Jim Kern and I went out on a clear, calm, warm night to take pictures of a bright new supernova (1999by in NGC 2841) and Mars.
I started taking flats soon after sunset. The sun was about 5 degrees below the horizon. I had the Wratten #25 Red filter in place. Exposure times of 10 to 90 seconds were necessary as the sun went further and further down in order to acquire about 6,000 electrons above the bias. Must start taking flats before sunset!
We tried fiddling with the RA motor settings to remove the slow East-West wobble we often see. We found an oscillation of period about 20 seconds this evening. We tried changing the DC Gain setting on the RA motor, but it didn't produce much change. We also tried changing the f(c) value, but that didn't help much, either. Rats.
We then put the Pictor CCD camera on (still with Wratten Red filter), and pointed to NGC 2841. We found it pretty easily, and took a set of pictures at focus setting -26,730. It turned not to be the best focus -- oops.
We found
Looks like an exposure of 15 to 20 seconds is probably best. Just take a bunch of such short exposures.
Below is one of the 45-second images. North is up and East to the left.
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
We collected enough photons to make a decent measurement. The peak value of the supernova was about 200 DN in the 15-second exposure, and the scatted in its instrumental magnitude relative to other stars in the field was about 0.03 mag.
The Wratten #25 Red filter is similar to the astronomical Cousins R filter, but not identical. Look at the instrumental relative magnitudes of stars A, B and C versus their standard values:
delta instr. mag delta V delta R
---------------------------------------------------------------
A - B 2.70 2.70 2.63
A - C 2.33 2.44 2.34
If we equate the instrumental system with R-band, then we find that on this night, at 10:30 PM EDT May 10, 1999 = JD 2,451,309.6032, we find SN 1999by had R = 13.14 +/- 0.10 mag.
After finishing with SN 1999by at around 10:40 PM, we moved to Mars. We set the camera not to use 2x2 binning, to provide the largest number of pixels across the face of the planet. We kept the Wratten Red filter in place. We settled on exposure time 8 milliseconds, which yielded maximum values of about 13,000 DN above the bias for Mars. We took two exposures each at
I'm not sure if we moved all the way through the best focus to the other side, alas. Here are the four best images we collected: first the raw images:
And now a sharpened (and enlarged) version of each one, next to its raw original. Next to the sharpened version is a chart of Mars, showing the features which should be visible.
