THE BRIGHTEST STARS IN NEARBY GALAXIES .9. COMPARISON OF GROUND-BASEDAND HST PHOTOMETRY OF THE BRIGHTEST STARS IN IC-4182

The distance to the Sdm dwarf galaxy IC 4182 is known from the measure ments of its Cepheids made with the prerepair HST by Saha et al. [ApJ, 425, 14 (1994)]. IC 4182 is the parent galaxy of the type Ia supernov a 1937C. Because of this it is important for calibrating the SNe Ia pr ime distance indicator as well as other secondary indicators. We compa re HST photometry for the brightest stars in IC 4182 with two independ ent sets of Palomar ground-based data, one using the Argelander step-s cale method tied to a photoelectric sequence; the other done with a CC D camera. Finding charts are given for all the stars that were measure d. The three purposes of the study are (1) to test the photometric zer o points used for the HST Cepheid measurements, (2) to obtain the magn itudes of the brightest blue and red stars in IC 4182 and to compare t hem with similar data in other galaxies that have Cepheid distances, a nd (3) to assess the effect of crowding on the brightest star problem by comparing the HST and the ground-based data where the angular resol utions differ by a factor of 10. For stars brighter than V=22, the V b and photometric zero points for the HST and the Palomar CCD data agree to within 0.05+/-0.03 mag, with an rms scatter of 0.16 mag. The I ban d zero points agree to within 0.02+/-0.04 mag, with an rms scatter of 0.14 mag. These confirm the magnitude zero points used in the HST Ceph eid photometry in IC 4182. The mean apparent magnitudes of the three b rightest blue stars are [B-3] = 20.34, [V-3] = 20.11, [R(3)] = 20.18, and [I-3] = 20.12. The respective absolute magnitudes, using the Cephe id modulus of m - M = 28.36, are -8.02, -8.25, -8.18, and -8.24. The c orresponding data for the brightest red stars are [B-3] = 22.36, [V-3] = 20.76, [R(3)] = 19.92, and [I-3] = 18.91. The absolute magnitudes a re -6.00, -7.60, -8.44, and -9.42. Problems of membership of the candi date stars are discussed. The absolute magnitudes in B and V fit well with similar data for the brightest stars in other galaxies, increasin g confidence in such stars as secondary distance indicators. (C) 1996 American Astronomical Society.