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 science.

• 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 here: 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.

  M101 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 to see if there is any near-UV bright component that may help to explain the observ ed 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 surveys.

  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.

  NGC 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.

  NGC 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 nuts@moo.uoregon.edu