The chemical composition and structure of the moon

Three types of igneous rocks, all ultimately related to basaltic liquids, appear to be common on the lunar surface. They are: (1) iron-rich mare basalts, (2) U-, REE-, and Al-rich basalts (KREEP), and (3) plagioclase-rich or anorthositic rocks. All three rock types are depleted in elements more volatile than sodium and in the siderophile elements when relative element abundances are compared with those of carbonaceous chondrites. The chemistry and age relationships of these rocks suggest that they are derived from a feldspathic, refractory element-rich interior that becomes more pyroxenitic; that is, iron/magnesium-rich; with depth.It is suggested that the deeper parts of the lunar interior tend toward chondritic element abundances. The radial variation in mineralogy and bulk chemical composition inferred from the surface chemistry is probably a primitive feature of the Moon that reflects the accretion of refractory elementenriched materials late in the formation of the body.     

30 Doradus as the active centre of the Large Magellanic Cloud

Evidence is presented for the hypothesis that the supergiantHii-complex 30 Doradus (NGC 2070) is the mildly active galactic nucleus of the Large Magellanic Cloud. For this purpose the general properties of galactic nuclei and the characteristics of active nuclei are reviewed (Section 2). Examination of 30 Doradus shows that it plasy the same exceptional role among allHii-regions of the LMC as Sgr A among those of our Galaxy, and has all the properties of a galactic nucleus (luminosity, emission spectrum, IR source, semistellar central object R 136, symmetry centre of an starting point of spiral structure). Evidence for the activity is given by the peculiar filamentary structure (Figure 1), the young spiral filaments superposed on old, broad and smooth near-circular arms (Figure 2), the splitting of the [Oiii] 5007 profile in two components corresponding to an expansion velocity of 50 km s^–1, and the strong non-thermal component (Section 3). The mass loss of 30 Dor is estimated at 0.05M /a. It is speculated that the nucleus of a galaxy may be wandering due to explosive events.     

The global magnetic topology of AB Doradus

We have used Zeeman–Doppler maps of the surface field of the young, rapid rotator AB Dor  ( P _rot=0.514 d)  to extrapolate the coronal field, assuming it to be potential. We find that the topology of the large-scale field is very similar in all three years for which we have images. The corona divides cleanly into regions of open and closed field. The open field originates in two mid-latitude regions of opposite polarity separated by about 180° of longitude. The closed field region forms a torus extending almost over each pole, with an axis that runs through these two longitudes. We have investigated the effect on the global topology of different forms of flux in the unobservable hemisphere and in the dark polar spot where the Zeeman signal is suppressed. The flux distribution in the unobservable hemisphere affects only the low-latitude topology, whereas the imposition of a unidirectional polar field forces the polar cap to be open. This contradicts observations that suggest that the closed field corona extends to high latitudes and leads us to propose that the polar cap may be composed of multipolar regions.     

The chemical composition of the Sun

We present a redetermination of the solar abundances of all available elements. The new results have very recently been published by Asplund et al. (Annu. Rev. Astron. Astrophys. 47:481, 2009). The basic ingredients of this work, the main results and some of their implications are summarized hereafter.     

The chemical composition of the halo and evolutionary problems

The chemical composition of the Milky-Way halo is studied on the basis of a sample of metal-poor (logarithmic metallicity less than –1) globular clusters. The histogram obtained may be interpreted in the terms of the classical galaxy formation theory of Eggen, Lynden-Bell and Sandage. Interestingly enough, this is in a rough agreement with the data on metallicity of high-redshift damped Ly-alpha and Ly-alpha forest systems. This may serve the important purpose of constraining the nature and the formation timescale of MACHOs discovered through gravitational microlensing experiments. This revised version was published online in August 2006 with corrections to the Cover Date.     

