PKS2250-41 and the Role of Jet Cloud Interactions in Powerful Radio Galaxies

We have studied the effects of the interaction between the radio jet and the ambient gas in the powerful radio galaxy PKS2250-41 (z = 0.31). Our results show that the gas has been accelerated, compressed, heated and collisionally ionized by the shock. This study helps us to understand the processes which determine the observed properties of many high redshift radio galaxies. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Filament Disappearance of 7 May 1992 (the Ebi)

The 7 May 1992 filament disappearance in the low corona is analyzed. The cool and hot components of this event are studied, using H, soft X-ray and radio data. We first show the general effect of the disparition brusque (DB) on the life of the filament, which was a quiescent filament in the vicinity of an active region, and then give the history of the development of the 7 May event. The main stages of the event are: (i) the formation of hot arches spanning the cool filament; (ii) rise of the filament, with plasma ejection into the corona, in which we note some spreading of loops from the main body, with two distinct rising velocity phases of the H filament; (iii) formation of X-ray arches below the filament, the foot points of the arcades being two-ribbon H flare patches. The dynamics of H and X-rays features are given.     

Mariner 9 ultraviolet spectrometer experiment: Vertical distribution of ozone on Mars

The vertical distribution of ozone in the atmosphere of Mars is computed from ultraviolet spectra obtained by the Mariner 9 spacecraft. In the Northern Hemisphere the ozone scale height is much smaller than the atmospheric scale height in midlatitudes and increases rapidly to a maximum farther north. At high latitudes (above 60°) there is no significant difference between the scale heights of ozone in the Northern (winter) Hemisphere and the Southern (summer) Hemisphere. Comparison of the ozone distribution with atmospheric temperature structure indicates that at some locations in the North, the density of water vapor increases with altitude, and the time for vertical mixing is about 3 days or more.     

The effect of surface roughness on the transmission of microwave radiation through a planetary surface

To account for surface roughness, the transmission of microwave radiation through a planetary surface to an observer is treated by a Monte Carlo technique. Sizable effects are found near the limb of the planet, and they should be included in analyses of high-resolution observations and high-precision integrated disk observations.     

Some comments on the limb shift of solar lines

We searched for a variation with heliographic latitude of the solar limb effect by comparing the relative wavelengths of weak and strong Fraunhofer lines. The blue shifts associated with the limb effect appear 9%±5% larger in the polar radius vector than in an equatorial radius vector at cos = 0.5. This should perhaps be interpreted as an increase with latitude of either solar convection or of convective overshoot. Recent observations of poleward meridional flows of 30m s^–1 should be corrected for this limb effect variation. This correction increases this flow velocity to 70 m s^–1. A search for a similar variation in plages and in network boundaries had negative results, the variation being +1%±5% and -1%±6% respectively.Now at the Multiple Mirror Telescope Observatory, University of Arizona, Tucson, Ariz. 85721, U.S.A. The MMTO is jointly operated by the University of Arizona and the Smithsonian Institution.The Sacramento Peak Observatory is operated by the Association of Universities for Research in Astronomy, Inc. under contract AST 78-17292 with the National Science Foundation.     

Motions in the field of two rotating magnetic dipoles. III: Zero-velocity curves and surfaces

The zero-velocity curves and surfaces created by two parallel or antiparallel magnetic dipoles moving on concentric circles are computed. It is found that for all combinations of values of the mass parameter µ and the ratio of the magnitudes of the magnetic moments of the two dipoles, there exist closed regions inside of which charged particles are permanently trapped.     

A comparison of theoretical line strengths for the 2s 22p 2 − 2s2p 3 transitions in Ne v with solar data

Results are presented for several theoretical line ratios in Nev involving transitions between multiplets in the 2s ²2p ² and 2s2p ³ configurations. A comparison of these with solar data from the S082A and S-055 instruments on board Skylab reveals generally good agreement between theory and experiment, especially in the case of the high-resolution (S082A) observations. However the 2s ²2p ^{2 1} D – 2s2p ^{3 1} P (365.6 Å) and 2s ²2p ^{2 3}P – 2s2p ^{3 3} S (359 Å) lines appear to be blended, possibly with transitions in Fex and Fexi/Fexiii, respectively. We note that the intensity ratio I(365.6 Å)/I(416.2 Å) should be a valuable calibration check for a high-resolution extreme ultraviolet instrument in the spectral range 360–420 Å.     

Starbursts at space ultraviolet wavelengths

Starbursts are systems with very high star formation rate per unit area. They are the preferred place where massive stars form; the main source of thermal and mechanical heating in the interstellar medium, and the factory where the heavy elements form. Thus, starbursts play an important role in the origin and evolution of galaxies. The similarities between the physical properties of local starbursts and high-z star-forming galaxies, highlight the cosmological relevance of starbursts. On the other hand, nearby starbursts are laboratories where to study violent star formation processes and their interaction with the interstellar and intergalactic media, in detail and deeply. Starbursts are bright at ultraviolet (UV) wavelengths, as they are in the far-infrared, due to the ‘picket-fence’ interstellar dust distribution. After the pioneering IUE program, high spatial and spectral resolution UV observations of local starburst galaxies, mainly taken with HST and FUSE, have made relevant contributions to the following issues:

The determination of the initial mass function (IMF) in violent star forming systems in low and high metallicity environments, and in dense (e.g. in stellar clusters) and diffuse environments: A Salpeter IMF with high-mass stars constrains well the UV properties.

The modes of star formation: Starburst clusters are an important mode of star formation. Super-stellar clusters have properties similar to globular clusters.

The role of starbursts in AGN: Nuclear starbursts can dominate the UV light in Seyfert 2 galaxies, having bolometric luminosities similar to the estimated bolometric luminosities of the obscured AGN.

The interaction between massive stars and the interstellar and intergalactic media: Outflows in cold, warm and coronal phases leave their imprints on the UV interstellar lines. Outflows of a few hundred km s^?1 are ubiquitous phenomena in starbursts. These metal-rich outflows and the ionizing radiation can travel to the halo of galaxies and reach the intergalactic medium.

The contribution of starbursts to the reionization of the universe: In the local universe, the fraction of ionizing photons that escape from galaxies and reach the intergalactic medium is of a few percent. However, in high-z star-forming galaxies, the results are more controversial.

Despite the very significant progress over the past two decades in our understanding of the starburst phenomenon through the study of the physical processes revealed at satellite UV wavelengths, there are important problems that still need to be solved. High-spatial resolution UV observations of nearby starbursts are crucial to further progress in understanding the violent star formation processes in galaxies, the interaction between the stellar clusters and the interstellar medium, and the variation of the IMF. High-spatial resolution spectra are also needed to isolate the light from the center to the disk in UV luminous galaxies at z = 0.1–0.3 found by GALEX. Thus, a new UV mission furnished with an intermediate spectral resolution long-slit spectrograph with high spatial resolution and high UV sensitivity is required to further progress in the study of starburst galaxies and their impact on the evolution of galaxies.