De Vaucouleurs Atlas Type: SA(rs)bc
Telescope: SDSS 2.5-m
North right , East up
Field Dimensions: 9.1 x 6.9 arcminutes
RC3 Type: SA(r:)bc
RSA Type: Sb(r)I
Surface Brightness Range Displayed: 17.5-25.5 mag per square arcsec
Absolute Blue Magnitude: -20.7
Elmegreen Spiral Arm Class: AC 9
De Vaucouleurs Atlas Description:
The inner ring refers to a feature about 25'' in diameter. Most interesting is that inside this feature is a strong one-armed spiral. The galaxy has a two-zone structure with a tight inner spiral and a complex, open outer spiral.
Verdes-Montenegro, Bosma, and Athanassoula (2002) also note the inner one-armed spiral and suggest that NGC 3642 has recently captured a gas-rich dwarf companion. They also suggest that the inner one-armed spiral could drive nuclear accretion.