Physical processes in the protoplanetary disk

Protoplanetary evolution is discussed in both its global and local aspects. The global turbulent evolution implies large scale average chemical fractionation and chondrule-sized grains as the building blocks of planetary and possibly also cometary material. Local processes such as electric discharges and associated flash heating of grains allow for chemical, mineralogical, and morphological alterations of the disk material. Large scale turbulence keeps the disk well stirred, however, time dependent (or intermittent) turbulence, associated with e.g. optical depth variations, could lead to dust sedimentation within the disk and subsequent planetesimal formation. Recent relevant astronomical observations of young T Tauri stars are briefly reviewed.     

Calibration of the VIS-channel of meteosat-2

The “VIS-channel” (the channel is sensitive between about .4 and 1.1 μm wavelength) of the European geostationary satellite Meteosat-2 is calibrated by the method of “vicarious calibration by means of calculated radiances”. The calibration constant, which connects the 6-bit-counts of the VIS-channel of the Meteosat-2 with the corresponding “effective radiances” is determined to be c_SAT = 2.3 W·m^?2·sr^?1/count with an accuracy of ± 10% (preliminary values). The calibration constant is valid for “gain 0” and the period until October 1981. The result means, that the VIS-channel of Meteosat-2 at the beginning of its lifetime is about 15% more sensitive than that of Meteosat-1 was at its end.     

Some properties of the polar energy source and of the associated atmospheric perturbations

The magnitude, dissipation mechanism, and spatial distribution of the solar wind - magnetospheric energy source are discussed briefly. Using N₂ measurements of the ESRO 4 satellite, the temperature increase in the polar thermosphere associated with this energy source are investigated. Part of the locally dissipated energy is transported toward lower latitudes. Possible modes of energy transfer are reviewed, and local time variations are documented. Some suggestions are made with respect to future empirical models of the thermosphere.     

The Sixth Catalogue of galactic Wolf-Rayet stars,their past and present

This paper presents the Sixth Catalogue of galactic Wolf-Rayet stars (Pop. I), a short history on the five earlier WR catalogues, improved spectral classification, finding charts, a discussion on related objects, and a review of the current status of Wolf-Rayet star research.The appendix presents a bibliography on most of the Wolf-Rayet literature published since 1867.Visiting astronomer, Kitt Peak National Observatory and Cerro Tololo Inter-American Observatory.Visiting astronomer, European Southern Observatory.     

The cold summer mesopause

One of the most characteristic features of the summer mesopause at high latitudes is the very low temperature. Earlier measurements have shown temperatures in the range down to 135 K around 86 km altitude, whereas the most recent $\text{in situ}$ measurements have revealed temperatures still much lower than that in a rather wide altitude region. The reasons for these low temperatures are to be found in the dynamics of the strato- and mesospheres. Upwinds and gravity wave activity over the summer hemisphere cause efficient cooling of the atmosphere.Also other effects are caused by the updrafts. The vertical transport velocity for important minor constituents is increased, which for instance causes the concentration of water vapor around the mesopause to be enhanced by large factors. This situation is of major importance for the possibility of forming noctilucent clouds (NLC).NLC are believed to be composed of small water ice particles, which because of the low temperatures can be formed on existing condensation nuclei. Two of the main questions regarding the formation of NLC concern the water vapor budget of the upper mesosphere and the origin of the condensation nuclei.This paper gives a general introduction to mesospheric physics and composition. Some results from recent satellite and rocket experiments are reviewed and the campaign layout and the performed experiments within the MAP project CAMP are described. The results from the different experiments are presented in four accompanying papers on CAMP results.     

The acquisition of survey knowledge for local and global landmark configurations under time pressure

The influence of stress states on cognition is widely recognized. However, the manner in which stress affects survey knowledge acquisition is still unresolved. For the present study, we investigated whether survey knowledge acquisition during a stressful task (i.e., under time pressure) is more accurate for the mental representation of global or local landmarks. Participants navigated through virtual cities with a navigation aid and explicit learning instructions for different landmark configurations. Participants’ judgments of relative direction (JRDs) suggest that global landmark configurations were not represented more accurately than local landmark configurations and that survey knowledge acquisition was not impaired under time pressure. In contrast to prior findings, our results indicate the limitations of the utility of global landmarks for spatial knowledge acquisition.     

