SCIENTIFIC ABSTRACT:
It is well known that morphological peculiarities in galaxies like bars and
rings correlate with star formation activity and that the most favorable
wavelength region to observe them is the infrared.
ISOCAM is the instrument operating at the highest spatial resolution available
on ISO. It will be possible to resolve nuclear and circumnuclear regions,
where starbursts principally occur in barred spiral galaxies, or diffuse
components.
We propose a broad band mapping with ISOCAM to study the phenomenology of
infrared activity in barred spiral galaxies in order to investigate the
distribution of star formation within the galaxies.
The goal of this program is to study the distribution of warm dust inside
the HII regions and the distribution of PAHs, stressing the mechanisms of
destruction of small grains.
Correlations with optical (H alpha) and radio (HI, CO) maps will permit an
assessment of the relationship between star formation and global dynamics
of the systems.
A comparison sample of unbarred spiral galaxies, with both high and low FIR
luminosity, will be provided by the study of the Virgo cluster spirals
considered in the complementary proposal: "A coordinated study of galaxies
in the Virgo cluster".
OBSERVATION SUMMARY:
A sample of barred spiral galaxies was selected with the following criteria:
almost face-on;
within a distance of nearly 25 Mpc;
with absolute B magnitudes around -20.5;
with a FIR luminosity >= 5 E9 L(sun).
Each galaxy will be observed with 2 filters: LW2 (5.0-8.5 micron,
resolution = 2) and LW3 (12.0-18.0 micron, resolution = 3) and in two
optical configurations: 6 arcsec and 3 arcsec PFOV.
LW3 will allow to determine the "normal" warm dust emission, while the LW2
will trace the strongest very small grains or PAH emissions at 6.2 and
7.7micron. This filter strategy is identical  to the one used in the proposal
for mapping nearby normal galaxies.
From known examples (e.g. NGC 1097 (Osmer and Smith, Ap.J. 192, 279, 1974)
or NGC 1068 (Telesco and Decher, Ap.J. 334, 573, 1988)) the diameter of the
circumnuclear rings is between 1.5 to 2 kpc.
At a distance of 20 Mpc, this corresponds to  nearly 20 arcsec and, in the
configuration of PFOV=6 arcsec, corresponds to 3-4 pixels, and to 6-8 pixels
with PFOV=3 arcsec.
Observations with the 3 arcsec will be used to separate the nuclear emission
from the ring emission, if any; and the 6 arcsec will be used to measure the
relative contribution of star forming regions and the diffuse disk component.
The AOT used will be CAM01 with micro-scanning for both optical configurations,
but with different raster parameters. 
The estimated TDT depends on the galaxy dimensions and then on the raster
parameters used.
This time is comprehensive of stabilisation, repointing and slew times.
As far as the detectability of the faintest external regions is concerned,
the achieved S/N ratio depends on the background intensity.
We estimated the background level with the IRSKY facility (IPAC) for each
galaxy position and wavelength range; with this constraint, the limit flux
was evaluated as 3-6 microJy/arcsec2 with a S/N ratio between 2 and 3.