Search Publications

Noise reduction in helioseismic power spectra\ by non-orthogonal wavelets

Solanki, S. K.; Kosovichev, A. G.; Régulo, C. +1 more

We present a method to reduce noise in helioseismic power spectra using a non-orthogonal wavelet transform based on quadratic spline functions. The quality of our method is tested by applying it to artificially generated time-series approximating solar p-modes. The mode frequencies and line widths obtained from least-squares fits to the smoothed s…

Comparison of ≳40 keV Electron Events at High and Low Heliolatitudes: Ulysses/HI-SCALE and ACE/EPAM

Lario, D.; Roelof, E. C.; Ho, G. C. +2 more

We have performed a joint survey of anisotropic ≳40 keV electron events from August 1997 to September 2000 using the matched detectors on the Ulysses (ULS)/HI-SCALE and the ACE/EPAM instruments. A computer algorithm selected events with strong, statistically significant pitch-angle anisotropies. Electron pitch-angle distributions at ACE (∼1 AU) ar…

Analysis of IUE Spectra for the Star V1016 Ori

Vitrichenko, É. A.

Survey of MeV proton anisotropies measured by Ulysses

Balogh, André; Dalla, Silvia

The Anisotropy Telescopes (ATs) instrument, part of the COSPIN experiment on board Ulysses, measures fluxes and anisotropies of protons in the MeV range. We survey data from this instrument throughout the Ulysses mission, with particular emphasis on solar maximum, when large particle intensities were measured. The only significant fluxes detected …

Time-dependent 3-D modelling of the heliospheric propagation of few-MeV electrons

Fichtner, H.; Ferreira, S. E. S.; Potgieter, M. S. +2 more

With a recently developed steady-state model of the propagation of Jovian and galactic electrons in the inner three-dimensional heliosphere we were able to demonstrate both the necessity and value of such modelling for (i) the determination of the diffusion tensor of energetic particles, (ii) an observational discrimination between Jovian and inte…

Coronal Heating and Solar Wind Acceleration: Future Work on Observations

Peter, Hardi

The space-based observatories SOHO and TRACE have shown some very interesting results on the structure and dynamics of the Sun and its atmosphere, e.g., the extremely high ion temperatures or the enormous variability in the corona. But one question is still open to debate: how to use these data to distinguish between different types of physical he…

What can HST-GHRS Fe II observations of α Orionis (M2 Iab) tell us about short-period heating?

Cuntz, M.; Harper, G. M.; Bennett, P. D.

Cuntz (\cite{Cuntz97}) suggested that apparent velocity shifts in Fe II emission lines observed in Betelgeuse (alpha Orionis: M2 Iab) indicate that non-magnetic wave modes are relevant for the heating and dynamics of alpha Ori's chromosphere. This claim was based on the similarity of computed stochastic velocities in 1-D short-period acoustic wave…

Measurements of Rotational Frequency Splitting of Low Angular Degree Modes

Toutain, Thierry

The rotational splitting of low-degree p modes is still a controversial issue. There are small but nevertheless real discrepancies between the different measurements of splittings obtained with the existing helioseismology experiments from ground (BISON, IRIS, GONG, LOWL) or from space (VIRGO, GOLF, MDI). I review the current status of rotational …

Private life of an integrating sphere: the radiant homogeneity of the Descent Imager -Spectral Radiometer calibration sphere

Rizk, Bashar

Perturbations to an integrating sphere's radiant uniformity by a protruding optical system are mapped. A sphere provides the Descent Imager-Spectral Radiometer sensor head (DISR SH), a practical platform for many of its subsystems' calibrations, but the resulting nonuniformity threatens the goal of accurate radiometry. An apparatus with a nearly i…

Intensities of galactic cosmic ray nuclei from the ecliptic to the south solar polar regions near solar maximum: observations from the ULYSSES COSPIN high energy telescope

Heber, B.; McKibben, R. B.; Zhang, M. +2 more

Ulysses reached its maximum south heliographic latitude of 80.2° S in late November 2000, near the maximum in the solar activity cycle and is now embarked on a fast latitude scan that will bring it to a perihelion at 1.34 AU near the solar equator by mid-May 2001. Throughout the period of increasing solar activity since Ulysses left the ecliptic i…