We present narrow-band observations of the H \alpha emission in a sample of 31 satellite orbiting isolated giant spiral galaxies .
The sample studied spans the range -19 < M _ { B } < -15 mag .
The H \alpha emission was detected in all the spiral and irregular objects with fluxes in the range 1.15 - 49.80 \times 10 ^ { -14 } erg cm ^ { -2 } s ^ { -1 } .
The average and maximum values for the current star formation rates are 0.68 and 3.66 M _ { \sun } yr ^ { -1 } respectively .
Maps of the spatial distribution of ionized gas are presented .
The star-forming regions show a rich structure in which frequently discrete complexes are imposed over more diffuse structures .
In general , the current star formation rates are smaller that the mean values in the past obtained from the current stellar content ; this probably indicates a declining rhythm with time in the generation of new stars .
However , the reserve of gas is enough to continue fueling the current levels of star formation activity for at least another Hubble time .
Four of the objects ( NGC 2718b , NGC 4541e , NGC 5965a _ { 1 } and NGC 5965a _ { 2 } ) with higher current star formation rates show clear signs of interaction with close companions of comparable brightness at projected distances of 25 , 20 and 2 kpc respectively .
The only two galaxies in our sample that do not show star formation activity are members of these interacting systems , and it is unclear if this is a consequence of intrinsic properties ( both are Hubble early types ) or if it is related with possible disruption of the external parts due to the interaction .
In the case of the pair NGC 2718a-b there are indications of gas transport between both galaxies .