Some Proposed UIT Targets
Here we show some optical photographs of some of the designated
UIT Targets together with some brief explanation of the proposed
- M13 is a globular
cluster. The large field size of UIT is ideal for studies of
globular clusters. Although globular clusters are quite old,
they can still produce hot stars through post Red Giant
evolution and arrival onto the horizontal branch. Very metal
poor clusters are conducive for the formation of very hot
horizontal branch stars which radiate most of that energy in the
UV part of the spectrum.
- The Large Magellanic Cloud
is very large, about 6x6 square degrees in the sky. Its
most active region of star formation, the 30 Doradus region, is
about 1/2x1/2 square degree and hence comfortable fits into one
UIT field. This image is an H-alpha image of the entire LMC.
The hydrogen is ionized by O-stars and hence each region of
emission should have several 10's to hundreds of 0-stars. Many
of these sites are good targets for UIT.
M31 is the nearest
large spiral galaxy to us. Some of its properties are described
M31 is not very actively star forming and seems to have a general
dearth of hot, young massive stars. This can be verified by UIT
observations. In addition, the two main companions (visible in the
image and the movie), M31 and NGC 205 are also UIT targets. These
are small dwarf galaxies and NGC 205 is a bit unusual because it
still has retained some gas for star formation despite its low mass.
M33 is an actively star forming spiral galaxy in the local
group. Its overall size is slightly larger than the UIT field but
most of the galaxy can be imaged in one exposure. There are many
H II regions in M33 and, like
the LMC, UIT studies of M33 will provide an improved census of its
hot star content.
is the most actively star forming nearby galaxy. It has very high
surface brightness and has very large H II regions, particularly
at large distances from its center. Previous UV imaging shows that
the UV size of M101 is actually larger than its optical size,
indicating that low level star formation is occurring in the extreme
outer regions of M101.
Low Surface Brightness galaxies are objects with very low
contrast with respect to the night sky background. Many of these
galaxies have not been catalogued or discovered until very recently.
A recent analysis , in fact, suggests that most of the disk galaxies
in the nearby universe are in this population and thus have been missed
by most previous surveys. The three specific objectives of the UIT
campaign on Low Surface Brightness galaxy imaging are:
- to determine the efficiency of detecting/discovering LSB galaxies in
the near-UV in comparison with ground-based optical observations.
- to extend the wavelength coverage over which colors are determined and
see if there is any near-UV bright component that may help to explain the observ
blue colors in systems with little or no on-going star formation.
- to determine the mean surface brightnesses at 2500 Angstroms in order
to compare with normal galaxies and to estimate if LSB galaxies have enough
near-UV flux for higher-redshift examples to appear in ground based optical
To meet these goals, the exposure times will be 2000 seconds. The
longest exposure times which were obtained on the Astro I mission with
UIT were around 600 seconds. Thus, in addition to gaining information
on LSB galaxies, these observations will also constitute a deep
Ultraviolet Survey over a fairly large field of view. We hope,
if the Universe is cooperative, to be able to discover new objects
in these deep fields.
1097 is a nearby barred spiral with some sites of very active
star formation. The galaxy also has some collimated jets of
emission coming from the nuclear regions.
5128 is a really whacked out galaxy. It is suspected to be the
result of a merger between galaxies and has an overall morphology
that looks like suspiciously like this
model merger remnant . UIT observations of NGC 5128 or
Centaurus A will be quite interesting.
The Electronic Universe Project