Astronomy
More IC 443. . .
December 16-17. We got back from a neighborhood party about 9:00. I decided to use AC line power tonight rather than horse the battery out. That let me set things up without thinking about the power I was using that could go toward imaging. And it means I can run just as long as my patience lasts tonight. I rotated the diagonal to put the camera on the side of the tube farthest from the pier. This allows at least two extra hours of tracking beyond the meridian at interesting declinations.
I again aimed at IC 443. I want to be able to compare tonight's images directly with earlier ones and also I want to use the best images from multiple nights to contribute to a very long exposure of this spectacular subject. (To see the effects of increasing exposure, see the sequence at right.)
The CCD is working hard to maintain -35C on this warm December evening. The air is around 45F and the camera's cooler is running at 80-85% capacity. It should only go down. (Three hours later, it's running at only 74% capacity.)
The bore scope illuminator is a little dim on its 3v battery pack. Could I use a 9v battery and get more light? Will I kill it doing that? Google LED's and voltage issues. I reverted to the red-filtered MiniMag light and nailed polar alignment before starting anything else.
The focus mask worked great! I tweaked the focus with the micrometer for drill; it works too but it really wasn't needed tonight. FWHM value in a 10 minute exposure: 1.62 pixels, 3.2 arcseconds.
I had some trouble getting the guider to calibrate. It really prefers one conspicuously brighter star in the frame to guide on. So tonight I offset the ST80 to give the guider Eta Gem. I'm using 1/10 second guide exposures every 2 seconds. I started a series of 10 minute Ha exposures at about 10:15. Errors are tiny for the most part. The field passes through the outermost twigs of one of the trees in the sideyard. Even there. guide corrections have stayed under 1 pixel consistently and results look great. Away from the twigs, I'm seeing corrections of 0.1 to 0.2 pixels, on the order of half an arcsecond.
And then, 16 frames into the evening, I got multiple pixel (10?) trailing on the CCD while the guider continued to report sub-pixel guiding. I imagined that the CCD had contacted something. The pier, a cable, the chair that holds the electricals tonight. But when I went outside, I found that the CCD still had well over an hour's clearance from any obstacles. Something shifted in frame 16 and continued to shift in frame 17 without affecting guiding. The clamp screw on the 2-inch nosepiece, perhaps? The T-adapter itself? I called it a night with 2+ hours of excellent data collected. Tomorrow, I'll see what happens when I add tonight's take to the previous take [not much good; tonight's stuff is so much better that it's damaged by including the older stuff].
Practical notes from tonight: Don't forget to undo the offset of the ST80 from IC 443 to Eta Gem unless you return to this subject tomorrow; put a finder on the AP so you can independently aim the guider and still find targets for the CCD; drill additional mounting holes for the micrometer bracket to get a less fine movement (what a nice problem to have); if you use the CCD rotated up in the diagonal to get clearance beyond the meridian, add some weight to the counterweight shaft.
IC443, First 10 minutes data.
The usual tech specs.
First hour's data.
First 2 hours' data.
Quick look.
Data filet, the best 13 frames.
13x600, summed, eq, etc.
Probably over-stretched. More signal!
You're on Page 15
Cameras behind Telescopes:
1
| 2
| 3
| 4
| 5
| 6
| 7
| 8
| 9
| 10
| 11
| 12
| 13
| 14
15
| 16
| 17
| 18
| 19
| 20
| 21
| 22
| 23
| 24
| 25
26
| 27
| 28
| 29
Text & Photos by David
Cortner
Link all you like; please
get in touch for other uses.