Diffuse radio emission from the intracluster medium

An important aspect of the radio emission from galaxy clusters is represented by the diffuse radio sources associated with the intracluster medium: radio halos, relics and mini-halos. The radio halos and relics are indicators of cluster mergers, whereas mini-halos are detected at the center of cooling core clusters. SKA will dramatically improve the knowledge of these sources, thanks to the detection of new objects, and to detailed studies of their spectra and polarized emission. SKA will also provide the opportunity to investigate the presence of halos produced by radiation scattered by a powerful radio galaxy at the cluster centers.     

Galaxy evolution, cosmology and dark energy with the Square Kilometer Array

The present-day Universe is seemingly dominated by dark energy and dark matter, but mapping the normal (baryonic) content remains vital for both astrophysics – understanding how galaxies form – and astro-particle physics – inferring properties of the dark components.The Square Kilometer Array (SKA) will provide the only means of studying the cosmic evolution of neutral hydrogen (HI) which, alongside information on star formation from the radio continuum, is needed to understand how stars formed from gas within dark-matter over-densities and the rôles of gas accretion and galaxy merging.‘All hemisphere’ HI redshift surveys to z 1.5 are feasible with wide-field-of-view realizations of the SKA and, by measuring the galaxy power spectrum in exquisite detail, will allow the first precise studies of the equation-of-state of dark energy. The SKA will be capable of other uniquely powerful cosmological studies including the measurement of the dark-matter power spectrum using weak gravitational lensing, and the precise measurement of H₀ using extragalactic water masers.The SKA is likely to become the premier dark-energy-measuring machine, bringing breakthroughs in cosmology beyond those likely to be made possible by combining CMB (e.g. Planck), optical (e.g. LSST, SNAP) and other early-21st-century datasets.     

Study of bi-orthogonal modes in magnetic butterflies

We present a bi-orthogonal decomposition of the temporal and latitudinal distribution of solar magnetic fields from synoptic magnetograms. Results are compared with a similar decomposition of the distribution of sunspots since 1874. We show that the butterfly diagrams can be interpreted as the result of approximately constant amplitudes and phases of two oscillations with periods close to 22 years. A clear periodicity of 7 years can also be identified in the most energetic modes of both spatio-temporal series. These results can be used to obtain relevant information concerning the physics of the solar dynamo.     

What causes solar active region loops to exist at transition region temperatures?

High-lying, dynamic loops have been observed at transition region temperatures since Skylab observations. The nature of these loops has been debated for many years with several explanations having been put forward. These include that the loops are merely cooling from hotter coronal loops, that they are produced from siphon flows, or that they are loops heated only to transition region temperatures. In this paper we will make use of combined SOHO-MDI (Michelson-Doppler Imager), SOHO-CDS (Coronal Diagnostic Spectrometer) and Yohkoh SXT (Soft X-ray Telescope) datasets in order to determine whether the appearance of transition region loops is related to small-scale flaring in the corona, and to estimate the magnetic configuration of the loops. The latter allows us to determine the direction of plasma flows in the transition region loops. We find that the appearance of the transition region loops is often related to small-scale flaring in the corona and in this case the transition region loops appear to be cooling with material draining down from the loop top.     

MASS FLUX OF ASTEROIDAL ORIGIN METEOROIDS ON PERIODIC COMET NUCLEI

We examine the potential contamination of cometary nuclei through impacts from asteroidal origin meteoroids. The paper uses a simple model and has the goal of determining whether asteroidal contamination is potentially significant. We assume a meteoroid power law mass distribution with index values in the range from s=1.83 to s=2.09. We used maximum and minimum models which we believe will bracket the true meteoroid mass distribution. We identify those comets which are expected to be most significantly contaminated, and find values of up to 3.6 kg of asteroidal meteoroid impact per square meter of the cometary surface per orbital revolution. This is less than the expected mass loss per perihelion passage for most comets. Therefore any remnant effects of the contamination will depend on the penetration depth of the meteoroids in the cometary nucleus, and possibly on the distribution of active and inactive areas on cometary nuclei. We present a simple model which suggests that even small meteoroids will embed relatively deeply into a cometary nucleus.     

