Search Publications

SHORT COMMUNICATION: Alternative representation of degradation corrections to space-based measurements of total solar irradiance

Bawagan, A. D. O.

Degradation corrections to solar irradiance measurements in space along with a postulated 'hyperbolic' fitting formula were recently reported (Fröhlich 2003 Metrologia 40 S60-5). A simpler, alternative formula based on broadband synchrotron exposure experiments on polymeric mixtures is presented. The alternative formula is shown to be simil…

UV spectroscopy with SOHO

Brekke, P.; Harra, L. K.

The UV spectroscopy from SOHO has provided new and exciting results from a wide range of phenomena observed on the Sun. Determination of plasma parameters such as velocity, density, temperatures, line widths and abundances have provided new physical insight into fundamental problems in solar physics. These include magnetic reconnection, quiet Sun …

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…

Classification of Metal-Deficient Dwarfs in the Vilnius Photometric System

Bartkevičius, A.; Bartašiūtė, S.; Lazauskaitė, R.

Methods used for the quantitative classification of metal-deficient stars in the Vilnius photometric system are reviewed. We present a new calibration of absolute magnitudes for dwarfs and subdwarfs, based on Hipparcos parallaxes. The new classification scheme is applied to a sample of Population II visual binaries.

XMM and CHANDRA High Resolution X-Ray Spectroscopy of Magnetic Cataclysmic Variables and Low Mass X-Ray Binaries

Haberl, F.; Burwitz, V.; Predehl, P. +3 more

UV Piscium and the Radiative Flux Scale

Vivekananda Rao, P.; Radhika, P.

Studies of eclipsing binaries with Hipparcos parallaxes are found to define a radiative flux relation for main sequence stars in the spectral range from B6 – F0which is about as well as to the stars derived from angular diameters. At lower temperatures the fluxes of the components fall below this curve which is caused due to the large intrinsic va…

Perpendicular Diffusion and Drift of Solar Energetic Particles in Heliospheric Magnetic Fields

McKibben, R. B.; Zhang, Ming; Jokipii, J. R.

We present evidence for large perpendicular diffusive flows of solar energetic particles. Using anisotropy measurements of 40-90 MeV protons from the July 14th, 2000 event obtained by HET on Ulysses, we find periods of first order anisotropy directed at significant angles to the local magnetic field, which can only be satisfactorily explained by p…

X-ray emission diagnostics from the M87 jet

Wilson, A. S.; Perlman, E. S.

We use Chandra, HST and VLA observations of M87 to investigate the physics of X-ray emission from AGN jets. We find that X-ray hotspots in the M87 jet occur primarily in regions with hard optical-to-X-ray spectra and lower than average polarization. Particle injection appears to be required both continuously in the jet sheath as well as locally at…

Kinematic Analysis of Near and Far Stars in the Hipparcos Catalog

Vityazev, V. V.; Drobit'ko, E. V.

The proper motions of stars in the main sequence and of luminosity class III giants are analyzed kinematically. A new method has been used for reliably separating all the parameters of the Ogorodnikov-Milne model based on representing the proper motions of the stars in coordinate systems whose poles lie on each of the three principal axes of the g…

UV and EUV observations of stellar coronal structure and activity

Brown, Alexander

Ultraviolet (HST, FUSE) and extreme-ultraviolet (EUVE) observations of stellar coronae and flare-related activity are reviewed, with particular attention being devoted to the coronas information that is obtainable in the ultraviolet but not from the X-ray region. The coronas temperature, density, and emission measure distributions of active stars …