Composition of Cometary Dust: The Case against Silicates

It is argued that the infrared emission including 10 and 18 μ features observed in recent comets is unlikely to be due to silicates. The vaporization temperature of the emitting material∼ 500 K is consistent with emission by crystalline polyformaldehyde. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the Role of Dust Mass Loss in the Evolution of Comets and Dusty Disk Systems

We present the results of an ongoing optical/thermal infraredphotometric imaging survey of thedust mass loss and nuclear size ofcomets. We find an evolution with time of the kind of dust emittedfrom a comet's surface. Our results indicate that the mass loss ratefrom the short period comets alone is enough to supply the interplanetary dust (IPD) complexagainst losses. We conclude that the nature of the IPD cloud haschanged over time, with small particles dominating early, and largerparticles dominating in the present era. The rate of destruction of short period (SP)comets due to sublimation mass loss is found to be low compared to therate of surface mantle formation, but fast compared to the rate of their dynamical removal from the inner solar system.     

Carbon in Meteoroids: Wild 2 Dust Analyses, IDPs and Cometary Dust Analogues

Assuming that similar organic components as in comet 81P/Wild 2 are present in incoming meteoroids, we try to anticipate the observable signatures they would produce for meteor detection techniques. In this analysis we consider the elemental and organic components in cometary aggregate interplanetary dust particles and laboratory analyses of inter- and circumstellar carbon dust analogues. On the basis of our analysis we submit that (semi) quantitative measurements of H, N and C produced during meteor ablation will open an entire new aspect to using meteoroids as tracers of these volatile element abundances in active comets and their contributions to the mesospheric metal layers.     

Dust Grains and Circumstellar Motion: The Problem of the Henand the Egg

In the last ten years, the number of models of circumstellar envelopes has exponentially increased, both concerning evolved stars and forming stars with their planetary systems. The main progress was intoduction of chemistry and coupling with dynamics. However, paradoxically, the nucleation theories did not evolve at the same rate; moreover, dynamics and nucleation are rarely analysed at the same degree of accuracy: one is of them is always mostly drawing attention. At the same time observations showed the presence of dust grains at a lot of sites where it could not be expected from usual quasi equilibrium theories. Self consistent systems are omnipresent. Thus, it is important to distinguish causes and effects, even if the phenomena are are strongly coupled. This revised version was published online in July 2006 with corrections to the Cover Date.     

高速Ia型超新星的蓝色超出: 星周介质的尘埃散射

Ia型超新星起源于碳氧白矮星在质量接近钱德拉塞卡极限时的热核爆炸,并被广泛地用作宇宙学距离的标准烛光.然而, Ia型超新星的前身星系统和爆炸机制还存在很多不明确的地方.近几十年来, Ia型超新星的星周环境得到了越来越多的关注.星周介质的空间分布性质为探究Ia型超新星的物理起源提供了重要线索.同时星周尘埃的散射会在Ia型超新星晚期的光变曲线、光谱和偏振等方面产生可观测效应.光谱上正常的Ia型超新星可以分成两类:喷射物速度正常和高速Ia型超新星.对比两者的光变曲线可以发现高速Ia型超新星在光极大后几个月内有明显颜色偏蓝的超出.该蓝色超出可以通过星周介质中的尘埃散射拟合得到.同时, Ia型超新星晚期光谱的拟合可以限制星周尘埃的颗粒大小等性质,晚期的偏振信号可以有效地限制星周尘埃的空间分布.拟合结果表明针对Ia型超新星晚期的多次图像偏振观测是揭示其星周尘埃环境特征的重要手段.     

The Dust in Comet C/1999 S4 (LINEAR) during Its Disintegration: Narrow-Band Images, Color Maps, and Dynamical Models

