The LOI (Luminosity Oscillations Imager) is a low resolution solar photometer built at the SSD of ESA. It is one of the instruments in the VIRGO experiment on board the SOHO satellite. In May 1994, the Qualification Model of the LOI was installed at the Observatorio del Teide (Tenerife) and since then it has been working continuously (LOI-T). The

High quality observations of the low degree p-modes exist for almost two complete solar cycles using the solar spectrophotometer Mark-I, located and operating at the Observatorio del Teide (Tenerife, Spain). In this work, the observations available have been re-analyzed over a much wider time interval than before. We analyze the time variation of

We have analyzed the differences in the oscillation eigenfrequencies measured over four years of GONG, SOI/MDI and LOWL observations (1996 to 1999). We have inverted these data to look for signatures of the solar activity cycle on the stratification. A one-dimensional structure inversion code was used to study temporal variations of the radial

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Accurate determination of the rotation rate in the inner radiative zone (0.2 r/Rsolar 0.5) of the sun from helioseismic observations requires rotational frequency splittings of exceptional quality. Indeed, only low degree modes are sensitive to the dynamics of the deep interior. Low and intermediate degree splittings have been estimated from a

The stratification of acoustic oscillations through the solar photosphere in Lagrangian (comoving) coordinates has been evaluated from a quasi-NLTE inversion of the radiative transfer equation (RTE) applied to a temporal sequence of K I 7699 Å line spectra. The stratifications of amplitude and phase of the temperature and line-of-sight (LOS)