A quantitative analysis of the prototype [WCL] star CPD-56° 8032

We present a detailed, quantitative study of the standard [WC10] Wolf-Rayet central star CPD-56^o 8032 based on new high resolution AAT UCLES observations and the Hillier (1990) WR standard model. Our analysis of CPD-56^o 8032 gives the wind properties (T _*=34500K, lg (L/L )=3.8, lg (M/M a^–1)=–5.4,v =225 km s^–1) and chemistry (C/He=0.5, O/He=0.1, by number), the latter suggesting an intimate relationship with the Ovi PN central stars and the PG 1159-035 objects. A comparison between the wind properties of CPD-56^o 8032 and Sk-66^o 40 (WN 10) indicates that low excitation, low wind velocity WR winds are common to both low mass PN central stars (WC sequence) and high mass post-LBV's (WN sequence).     

A numerical study of the pre-ejection, magnetically-sheared corona as a free boundary problem

A class of magnetostatic equilibria with axial symmetry outside a unit sphere in the presence of plasma pressure and an r ^–2 gravitational field is constructed. The structure contains a localized current-carrying region confined by a background bipolar potential field, and the shape of the region changes subject to the variation of the electric current. The continuity requirement for the magnetic field and plasma pressures at the outer boundary of the cavity defines a free boundary problem, which is solved numerically using a spectral boundary scheme. The model is then used to study the expansion of the current-carrying region, caused by the buildup of magnetic shear, against the background confining field. The magnetic shear in our model is induced by the loading of an azimuthal field, accompanied by a depletion of plasma density.We show that due to the additional effect of confinement by the dense surrounding plasma, the energy of the magnetic field can exceed the energy of its associated open field, presumably a necessary condition for the onset of coronal mass ejections. (However, the plasma beta of the confining fluid is higher than that in the outer boundary of a realistic helmet-streamer structure.) Furthermore, under the assumption that coronal mass ejections are driven by magnetic buoyancy, the result from our model study lends further support to the notion of a suspended magnetic flux rope in the low-density cavity of a helmet-streamer as a promising pre-ejection configuration.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Jupiter: New retrieved thermal profiles and ammonia distributions

New thermal profiles of Jupiter are retrieved from recent far infrared spectral measurements and for H₂ mixing ratios varying from 0.8 to 0.94. The effective temperature corresponding to the inferred thermal profile is 123.15 ± 0.35°K. Far-infrared brightness temperature spectra computed from these profiles are compared to experimental data including measurements made at high spectral resolution in the NH₃ν₂ band at 10 μm and in NH₃ pure rotational bands between 40 and 110 μm. It is found that a strong depletion of NH₃ does occur in the Jovian stratosphere and that ammonia seems to be undersaturated in the upper troposphere.     

Formation of the regular satellites of giant planets in an extended gaseous nebula I: subnebula model and accretion of satellites

We model the subnebulae of Jupiter and Saturn wherein satellite accretion took place. We expect each giant planet subnebula to be composed of an optically thick (given gaseous opacity) inner region inside of the planet’s centrifugal radius (where the specific angular momentum of the collapsing giant planet gaseous envelope achieves centrifugal balance, located at rCJ ∼ 15R_J for Jupiter and rCS ∼ 22R_S for Saturn) and an optically thin, extended outer disk out to a fraction of the planet’s Roche-lobe (R_H), which we choose to be ∼R_H/5 (located at ∼150 R_J near the inner irregular satellites for Jupiter, and ∼200R_S near Phoebe for Saturn). This places Titan and Ganymede in the inner disk, Callisto and Iapetus in the outer disk, and Hyperion in the transition region. The inner disk is the leftover of the gas accreted by the protoplanet. The outer disk may result from the nebula gas flowing into the protoplanet during the time of giant planet gap-opening (or cessation of gas accretion). For the sake of specificity, we use a solar composition “minimum mass” model to constrain the gas densities of the inner and outer disks of Jupiter and Saturn (and also Uranus). Our model has Ganymede at a subnebula temperature of ∼250 K and Titan at ∼100 K. The outer disks of Jupiter and Saturn have constant temperatures of 130 and 90 K, respectively.Our model has Callisto forming in a time scale ∼10⁶ years, Iapetus in 10⁶-10⁷ years, Ganymede in 10³-10⁴ years, and Titan in 10⁴-10⁵ years. Callisto takes much longer to form than Ganymede because it draws materials from the extended, low density portion of the disk; its accretion time scale is set by the inward drift times of satellitesimals with sizes 300-500 km from distances ∼100R_J. This accretion history may be consistent with a partially differentiated Callisto with a ∼300-km clean ice outer shell overlying a mixed ice and rock-metal interior as suggested by Anderson et al. (2001), which may explain the Ganymede-Callisto dichotomy without resorting to fine-tuning poorly known model parameters. It is also possible that particulate matter coupled to the high specific angular momentum gas flowing through the gap after giant planet gap-opening, capture of heliocentric planetesimals by the extended gas disk, or ablation of planetesimals passing through the disk contributes to the solid content of the disk and lengthens the time scale for Callisto’s formation. Furthermore, this model has Hyperion forming just outside Saturn’s centrifugal radius, captured into resonance by proto-Titan in the presence of a strong gas density gradient as proposed by Lee and Peale (2000). While Titan may have taken significantly longer to form than Ganymede, it still formed fast enough that we would expect it to be fully differentiated. In this sense, it is more like Ganymede than like Callisto (Saturn’s analog of Callisto, we expect, is Iapetus). An alternative starved disk model whose satellite accretion time scale for all the regular satellites is set by the feeding of planetesimals or gas from the planet’s Roche-lobe after gap-opening is likely to imply a long accretion time scale for Titan with small quantities of NH₃ present, leading to a partially differentiated (Callisto-like) Titan. The Cassini mission may resolve this issue conclusively. We briefly discuss the retention of elements more volatile than H₂O as well as other issues that may help to test our model.     

