Search Publications
The comptonized X-ray source X 1724-308 in the globular cluster Terzan 2
Stella, L.; Parmar, A. N.; Guainazzi, M. +3 more
We report on the BeppoSAX observation of the X-ray source X 1724-308 in the globular cluster Terzan 2. The broadband spectrum can be described as the superposition of a power-law with photon spectral index Gamma =~ 1.6-1.9 and a thermal component with typical temperature kT ~ 1 keV. X 1724-308 is detected in the PDS up to 150 keV with a S/N ratio …
The blue-bump of 3C 273
Paltani, S.; Walter, R.; Courvoisier, T. J. -L.
We present optical and ultraviolet observations of 3C 273 covering the whole life of the IUE satellite. We analyze the variability properties of the light curves, and find that two variable components, written V_\nuAA\ and S_\nuBB\ respectively, must contribute to the S_\nuB\ emission in this object. The V_\nuAA\ component produces most of the var…
Spectral analysis of O(He)-type post-AGB stars
Rauch, T.; Dreizler, S.; Wolff, B.
We present an analysis of two recently discovered, very hot hydrogen-deficient post-AGB stars of spectral type O(He), namely HS 1522+6615 and HS 2209+8229, by means of state-of-the-art NLTE model atmospheres based on new optical, UV, and X-ray observations. In the spectra of HS 1522+6615 we discovered a variability of the \Ionw{O}{6}{5290} line co…
High-Frequency Peaks in the Power Spectrum of Solar Velocity Observations from the GOLF Experiment
García, R. A.; Pallé, P. L.; Turck-Chièze, S. +9 more
The power spectrum of more than 630 days of full-disk solar velocity data, provided by the GOLF spectrophotometer aboard the Solar and Heliospheric Observatory, has revealed the presence of modelike structure well beyond the acoustic cutoff frequency for the solar atmosphere (νac~5.4 mHz). Similar data produced by full-disk instruments …
Modeling of 3-D Corotating Cosmic-Ray Structures in the Heliosphere
Jokipii, J. R.; Kóta, J.
We present a brief review of the modeling of corotating 3-dimensional features in heliospheric cosmic rays. The model heliosphere incorporates a wavy current sheet and Corotating Interaction Regions (CIRs). We find that present models can qualitatively account for the observed extension of recurrent 26-day cosmic-ray variations to high heliospheri…
Nuclear stellar discs in early-type galaxies - I. HST and WHT observations
van den Bosch, Frank C.; van der Marel, Roeland P.; Jaffe, Walter
We present multi-colour (U, V and I) photometry obtained with the second Wide Field and Planetary Camera (WFPC2) on the Hubble Space Telescope (HST), and spectra taken with the William Herschel Telescope (WHT) and the HST Faint Object Spectrograph (FOS), for the early-type galaxies NGC 4342 and 4570. These galaxies are intermediate between ellipti…
ISOPHOT boosts dust masses in spiral galaxies
Siebenmorgen, R.; Chini, R.; Zota, V. +1 more
We report photometry with ISO between 60 and 200 -um of six galaxies. Three of them are active and the extension of their spectra beyond the IRAS bands up to 200 -um confirms our previous conception that most of the dust there is warm and has a fairly uniform temperature of phantom {0}im30K. In the other three galaxies which are inactive, we detec…
Type II radio emissions in the frequency range from 1-14 MHz associated with the April 7, 1997 solar event
St. Cyr, O. C.; Thompson, B. J.; Kaiser, M. L. +4 more
We present an analysis of radio emissions associated with the April 7, 1997 solar eruptive event. The event consisted of a filament disappearance, a complex two-phase coronal mass ejection (CME), and a C6.9, 2N flare. At the same time, intermittent type II radio emissions in the frequency range 1-10 MHz, corresponding to an altitude range of 2-15 …
The LMC distance modulus from HIPPARCOS RR Lyrae and classical Cepheid data
Luri, X.; Figueras, F.; Torra, J. +2 more
The LM method \cite{luri96}, designed to exploit the Hipparcos data to obtain luminosity calibrations, is applied to derive luminosity calibrations for RR Lyrae and classical Cepheids. From these calibrations the distance to the Large Magellanic Cloud (LMC) is estimated. The distance moduli provided by the two calibrations are in good agreement, g…
The fine structure of the Pleiades luminosity function and pre-main sequence evolution
Meusinger, H.; Piskunov, A. E.; Schilbach, E. +2 more
The luminosity function (LF) of the Pleiades cluster stars was constructed for the study of the LF fine structure related to pre-MS stellar evolution. Theoretical luminosity functions based on present-day pre-MS and MS stellar models were constructed and compared with observations. We tested both power- and log-normal laws describing the cluster s…