Long-period and Mira variables are important stages in the late
 stellar evolution of low and intermediate mass stars. In fact, they
 are the main sources of galactic dust production and of a large
 variety of chemical species originating from their circumstellar
 shells. A reliable quantitative diagnostic and interpretation of
 these objects demands both, appropriate theoretical models and
 specific detailed observations, in particular in the infrared regime.
 We propose periodic fixed time ISOPHOT observations of long--period
 variables (LPVs) at different wavelengths in the mid-- and
 far--infrared range.
 These measurements will yield informations about the temporal
 variation of the physical conditions in different spatial regions of
 the circumstellar dust shells and will allow a comparison with
 detailed dynamical model calculations.
 It is the aim of this project to study the wavelength--dependence of
 certain structures appearing in already observed near--infrared
 lightcurves and in theoretical lightcurves as well.
 The data obtained with this investigation, combined with ground-based
 monitoring, will also allow an interpretation of the long--term
 behaviour of Miras and LPVs in different wavelength regimes.

 This proposal is an extension of our Central Program proposal
 (OBSID: ESEDLMAY, PROPID: VACDSLPV), where only two objects will
 be observed. However, as these observations are concerned with a very
 special and short interval of the lightcurves, it is possible that
 the interesting phases may not be met accurately. Therefore,
 observations of a larger sample of objects are needed to ensure,
 that at least some of the objects will be observed during the
 interesting phases and thus the scientific goal will be reached in full
 depth.