Comet C/1999 S4 was observed with the 2m-telescopes of the Bulgarian National Observatory and Pik Terskol Observatory, Northern Caucasus, Russia, at the time of its disintegration. Maps of the dust brightness and color were constructed from images obtained in red and blue continuum windows, free from cometary molecular emissions. We analyze the dust environment of Comet C/1999 S4 (LINEAR) taking into account the observed changes apparent in the brightness images and in plots of Afρ profiles as function of the projected distance ρ from the nucleus. We also make use of the syndyne-synchrone formalism and of a Monte Carlo model based on the Finson-Probstein theory of dusty comets. The brightness and color of individual dust particles, which is needed to derive theoretical brightness and color maps of the cometary dust coma from the Monte Carlo model, is determined from calculations of the light scattering properties of randomly oriented oblate spheroids. In general, the dust of Comet C/1999 S4 (LINEAR) is strongly reddened, with reddening values up to 30%/1000 Å in some locations. Often the reddening is higher in envelopes further away from the nucleus. We observed two outbursts of the comet with brightness peaks on July 14 and just before July 24, 2000, when the final disintegration of the comet started. During both outbursts an excess of small particles was released. Shortly after both outbursts the dust coma “turns blue.” After the first outburst, the whole coma was affected; after the second one only a narrow band of reduced color close to the tail axis was formed. This difference is explained by different terminal ejection speeds, which were much lower than normal in case of the second outburst. In particular in the second, final outburst the excess small particles could originate from fragmentation of “fresh” larger particles.     

Evolution of Dust Shells and Jets in the Inner Coma of Comet C/1995 O1 (Hale-Bopp)

Comet Hale-Bopp was observed with the 80 cm reflector + CCD at the Haute-Provence observatory (OHP) and with the 62 cm reflector + CCD at the Saint-Véran observatory (Queyras, France). The morphology of the shells was followed from their first appearence on 1997 Jan. 30, until their disappearance on May 9. These shells spread from the nucleus region with a velocity in agreement with a nuclear rotation period of about 11.33 hours. We report also a short and bright dust ejection on May 8. CN images show a long spiral jet in the tailward side invisible on continuum images. The circumnuclear structures have been followed at Saint-Véran from Apr. 5 to Apr. 11, 1997 with a high spatial resolution (200 km/pixel). We have followed the emergence of a recurrent linear polar jet. Measurements of its expansion show a constant acceleration of material with typical expansion velocity of 1 km/s. The CCD frames show the interconnection between spiral jets and the successive shells. This revised version was published online in July 2006 with corrections to the Cover Date.     

The opacity of spiral galaxy disks: IX. Dust and gas surface densities

Our aim is to explore the relation between gas, atomic and molecular, and dust in spiral galaxies. Gas surface densities are from atomic hydrogen and CO line emission maps. To estimate the dust content, we use the disk opacity as inferred from the number of distant galaxies identified in twelve HST/WFPC2 fields of ten nearby spiral galaxies. The observed number of distant galaxies is calibrated for source confusion and crowding with artificial galaxy counts and here we verify our results with sub‐mm surface brightnesses from archival Herschel ‐SPIRE data. We find that the opacity of the spiral disk does not correlate well with the surface density of atomic (H I) or molecular hydrogen (H₂) alone implying that dust is not only associated with the molecular clouds but also the diffuse atomic disk in these galaxies. Our result is a typical dust‐to‐gas ratio of 0.04, with some evidence that this ratio declines with galactocentric radius, consistent with recent Herschel results. We discuss the possible causes of this high dust‐to‐gas ratio; an over‐estimate of the dust surface‐density, an under‐estimate of the molecular hydrogen density from CO maps or a combination of both. We note that while our value of the mean dust‐to‐gas ratio is high, it is consistent with the metallicity at the measured radii if one assumes the Pilyugin & Thuan (2005) calibration of gas metallicity. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Exo-Zodiacal Disk Mapper: A Space Interferometer to Detect and Map Zodiacal Dust Disks Around Nearby Stars

We present a concept for a space mission designed to make a mid-IR survey of potential zodiacal dust disks around nearby stars. We show that a two-aperture (0.6 m diameter), 10-m baseline, nulling interferometer located in a 1 × 4 AU, 4-yr solar orbit would allow for the survey of 400 stars in the solar neighborhood and permit a first-order determination of the disk inclination and radial dependences of density and temperature. The high dynamic range of the instrument may also be used to study additional astrophysical phenomena. Beyond its own scientific merit, such a mission would serve as a technological precursor to a larger interferometer of the type being considered for the detection of earth-like planets.     

