Brightness Variation and Proper Motions of Three Objects in the Cygnus Region

The results of an investigation of three peculiar objects in the Cygnus region are given. One of them was already known to be a Herbig-Haro object. In accordance with its observational characteristics, the second object is, in all probability, a T Tauri star. The physical character of the last object is not yet entirely clear, but from the properties of its emission in the near infrared range it is probably also a T Tauri star. The proper motions of the objects have been measured. It is shown that all three objects are members of a tight system of the Trapezium type and evidently are the results of the successive fragmentation of an original protostellar body.     

Water and other volatiles on the moon: A review

This paper presents a review of research findings on the various forms of water on the Moon. First, this is the water of the Moon’s interior, which has been detected by sensitive mass spectrometric analysis of basaltic glasses delivered by the Apollo 15 and Apollo 17 missions. The previous concepts that lunar magmas are completely dehydrated have been disproved. Second, this is H₂O and/or OH in a thin layer (a few upper millimeters) of the lunar regolith, which is likely a result of bombardment of the oxygen contained in the lunar regolith with solar wind protons. This form of water is highly unstable and quite easily escapes from the surface, possibly being one of the sources of the water ice reservoirs at the Moon’s poles. Third, this is water ice associated with other frozen gases in cold traps at the lunar poles. Its possible sources are impacts of comets and meteorites, the release of gas from the Moon’s interior, and solar wind protons. The ice trapped at the lunar polars could be of practical interest for further exploration of the Moon.     

Numerical simulation of the LCROSS impact experiment

This study presents the results of the numerical modeling of the Lunar Crater Observation and Sensing Satellite (LCROSS) space experiment, which is scheduled for 2009 by NASA. It is demonstrated that a spacecraft with a mass of 2 tons impacting the Moon at a velocity of 2.5 km/s creates an ejecta plume with a size of more than 100 km and a mass exceeding 100 tons. The detailed characteristics of the ejecta are given and their relation to the impactor structure is investigated.     

Low‐temperature primordial gas in merging halos

The thermal regime of the baryons behind shock waves arising in the process of virialization of dark matter halos is governed at certain conditions by radiation of HD lines. A small fraction of the shocked gas can cool down to the temperature of the cosmic microwave background (CMB). We estimate an upper limit for this fraction: at z = 10 it increases sharply from about q_T ∼ 10^–3 for dark halos of M = 5 × 10⁷ M_⊙ to ∼ 0.1 for halos with M = 10⁸ M_⊙. Further increase of the halo mass does not lead however to a significant growth of q_T – the asymptotic value for M ≫ 10⁸ M_⊙ is 0.3. We estimate the star formation rate associated with such shock waves, and show that they can provide a small but not negligible fraction of the star formation. We argue that extremely metal‐poor low‐mass stars in the Milky Way may have been formed from primordial gas behind such shocks. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Statistical considerations in the analysis of solar oscillation data by the superposed epoch method

Solar Physics - Although the method of superposed epochs (Chree analysis) has been utilized for seven decades, a procedure to determine the statistical significance of the results has not been...     

