This paper reports on nearly 1200 photometric observations of twelve
oxygen-rich Long
Period Variables (LPV) through the five filters of the 
system. All these
pulsating variables are classified as Miras
(
days and 
mag following the definition
proposed by Kholopov et al. 1985).
Due to their long-term variations, the study of Miras requires a large
amount of observations collected at different epochs and for several years.
Photometry is a useful and easy tool to get such data. Most of the
previous programs have studied the Mira visible and colour light-curves with
UBV photometry only (see Celis 1986a or 1995 and references therein).
On the other hand, as
soon as it was possible to collect near-infrared photometric data,
cool red giants became among the most interesting targets.
Luminosity variations were studied, spectral types - infrared colour indices
and colour or period-luminosity relations were also derived
(see Eggen 1975b or Celis 1995).
Nevertheless very few complete UBVRI light-curves of Miras have been
published up to now. Most of the observations were
indeed collected for quite a short term.
Only Eggen (1975a) reported UBVRI observations for ten LPV similar to
the ones that are presented in the present paper.
He monitored these Miras during five years and
discussed the data in Eggen (1975b).
He pointed out among others that large variations of magnitudes and colours
occur between different cycles especially
near the maximum of luminosity.
This confirmed previous results obtained from UBV studies claiming
that the repeatability of the light variations
in different cycles is poor.
Reconstruction of light-curves from observations collected during different
cycles should thus be avoided and consecutive observations may instead be used
to study LPV variations.
Finally infrared light-curves of Miras (where these stars radiate
most of their energy) have been published more recently
by Le Bertre (1988, 1992 and
1993)
and by Feast and collaborators (see for instance
Whitelock et al. 1991
and references therein).
Table 1: List of observed Miras. 
is the number of observations
collected for each star (see text for a complete description of the table).
The star properties are taken fromKholopov et al. (1985)
except
(
) fromCrowe & Garrisson (1988), 
fromCelis (1986a), 
from
Jura & Kleinmann (1992) and 
from
Celis (1984)
The number of collected UBVRI light-curves of LPV is thus quite small
up to now. This is
certainly due to the difficulty to monitor these stars for several
years: the periods are long, the minima are often very faint and
a large amount of telescope time is needed.
Furthermore this class of stars is actually
not homogeneous and the rather small sample of Eggen has thus to be increased.
More recent studies have also shown
that several characteristics (spectral type, distance) of these stars can
be deduced from their UBVRI photometry (see Celis 1995).
Let us finally point out that such data are
strongly needed to constrain model atmospheres.
The aim of this monitoring program of LPV
was thus to collect a large amount of homogeneous
photometric data covering several successive cycles.
We planned to study (i) the
simultaneous variations of the light-curves
in the visible and near-infrared filters together with spectral type changes
for a complete cycle, and (ii) the differences from cycle-to-cycle.
This paper is organized as follows. In the next section, the selection
criteria of the targets, the observations and their reduction
are presented. The final data and the derived spectral types at all phases are
given together with the visible and colour light-curves.
We then discuss in Sect. 3 the main properties of the light-curves and
spectral type variations. We also determine there the distance of
these Miras and estimate the precision of the method used.
The paper is finally summarized in Sect. 4.