Minor ions in the solar wind

Ions heavier than ⁴He are treated as “minors” in the solar wind. This is justified for many applications since minor ions have no significant influence on the dynamics of the interplanetary plasma. However, minor ions carry information on many aspects of the formation, on the acceleration and on the transfer of solar plasma from the corona into the interplanetary space. This review concentrates on various aspects of minor ions as diagnostic tracers. The elemental abundance patterns of the solar wind are shaped in the chromosphere and in the lower transition region by processes, which are not fully understood at this moment. Despite this lack of detailed understanding, observed abundance patterns have been classified and are now commonly used to characterize the sources, and to trace back solar-wind flows to their origins in the solar atmosphere. Furthermore, the solar wind is the most important source of information for solar isotopic abundances and for solar abundances of volatile elements. In order to fully exploit this information, a comprehensive understanding of elemental and isotopic fractionation processes is required. We provide observational clues to distinguish different processes at work.     

Radio Observations at 232 MHz and Multifrequency Spectral Studies of SNR HB21

Radio observational results at 232 MHz and multifrequency studies of supernova remnant (SNR) HB21 are presented. Its integrated flux density at 232 MHz is about 390 ± 30 Jy. Both the integrated spectral index and the spatial variations of spectral index of the remnant were calculated by combining the new map at 232 MHz with previously published maps made at 408, 1420, 2695, and 4750 MHz. The SNR has an integrated spectral index of about α = -0.43(S _ν ∝ ν^α) between 232 and 4750 MHz. In general the spectral index varies from –0.5 in southeast and west regions of the remnant to –0.3 in the central region and near the northwest edge. The new data of 232 MHz reveals that there is interaction between the remnant and the surrounding gas along the east edge of the remnant which causes the spectrum flattening at low frequency, while the very good agreement between the structure of X-ray emission and the central flat spectrum area suggests that the existence of thermal emission is the reason of spectrum flattening in the area. This revised version was published online in July 2006 with corrections to the Cover Date.     

Old stellar populations in NGC 5128

We have resolved the stars in the halo and in the diffuse northeastern shell of the nearest giant elliptical galaxy NGC 5128 using VLT with FORS1 and ISAAC. Dominating feature in the optical-near IR color-magnitude diagrams is abroad red giant branch, indicating a large spread in metallicity of the stars. We have detected a significant number of sources brighter than the tip of the red giant branch. The variability monitoring of these bright red giants shows that they are long period variables similar to Miras. This revised version was published online in September 2006 with corrections to the Cover Date.     

High-resolution solar spectroscopy with TESOS – Upgrade from a double to a triple system

We present the characteristics and demonstrate the performance of the Triple Etalon SOlar Spectrometer (TESOS) operated at the German Vacuum Tower Telescope (VTT) on Tenerife. The Fabry–Pérot interferometer TESOS is ideally suited for precise measurements of photospheric and chromospheric motion. Installed in 1997 and equipped with two etalons, TESOS has recently been completed with a third etalon and upgraded with two high-speed, backside-illuminated CCD cameras. The image scale of 0.089 arc sec pixel^–1 is adapted to the resolution of the telescope. The improved system enables frame rates up to 5 frames per second. The spectral resolution of 300000 allows for spectral diagnostics of weak photospheric lines, including individual CH-lines within the G-band at 430.6 nm.     

The X-ray spectrum of Cyg X-2

The spectra of disc accreting neutron stars generally show complex curvature, and individual components from the disc, boundary layer and neutron star surface cannot be uniquely identified. Here we show that much of the confusion over the spectral form derives from inadequate approximations for Comptonization and for the iron line. There is an intrinsic low-energy cut-off in Comptonized spectra at the seed photon energy. It is very important to model this correctly in neutron star systems as these have expected seed photon temperatures (from either the neutron star surface, inner disc or self-absorbed cyclotron) of ≈1 keV, clearly within the observed X-ray energy band. There is also reflected continuum emission which must accompany the observed iron line, which distorts the higher energy spectrum. We illustrate these points by a reanalysis of the Ginga spectra of Cyg X-2 at all points along its Z track, and show that the spectrum can be well fitted by models in which the low-energy spectrum is dominated by the disc, while the higher energy spectrum is dominated by Comptonized emission from the boundary layer, together with its reflected spectrum from a relativistically smeared, ionized disc.     

