Tuesday, March 25, 2014

Asteroid Data Hunter, Backlog Jupiter Data, Relative Photometry, Things To Do

Asteroid Data Hunter

I'm still sorta recovering from my marathon session creating my entry for the Asteroid Data Hunter competition.  I should know the results of the reviews later today.  I'm having very strong doubts that my proposal is "good enough", but that decision is out of my hands.  I look forward to seeing all the other entries.

This is a pretty big deal if I win, but for now I'm keeping my excitement to a minimum.

Backlog Jupiter Data

Wow -- I have a backlog of data that I still need to reduce and get prelim analysis.  Never thought I'd be saying such a thing for my own data.  It's just plain old work to reduce data.  Just gotta do it, that's all.

I've modified my data collection technique in that now I'm taking 300 images per "set" rather than 200.  While 846/1800 (48%) images actually have Jupiter in them, because of the geometry of the moons (Callisto being pretty far away), I'd say that something like 85% of the images have SOMETHING in them of value.  So that's something around 1500 new data points.

I'm pretty excited about these last couple of data sets since they contain my first known observations of eclipses.  The one involving Callisto ingress into eclipse on 20 Mar 2014 caught me totally by surprise.  The session from 23 Mar 2014 has an Io egress out of eclipse.   I look forward to plotting each of those light curves to see when and how these events occurred.  I need to go back though all of my data now to see if I've already recorded one of these events without knowing it.

Here are pics of the Io egress event:

Figure 1: Io egress event

The times for these images are:

Upper left: 05:22:04 UTC
Upper right: 05:22:27 UTC
Lower left: 05:24:02 UTC

I'd say my timing error is probably +/- 2 seconds but I'll have to compare the internal clock with the WWV to be certain.

Using the predictions from this site, I note that the time of this event is 05:24:54.  So I see that my timing is off by about three minutes (three minutes early).  Not sure why.  I need to check my internal clock on the computer but I doubt it's drifted that much in just a month.  I also don't know what this 05:24:54 time is -- if it's for the start of the egress, the end of the egress, or the middle.  All I can say at this point is that it appeared fairly suddenly over the course of about one or two minutes.  If my timings are correct, then I'd say that the time from IMCEE is the time of the END of the event (when Io reaches its nominal magnitude and is totally out of the shadow of Jupiter).

I guess there's nothing else I should really do until I get the atmospheric extinction stuff built into the code.  This requires me writing some software that'll do least-squares fitting to a polynomial of an arbitrary order.  I want to write a general fitting piece of software like this so I don't have to come back later an expand on just a simple linear fit.  This requires dusting off some old books and reminding myself how to compute things like determinants and cofactors.  Ah, mathematics.  So really, until I have some working code to do this kind of thin, there's no point in running through the data.  The data will be there and continue to collect it.  Tonight looks like it's gonna be a good night with Io at max elongation and Callisto and Ganymede in nice positions.  Europa is gonna be heading closer to Jupiter, so I'm likely not going to get anything useful outta her.

Relative Photometry

I was staring at a background star the other night in the same FOV as the Jupiter system and remarked to myself that I could be doing relative photometry of each moon with that star.  I can assume for the time being (until I find out what star this is) that the star maintained a constant brightness over the period of the session.  This means I can compute the ratio (of the difference) between the background star and the moons to see how they vary in brightness over time.  This kind of measurement mostly eliminates the need for extinction correction.  But it also pretty much eliminates all the noise from the system, leaving just the raw photometry.

Things To Do

Gadzooks!  So what first?  Do the extinction software work, or focus on relative photometry?  I guess I'm leaning more towards the latter because it probably involves a bit less work.  Linear algebra was never my strong point, although as I recall it was easy to encode.  I'll work on both today, for sure.  Just not sure which one first.  Probably the relative photometry part.

I've also started looking at geometry.  What I need to start doing asap is creating phase plots.  In order to do this, I need to know where in its orbit each of these moons are.  The three pieces of information I have about that is location, distance, and direction of motion.  Phase plots are likely the best way I can visualize any kind of variations in brightness.  The jury is still out on whether or not I'm seeing variations in brightness, but that'll come when I look at more data and put several sessions together (which I'm about able to do!).

Much to do and I'll have an update (hopefully) sometime later today.  For now I'm just trying to distract my brain from just focusing on the Asteroid Data Hunter results.

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