Merope is a bright star in the Pleiades that is embedded in a reflection
nebula that is very faint. The 600 second exposure taken south of Merope
barely detects the nebula but it is worth looking at.
Display the dark subtracted image
of m45_merope_s_600s_01d,
set the scale
to run from around 1000 to 1100. Now select Color->Contrast/Bias
and manually set them to about 4 and 0.2. This should show the nebula,
but all the stars will be saturated.
The nebula appears to have streaks across it. Which direction do they run in?
The other image m45_merope_100s_01d which is of Merope itself also shows
the nebula, but the star is extremely overexposed. The dark streak that runs
vertically across the image is the excess charge from the overexposed star.
Here if you adjust the range of the image grayscale to cover 220 to 800,
and use a contrast setting of about 6.0 with very low bias, a faint pattern of
striations will appear across the field.
What difference is the signal level in ADU in the striations less the signal in the ``black'' sky away from the star? This is a 100 second exposure. What exposure time would be required to make this difference 1000 units?