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A. Pasquali (ESO/ST-ECF), G. De Marchi (ESA/STScI), M.S. Brigas (ESO/ST-ECF)
The NICMOS NIC3 camera on board HST observed serendipitous stellar fields in several Galactic globular clusters during the parallel campaign. In particular, deep exposures were taken in the J and H bands of NGC 288 and NGC 7078, which allowed us to derive the mass function in the cluster outskirts. Observations of a field located 5'.4 SE of the centre of NGC 288 and reaching limiting magnitudes J=25 and H=24 have allowed us to trace, for the first time, the luminosity function of NGC 288 over the range 3 < MH < 9 and peaking at MH = 6.8. We have used this information to constrain the cluster mass function which is best fitted by a log-normal distribution with characteristic mass of 0.42 Mo. This is fully consistent with the recent analysis of the luminosity functions of all globular clusters observed so far with HST showing a mass function at the half-light radius that appears ``undistorted'' by evaporation or tidal interactions with the Galaxy. This scenario is further confirmed by the data collected with NIC3 in three fields located 7' NE of the centre of NGC 7078, which reveal a luminosity function extending in the range 2 < MH < 9 with a peak at MH = 6.89. The corresponding mass function is best fitted with a log-normal distribution with characteristic mass of 0.30 Mo. When compared with WFPC2 data obtained 4'.6 NW of the cluster centre, the mass distribution at 7' indicates that there are no radial variations in the mass function of NGC 7078 outside the central ~ 20'' radius, where mass segregation is dominant. These results strengthen the recently proposed hypothesis that the present mass function observed at the cluster half-light radius reflects very closely the IMF, which might be generally represented by a log-normal distribution peaked at ~ 0.3 Mo.