Walter's LogBook
	February 2007

Overview

The Live Session page detected a USB lockup just a few minutes after I went to bed one night and so saved most of a night! Fortunately there haven't been any lockups since. My variable star program was doubled to about 600 stars total by the inclusion of Miras from the AAVSO Bulletin. There are notes about this below.

The RA gears in my telescope are starting to fail due to wear and this is causing about ¼ of the images taken per night to be trailed. My LX-200 will be 10 years old this October, so I decided it was time to rebuild or replace the scope. My ultimate decision was to have the scope SuperCharged since replacement would be much more costly (even with a used scope) and since it would not be possible to replace it with an f/6.3 system (as they are not manufactured any more).

The SXV-H9 is the imaging camera, with exposures for variable stars of 120 seconds at 4x4 binning (unguided). This month's session notes are below the overview section.

Monthly Statistics, February 2007
Night	Imaging Time (s)	Exposure Time (s)	# Targets	# Exposures	T (C)	/\T
2007-02-06	27335	24000	51	200	-3.3	-3.1
2007-02-09	32216	27480	55	229	-5.3	-1.8
2007-02-10	28591	24240	49	202	-1.8	-5.4
2007-02-12	41452	28800	62	240	-5.2	-7.0
2007-02-16	26590	23160	48	193	-0.6	-3.1
2007-02-21	6913	6240	16	52	3.1	-1.0
2007-02-24	38280	28820	98	471	-0.6	-4.8
2007-02-26	37649	31560	66	288	3.6	-9.2
2007-02-27	37866	31380	60	284	6.8	-8.9
2007-02-28	37308	26280	45	219	2.6	-9.8
10 nights	314200 (87.28 hr)	251960 (69.99 hr)	550	2378

Session Notes

RA Tracking Problem

Well, it was bound to happen eventually! After almost 10 years of very heavy use, the RA gears are starting to give up the ghost. At first I thought it was just because the scope was pointing so low in the west, but as time went on, it became obvious that bad tracking was happening all over the sky!

RA Tracking Problem

SXV-H9 binned 4x4, Johnson V filter, 1 x 120 seconds.

Expanding My Universe Again!

Now that I have added about 300 Miras to my program (doubling the number of stars I follow), looking up coordinates and building plan files has become a problem.

Star Lookup:
My old star lookup utility was simply a registered Windows Script Component that in simple terms was simply a glorified "if/elseif" block. Now with about 600 stars on my to-do list, I needed to move to a database of some kind. Fortunately, ACP's help file tells how to use Windows Scripting to build an MS Access databases (MDB file) without the need to own a copy of MS Access! So the practical upshot is that I now maintain the star data in a text file, and then when I make changes to the data I simply regenerate the MDB file! This is a much nicer system than I was using before! As a final step, I modified my customized version of ACP's AcquireImages script to utilize this MDB file lookup. It works great!

Plan Building
The other problem created by having so many stars on my list was building a plan file for ACP. With all the Miras, which only have to be done once per 7-10 days (as opposed to every night with the CV's), I was having to comment them out once they were done, and then de-comment them when it was time to do them again. This was a lot of editing to do on the plan file. Also, I needed a way to remove Miras that are brighter than about Mv=9.5 since those will be saturated even with a 20-second exposure.

As a result, I constructed an Excel workbook to keep track of when the Miras were imaged, retrieve the latest Mira data from the AAVSO's Quick Look page, and build the ACP plan file -- in the process excluding any Miras that were imaged in the last 7 nights or that are brighter than Mv=9.5 as indicated by the Quick Look data. Very nice!!!

The system isn't perfect, but it's close! Sometimes there won't be any QL data for a Mira in the last 20 days, so it won't be possible to determine if a particular Mira is brighter than my limit (Mv=9.5). As a test, I ran a full plan with all Miras so I could see for myself how bright they were. Then I ran the plan builder and looked at its output: it had removed 23 Miras as being too bright and this correlated almost perfectly with what I was seeing in the CCD images. Mission accomplished!

Exposure Throttling:
With a little experimentation I determined that 20-second exposures would be good for working the 9.5-14 magnitude range. What I needed was a realtime exposure throttle for Miras. I already had this for CVs, so all I needed to do was add a second "if" block to AcquireImages to adjust the number of exposures for Miras in real time according to their observed brightness. This was easy to do and works perfectly!

Column summary:
B: Putting in a "1" enables the star.
C: Exposure time in seconds.
D: # of exposures ("repeat").
E: autofocus before imaging the star.
F: RA
G: Dec
H: Type of star (M=Mira).
I: Last time I imaged the star.
J: Latest Quick Look (QL) magnitude (if red, star will not be put in plan).
M: Date of QL magnitude.