Excitation of Sr ii lines in Eta Carinae

We study the nature of the peculiar [Sr  ii ] and Sr  ii emission filament found in the ejecta of Eta Carinae. To this purpose we carry out ab initio calculations of radiative transition probabilities and electron impact excitation rate coefficients for Sr  ii . Then we build a multilevel model for the system which is used to investigate the physical condition of the filament and the nature of the observed allowed and forbidden Sr  ii optical emission. It is found that the observed spectrum is consistent with the lines being pumped by the continuum radiation field in a mostly neutral region with electron density near 10⁷ cm⁻³. Under these conditions, the observed emission can be explained without the need for a large Sr overabundance.     

Characterization of zonal winds in the stratosphere of Titan with UVES

Titan has been observed with UVES, the UV-Visual Echelle Spectrograph at the Very Large Telescope, with the aim of characterizing the zonal wind flow. We use a retrieval scheme originally developed for absolute stellar accelerometry [Connes, P., 1985. Astrophys. Space Sci., 110, 211-255] to extract the velocity signal by simultaneously taking into account all the lines present in the spectrum. The method allows to measure the Doppler shift induced at a given point by the zonal wind flow, with high precision. The short-wavelength channel (4200-5200 Å) probes one scale height higher than the long-wavelength one (5200-6200 Å), and we observe statistically significant evidence for stronger winds at higher altitudes. The results show a high dispersion. Globally, we detect prograde zonal winds, with lower limits of 62 and 50 m s⁻¹ at the regions centered at 200 and 170 km altitude, but approximately a quarter of the measurements indicates null or retrograde winds.     

Genesis—An artificial,low velocity “meteor” fall and recovery: September 8, 2004

Abstract— On September 8, 2004, Genesis, a manmade space capsule, plummeted to Earth after almost three years in space. A ground‐based infrasound array was deployed to Wendover, Nevada, to measure the “hypersonic boom” from the reentry, since the expected initial reentry speed of the body was about 11 km/sec. Due to the complete failure of its dual parachute system, we had a unique opportunity to assess the degree of reliability of our previously developed relations for natural meteors and bolides to analyze this well‐characterized manmade body. At ?20–50 km from the nominal trajectory, we succeeded in recording over two minutes of infrasonic signals from Genesis. Here we report on subsequent analyses of these infrasonic data, including an assessment of the expected entry characteristics on the basis of a bolide/meteor/fireball entry model specifically adapted to modeling reentering manmade objects. From these simulations, we were able to evaluate the line source blast wave relaxation radius, the differential acoustic efficiency, etc., to compute an approximate total power balance during entry. Next, we analyzed the detailed signals arriving from Genesis using a numerical, signal detection and wave processing software package (Matseis/Infra_Tool). We established the initial and subsequent arrivals and evaluated its plane wave back azimuths and elevation arrival angles and the degree of maximum, pair‐wise cross‐correlation, its power spectrum, spectrogram analysis, standard seismic f‐k analysis, etc. From the associated entry parameters, we computed the kinetic energy density conservation properties for the propagating line source blast waves and compared these predictions against observed ground‐based infrasound amplitude and wave period data as a function of range. We discovered that previously computed differential acoustic efficiencies were unreliable at Mach numbers below about 10. This is because we had assumed that a line source explosion was applicable, whereas at very low Mach numbers, typical of recovered meteorites, the detailed source characteristics are closer to those of supersonic objects. When corrections for these unphysical, very high efficiencies were made, agreement between theory and observations improved. We also made an assessment for the energy of the blast wave source from the ground‐based infrasound data using several other techniques that were also adapted from previous bolide studies. Finally, we made a top‐down‐bottom‐up assessment of the line source wave normals propagating via refraction downward into the complex middle atmospheric environment. This assessment proved to be generally consistent with the digital signal processing analysis and with the observed time delay between the known Genesis reentry and the infrasonic observations.