The effects of topographically-controlled thermal tides in the martian upper atmosphere as seen by the MGS accelerometer

Mars Global Surveyor accelerometer observations of the martian upper atmosphere revealed large variations in density with longitude during northern hemisphere spring at altitudes of 130-160 km, all latitudes, and mid-afternoon local solar times (LSTs). This zonal structure is due to tides from the surface. The zonal structure is stable on timescales of weeks, decays with increasing altitude above 130 km, and is dominated by wave-3 (average amplitude 22% of mean density) and wave-2 (18%) harmonics. The phases of these harmonics are constant with both altitude and latitude, though their amplitudes change significantly with latitude. Near the South Pole, the phase of the wave-2 harmonic changes by 90° with a change of half a martian solar day while the wave-3 phase stays constant, suggesting diurnal and semidiurnal behaviour, respectively. We use a simple application of classical tidal theory to identify the dominant tidal modes and obtain results consistent with those of General Circulation Models. Our method is less rigorous, but simpler, than the General Circulation Models and hence complements them. Topography has a strong influence on the zonal structure.     

Implications for behavior of volatile elements during impacts—Zinc and copper systematics in sediments from the Ries impact structure and central European tektites

Moldavites are tektites genetically related to the Ries impact structure, located in Central Europe, but the source materials and the processes related to the chemical fractionation of moldavites are not fully constrained. To further understand moldavite genesis, the Cu and Zn abundances and isotope compositions were measured in a suite of tektites from four different substrewn fields (South Bohemia, Moravia, Cheb Basin, Lusatia) and chemically diverse sediments from the surroundings of the Ries impact structure. Moldavites are slightly depleted in Zn (~10–20%) and distinctly depleted in Cu (>90%) relative to supposed sedimentary precursors. Moreover, the moldavites show a wide range in δ⁶⁶Zn values between 1.7 and 3.7‰ (relative to JMC 3‐0749 Lyon) and δ⁶⁵Cu values between 1.6 and 12.5‰ (relative to NIST SRM 976) and are thus enriched in heavy isotopes relative to their possible parent sedimentary sources (δ⁶⁶Zn = ?0.07 to +0.64‰; δ⁶⁵Cu = ?0.4 to +0.7‰). In particular, the Cheb Basin moldavites show some of the highest δ⁶⁵Cu values (up to 12.5‰) ever observed in natural samples. The relative magnitude of isotope fractionation for Cu and Zn seen here is opposite to oxygen‐poor environments such as the Moon where Zn is significantly more isotopically fractionated than Cu. One possibility is that monovalent Cu diffuses faster than divalent Zn in the reduced melt and diffusion will not affect the extent of Zn isotope fractionation. These observations imply that the capability of forming a redox environment may aid in volatilizing some elements, accompanied by isotope fractionation, during the impact process. The greater extent of elemental depletion, coupled with isotope fractionation of more refractory Cu relative to Zn, may also hinge on the presence of carbonyl species of transition metals and electromagnetic charge, which could exist in the impact‐induced high‐velocity jet of vapor and melts.     

