NGC 2640--This galaxy displays several interesting features in our PC image
(not all of which are apparent in Fig. 1). The most striking feature is the
prominent oval dust ring (semimajor axis ~1.8" or ~120 pc) surrounding what
appears to be a ring of enhanced surface brightness. A steep-pitch-angle dust
lane joins the dust ring near its major axis, and there is evidence of a
similar but less prominent lane joining at the other end. The overall
morphology is similar to the dust lanes and circumnuclear rings found in
intermediate-stage barred spirals (i.e., types SBab and SBb). There is an
abrupt turn in the alignment of the isophotes outside the dust oval; the
alignment become roughly perpendicular to the oval, revealing the presence of
a broad bar or oval distortion. Beyond about 3.5" the isophotes again reverse
their orientation, and tightly wrapped spiral arms of low contrast are
visible. These arms can be clearly seen only on the N half of the disk.
Interestingly, the steep dust lane can be traced across the tightly wound arms
out to at least 11" from the center. The steep dust lanes, dust oval and
enhanced ring (without prominent knots) point to a past episode of mass
transport, which may be continuing but at a rate too small to support vigorous
star formation in the nuclear ring. The center of this galaxy is highly
concentrated and its appearance is suggestive of a weak unresolved nucleus.
The presence of large-scale tightly wound spiral structure argues that this
galaxy should be classified as (very early) Sa.
Overexposed elongated nucleus, very faint lens; many stars superposed.