On May 16, 1999, I went out to the Observatory with my laptop computer, hoping to use the VNC software to connect the laptop to the computer running Linux in my office. I had been frustrated by the poor image-display capabilities of the Meade Pictor software, and was hoping to use my own XVista software. It is very important to be able to check the PSF during the night, both for initial focusing, and to monitor the focus later on.
Fortunately, it all worked, although it took some effort. I did the following:
Taking a batch of images, then transferring and analyzing them all at once, alleviates some of the repetition.
I used the 2-hole mask to focus. Here are a few examples of the images it provides at different focus positions. Below are three images, at
One simply measures the distance between the two dots on each image, then interpolates to find the focus setting which yields a distance of zero. On this night, I chose focus -26,880. Later on during the night, I discovered that -26,900 was slightly better.
The visual focus (for examining the field through an eyepiece with the mirror flipped into place) was about +500 steps from the best CCD focus.
I was unable to get twilight sky flats, so I used May 11's master flat to reduce data from this night.
I took a number of images of SN 1999by in NGC 2841, using an exposure time of 10 seconds and the Wratten #25 red filter. One set of images showed no trailing, but a later set showed a small amount. I'm not sure if the distortion is really due to trailing, or due to the wobbling that sometimes (but not always) afflicts the 16-inch telescope. Whatever was responsible was present only some of the time. Rats -- that makes debugging difficult.
Below is one of the nicest images, together with a radial profile plot of the bright star "B" in the upper right-hand corner. North is up and East to the left.
I used simple aperture photometry to measure the relative instrumental magnitudes of the SN and stars "A", "B", and "C" (see reports from May 10 and May 11 for star IDs and details). The SN was clearly fainter than it had been on earlier nights. I measured
May 10 May 11 May 16
delta mag delta mag delta mag
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SN - B 2.40 +/- 0.01 2.43 +/- 0.03 2.52 +/- 0.04
If we equate the instrumental system with R-band, then we find that on this night, at 10:50 PM EDT May 16, 1999 = JD 2,451,315.6183, we find SN 1999by had "R" = 13.26 mag.