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| Three dimensional anisotropic k spectra of turbulence at subproton scales in the solar wind |
| We show the first three dimensional (3D) dispersion relations and k spectra of magnetic turbulence in the solar wind at subproton scales. We used the Cluster data with short separations and applied the k-filtering technique to the frequency range where the transition to subproton scales occurs. We show that the cascade is carried by highly oblique kinetic Alfvén waves with wplas below 0.1wci down to kperpRhoi ~ 2.
Each k spectrum in the direction perpendicular to Bo shows two scaling ranges separated by a breakpoint (in the interval [0.4, 1]kperpRhoi): a Kolmogorov scaling kperp-1.7 followed by a steeper scaling kperp-4.5. We conjecture that the turbulence undergoes a transition range, where part of the energy is dissipated into proton heating via Landau damping and the remaining energy cascades down to electron scales where electron Landau damping may predominate. |
| Publication date: 27 Sep 2010 |
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| Observing Supernova 1987A with the Refurbished Hubble Space Telescope |
| Observations with the Hubble Space Telescope (HST), conducted since 1990, now offer an unprecedented glimpse into fast astrophysical shocks in the young remnant of supernova 1987A. Comparing observations taken in 2010 with the use of the refurbished instruments on HST with data taken in 2004, just before the Space Telescope Imaging Spectrograph failed, we find that the Ly-a and H-a lines from shock emission continue to brighten, whereas their maximum velocities continue to decrease. We observe broad, blueshifted Ly-a, which we attribute to resonant scattering of photons emitted from hot spots on the equatorial ring. We also detect N v ll1239, 1243 angstrom line emission, but only to the red of Ly-a. The profiles of the N v lines differ markedly from that of H-a, suggesting that the N4+ ions are scattered and accelerated by turbulent electromagnetic fields that isotropize the ions in the collisionless shock. |
| Publication date: 24 Sep 2010 |
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| A&A Special: Pre-launch status of Planck mission |
This A&A issue features 13 articles describing the pre-flight status of the European Space Agency Planck mission, launched
together with the Herschel satellite on 14 May 2009. The Planck mission is designed to image the anisotropies of the cosmic
background radiation field over the whole sky, with unprecedented sensitivity and angular resolution, as well as a wide frequency
range. As a byproduct of that main goal, it will simultaneously address a wide range of galactic and extragalactic science. The
mission involves more than four hundred scientists, who are currently working on data processing, calibration, and data analysis. The satellite is scheduled to continuously acquire high-quality science data until the end of 2011. An early release of the compact source catalogue will be delivered in January 2011, together with a small set of science papers related to foreground astrophysical sources. The first major cosmology results will be delivered in December 2012. In this special feature, the telescope's optical system and the design, ground calibration, and performance of the Planck lowand
high-frequency instruments are described in detail. |
| Publication date: 15 Sep 2010 |
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| The large-scale magnetospheric electric field observed by Double Star TC-1 |
| The relationship between the average structure of the inner magnetospheric large-scale electric field and geomagnetic activity levels has been investigated by Double Star TC-1 data for radial distances between 4.5 Re and 12.5 Re and MLT between 18:00 h and 06:00 h from July to October in 2004 and 2005. The sunward component of the electric field decreases monotonically as radial distance increases and approaches zero as the distance off the Earth is greater than 10 Re. The dawn-dusk component is always duskward. It decreases at about 6 Re where the ring current is typically observed to be the strongest and shows strong asymmetry with respect to the magnetic local time. Surprisingly, the average electric field obtained from TC-1 for low activity is almost comparable to that observed during moderate activity, which is always duskward at the magnetotail (8 Re~12 Re). |
| Publication date: 03 Sep 2010 |
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| Warm water vapour in the sooty outflow from a luminous carbon star |
| The detection of circumstellar water vapour around the ageing carbon star IRC +10216 challenged the current understanding of chemistry in old stars, because water was predicted to be almost absent in carbon-rich stars. Several explanations for the water were postulated, including the vaporization of icy bodies (comets or dwarf planets) in orbit around the star, grain surface reactions, and photochemistry in the outer circumstellar envelope. With a single water line detected so far from this one carbon-rich evolved star, it is difficult to discriminate between the different mechanisms proposed. Here we report the detection of dozens of water vapour lines in the far-infrared and sub-millimetre spectrum of IRC +10216 using the Herschel satellite. This includes some high-excitation lines with energies corresponding to ~1000 K, which can be explained only if water is present in the warm inner sooty region of the envelope. A plausible explanation for the warm water appears to be the penetration of ultraviolet photons deep into a clumpy circumstellar envelope. This mechanism also triggers the formation of other molecules, such as ammonia, whose observed abundances are much higher than hitherto predicted. |
| Publication date: 01 Sep 2010 |
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