Search Publications
Background reduction for quiet time particle fluxes aboard the Solar and Heliospheric Observatory
Valtonen, E.; Torsti, J.; Kunow, H. +2 more
Two versions of a method are presented to determine the background of energetic particle telescopes during low-flux periods at low energies. Traditional procedures first evaluate pulse heights of particle sensors working in coincidence then select certain areas of the ΔE/Δx versus E plane, where E is energy, and finally, accept all events falling …
Evidence for prolonged main sequence stellar evolution of F stars in close binaries
Suchkov, A. A.
Binary F stars exhibit large brightness anomaly, which is defined here as the difference between the absolute magnitude from the \mboxuvby photometry and the actual absolute magnitude of the star. We have found that the anomaly inversely correlates with the binary components separation. There is evidence that the correlation reflects actual popula…
The late-time expansion of the ejecta of SN 1987A
Jakobsen, P.; Jansen, R. A.
The evolution of the shape and size of the ejecta of SN 1987A is analyzed over a period of ~ 8 years based on HST images and spectra taken between 1278 and 4336 days after the supernova outburst. We combine both proprietary and archival HST data obtained with the FOC, WFPC2 and STIS. The low resolution near-UV prism FOC spectrum obtained at day 30…
Recurrent Depressions of Galactic Cosmic Rays in CIRs: 22-Year Cycle
Jokipii, J. R.; Kota, J.
Recurrent variations in the galactic cosmic-ray flux are produced by the interplay of diffusion and particle drifts. The enhanced scattering and consequent small diffusion in the compressed field of Corotating Interaction Regions (CIRs) causes recurrent cosmic-ray depressions at the passage of CIRs. Drift effects are primarily controlled by the st…
Two-colour photometric selection of high-redshift galaxies
Lacy, Mark; Stevens, Robin
In this paper we describe a set of models to predict the colours of galaxies over a wide range of redshifts. We present examples of output from the simulations, and discuss their application to the selection of galaxies at high redshifts, particularly through identification of the Lyman break. Additionally we consider the optimal choices of filter…
Modelling the H Lyman lines in evolved late-type stars
Sim, S. A.
The importance of partial redistribution (PRD) in the modelling of the Lyman α and Lyman β emission lines of hydrogen in stellar atmospheres is examined using simple atmospheric models of a range of late-type stars. These models represent the subgiant Procyon (F5 IV-V), and the two giants β Gem (K0 III) and α Tau (K5 III). These stars are selected…
Contribution to the search of binaries among Am stars. II. HD 81976 and HD 98880, double-lined spectroscopic binaries
Ginestet, N.; Prieur, J. -L.; Carquillat, J. -M.
We present the results of the observations of two Am stars of eighth magnitude, the double-lined spectroscopic binaries HD 81976 and HD 98880, carried out with the CORAVEL instrument at the Observatoire de Haute-Provence in order to determine their orbital elements. We found 1) for HD 81976: P = 5.655750 days, T = 2449785.941 HJD, omega = 341.4
Waves close to the crossover frequency in the Jovian middle magnetosphere
Dougherty, Michele K.; Petkaki, Panagiota
The presence of heavy ions in a plasma introduces additional characteristic frequencies one of which is a crossover frequency between each adjacent pair of gyrofrequencies of the ions present. The crossover frequency is controlled by the fractional ion charge densities. The phase speed of the L and R wave modes have the same phase velocity at this…
ROSAT/Chandra observations of a bright transient in M 81
Tennant, A. F.; Wu, K.; Swartz, D. A. +1 more
We present a 10-year X-ray light curve and the spectra of a peculiar X-ray transient in the spiral galaxy M 81. The source was below the detection limit of ROSAT PSPC before 1993, but it brightened substantially in 1993, with luminosities exceeding the Eddington limit of a 1.5-M_sun compact accretor. It then faded and was not firmly detected in th…
Planar Structuring of Magnetic Fields at Solar Minimum and Maximum
Balogh, André; Jones, Geraint H.
Planar magnetic structures are regions of the solar wind where the magnetic field is oriented parallel to a fixed plane for several hours or more. Discontinuities in the field direction may be encountered during these periods, their surfaces also being parallel to the plane containing the field. A survey of Ulysses magnetic field data returned dur…