- The PN.S instrument in operation on La Palma
(See Douglas et al, PASP 114, 1234, 2002
for details, and the current dispersion given here below)
has been taking data for several years.
These data consist of the slitless spectra of
a number of galaxy fields. The primary purpose is to detect
planetary nebulae gravitationaly bound to the galaxy in question,
and to measure the radial velocity of these.
At this time (February 2006) the
images of NGC821 and NGC3379 are the most advanced.
- During the process of stacking images to increase
the signal-to-noise we noticed that several images appeared which were
spatially extended and which therefore clearly were not due to
planetary nebulae at the distance of these galaxies (about 10 Mpc).
- We would like to know:
- what are these objects? - this can
hopefully be ascertained by determining their inherent shape,
brightness, and velocity structure. This is in principle possible
because we have in each case a pair of images in which the
dispersion directions are opposed.
- are the objects detected in any other
catalogues?
- are there objects in other catalogues which
we should have detected but did not?
- allowing for systematic effects, notably the
bright foreground galaxy, are the objects seen
in the same numbers as in other fields, and
with the same luminosity function - if not, can
one determine an extinction coefficient
- which objects might have been mistaken for
planetary nebulae and would these have been
recognised with an H-alpha camera? (such
a camera is currently being constructed)
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