Preparing For Hyperseed MAC: An Observing Campaign To Monitor The Entry Of The Genesis Sample Return Capsule

The imminent return of the Genesis Sample Return Capsule (SRC) from the Earth’s L1 point on September 8, 2004, represents the first opportunity since the Apollo era to study the atmospheric entry of a meter-sized body at or above the Earth’s escape speed. Until now, reentry heating models are based on only one successful reentry with an instrumented vehicle at higher than escape speed, the 22 May 1965 NASA “FIRE 2” experiment. In preparation of an instrumented airborne and ground-based observing campaign, we examined the expected bolide radiation for the reentry of the Genesis SRC. We find that the expected emission spectrum consists mostly of blackbody emission from the SRC surface (T∼ ∼2630 K@peak heating), slightly skewed in shape because of a range of surface temperatures. At high enough spectral resolution, shock emission from nitrogen and oxygen atoms, as well as the first positive and first negative bands of N₂⁺, will stand out above this continuum. Carbon atom lines and the 389-nm CN band emission may also be detected, as well as the mid-IR 4.6-μm CO band. The ablation rate can be studied from the signature of trace sodium in the heat shield material, calibrated by the total amount of matter lost from the recovered shield. A pristine collection of the heat shield would also permit the sampling of products of ablation.     

Alignment of Fabry-Pérot Interferometer Plates in a Solar Vector Magnetograph

I describe a method for quickly and accurately determining the plate parallelism in a tunable Fabry-Pérot interferometer. The method takes advantage of the fact that our Fabry-Pérot is installed in a spectropolarimeter: we measure profiles of solar or telluric absorption lines in three differently polarized telescope subapertures and use the residual polarization profiles to determine the plate parallelism error. An example of the error as a function of time during the observing day is also shown; it changes in a consistent way with telescope hour angle but the drift is enough to require frequent adjustment.     

On the Dynamic Disconnection of Rising Omega Loops

The tilt-angle variation of solar bipolar magnetic regions (BMRs) in space and time is a probable indicator of large-scale properties of magnetic field distribution, the dynamo and other different processes affecting the rising of magnetic flux tubes. We analyze the tilt-angle distribution and evolution of clearly oriented BMRs using sunspot position and area measurements from the Greenwich Photo-Heliographic Results (GPHR) supplemented by high-quality full-disk sunspot drawings made in the Haynald Observatory in Hungary. Our work is made on the basis of the 14th sunspot cycle and we compare our results with present theories of magnetic flux evolution in the convective zone. Our results support the assumption that the scatter of tilt angles of BMRs around Joy`s law is determined by the convective turbulence. Furthermore, we find that regular BMRs grouped by age generally do not show the phenomenon of toroidal relaxation towards the east–west direction. We interpret this by the disconnection of -loops from the bottom of the convection zone.     

Impacts of Large Planetesimals on the Early Earth

We considered the impacts of very large cosmic bodies (with radii in the range 100–200 to 1000–2000 km) on the early Earth, whose mass, radius and density distribution are close to the current values. The impacts of such bodies were possible during the first hundreds of million years after the formation of the Earth and the Moon. We present and analyze the results of a numerical simulation of the impact of a planetesimal, the size of which is equal to that of the contemporary Moon (1700 km). In three-dimensional computations, the velocity (15 and 30 km/s) and the angle (45°, 60°, and 90°) of the impact are varied. We determined the mass losses and traced the evolution of the shape of the Earth's surface, taking into account the self-consistent gravitational forces that arise in the ejected and remaining materials in accordance with the real, time-dependent mass distribution. Shock waves reflected from the core are shown to propagate from the impact site deep into the Earth. The core undergoes strong, gradually damped oscillations. Although motions in the Earth's mantle gradually decline, they have enough time to put the Earth in a rotational motion. As a result, a wave travels over the Earth's surface, whose amplitude, in the case of an oblique impact, depends on the direction of the wave propagation. The maximum height of this wave is tremendous—it attains several hundred kilometers. Some portion of the ejected material (up to 40% of the impactor mass) falls back onto Earth under the action of gravity. This portion is equivalent to the layer of a condensed material with a thickness on the order of ten kilometers. The appearance of this hot layer should result in a global melting of near-surface layers, which can limit the age of terrestrial rocks by the time of the impact under consideration. For lesser-sized impactors, say, for impactors with radii of about 160 km, the qualitative picture resembles that described above but the amplitude of disturbances is considerably smaller. This amplitude, however, is sufficient to cause a crustal disruption (if such a crust has already formed) and intense volcanic activity.