated from the Fei/Feii and Ti I/Ti II equilibria. Results.We determined accurate abundances for 39 elements, including 19 neutron-capture elements. HE 1405-0822 is a red giant. Its strong enhancements of C, N, and s-elements are the consequence of enrichment by a former AGB companion with an initial mass of less than 3 M_Sun. The heavy n-capture element abundances (including Eu, Yb, and Hf) seen in HE 1405-0822 do not agree with the r-process pattern seen in strongly r-process-enhanced stars. We discuss possible enrichment scenarios for this star. The enhanced alpha elements can be explained as the result of enrichment by supernovae of type II. Na and Mg may have partly been synthesized in a former AGB companion, when the primary 22^Ne acted as a neutron poison in the 13^C-pocket.

Massive Quiescent Cores in Orion: V. The Physical Structures on Sub-Jeans Scale and the Chemical Properties in Two Extremely Dense Cores

We present a high-resolution (~1.5") observational study towards two massive molecular cores, ORI8nw_2 and ORI2_6 in the Orion Molecular Cloud using the Combined Array for Research in Millimeter-wave Astronomy (CARMA). In both regions the 3.2 mm continuum emission reveals a dense and compact dust core of 1 to 3 solar masses. The cores are estimated to have a number density more than 10^9 cm^-3, which is among the highest volume density ever published for molecular cores. In both regions the N2H+ shows multiple gas clumps which are spatially displaced from the HCO+ and the 3.2 mm continuum emission. We analyzed the gravitational instabilities of the N2H+ clumps. They have spatial scales comparable to the thermal Jeans length, and masses lower than the virial mass. This indicates that the clumps may result from thermal fragmentation but are currently unbounded or loosely bounded by the self-gravity. The thermal fragmentation may have largely prevented the formation of high-mass stars despite the fact that the two cores both have large total mass. We also examined the molecular abundances and found that in both regions the abundance ratio of [N2H+]/[HCO+] appears to be higher than that in infrared dark clouds. By comparing the chemical models, we suggest this to be a result of CO depletion.

 

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