Aug 4/5, 1980
103aO + GG385
NGC 7424 is of very large angular diameter
(D_25_ = 7.6') and clearly is nearby, judging from
the high degree of resolution of the arms into HII
regions and individual stars. The largest of the
many HII-region candidates have angular
diameters (halo) of about 2". The individual stars
that can be guessed not to be HII regions start to
resolve at about B = 22. The stars and the HII
regions have yet (1991) to be identified by standard
The redshift is v_o = 925 km/s.
Although the H II regions in NGC 7424 follow the curves of the spiral
arms, their spatial distribution is almost stochastic, preferring to
cluster together in some areas and not in others. Even the "interarm"
regions are not entirely devoid of star formation. Such patterns are not
uncommon in spirals later than type Sc. Only one of the inner arms is
joined directly to the elongated nucleus/bar by H II regions. Emission-
line ratios for 5 of these H II regions plus the nucleus have been
measured by Brand, Coulson, & Zealey (1981), from which there is clear
evidence for an abundance gradient in NGC 7424.
Very bright bar, (r'): 2.2 x 1.5, very patchy knotty arms.
Large angular diameter, but faint-surface-brightness disk and arms.
Many HII regions that are good candidates
for resolution at the 2 arcsec level.
Description and Classification:
P.A.S.P., 77, 287, 1965.
P.A.S.P., 79, 152, 1967.
M.N.R.A.S., 131, 351, 1966.
Atlas Gal. Australis, 1968.
Small, bright, elongated, diffuse nucleus: 0.2 arcmin x 0.12 arcmin in a short
diffuse bar: 0.6 arcmin x 0.3 arcmin. Pseudo (r): 1.2 arcmin x - . 2 main,
partially resolved, filamentary arms with many branches. Similar to M 101.
Low surface brightness.
Lund 7 and Lund 10 dimensions are for the bright part only.