Bandpass calibration of a wideband spectrometer using coherent pulse injection

We present a relatively simple time domain method for determining the bandpass response of a system by injecting a nanosecond pulse and capturing the system voltage output. A pulse of sub-nanosecond duration contains all frequency components with nearly constant amplitude up to 1 GHz. Hence, this method can accurately determine the system bandpass response to a broadband signal. In a novel variation on this impulse response method, a train of pulses is coherently accumulated providing precision calibration with a simple system. The basic concept is demonstrated using a pulse generator-accumulator setup realised in a Bedlam board which is a high speed digital signal processing unit. The same system was used at the Parkes radio telescope between 2–13 October 2013 and we demonstrate its powerful diagnostic capability. We also present some initial test data from this experiment.     

Secondary‐volatiles linked metallic iron in eucrites: The dual‐origin metals of Camel Donga

The unique occurrence of abundant (~1 vol%) near‐pure‐Fe metal in the Camel Donga eucrite is more complicated than previously believed. In addition to that component of groundmass metal, scattered within the meteorite are discrete nodules of much higher kamacite abundance. We have studied the petrology and composition of two of these nodules in the form of samples we call CD2 and CD3. The nodules are ovoids 11 (CD2) to 15 (CD3) mm across, with metal, or inferred preweathering metal, abundances of 12–17 vol% (CD2 is unfortunately quite weathered). The CD3 nodule also includes at its center a 5 mm ovoid clumping (6 vol%) of F‐apatite. Both nodules are fine‐grained, so the high Fe metal and apatite contents are clearly not flukes of inadequate sampling. The metals within the nodules are distinctly Ni‐rich (0.3–0.6 wt%) compared to the pure‐Fe (Ni generally 0.01 wt%) groundmass metals. Bulk analyses of three pieces of the CD2 nodule show that trace siderophile elements Ir, Os, and Co are commensurately enriched; Au is enriched to a lesser degree. The siderophile evidence shows the nodules did not form by in situ reduction of pyroxene FeO. Moreover, the nodules do not show features such as silica‐phase enrichment or pyroxene with reduced FeO (as constrained by FeO/MgO and especially FeO/MnO) predicted by the in situ reduction model. The oxide minerals, even in groundmass samples well away from the nodules, also show little evidence of reduction. Although the nodule boundaries are generally sharp, groundmass‐metal Ni content is anti‐correlated with distance from the CD3 nodule. We infer that the nodules represent materials that originated within impactors into the Camel Donga portion of the eucrite crust, but probably were profoundly altered during later metamorphism/metasomatism. Origin of the pure‐Fe groundmass metal remains enigmatic. In situ reduction probably played an important role, and association in the same meteorite of the Fe‐nodules is probably significant. But the fluid during alteration was probably not (as previously modeled) purely S and O, of simple heat‐driven internal derivation. We conjecture a two‐stage metasomatism, as fluids passed through Camel Donga after impact heating of volatile‐rich chondritic masses (survivors of gentle accretionary impacts) within the nearby crust. First, reduction to form troilite may have been triggered by fluids rich in S₂ and CO (derived from the protonodules?), and then in a distinct later stage, fluids were (comparatively) H₂O‐rich, and thus reacted with troilite to form pure‐Fe metal along with H₂S and SO₂. The early eucrite crust was in places a dynamic fluid‐bearing environment that hosted complex chemical processes, including some that engendered significant diversity among metal+sulfide alterations.     

Charge-coupled device imaging spectroscopy of Mars. 1. Instrumentation and data reduction/analysis procedures

This paper describes the collection, reduction, and analysis of 0.4–1.0 m Mars imaging spectroscopy data obtained during the 1988 and 1990 oppositions from Mauna Kea Observatory and provides a general outline for the acquisition and analysis of similar imaging spectroscopy data sets. The U.H. 2.24-m Wide Field Grism CCD Spectrograph was used to collect 13 three-dimensional image cubes covering 90% of the planet south of 50°N in the 0.4–0.8 m region (/=245 at 0.6 m) and covering 55% of the planet south of 50°N in the 0.5–1.0 m region (/=293 at 0.75 m). Spectra extracted from these image cubes reveal the detailed character of the martian near-UV to visible spectrum. Images at red wavelengths reveal the classical albedo markings at 100–500 km spatial resolution while images at blue wavelengths show little surface feature contrast and are dominated by condensate clouds/hazes and polar ice. Many of the data acquisition, reduction, and analysis steps discussed here are new or unique to imaging spectroscopy data sets. These techniques exploit the information contained within the spatial domain of data such as these, thus allowing more traditional point-spectral analysis techniques to be expanded into an imaging format.