Search Publications
Components of the ultraviolet continuum in active galactic nuclei.
Paltani, S.; Walter, R.
The ultraviolet spectral slope of individual active galactic nuclei (AGN), measured using IUE observations, varies considerably with time. Neither accretion disks nor optically thin emission models can explain these variations. We propose here a method based on the variability properties of these objects to disentangle various components of consta…
ULYSSES COSPIN/LET: latitudinal gradients of anomalous cosmic ray O, N and Ne.
Klecker, B.; Bothmer, V.; Sanderson, T. R. +4 more
A key goal of the Ulysses mission is the measurement of the latitudinal gradient of the Anomalous Cosmic Ray (ACR) component. Earlier studies using data from the COSPIN/LET experiment on board Ulysses together with in-ecliptic data from the HILT instrument on SAMPEX have shown a small (~2% per degree) positive latitudinal gradient for anomalous ox…
Is 2RE J0357+283 the most coronally active star in the Galaxy?
Jeffries, R. D.; Burleigh, M. R.; Robb, R. M.
The late-type stellar counterpart to the EUV source 2RE J0357+283 is found to be an ultra-fast rotating K2V star, with a rotation period of 8.76 hrs and vsini of 141+/-5km/s. If this were the only source of the EUV emission, then it would be the most coronally active star known, by an order of magnitude, and requires a reappraisal of current ideas…
First results from a photometric infrared survey for Vega-like disks around nearby main-sequence stars.
Waters, L. B. F. M.; Kessler, M. F.; Siebenmorgen, R. +12 more
We have undertaken a survey for Vega-like disks around nearby main-sequence stars by making photometric measurements with ISOPHOT at four wavelengths between 25 and 180µm. Our goal is to establish how common Vega-like disks are, and how their presence depends on the fundamental properties of main-sequence stars (mass, age, rotation etc.). He…
Nuclear disks of gas and dust in Fanaroff-Riley type I radio host galaxies: 3C 402N and NGC 7052.
de Juan, L.; Colina, L.; Golombek, D.
A nuclear disk of gas and dust is detected in the host galaxy of the Fanaroff-Riley type I (FR-I) radio source 3C 402N, using pre-COSTAR HST/FOC images, and high spatial resolution ground-based broad-band and Hα+[NII] narrow-band images. The physical properties of the nuclear disk in the B2 2116+26 host galaxy (NGC 7052) are also presented. On ave…
Are the pulses of the Crab pulsar modulated?
Cadez, A.; Galicic, M.
We present the results of optical Crab pulsar observations which were designed to search for short-time variations in pulsar's light-curve. Hubble Space Telescope (High Speed Photometer) data and photometric data obtained at the Asiago 1.82m telescope using a specially designed stroboscopic chopper have been analysed and compared. We find a very w…
A new HST image of Cygnus A .
Sparks, W. B.; Macchetto, F.; Miley, G. K. +2 more
We present a new HST image of Cygnus A, taken in the V-band. This image includes both continuum and lines of [0III], and shows the major, northwestern and southeastern components, together with the weaker central component. Filamentary structure is present at this resolution of 0.045". This structure runs generally parallel to the radio jet and ma…
The high latitude pass of ULYSSES: energetic particle observations with EPAC.
Keppler, E.; Korth, A.; Fraenz, M. +4 more
We report on observations of energetic particles (EP) during the ascent of ULYSSES to the south pole, on the fast pass from south to north and in the first few months after the north polar pass. After it left the ecliptic plane the spacecraft moved periodically into a corotating (26 days period) fast solar wind stream and observed the accelerated …
On the spread of ages among the young stars in the LMC association NGC 1948.
Bomans, D. J.; de Boer, K. S.; Vallenari, A. +2 more
The ages of the young associations located at the border of the supergiant shell LMC4 are essential parameters to understand the formation and the evolution of that supergiant shell. We present spectra in the UV and the optical wavelength range of eleven stars in NGC 1948 in order to establish the location of the top of the main sequence more accu…
An ISOPHOT study of the disk of galaxy NGC 6946: 60µminfrared and radio continuum correlation.
Helou, G.; Malhotra, S.; Xu, C. +4 more
We use the ISOPHOT 60µmimage of Tuffs et al. (1996) to study the 60µmlight distribution and its correlation with radio continuum within the disk of spiral galaxy NGC 6946, and to resolve the long-standing IRAS controversy as to whether the infrared-to-radio continuum ratio, Q, decreases radially out in galaxy disks. Our main results ar…