Search Publications
X-ray sources in globular clusters
Webb, N. A.; Barret, D.; Gendre, B.
We present XMM-Newton observations of 4 globular clusters (GCs): M 22 (NGC 6656); omega Centauri (NGC 5139) M 13 (NGC 6205); and NGC 6366. We provide evidence for close binaries in the centre of GCs, including an accreting neutron star and cataclysmic variables. We present results of a colour-colour study of the sources in the FOV and we make some…
Does the ion cyclotron exist in the inner corona?
Raouafi, N. -E.
The present work is about the interpretation of the linear polarization of the O {vi} D_2 (lambda1032 ) coronal line observed by SUMER/SoHO. We take into account the effect of the Doppler redistribution due to the scattering ions motion. We consider the cases of isotropic and anisotropic velocity field distributions. The latter can be interpreted …
Decay of sunspots
Martínez Pillet, V.
The photometric decay of sunspots is studied in some detail. Aspects related to leader vs. follower sunspot decay are presented and our current understanding of the physical mechanisms involved critically reviewed. The intrinsic instability of follower spots to form a stable sunspot cannot be understood in terms of the fluting stability as propose…
Subsurface structure of sunspots
Kosovichev, A. G.
The subsurface structure of sunspots is probed by measuring travel-time delays of acoustic waves propagating beneath the spots, and using a helioseismic inversion method to infer the internal sound-speed perturbations and mass flows. The initial results obtained from the MDI instrument on SOHO reveal under sunspots zones of the relatively low soun…
Solar irradiance variability and climate
Fröhlich, C.; Lean, J.
Since November 1978 a complete set of total solar irradiance (TSI) measurements from space is available, yielding a time series of more than 23 years. From measurements made by different space-based radiometers (HF on NIMBUS 7, ACRIM I on SMM, ACRIM II on UARS and VIRGO on SOHO) a composite record of TSI is compiled with an overall precision of or…
Time series photometric spot modelling V. Phase coherence of spots on UZ Librae
Strassmeier, K. G.; Granzer, T.; Oláh, K.
We present spot models for nine years of continuous VI_C photometry of UZ Lib from 1993-2001. The relatively stable double-humped light curve shape suggests extreme phase coherence. From the spot-modelling analysis, we found that the major spots or spot groups are always located on the hemisphere facing the secondary star and exactly in the opposi…
New radio instrumentation for the study of sunspots and starspots
White, S. M.
Much of the radio emission from the Sun and similar stars depends directly on magnetic fields for its origin. For this reason, radio emission contains important diagnostic information on solar and stellar magnetic fields. This paper reviews radio measurements of coronal magnetic fields and discusses new radio instrumentation that will exploit this…
Radial velocities of population II binary stars. I.
Bartkevicius, A.; Sperauskas, J.
Radial velocities for 114 Hipparcos stars, mostly high transverse velocity binaries without previous radial velocity measurements, are published. Measurements are made with the CORAVEL-type radial velocity spectrometer. The accuracy of measurements is better than 1 km/s. Two stars, BD +30 deg 2129A and HD 117466AB are found to be radial velocity v…
On stellar encounters and their effect on cometary orbits in the Oort cloud
Grothues, H. -G.; Serafin, R. A.
We systematically investigate the encounters between the Sun and neighbouring stars and their effects on cometary orbits in the Oort cloud, including the intrinsic one with the star Gl 710 (HIP 89 825), with some implications to stellar and cometary dynamics. Our approach is principally based on the combination of a Keplerian-rectilinear model of …
The galactic motion field of K0-5 giants from Hipparcos data
Schwan, H.; Brosche, P.; Schwarz, O.
We have investigated the motions of all K0-5 stars which have a proper motion in the Hipparcos catalogue and a known luminosity class III (due to the incompleteness of the ongoing classification, the distribution of these stars at the celestial sphere is rather uneven). We have used the apparent magnitudes and colours together with adopted means a…