Search Publications

An XMM-Newton observation of the very young open cluster NGC 6383

Gosset, E.; Rauw, G.; De Becker, M. +2 more

We report the detection of a number of X-ray sources associated with the very young open cluster NGC 6383. About two thirds of these objects are correlated with a rather faint optical source and all but one have at least one infrared counterpart within a correlation radius of 8 arcsec. Although NGC 6383 is not associated with a prominent star form…

An intense and broad Fe K_alpha line observed in the X-ray luminous quasar Q 0056-363 with XMM-Newton

Porquet, D.; Reeves, J. N.

We present an XMM-Newton observation of the radio-quiet quasar Q0056-363 (z=0.162). This is the first time that this quasar is observed in the hard X-ray range (above 2 keV). We find that Q0056-363 is a powerful X-ray quasar, with a 0.3-12 keV unabsorbed luminosity of about 1.2 x 10⁴⁵ erg s^-1 with the large…

XMM-Newton observation of PG 0844+349

Branduardi-Raymont, G.; Brinkmann, W.; Grupe, D. +1 more

In a ~ 20 ksec XMM-Newton observation the X-ray transient radio-quiet quasar PG 0844+349 was found in a historically high state compared to previous X-ray observations. The quasar showed a featureless spectrum with a strong soft excess over the extrapolation of a hard power law. Comptonization models or a broken power law with Gamma_soft…

Is Praesepe really different from the coeval Hyades cluster? The XMM-Newton view

Pallavicini, R.; Franciosini, E.; Randich, S.

The Praesepe open cluster represents a puzzle since it has about the same age as the Hyades, and only slightly different metallicity, yet previous ROSAT observations resulted in a detection rate of cluster sources significantly lower than for the Hyades. We present a new 50 ksec observation of Praesepe performed with the EPIC instrument on board X…

Cosmic rays tracks on the PICsIT detector

Bird, A. J.; Segreto, A.; Bazzano, A. +3 more

Since the first in orbit activation of the PICsIT detector, frequent spikes have been noticed in its count rate. Tracks in the detector images, corresponding to the spikes, indicate that these events are generated by interaction of cosmic rays with the detector plane.

Since these events constitute a significant fraction of the instrument back…

Explosive events and transition region blinkers: Time variability of non-Gaussian quiet Sun EUV spectra

Peter, H.; Brković, A.

The transition region (TR) from the chromosphere to the corona of the Sun and solar type stars is a very dynamic regime. On the Sun at least two major observational classes of transients can be seen: explosive events and blinkers. Besides these transients there is also a more steady spectral component in transition region lines that accounts for t…

On the evolutionary status of chemically peculiar stars of the upper main sequence

Paunzen, E.; Maitzen, H. M.; Pöhnl, H.

We present further evidence that the magnetic chemically peculiar stars (CP2) of the upper main sequence already occur at very early stages of the stellar evolution, significantly before they reach 30% of their life-time on the main sequence. This result is especially important for models dealing with dynamo theories, angular momentum loss during …

The 3-D ionization structure of NGC 6818: A Planetary Nebula threatened by recombination

Sabbadin, F.; Turatto, M.; Cappellaro, E. +2 more

Long-slit NTT+EMMI echellograms of NGC 6818 (the Little Gem) at nine equally spaced position angles, reduced according to the 3-D methodology introduced by Sabbadin et al. (\cite{Sabbadin00}a,b), allowed us to derive: the expansion law, the diagnostics and ionic radial profiles, the distance and the central star parameters, the nebular photo-ioniz…

Spatial and temporal fluctuations in sunspots derived from MDI data

Solanki, S. K.; Rüedi, I.

The penumbra radiates an energy flux that is 0.75-0.8 times the photospheric value. One mechanism proposed to bring this flux to the surface is interchange convection according to which hot flux tubes rise to the surface, lie horizontally there while they cool and finally sink down again. We search for possible signatures of such a process using t…

Response of the groove in heliospheric Lyman-alpha glow to latitude-dependent ionization rate

Bzowski, M.

I study the model response of the latitudinal profile of the heliospheric Lyman-alpha glow to various profiles of the ionization rate. The two profiles are characterized by their range separately in the north and south hemisphere, and by the contrast between the equator values and north and south pole values. These parameters define a mesh of the …