The surface properties of small asteroids: Peculiar Betulia—A case study

We present the results of extensive thermal-infrared observations of the C-type near-Earth Asteroid (1580) Betulia obtained in June 2002 with the 3-m NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. Betulia is a highly unusual object for which earlier radiometric observations, interpreted on the basis of simple thermal models, indicated a surface of high thermal inertia. A high thermal inertia implies a lack of thermally insulating regolith. Radiometric observations of other asteroids of comparable size indicate that regolith is present in nearly all cases. Knowledge of the surface thermal properties of small near-Earth asteroids is crucial for meaningful calculations of the Yarkovsky effect, which is invoked to explain the delivery of collisional fragments from the main belt into near-Earth orbits, and apparently has a significant influence on the orbital evolution of potentially hazardous near-Earth asteroids. Furthermore, apart from being an indicator of the presence of thermally insulating regolith on the surface of an asteroid, the thermal inertia determines the magnitude of the diurnal temperature variation and is therefore of great importance in the design of instrumentation for lander missions to small asteroids. In the case of Betulia our database is sufficiently broad to allow the use of more sophisticated thermal models than were available for earlier radiometric observations. The measured fluxes have been fitted with thermal-model emission continua to determine the asteroid's size and geometric albedo, pv. Fits obtained with a new thermophysical model imply an effective diameter of 4.57±0.46 km and an albedo of 0.077±0.015 and indicate a moderate surface thermal inertia of around 180 J m⁻² s^−0.5 K⁻¹. It is difficult to reconcile our results with earlier work, which indicate a larger diameter for Betulia and a high-thermal-inertia surface of bare rock.     

The Preboreal climate reversal and a subsequent solar‐forced climate shift

Accurate chronologies are essential for linking palaeoclimate archives. Carbon‐14 wiggle‐match dating was used to produce an accurate chronology for part of an early Holocene peat sequence from the Borchert (The Netherlands). Following the Younger Dryas–Preboreal transition, two climatic shifts could be inferred. Around 11 400 cal. yr BP the expansion of birch (Betula) forest was interrupted by a dry continental phase with dominantly open grassland vegetation, coeval with the PBO (Preboreal Oscillation), as observed in the GRIP ice core. At 11 250 cal. yr BP a sudden shift to a humid climate occurred. This second change appears to be contemporaneous with: (i) a sharp increase of atmospheric ¹⁴C; (ii) a temporary decline of atmospheric CO₂; and (iii) an increase in the GRIP ¹⁰Be flux. The close correspondence with excursions of cosmogenic nuclides points to a decline in solar activity, which may have forced the changes in climate and vegetation at around 11 250 cal. yr BP. Copyright © 2004 John Wiley & Sons, Ltd.     

Dissipationless mergers of elliptical galaxies and the evolution of the fundamental plane

We carry out numerical simulations of dissipationless major mergers of elliptical galaxies using initial galaxy models that consist of a dark matter haloes and a stellar bulge with properties consistent with the observed fundamental plane. By varying the density profile of the dark matter haloes [standard Navarro, Frenk & White (NFW) profile versus adiabatically contracted NFW profile], the global stellar to dark matter mass ratio and the orbit of the merging galaxies, we are able to assess the impact of each of these factors on the structure of the merger remnant. Our results indicate that the properties of the remnant bulge depend primarily on the angular momentum and energy of the orbit; for a cosmologically motivated orbit, the effective radius and velocity dispersion of the remnant bulge remain approximately on the fundamental plane. This indicates that the observed properties of elliptical galaxies are consistent with significant growth via late dissipationless mergers. We also find that the dark matter fraction within the effective radius of our remnants increases after the merger, consistent with the hypothesis that the tilt of the fundamental plane from the virial theorem is due to a varying dark matter fraction as a function of galaxy mass.     

The Relationship of Green-Line Transients to White-Light Coronal Mass Ejections

We report observations by the Large Angle Spectrometric Coronagraph (LASCO) on the SOHO spacecraft of three coronal green-line transients that could be clearly associated with coronal mass ejections (CMEs) detected in Thomson-scattered white light. Two of these events, with speeds >25 km s^-1, may be classified as ‘whip-like’ transients. They are associated with the core of the white-light CMEs, identified with erupting prominence material, rather than with the leading edge of the CMEs. The third green-line transient has a markedly different appearance and is more gradual than the other two, with a projected outward speed <10 km s^-1. This event corresponds to the leading edge of a ‘streamer blowout’ type of CME. A dark void is left behind in the emission-line corona following each of the fast eruptions. Both fast emission-line transients start off as a loop structure rising up from close to the solar surface. We suggest that the driving mechanism for these events may be the emergence of new bipolar magnetic regions on the surface of the Sun, which destabilize the ambient corona and cause an eruption. The possible relationship of these events to recent X-ray observations of CMEs is briefly discussed. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004981125702     

Some comments on the asymptotic limit of antiproton-proton flux ratio at the top of the atmosphere

Using the leaky-box model the upper limit of the antiproton-proton flux ratio at the top of the atmosphere has been estimated from the latest primary nucleon spectrum and accelerator data on inclusive reactions. The estimated value of flux ratio comes out to be (3.6±0.3)×10^–4 is in accord with the previous results but still far from the measurements.     

