Jim Kern and I used the 16-inch Autoscope plus the Meade Pictor CCD camera with Wratten #25 Red filter to take pictures of SN 1999by and Mars on the night of May 11, 1999. The skies were not clear -- thin clouds came and went throughout the evening.
While the sun was still above the horizon, I took a set of flatfield exposures. The typical sky level was about 11,000 DN above the bias. A median flatfield image, created from 10 individual flatfield exposures, is shown below:
In this image, the center is around 11,400 DN, and the corners about 10,700 DN, so the difference center-to-edge is about 6 percent of the mean value. Not too bad. There are clearly many dust donuts, and also several sets of bad pixels in small clumps.
We focused with Jim's two-hole mask, using Spica as a target. It worked pretty well, I recall. I set the focus to a value -26,780 around 10:15 PM, and left it there for the rest of the night. As we shall see, it wasn't perfectly in focus.
I then took six images of Mars. Since the camera was still binning 2x2 pixels, the planet's disk covers only 25 pixels in each image. They aren't great, but here they are: each of the 4 best images is shown after some Unsharp Masking in Photoshop:
I then moved to SN 1999by in NGC 4128. After some experimentation, I found that
Here's some information on the stars labelled in the image, taken from Brian Skiff's big photometric data file:
Name RA (2000) Dec s GSC V B-V V-R V-I NGC 2841 2 "B" 9 21 50.8 +51 00 36 G 3431-0625 11.07 0.59 0.33 0.65 NGC 2841 3 "C" 9 21 47.3 +50 58 50 G 3431-0053 13.51 0.75 0.43 0.83 NGC 2841 4 "A" 9 21 58.2 +51 00 16 G 3431-0495 13.77 0.60 0.40 0.74
The images weren't quite in focus. The FWHM of the best image was about 4.1 pixels, or 2.6 arcseconds (images taken the previous night provide a scale factor of 0.640 arcsec per pixel). It showed a slightly "lumpy" appearance, with very small wings out to one side.
I made measurements of raw, instrumental magnitude through a circular aperture of radius 5 pixels on the final five frames (which showed all four stars and no trailing). Here are the differential magnitudes:
May 10 May 11
delta mag delta mag delta V delta R
-----------------------------------------------------------------------
A - B 2.70 2.71 +/- 0.05 2.70 2.63
C - B 2.33 2.34 +/- 0.03 2.44 2.34
As before, I find that the Wratten #25 red filter is not an exact match to either Johnson V or Cousins R, but it's not far from either one.
Here are measurements of the supernova's instrumental differential magnitude:
May 10 May 11
delta mag delta mag
-----------------------------------------------
SN - B 2.40 +/- 0.01 2.43 +/- 0.03
It's hard to say that the SN is fading -- the difference just isn't large enough to be significant.
If we equate the instrumental system with R-band, then we find that on this night, at 11:00 PM EDT May 11, 1999 = JD 2,451,310.6250, we find SN 1999by had "R" = 13.17 mag.