The Chemical Evolution of the Universe on its Smallest Scales: Dust in Stars,Disks and Planets

D15 Dust and gas in the inner accretion disk around the Herbig star MWC 147 resolved with infrared spectro‐interferometry D21 The effective temperature of OGLE‐TR‐10 – The Balmer α line D29 Metal Injection into the Intracluster Medium D30 Eigenmodes of circumstellar dust shells D40 Numerical Modelling Approach of Circumstellar Dust Shells Around Pulsating AGB Stars Aiming at Multi Time Scale Processes D45 UV radiation induced CO molecule formation patterns in low density PDRs D46 IR properties of calcite and dolomite at low temperatures D47 Observations and Models of Dusty Giants – Past and Present D51 A multi‐method approach to the outer layers of AGB stars D53 On the convective energy transport in M‐type brown dwarf atmospheres D70 Structure and Dust Composition of the TW Hya Disc D75 Chemical Abundances in the Carina Dwarf Spheroidal Galaxy D76 Kinematic and chemical constraints on the formation of M31's inner halo structures D77 IR band profiles of silicate and oxide dust obtained by laboratory measurements of free‐flying particles D98 Dust particle growth in protoplanetary disks D134 Comparative study of dust cloud modelling for substellar atmospheres D137 Photometric study of neglected binary DV Psc D154 Quantitative Spectroscopy of Deneb D160 Hot subluminous Ostars from the SDSS D166 Simultaneous Observations of Solar Ca II H and Ca II 8662 lines and Numerical Simulation of these lines D182 Present‐day carbon abundances in the solar vicinity D189 Detection of a giant planet around a pulsating extreme horizontal branch star: the oldest known planet? D200 Confirmation of a very young binary brown dwarf candidate with disk in Chamaeleon D208 Galaxy ages and metallicities in the cluster A1314 D217 Charge‐dipole induced dust gelation – fastening the process of dust growth in protoplanetary disks D246 Protoplanetary Disk Structure and Evolution     

The Meteors, Meteoroids and Interplanetary Dust Program of the International Heliophysical Year 2007/9

Under the title ‘Meteors, Meteoroids and Interplanetary Dust’, meteor research is included in the program of the International Heliophysical Year 2007/9.We list issues for coordinated meteor research within the framework of this global international program.     

Cometary—Meteoric Gas in the Solar Corona: The Dynamics of Ca Ions

Prolonged searches for the cold matter brought into the solar corona from the outskirts of the Solar system have finally been crowned with success. After the first prediction about the possibility of detecting emission from certain atoms and low-charge ions made by Shestakova in 1990, several attempts have been made to detect the resonance emission of Ca ions in the solar corona. The wide-field interferometric observations of the corona in the Ca II H and K lines performed by Gulyaev on Shcheglov's facility revealed an extended emission region to the west of the Sun only during the solar eclipse of February 26, 1998. We attempt to construct a model for the motion of Ca ions after their separation from the parent body. The ions move away from the Sun mainly under light pressure. Reasonably good agreement of the model with the observed radial velocities and the emission configuration is achieved by assuming that the chain of parent bodies moves from the south northward in a parabolic orbit almost perpendicularly to the plane of the ecliptic.     

The Contribution of Asteroid Dust to the Interplanetary Dust Cloud: The Impact of ULYSSES Results on the Understanding of Dust Production in the Asteroid Belt and of the Formation of the IRAS Dust Bands

Investigations of the zodiacal dust cloud give evidence for a significant contribution of asteroidal dust to the interplanetary dust cloud, a result which can now be compared to measurements of the ULYSSES dust detector during its passage of the asteroid belt. Especially we discuss the ULYSSES data with respect to the IRAS dust bands and consider geometric selection effects for the detector. From calculations of radiation pressure forces, we conclude that particles in the IRAS dust bands with massesm≥ 10⁻¹²g will stay in bound orbits after their release from asteroid fragmentation. This is already in the mass range (10⁻¹⁶–10⁻⁷g) of particles detectable with the dust detector onboard ULYSSES. The absence of these particles in the ULYSSES data cannot be explained exclusively in terms of their small detection probability. Thus we conclude that the size distribution of particles in the IRAS dust bands most probably cannot be continued to the submicrometer range. Concerning the global structure of the inner zodiacal cloud (i.e., about solar distancer< 3.5 AU) the ULYSSES data are not inconsistent with present models. Recent estimates of the total mass of the interplanetary cloud require a dust production rate of about 10¹⁴g/year of which a significant amount is assumed to result from the asteroids. Our estimate for the production of dust particles in an IRAS dust band, based on the assumption that the dust band results from a single destruction of an asteroid of 100 km size, yields a production rate of 10¹⁰g/year. Other models of the IRAS dust bands suggest production rates up to 10¹²g/year and also cannot provide a significant source of the dust cloud.     

