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My first "real" light curve

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13 years 9 months ago #86588 by dmcdona
My first "real" light curve was created by dmcdona
This has been a long journey - started in earnest about 3 or 4 years ago. Now, having read my head off and got to grips with processes, software, analysis, severe headaches and night-sweats, I finally come up with my first light-curve for an asteroid.

I've starting off simple so this example is comparitive photometry with no filters. I haven't gone down the road of nightly zero points and extinction co-efficients - yet...

I chose an object with a well know light curve, bright, and in a good position right now. So (132) Aethra was it. The current period (on the MPC page) is given as 5.168 with a variation of 0.10 to 0.52hr.

So over two nights (seperated by a couple of weeks) I managed to get a period of 5.1 +/- 0.01hr. Not bad. The data at the far end of the period (see the chart below) is a bit ropey - so I'll try and get a third night and clean that up a bit. I would have gotten the dat the other night but I was distracted looking at some pesky supernova ;)

Of interest, checking out the logs generated by the software (Canopus) I'm getting down to a level of 0.003 mags differentials. Now I'm not certain if that's just generated data or actual performance. But for sure, if you look at the scale on the chart (try the larger version), my system is working at the millimag level. That's very encouraging.

I'm still on a fairly steep learning curve (pun intended) but this is good progress and as a proof of concept, shows that I can probably mix it with other photometrists.

Anyhow, the full version of the chart is here: www.astroshack.net/images/00132Aethra_LQ.jpg

And here's a (very) condensed version for you to look at right now:

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13 years 9 months ago #86589 by mjc
Replied by mjc on topic Re:My first "real" light curve
Dave that's excellent stuff. There's always somewhere further an amateur can take himself - there's so much that the amateur can do.

How many hours capture are you working with and do you have any strategies in mind for smoothing the light-curves?

Very best of luck
Mark C

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13 years 9 months ago #86603 by dmcdona
Replied by dmcdona on topic Re:My first "real" light curve
Thanks Mark - for sure, Astronomy is one field where amateurs have a lot to contribute in terms of meaningful data. Certainly the pros recognis this and appreciate it very much. Its always been a goal for me that "science" would form the core of my astronomy work. For others, a different goal beckons. And that's the beauty of astronomy.

Regarding (132) Aethra, I chose it knowing the period was 5 hours or so and therefore, two nights of data would get most if not all of the light-curve. It was very much a proof-of-concept exercise for me. I managed to get a tad over 7 hours of usable data plus another two or so hours of unusable data (clouds, star too close to the target etc). So that's what the graph shows - hence the overlap of course. The blip at the end needs to be cleaned up - which I might do, or not...

The problem with asteroids of unknown light-curves, is that it could be a short period curve (easy peasy) or a long period curve running into many hours/weeks ro God forbid, months. If it is say 12 hours long, you'd need a good four or five or more nights of data - a challenge from Ireland certainly. An additional problem would be that comparing night-to-night data becomes difficult where they are spread over weeks or months. That's where filtered data needs to be taken and you put it onto a "standard" system - nightly zero points, 1st order and 2nd order co-efficeints etc. The advantage is that you can then directly compare nights and indeed, compare your data to any data from other observatories that are using a standard system - a requirement therefore for collaborations. But that's further down the road for me. I want to get a few more asteroids under the belt as they say and branch out into variable stars and exoplanets.

As regards "smoothing" the curve, there isn;t any need to if I was just reporting the period. Though I'd like to fix the "blip" at the end of the period alright. The error bars are as small as 3 millimags - that's pretty good and certainly enough to report an accurate period. Certainly, more data would make the curve smoother - but the period would remain the same, pretty much.

Of course, if I wanted to go down the road of report a Pole position, more data would be required. And even more data would allow shape-modelling to be carried out. But given the number of asteroids out there with no period reported, there is a huge amount of the basic work to be done.

For now, I'll just keep at the basic data gathering and analysis and gently complicate things as I go along!

Cheers
Dave

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13 years 9 months ago #86614 by ayiomamitis
Replied by ayiomamitis on topic Re:My first "real" light curve
Dave,

Welcome to the world of differential photometry (if I read your message above correctly).

The curve is quite impressive and something which is new to me since my work has been exclusively around variable stars and exoplanets.

As for the weather, we are also stuck in the middle of an extended front and with no end in sight. To add insult to injury, all of this is occurring around new moon.

Anthony.

Anthony Ayiomamitis
Athens, Greece
www.perseus.gr

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13 years 9 months ago #86623 by dmcdona
Replied by dmcdona on topic Re:My first "real" light curve
Hi Anthony - of course, I've done this before with TReS-3. But now I'm serious ;)

We've been lucky the last few nights with extended clear spells. So, I've been able to update my data :)

I've re-calculated the period:

(132) Aethra
Period: 5.17 +/- 0.005h
Amplitude: 0.2

This concurs perfectly with the published data - the latest reference giving a period of 5.168h (no error given).
I checked my errors and I'm getting as low as 3 millimags. Average would be about 10 millimags or so.

As far as the "bump" at the far end of the curve is concerned, the new data really didn't clean it up. In fact, it seems to have confirmed that there is in fact a "real" bump. I'm not sure what the reason could be. I'm going to see if the MPB is interested in publishing the data, though published lightcurves (well, one...) do already exist.

Anyhow, proof of concept complete, now to do some more :)

Cheers
Dave


Full res light-curve: www.astroshack.net/images/00132Aethra-3.jpg


Condensed light curve:

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13 years 9 months ago #86626 by michaeloconnell
Replied by michaeloconnell on topic Re:My first "real" light curve
That's very interesting Dave.
I must try and give that a go.

Michael.

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