Any star within 
of the ecliptic passes within 10 
of the sun
for about 5 days once per year.
There are
10-20 UV bright stars which pass close enough to
the sun to be observed and which have been observed
with Voyager and IUE.
A star will move across the slit or a resolution
element in the spatial direction in about 5 minutes.
If the pointing can
be accurately enough predicted, we can let a star move
along the length of the slit to build up counts and
evaluate the detector uniformity.
It may be possible to measure the O VI
absorption profile in the solar wind. The O VI
absorption of the solar wind will be weak,
but if measurable it provides a way to see O VI after
Doppler dimming has made the scattered intensity too small
to detect. An estimate for a streamer is 
(with very large uncertainty) at 1.5 
,
so high signal-to-noise will be needed.
An example of a possible target is 
Sco, which passes 1.7 
from sun center on Nov. 27. Its brightness is about 36 
at 1032 
, or about 36 counts per pixel during the 300 seconds the
star takes to cross a resolution element (for the occulter position at 1.7 
).
By allowing the star to slide
along the slit, one acquires about 4000 counts per wavelength pixel, which
makes implies a detection limit of about 
. Unfortunately, a star
moves along the length of the slit only in passing more or less over the
solar pole, where the O VI optical depth will be smaller. This
observation will also challenge the flat field accuracy. Observations farther
from sun center will acquire more counts, but the predicted optical depth
drops faster than 1/r. The numbers in the tables pertain to 
Sco.
It will also be possible to observe a few stars, such as V471 Tau,
for their own sake. This is
probably only worthwhile for stars detectable in the O VI channel, as IUE
or HST have larger collecting areas than UVCS at 1200 
. One might
observe the O VI emission profile of a solar-type star, but a rough search
in the Bright Star Catalogue did not turn up any very bright candidates.
Most of the hundreds of stars in the Bright Star Catalogue within
of the ecliptic are A stars (including chemically peculiar and
magnetic stars) or red giants. The main usefulness of UVCS stellar observations
may be interstellar absorption line studies on stars such as 
Sco, because
dozens of strong lines of ions such as O VI and molecules such as 
and CO
lie below the wavelength range accessible to HST.
Stellar Observations with UVCS
** For this example, the slit is placed at 5 
at a roll angle
of 
from ecliptic north, and the star drifts across the middle of the
slit in about 6 minutes. The start time for this exposure must be specified carefully.