IGU commission health and development UGI commission sante et developpement In conjunction with medical geography specialty groups of the AAG,CAG, and IBG

The International Geographical Union Reports

IGU commission health and development UGI commission sante et developpement In conjunction with medical geography specialty groups of the AAG, CAG, and IBG International medical geography symposium     

Simulation of the ice age atmosphere — January and July means

A simulation of the atmospheric state under ice age conditions (18,000 years before present) is presented. The T21 Atmospheric General Circulation Model (AGCM), originally developed at the European Centre for Medium-Range Weather Forecasts, was used for the calculation of six annual cycles. Results of the near-surface climatology (2 m-temperature, 10 m-wind, and precipitation), averaged over the last five model years, are presented. The presentation is restricted to January and July means in order to demonstrate the glacial changes in summer and winter. The model's response to ice age boundary conditions was quite consistent with paleogeological data on land and with AGCM experiments of other studies. Although the differences between the mean climate states of the model atmosphere under glacial and modern boundary conditions were statistically significant, the basic structure of the simulated atmospheric circulation was not altered substantially.

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Zusammenfassung Eine Simulation des Zustands der eiszeitlichen Atmosphäre (18000 Jahre vor heute) wird vorgestellt. Das T21-Modell (allgemeines Zirkulationsmodell der Atmosphäre), entwickelt am Europäischen Zentrum für Mittelfrist-Wettervorhersage, wurde zur Berechnung von sechs Jahresgängen verwendet. Die Ergebnisse der oberflächennahen Klimatologie (2 m-Temperatur, 10 m-Wind und Niederschlag) werden präsentiert als Mittel über die letzten fünf Modelljahre. Die Darstellung ist eingeschränkt auf Januar- und Julimittel, um die eiszeitlichen Änderungen im Sommer und Winter deutlich zu machen. Die Antwort des Modells auf die eiszeitlichen Randbedingungen stimmt recht gut überein mit paläogeologischen Landdaten und mit anderen Simulationsrechnungen. Obgleich die Klimaunterschiede in der eiszeitlichen und der heutigen Modellatmosphäre statistisch signifikant sind, wurde die Grundstruktur der atmosphärischen Zirkulation vom T21-Modell nur wenig verändert.

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Résumé Cette note présente une simulation de l'état de l'atmosphère dans les conditions de l'âge glaciaire, il y a 18.000 ans. Le calcul de 6 cycles annuels a été effectué au moyen du modèle T 21 de la circulation atmosphérique générale développé au Centre Européen de prévision du temps à moyen terme. Les éléments du climat proche de la surface (température à 2 m, vent à 10 m, précipitations) sont présentés en moyenne des cinq dernières années du modèle. Ces éléments sont limités aux moyennes de janvier et de juillet, de manière à mettre en évidence les changements hiver/été. La réponse du modèle aux conditions aux limites de l'âge glaciaire est en bon accord avec les données paléontologiques de terrain ainsi qu'avec d'autres calculs de simulation. Bien qu'il existe d'importantes différences climatiques entre les modèles d'atmosphère de l'âge glaciaire et d'aujourd'hui, la structure de base de la circulation atmosphérique du modèle T 21 est peu modifiée.

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, 18000 . 21 = , = , 6 . , — 2 10 , 5 . , , , . . , 21 .

     

Can Brans-Dicke universes in five dimensions be interpreted as 4-dimensional general relativity cosmologies?

The 5-dimensional Jordan-Brans-Dicke cosmologies in vacuum are found for the Bianchi type I metric, their relation with general relativity cosmologies is studied. Two solutions are possible, both produce effective pressure and energy density in the 4-dimensional G.R.-universes. One is a power-law relation, with two cases, the first one is forp _eff=_eff and the other forp _eff=_eff(– 1 < < 1) has a behaviour as the open flat universe. The second solution is an exponential only valid forp _eff=–_eff. In all cases the three-space expansion reaches infinity ast and the fifth dimension can be made to decrease approaching zero. The scalar field can increase or decrease with time.     

Photometric observations of CH Cygni in the period 1978–1987. Dust matter condensation in its circumstellar envelope during 1985–1987

We present the results of the photometric observations, in theUBVRJHKLMNQ system, of CH Cyg, made in the period 1978–1987. They have shown that from 1985 to 1987 dust condensed in its circumstellar envelope have taken place the condensation of the dust matter. In 1987 its mass and temperature were about 3×10^–8 M and 800 K, respectively.