A three-wavelength sun-photometer was designed and built. The attenuation of direct solar light, at wavelengths of 0.38 micrometers , 0.50 micrometers and 1.00 micrometers were measured. Silicon photodiodes and interference filters of 10 nm FWHM were used. Aerosols were characterized by angstrom's turbidity formula in terms of coefficients (alpha)

A ring-diagram analysis technique has been applied to a region of the Sun of about 15 deg^2 area close to the disk center at dates chosen for several solar rotations in 1996: April 5, May 1, May 28, June 27, July 23, August 20, August 21, and September 18. The horizontal velocity flows inferred directly beneath the solar surface have thus been

From the inversion of a time series of high resolution slit spectrograms obtained from the quiet sun, the spatial and temporal distribution of the thermodynamical quantities and the vertical flow velocity is derived as a function of optical depth (logτ) and geometrical height (z). Spatial coherence and phase shift analyses between temperature and

Since the launch of SOHO, the Solar Heliospheric Orbital Observatory, the helioseismic observations are nearly uninterrupted. The GOLF instrument (A. Gabriel et al., 1997) measures the mean velocity integrated over the disk. The autocorrelation function of this velocity shows two main features: Firstly, the initial decrease of the peak amplitudes

Recent works (Steeghs & Casares 2002, Casares et al. 2003, Hynes et al. 2003) have demonstrated that Bowen flourescence is a very efficient tracer of the companion star in LMXBs. We present a numerical code to simulate time-delayed transfer functions in LMXBs, specific to the case of reprocessing in emission lines. The code is also able to obtain

At present, ten years after they were first discovered, ten accreting millisecond pulsars are known. I present a study of the aperiodic X-ray variability in three of these systems, which led to the discovery of simultaneous kHz quasi periodic oscillations in XTE J1807-294 and extremely strong broadband noise at unusually low variability frequencies