The Theory of Gamma-Ray Bursts

This chapter gives a brief review on the theory of gamma-ray bursts (GRBs), including the models of multi-messengers (e.g., prompt multiwavelength electromagnetic emissions, high-energy neutrinos, ultra-high-energy cosmic rays, and gravitational waves) and central engines (in particular, mergers of binary neutron stars for short GRBs). For detailed reviews, please see (Piran in Phys. Rep. 314:575, 1999; Rev. Mod. Phys. 76:1143, 2004; Mészáros in Annu. Rev. Astron. Astrophys. 40:137, 2002; Rep. Prog. Phys. 69:2259, 2006; Zhang and Mészáros in Int. J. Mod. Phys. A 19:2385, 2004; Zhang in Chin. J. Astron. Astrophys. 7:1, 2007; Nakar in Phys. Rep. 442:166, 2007; Kumar and Zhang in Phys. Rep. 561:1, 2015).     

Ages and Geologic Histories of Martian Meteorites

We review the radiometric ages of the 16 currently known Martian meteorites, classified as 11 shergottites (8 basaltic and 3 lherzolitic), 3 nakhlites (clinopyroxenites), Chassigny (a dunite), and the orthopyroxenite ALH84001. The basaltic shergottites represent surface lava flows, the others magmas that solidified at depth. Shock effects correlate with these compositional types, and, in each case, they can be attributed to a single shock event, most likely the meteorite's ejection from Mars. Peak pressures in the range 15 – 45 GPa appear to be a "launch window": shergottites experienced ～30 – 45 GPa, nakhlites ～20 ± 5 GPa, Chassigny ～35 GPa, and ALH84001 ～35 – 40 GPa. Two meteorites, lherzolitic shergottite Y-793605 and orthopyroxenite ALH84001, are monomict breccias, indicating a two-phase shock history in toto: monomict brecciation at depth in a first impact and later shock metamorphism in a second impact, probably the ejection event. Crystallization ages of shergottites show only two pronounced groups designated S₁ (～175 Myr), including 4 of 6 dated basalts and all 3 lherzolites, and S₂ (330 – 475 Myr), including two basaltic shergottites and probably a third according to preliminary data. Ejection ages of shergottites, defined as the sum of their cosmic ray exposure ages and their terrestrial residence ages, range from the oldest (～20 Myr) to the youngest (～0.7 Myr) values for Martian meteorites. Five groups are distinguished and designated S_Dho (one basalt, ～20 Myr), S_L (two lherzolites of overlapping ejection ages, 3.94 ± 0.40 Myr and 4.70 ± 0.50 Myr), S (four basalts and one lherzolite, ～2.7 – 3.1 Myr), S_DaG (two basalts, ～1.25 Myr), and S_E (the youngest basalt, 0.73 ± 0.15 Myr). Consequently, crystallization age group S₁ includes ejection age groups S_L, S_E and 4 of the 5 members of S, whereas S₂ includes the remaining member of S and one of the two members of S_DaG. Shock effects are different for basalts and lherzolites in group S/S₁. Similarities to the dated meteorite DaG476 suggest that the two shergottites that are not dated yet belong to group S₂. Whether or not S₂ is a single group is unclear at present. If crystallization age group S₁ represents a single ejection event, pre-exposure on the Martian surface is required to account for ejection ages of S_L that are greater than ejection ages of S, whereas secondary breakup in space is required to account for ejection ages of S_E less than those of S. Because one member of crystallization age group S₂ belongs to ejection group S, the maximum number of shergottite ejection events is 6, whereas the minimum number is 2. Crystallization ages of nakhlites and Chassigny are concordant at ～1.3 Gyr. These meteorites also have concordant ejection ages, i.e., they were ejected together in a single event (NC). Shock effects vary within group NC between the nakhlites and Chassigny. The orthopyroxenite ALH84001 is characterized by the oldest crystallization age of ～4.5 Gyr. Its secondary carbonates are ～3.9 Gyr old, an age corresponding to the time of Ar-outgassing from silicates. Carbonate formation appears to have coincided with impact metamorphism, either directly, or indirectly, perhaps via precipitation from a transient impact crater lake. The crystallization age and the ejection age of ALH84001, the second oldest ejection age at 15.0 ± 0.8 Myr, give evidence for another ejection event (O). Consequently, the total number of ejection events for the 16 Martian meteorites lies in the range 4 – 8. The Martian meteorites indicate that Martian magmatism has been active over most of Martian geologic history, in agreement with the inferred very young ages of flood basalt flows observed in Elysium and Amazonis Planitia with the Mars Orbital Camera (MOC) on the Mars Global Surveyor (MGS). The provenance of the youngest meteorites must be found among the youngest volcanic surfaces on Mars, i.e., in the Tharsis, Amazonis, and Elysium regions.