The chemical atmospheric composition of the giant planets

For a long time it was believed that the atmospheres of the giant planets, dominated by molecular hydrogen and helium, were similar in composition to the primordial nebula from which they formed. However, this image has strongly evolved over the past twenty years, due to new developments of ground-based infrared spectroscopy, coupled with the success of the Voyager space mission.Significant differences were measured in the abundances of helium, deuterium and carbon of the four giant planets. The variations in the C/H and D/H ratios have given support to the "nucleation" formation scenario, in which the four giant planets first accreted a nucleus of about ten terrestrial masses, big enough to bind gravitationally the surrounding gaseous nebula; the helium depletion in Saturn has been interpreted as a differentiation effect in Saturn's interior; the apparent helium excess in Neptune, coupled with the recent unexpected detection of CO and HCN in this planet, might imply the presence of molecular nitrogen. In the case of Jupiter and Saturn, disequilibrium species have been detected (CO, PH₃, GeH₄, AsH₃), which are tracers of vertical dynamical motions.In the future, significant progress in our knowledge of the Jovian composition, including the noble gases, should be obtained with the mass spectrometer of the Galileo probe. The ISO mission is expected to provide new far-infrared spectroscopic data which should lead to the detection of new minor species and a better determination of the D/H ratio.     

The chemical composition of the Small Magellanic Cloud

The Small Magellanic Cloud is a close, irregular galaxy that has experienced a complex star formation history due to the strong interactions occurred both with the Large Magellanic Cloud and the Galaxy. Despite its importance, the chemical composition of its stellar populations older than ∼ 1–2 Gyr is still poorly investigated. I present the first results of a spectroscopic survey of ∼ 200 Small Magellanic Cloud giant stars performed with FLAMES@VLT. The derived metallicity distribution peaks at [Fe/H] ∼ –0.9/–1.0 dex, with a secondary peak at [Fe/H] ∼ –0.6 dex. All these stars show [α /Fe] abundance ratios that are solar or mildly enhanced (∼+0.1 dex). Also, three metal‐poor stars (with [Fe/H] ∼ –2.5 dex and enhanced [α /Fe] ratios compatible with those of the Galactic Halo) have been detected in the outskirts of the SMC: These giants are the most metal‐poor stars discovered so far in the Magellanic Clouds. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Studies of the chemical composition of cosmic rays withZ=3–30 at high and low energies

We have measured the chemical composition of cosmic rays withZ2 over an energy range from 100 MeV/nuc to >2 GeV/nuc using 2 new large area counter telescopes. One of these instruments was a 4 element dE/dx×E× Range telescope, the other a 4 element dE/dx×Cerenkov× ×Range telescope. Two balloon flights with these telescopes at Ft. Churchill in the summer of 1970 provided a total of nearly 1000 Fe nuclei with a charge resolution ranging from 0.10 charge unit at Carbon to 0.25 charge unit at Fe. A detailed charge spectrum is obtained at both high and low energies. Some important differences exist between the present results and those obtained earlier, due in part to the improved statistical accuracy and in part to the improved background rejection of the present data. In particular, the abundance of Cr and Mn are each found to be 0.10×Fe in contrast to the earlier ratio of 0.30 found by some workers for each of these nuclei. The abundance of these two nuclei, as well as others in the 15–25 range, shows no strong dependence on energy. We have extrapolated our composition data to the cosmic ray sources using a variety of interstellar path length distributions. The abundances ofall secondary nuclei withZ between 3–25 are consistent only with propagation models which have vacuum path length distributions which do not differ greatly from exponential. The source abundances of nuclei withZ=15, 17, 18, 19, 21, 22, 23, 24, and 25 are found to be <0.02×Fe. For the remaining nuclei, Na, Al, S, and Ca are found to have source abundances of 0.07, 0.11, 0.18 and 0.13 of Fe respectively. The source abundance of C and O relative to Fe is also much different than some earlier compilations. A comparison of solar and cosmic ray abundances reveals certain selective differences, rather than a systematic overabundance of heavy nuclei in cosmic rays, as has been suggested in the past. These differences are discussed in terms of a common nucleosynthesis origin of the two species of particles.Research sponsored by the National Aeronautics and Space Administration under Grant No. NGR-30-002-052.     

Asteroseismology of δ Scuti and γ Doradus stars

We give an overview of past and present efforts to make seismology of δ Scuti and γ Doradus stars possible. Previous work has not led to the observational detection and identification of a sufficient number of pulsation modes for these pulsators for the construction of unique seismic models. However, recent efforts including large ground-based observational campaigns, work on pre-main sequence pulsators, asteroseismic satellite missions, theoretical advances on mode identification methods, and the discovery of a star showing simultaneous self-excited δ Scuti and γ Doradus oscillations suggest that we may be able to explore the interiors of these pulsators in the very near future.     

