Two-temperature accretion flows in magnetic cataclysmic variables: structures of post-shock emission regions and X-ray spectroscopy

We use a two-temperature hydrodynamical formulation to determine the temperature and density structures of the post-shock accretion flows in magnetic cataclysmic variables (mCVs) and calculate the corresponding X-ray spectra. The effects of two-temperature flows are significant for systems with a massive white dwarf and a strong white-dwarf magnetic field. Our calculations show that two-temperature flows predict harder keV spectra than one-temperature flows for the same white-dwarf mass and magnetic field. This result is insensitive to whether the electrons and ions have equal temperature at the shock, but depends on the electron–ion exchange rate, relative to the rate of radiative loss along the flow. White-dwarf masses obtained by fitting the X-ray spectra of mCVs using hydrodynamic models including the two-temperature effects will be lower than those obtained using single-temperature models. The bias is more severe for systems with a massive white dwarf.     

Observations of magnetic anomaly signatures in Mars Express ASPERA-3 ELS data

Mars Express (MEX) Analyser of Space Plasmas and Energetic Atoms (ASPERA-3) data is providing insights into atmospheric loss on Mars via the solar wind interaction. This process is influenced by both the interplanetary magnetic field (IMF) in the solar wind and by the magnetic ‘anomaly’ regions of the martian crust. We analyse observations from the ASPERA-3 Electron Spectrometer near to such crustal anomalies. We find that the electrons near remanent magnetic fields either increase in flux to form intensified signatures or significantly reduce in flux to form plasma voids. We suggest that cusps intervening neighbouring magnetic anomalies may provide a location for enhanced escape of planetary plasma. Initial statistical analysis shows that intensified signatures are mainly a dayside phenomenon whereas voids are a feature of the night hemisphere.     

Structure of the martian wake

We present the first results from the ion mass analyzer IMA of the ASPERA-3 instrument on-board of Mars Express. More than 200 orbits for May 2004-September 2004 time interval have been selected for the statistical study of the distribution of the atmospheric origin ions in the planetary wake. This study shows that the martian magnetotail consists of two different ion regimes. Planetary origin ions of the first regime form the layer adjacent to the magnetic pile-up boundary. These ions are accelerated to energy greater than 2000 eV and exhibit a gradual decreasing of energy down to the planetary tail. The second plasma regime is observed in the planetary shadow. The heavy ions (considered as planetary ones) are accelerated to the energy of the solar wind protons. Obviously the acceleration mechanism is different for the different plasma regimes. Study of two plasma regimes in the frame referred to the interplanetary magnetic field (IMF) direction (we used MGS magnetometer data to obtain the IMF clock angle) clearly shows their spatial anisotropy. The monoenergetic plasma in the planetary shadow is observed only in the narrow angular sector around the positive direction of the interplanetary electric field.     

First ENA observations at Mars: Subsolar ENA jet

The Neutral Particle Detector (NPD), an Energetic Neutral Atom (ENA) sensor of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) on board Mars Express, detected intense fluxes of ENAs emitted from the subsolar region of Mars. The typical ENA fluxes are (4-7) × 10⁵ cm⁻² sr⁻¹ s⁻¹ in the energy range 0.3-3 keV. These ENAs are likely to be generated in the subsolar region of the martian exosphere. As the satellite moved away from Mars, the ENA flux decreased while the field of view of the NPD pointed toward the subsolar region. These decreases occurred very quickly with a time scale of a few tens of seconds in two thirds of the orbits. Such a behavior can be explained by the spacecraft crossing a spatially constrained ENA jet, i.e., a highly directional ENA emission from a compact region of the subsolar exosphere. This ENA jet is highly possible to be emitted conically from the subsolar region. Such directional ENAs can result from the anisotropic solar wind flow around the subsolar region, but this can not be explained in the frame of MHD models.     

