The B3-Vla CSS sample. III: Evn & Merlin images at 18 cm

EVN and MERLIN observations at 18 cm are presented for 18 Compact Steep--spectrum radio Sources (CSSs) from the B3-VLA CSS sample. These sources were marginally resolved in previous VLA A-configuration observations at 4.9 and 8.4 GHz or had peculiar morphologies, two of them looking like core-jets. The MERLIN images basically confirm the VLA structures at 8.4 GHz while the EVN and/or the combined images reveal several additional details.Comment: 17 pages, many low resoltion figures, A&A accepted. A higher resolution gzipped postscript file can be found at http://www.ira.cnr.it/~ddallaca/h3443.ps.g

Synchrotron Spectra and Ages of Compact Steep Spectrum Radio Sources

The high-frequency integrated spectra of Compact Steep Spectrum (CSS) sources show breaks with a moderate spectral steepening well fitted by continuous injection synchrotron spectra. In lobe-dominated CSS sources the radiative ages deduced by the synchrotron theory are in the range of up to 0.1 Myears, if equipartition magnetic fields are assumed. These radiative ages are well correlated with the source size indicating that the CSS sources are young. In order to maintain the frustration scenario, in which the sources' lifetimes are about 10 Myears, their equipartition magnetic field would be systematically decreased by a factor of more than 20. To complete the sample used in this work, we conducted observations at 230 GHz with the IRAM 30-m telescope of those sources which did not have such high-frequency observations up to now.Comment: 10 pages, 6 figures, 2 tables, accepted for publication in Astron. & Astrophys.; typos corrected; gzipped postscript version also available at: http://multivac.jb.man.ac.uk:8000/ceres/papers/papers.html http://gladia.astro.rug.nl:8000/ceres/papers/papers.htm

Parsec-scale morphology and spectral index distribution in faint high frequency peakers

We investigate the parsec-scale structure of 17 high frequency peaking radio sources from the faint HFP sample. VLBA observations were carried out at two adjacent frequencies, 8.4 and 15.3 GHz, both in the optically-thin part of the spectrum, to obtain the spectral index information. We found that 64% of the sources are resolved into subcomponents, while 36% are unresolved even at the highest frequency. Among the resolved sources, 7 have a morphology and a spectral index distribution typical of young radio sources, while in other 4 sources, all optically associated with quasars, the radio properties resemble those of the blazar population. The equipartition magnetic field of the single components are a few tens milliGauss, similar to the values found in the hotspots of young sources with larger sizes. Such high magnetic fields cause severe radiative losses, precluding the formation of extended lobe structures emitting at centimeter wavelengths. The magnetic fields derived in the various components of individual source are usually very different, indicating a non self-similar source evolution, at least during the very first stages of the source growth.Comment: 14 pages, 5 figures, accepted for publication in MNRA

Spectral variability in faint high frequency peakers

We present the analysis of simultaneous multi-frequency Very Large Array (VLA) observations of 57 out of 61 sources from the ``faint'' high frequency peaker (HFP) sample carried out in various epochs. Sloan Digital Sky Survey (SDSS) data have been used to identify the optical counterpart of each radio source. From the analysis of the multi-epoch spectra we find that 24 sources do not show evidence of spectral variability, while 12 objects do not possess a peaked spectrum anymore at least in one of the observing epochs. Among the remaining 21 sources showing some degree of variability, we find that in 8 objects the spectral properties change consistently with the expectation for a radio source undergoing adiabatic expansion. The comparison between the variability and the optical identification suggests that the majority of radio sources hosted in galaxies likely represent the young radio source population, whereas the majority of those associated with quasars are part of a different population similar to flat-spectrum objects, which possess peaked spectra during short intervals of their life, as found in other samples of high-frequency peaking objects. The analysis of the optical images from the SDSS points out the presence of companions around 6 HFP hosted in galaxies, suggesting that young radio sources resides in groups.Comment: 16 pages, 5 figures; accepted for publication in MNRA

Valutazione delle competenze e lifelong learning: la creazione partecipata di rubriche per l\u2019autovalutazione della figura dell\u2019operatore di rete.