Morphologic and gravimetric investigations of Bell and Eisila Regiones on Venus

Bell Regio is a highland fragment south of Ishtar Terra, extending 1300 km in N-S direction and 900 km in E-W direction. South of this region Eisila Regio is located with an E-W extension of 8000 km and a width of 2000 km. Bell Regio consists of two large massifs: a northern massif with maximum altitudes of 2.5 to 3.0 km above the 6051 km datum and with a semi-corona (other coronae on Venus are associated with volcanic-tectonic processes) and a southern massif with a maximum of 4 to 4.5 km above the datum. The possible shield volcano Tepev Mons of 250 km in diameter is superimposed on the southern massif. It shows a radar dark crater of 40 km diameter on its eastern flank, a crater-like feature of 15 km diameter on the top and a radar bright area extending from the dark crater across the summit. South of Tepev Mons are several volcanic structures with summit depressions. The crest of Bell Regio exhibits a N-S extending fossa system. The whole fresh appearing plain-like area has been classified as rather young compared to other units. Gravity data show a maximum of 33 mGal at Bell Regio and 35 mGal at eastern Eisila Regio. The basins north and south of the highland fragments are associated with gravity lows.Density models have been calculated along the gravity profile Rev. 163 of Pioneer Venus Orbiter across Bell and Eisila Regiones assuming Airy isostatic compensation of the topography and considering several boundary conditions (e.g. mean crustal thickness T<- 100 km). There are two groups of density models in the case of Airy compensation. In the first group global total compensation is assumed along the profile and regional partial compensation for Bell and Eisila Regiones. This solution gives a range of possible models with 10 km <- T <- 100 km and a partial compensation for Bell and Eisila Regiones between 12% and 55%. Thus these two highland fragments show subsurface surplus masses.The second group of models considers for the whole profile total compensation with a global T <- 100 km and a regional very large depth of compensation for Bell and Eisila Regiones, i.e. T > 100 km.The highland of Beta Regio has, like Bell Regio, a N-S rifting system, volcanic structures, a fresh appearing plain-like surface and either deep-seating compensating masses or near surface surplus masses. Bell can be considered as little sister of Beta. The geological and geophysical results imply a volcanic-tectonic uplift over a hot spot. The conditions of Atla Regio in eastern Aphrodite Terra are similar. Thus the existence of volcanic-tectonic uplifts support the important role of hot spot volcanism on Venus.Contribution Nr. 343, Institut für Geophysik der Universität Kiel, F.R.G.     

Physico-chemical phenomena in comets—III: The continuum of comet Burnham (1960 II)

The new model of the cometary head proposed in papers I and II is developed and applied to comet Burnham. It takes into account the likely existence of a halo of large icy particles surrounding the nucleus. These particles are steadily stripped from the nucleus by evaporating gases. Their terminal velocity and their rate of evaporation set the size of the halo. The existence of the icy halo influences in two ways the photometric characteristics of the coma. This paper establishes the photometric shape of the continuum as reflected by the icy grains, and compares it to the observed continuum of comet Burnham. Paper IV will compare the predictions of the model with the photometric profile of the molecular emission bands of C₂, in the same comet.     

Particle motion and currents in the neutral sheet of the magnetospheric tail

The trajectories of plasma-sheet protons are computed numerically in magnetic-field models which simulate the neutral-sheet-type configuration observed in experiments. No electric field is included, in contrast with the reconnection theory. Entering the neutral sheet and then exiting from it, the particle performs an ordered displacement across the tail. A continuous interchange between the neutral and plasma sheets will give rise to an electric current which may be responsible for the observed magnetic-field configuration. An estimate of this current is made from the tension balance requirement, showing that a substantial anisotropy of the plasma-sheet pressure is necessary to maintain the steady state. It is shown that the neutral sheet itself can be a source of such an anisotropy, due to the non-adiabatic behaviour of protons. Other anisotropy origins are discussed briefly.     

Understanding the mechanisms of formation of nanophase compounds from Stardust: Combined experimental and observational approach

Abstract– We have experimentally produced nanophase sulfide compounds and magnetite embedded in Si‐rich amorphous materials by flash‐cooling of a gas stream. Similar assemblages are ubiquitous, and often dominant components of samples of impact‐processed silica aerogel tiles and submicron grains from comet 81P/Wild 2 were retrieved by NASA’s Stardust mission. Although the texture and compositions of nanosulfide compounds have been reproduced experimentally, the mechanisms of formation of these minerals and their relationship with the surrounding amorphous materials have not been established. In this study, we present evidence that both of these materials may not only be produced through cooling of a superheated liquid but they may have also been formed simultaneously by flash‐cooling and subsequent deposition of a gas dominated by Fe‐S‐SiO‐O₂. In a dust generator at the Goddard Space Flight Center, samples are produced by direct gas‐phase condensation from gaseous precursors followed by deposition, which effectively isolates the effects of gas‐phase reactions from the effects of melting and condensation. High‐resolution transmission electron microscopy images and energy‐dispersive spectroscopy analysis show that these experiments replicate key features of materials from type B and type C Stardust tracks, including textures, distribution of inclusions, nanophase size, and compositional diversity. We argue that gas‐phase reactions may have played a significant role in the capture environment for nanophase materials. Our results are consistent with a potential progenitor assemblage of micron and submicron‐sized sulfides and submicron silica‐bearing phases, which are commonly observed in chondritic interplanetary dust particles and in the matrices of the most pristine chondritic meteorites.