Accretion of matter by condensed objects

The equations of motion for steady-state spherical symmetric flow of matter into or out of a condensed object (e.g. neutron stars, black holes, etc.) are displayed and solved for simple polytropic gases. It appears that infalling matter may be heated as hot as 10¹²K and that X-ray luminosities of the order of 10³⁷ erg s^–1 could result. The two fluid (electrons and ions separately) approach is also examined and it is shown that electrostatic fields of the order of 10⁵ V m^–1 are required near the surface of the object. Such fields are not strong enough to significantly modify the space-time metric.     

First ENA observations at Mars: Solar-wind ENAs on the nightside

We present measurements with an Energetic Neutral Atom (ENA) imager on board Mars Express when the spacecraft moves into Mars eclipse. Solar wind ions charge exchange with the extended Mars exosphere to produce ENAs that can spread into the eclipse of Mars due to the ions' thermal spread. Our measurements show a lingering signal from the Sun direction for several minutes as the spacecraft moves into the eclipse. However, our ENA imager is also sensitive to UV photons and we compare the measurements to ENA simulations and a simplified model of UV scattering in the exosphere. Simulations and further comparisons with an electron spectrometer sensitive to photoelectrons generated when UV photons interact with the spacecraft suggest that what we are seeing in Mars' eclipse are ENAs from upstream of the bow shock produced in charge exchange with solar wind ions with a non-zero temperature. The measurements are a precursor to a new technique called ENA sounding to measure solar wind and planetary exosphere properties in the future.     

Ion escape at Mars: Comparison of a 3-D hybrid simulation with Mars Express IMA/ASPERA-3 measurements

We have analysed ion escape at Mars by comparing ASPERA-3/Mars Express ion measurements and a 3-D quasi-neutral hybrid model. As Mars Express does not have a magnetometer onboard, the analysed IMA data are from an orbit when the IMF clock angle was possible to determine from the magnetic field measurements of Mars Global Surveyor. We found that fast escaping planetary ions were observed at the place which, according to the 3-D model, is anticipated to contain accelerated heavy ions originating from the martian ionosphere. The direction of the interplanetary magnetic field was found to affect noticeably which regions can be magnetically connected to Mars Express and to the overall 3-D Mars-solar wind interaction.     

Sedimentation and Organic Carbon Burial in the Yangtze River and Hudson River Estuaries: Implications for the Global Carbon Budget

One of the most important challenges in global climate change research is balancing the carbon budget within the global carbon cycle. Carbon burial in sediments at the land–ocean interface has been difficult to quantify and model because it represents non-steady-state boundary conditions that are also affected by human activities. In this study, we document carbon burial rates in the Yangtze River (1.6–4.9 × 10¹² gC year^?1) and Hudson River (1.8–3.6 × 10¹⁰ gC year^?1) estuaries and integrate our results with carbon burial rates determined by others in the world’s 25 largest river-estuarine systems (6–11 × 10¹³ gC year^?1). Our results indicate that carbon burial in estuaries, bays, coves, lagoons, mud flats, marshes, mangroves, and other highly productive or protected low-energy areas at the land–ocean interface along the entirety of the world’s coastlines may serve as an unrecognized sink within the global carbon budget.     

Environmental and cultural changes in highland Guatemala inferred from Lake Amatitlán sediments

We inferred the late Holocene environmental history of the Guatemala highlands from multiple lines of evidence in a sediment core from Lake Amatitlán. Inferred environmental changes are generally synchronous with archaeologically documented highland Maya cultural shifts. Population increases in the Middle Preclassic, Early Classic, and Late Postclassic are associated with deforestation and soil erosion. Land abandonment in the Late Preclassic, Late Classic, and Early Postclassic is associated with evidence for reforestation and soil stabilization. Diatoms indicate relatively lower lake level and greater trophic status at times of reduced human impact, from ca. 250 B.C. to A.D. 125 and from ca. A.D. 875 to 1375. Decreased water levels were probably due to drier climate, to reforestation, or both. Lake eutrophication was caused by reduced water volume combined with a legacy of long‐term agricultural activity. Our data contribute to the understanding of relations among ancient Maya culture, climate, and environment. © 2011 Wiley Periodicals, Inc.