Il tema della valutazione delle competenze, legato a quello del lifelong learning, \ue8 in forte espansione, soprattutto grazie alla spinta dell\u2019Unione Europea. L\u2019esigenza di fare valutazione anche nei servizi alla persona si \ue8 fatta pi\uf9 premente con l\u2019arrivo della crisi, la contrazione di risorse e la crescita della complessit\ue0 e dell\u2019incertezza sociale. La ricerca qui presentata descrive e documenta un processo partecipato di mappatura delle competenze della figura dell\u2019operatore di rete in un servizio socio-sanitario, finalizzata alla creazione del profilo professionale di tale figura e d i u n o s t r ume n t o ( r u b r i c a ) p e r l\u2019autovalutazione delle competenze da adottare nei percorsi di riflessione e di crescita professionale

Coulomb interaction effects on nonlinear optical response in C60, C70, and higher fullerenes

Nonlinear optical properties in the fullerene C$_{60}$ and the extracted higher fullerenes -- C$_{70}$, C$_{76}$, C$_{78}$, and C$_{84}$ -- are theoretically investigated by using the exciton formalism and the sum-over-states method. We find that off-resonant third order susceptibilities of higher fullerenes are a few times larger than those of C$_{60}$. The magnitude of nonlinearity increases as the optical gap decreases in higher fullerenes. The nonlinearity is nearly proportional to the fourth power of the carbon number when the onsite Coulomb repulsion is $2t$ or $4t$, $t$ being the nearest neighbor hopping integral. This result, indicating important roles of Coulomb interactions, agrees with quantum chemical calculations of higher fullerenes.Comment: 8 pages; 3 figures; Figures should be requested to the author (E-mail: [email protected]

FIRST-based survey of Compact Steep Spectrum sources I. MERLIN images of arc-second scale objects

Compact Steep Spectrum (CSS) sources are powerful extragalactic radio sources with angular dimensions of the order of a few arcseconds or less. Such a compactness is apparently linked to the youth of these objects. The majority of CSSs investigated so far have been known since the early 1980s. This paper is the first in a series where we report the results of an observational campaign targeted on a completely new sample of CSSs which are significantly weaker than those investigated before. The ultimate goal of that campaign is to find out how ``weak'' CSSs compare to ``strong'', classical ones, especially with regard to the morphologies. Here we present an analysis of morphological and physical properties of five relatively large sources based on MERLIN observations at 1.6 and 5 GHz.Comment: 8 pages, 7 figures, A&A in pres

Low Power Compact Radio Galaxies at High Angular Resolution

We present sub-arcsecond resolution multi-frequency (8 and 22 GHz) VLA images of five low power compact (LPC) radio sources, and phase referenced VLBA images at 1.6 GHz of their nuclear regions. At the VLA resolution we resolve the structure and identify component positions and flux densities. The phase referenced VLBA data at 1.6 GHz reveals flat-spectrum, compact cores (down to a few milliJansky) in four of the five sources. The absolute astrometry provided by the phase referencing allows us to identify the center of activity on the VLA images. Moreover, these data reveal rich structures, including two-sided jets and secondary components. On the basis of the arcsecond scale structures and of the nuclear properties, we rule out the presence of strong relativistic effects in our LPCs, which must be intrinsically small (deprojected linear sizes <~ 10 kpc). Fits of continuous injection models reveal break frequencies in the GHz domain, and ages in the range 10^5-10^7 yrs. In LPCs, the outermost edge may be advancing more slowly than in more powerful sources or could even be stationary; some LPCs might also have ceased their activity. In general, the properties of LPCs can be related to a number of reasons, including, but not limited to: youth, frustration, low kinematic power jets, and short-lived activity in the radio.Comment: 15 pages, 9 .eps figures, accepted by A&