Dust production from the hypervelocity impact disruption of the Murchison hydrous CM2 meteorite: Implications for the disruption of hydrous asteroids and the production of interplanetary dust

More than half of the C-type asteroids, the dominant type of asteroid in the outer half of the main-belt, show evidence of hydration in their reflectance spectra. In order to understand the collisional evolution of asteroids and the production of interplanetary dust and to model the infrared signature of small particles in the Solar System it is important to characterize the dust production from primary impact disruption events, and compare the disruption of hydrous and anhydrous targets. We performed a hypervelocity impact disruption experiment on an ∼30 g target of the Murchison CM2 hydrated carbonaceous chondrite meteorite, and compared the results with our previous disruption experiments on anhydrous meteorites including Allende, a CV3 carbonaceous chondrite, and nine ordinary chondrites. Murchison is significantly more friable than the ordinary chondrites or Allende. Nonetheless, on a plot of mass of the largest fragment versus specific impact energy, the Murchison disruption plots within the field of the anhydrous meteorites points, suggesting that Murchison is at least as resistant to impact disruption as the anhydrous meteorites, which require about twice the energy for disruption as terrestrial anhydrous basalt targets. We determined the mass-frequency distribution of the debris from the Murchison disruption over a nine order-of-magnitude mass range, from ∼10⁻⁹ g to the mass of the largest fragment produced in the disruption. The cumulative mass-frequency distribution from the Murchison disruption is fit by three power-law segments. For masses >10⁻² g the slope is only slightly steeper than that of the corresponding segment from the disruption of most anhydrous meteorites. Over the range from ∼10⁻⁶ to 10⁻² g the slope is significantly steeper than that for the anhydrous meteorites. For masses <10⁻⁶ g the slopes of both the Murchison and the anhydrous meteorites are almost flat. Thus the Murchison disruption significantly over-produced small fragments (10⁻⁶-10⁻³ g) compared to anhydrous meteorite targets. If the Murchison results are representative of hydrous asteroids, the hydrous asteroids may dominate over anhydrous asteroids in the production of interplanetary dust >100 μm in size, the size of micrometeorites recovered from the polar ices, while both types of asteroids might produce comparable amounts of ∼10 μm interplanetary dust. This would explain the puzzle that polar micrometeorites (>100 μm in size) are similar to hydrous meteorites, while the majority of the ∼10 μm interplanetary dust particles are anhydrous.     

Dust radiation fields and pumping of excited state OH masers in W3(OH)

I show that it is quite possible to obtain saturating amplification in the 13.44-GHz maser which is so far unique to W3(OH), using a combined radiative and collisional pumping scheme. The dominant radiative part of the pump involves far-infrared line overlap, and the far-infrared continuum is provided by dust, modelled as either a two-component mixture or composite grains. Transport of the far-infrared radiation is carried out via the accelerated lambda iteration method. The observational link between 13.44-GHz and 6035-MHz masers is reproduced by the model. Inadequate amplification in Sobolev models probably results from the optical depth limitations imposed by this approximation. I review the dust models used in far-infrared pumping models of OH masers, and conclude that the main consequence of moving from skewed blackbody functions to more sophisticated models is a selective pumping enhancement when ice mantles are included.     

The Diagnosis of Complex Rotation in the Lightcurve of 4179 Toutatis and Potential Applications to Other Asteroids and Bare Cometary Nuclei

The analysis of radar observations of the asteroid 4179 Toutatis by Hudson and Ostro (1995, Science270, 84-86) yielded a complex spin state. We revisit the visible lightcurve data on Toutatis (Spencer et al. 1995, Icarus117, 71-89) to explore the feasibility of using a rotational lightcurve to recover the signature of an excited spin state. For this, we apply Fourier transform and CLEAN algorithm (WindowCLEAN). WindowCLEAN yields clear and precise frequency signatures associated with the precession of the long axis about the total angular momentum vector and a combination of this precession and rotation about the long axis. For a long-axis mode state, our periodicities for Toutatis yield a mean long-axis precession period, P_φ, of 7.38 days and a rotation period around the long axis, P_ψ, of 5.38 days, which compare well with the respective periods of 7.42 and 5.37 days derived by Ostro et al. (1999, Icarus137, 122-139) and represent an independent confirmation of these values. We explain why the dramatic change in the Earth-Toutatis-Sun geometry during the time that the lightcurve was obtained has little effect on the final results obtained. Using the Toutatis example as a guide, we discuss the capabilities as well as the limitations on deriving information about complex spin states from asteroidal lightcurves.