The spatial structure of the HH 30 jet

New, deep, wide-field [SII] images of the HL Tauri region show the extended spatial structure of the HH 30 jet and counter-jet. At an angular distance of 300 arcsec toward the NE, the HH 30 jet ends in a group of scattered condensations. This previously undetected structure might correspond to a broken-up working surface. Our images also include HH 262, which is shown to have a previously undetected extended emission region.     

The chemical composition of matter in the early universe

The results of the computations of the chemical evolution for a galaxy cluster are presented. The matter exchange between galaxies and intergalactic medium is taken into account. Two dependences of star formation rate on time are considered: (i) monotonously decreasing dependence characteristic of elliptical galaxies, (ii) dependence having two peaks associated with creation of spiral galaxy subsystems, with suppression of star formation at the period between maxima. It is assumed that galactic ejection is due to explosions of II-type supernova with massesm5M , and that the accretion on to a galaxy depends but weakly on the time. By comparing the obtained results with total combination of available observations, it is established that the rate of gaseous exchange between a galaxy and intergalactic medium should be rather large: 0.03M _gal Gyr^–1. Besides, the activity of each type of galaxy leads to an approximately equal enrichment of intergalactic gas by new elements synthesized in the stars. The existence of a large accretion on to the Galaxy leads to the decrease of primordial deuterium abundance by a factor of no more than 2 during the galaxy evolution time. It enables us to assume that the standard Big Bang model with baryon density parameter _b 0.1 may be considered as true.     

The chemical composition of stars with extrasolar planetary systems

Spectroscopic studies of stars with and without planetary systems have concluded that planet hosts are more metal‐rich. This enrichment is also seen in the other chemical elements studied and is likely to be primordial in nature. Interesting trends of different chemical elements begin to appear as the number of extrasolar planets continues to grow. I present our current knowledge concerning the observed abundance trends of chemical elements in planet hosts and their possible implications. In most cases the abundance trends of planet host stars are identical to those of the comparison sample. However, some exceptions (such as Li) have been reported too. No clear correlation was found between orbital parameters of planets and host star metallicity. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The main sequence location as function of chemical composition

Available data for computed zero-age lines are analyzed, and empirical formulae giving the luminosity as function of the chemical composition are derived. Mass-luminosity relations are also presented for a very wide range of the chemical composition parameters (X, Y, Z). Comparison with the observed zero-age lines are discussed.     

The motions of the neutral and ionized material in the supermassive Doradus Nebula

A close association between the large scale motions of the neutral and ionized gas in the 30 Doradus Nebular Complex is established. A series ofHi/Hii shells are suggested to explain this phenomenon. The evidence favours a contracting situation, but is not yet conclusive.     

The mass ratio and the orbital parameters of the sdOB binary AA Doradus

The time sequence of 105 spectra covering one full orbital period of AA Dor has been analysed. Direct determination of   V  sin  i   for the sdOB component from 97 spectra outside of the eclipse for the lines Mg  ii 4481 Å and Si  iv 4089 Å clearly indicated a substantially smaller value than estimated before. Detailed modelling of line-profile variations for eight spectra during the eclipse for the Mg  ii 4481 Å line, combined with the out-of-eclipse fits, gave   V  sin  i = 31.8 ± 1.8 km s⁻¹  . The previous determinations of   V  sin  i   , based on the He  ii 4686 Å line, appear to be invalid because of the large natural broadening of the line. With the assumption of the solid-body, synchronous rotation of the sdOB primary, the measured values of the semi-amplitude K ₁ and   V  sin  i   lead to the mass ratio   q = 0.213 ± 0.013  which in turn gives K ₂ and thus the masses and radii of both components. The sdOB component appears to be less massive than assumed before,   M ₁= 0.25 ± 0.05 M_⊙  , but the secondary has its mass–radius parameters close to theoretically predicted for a brown dwarf,   M ₂= 0.054 ± 0.010 M_⊙  and   R ₂= 0.089 ± 0.005 R_⊙  . Our results do not agree with the recent determination of Vŭcković et al. based on a K ₂ estimate from line-profile asymmetries.