From: albe albo <richter1956@yahoo.com>

Date: September 21, 2009 12:49:30 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Eros Light Curve Data Captured


Very nice Milton.

uhu? so huge fonts in this mail message?


Better big to say that i like very much your work.

I'ts a real satisfaction to process apparently messed up numbers and eventually discover that they are not messed at all!

Isn't it?

Your patience and you hard work produced the deserved results.

It's a very interesting field... that periodic curve thrilled me.


TTYL

Alberto


Da: milton_aupperle <milton@outcastsoft.com>

A: Astro_IIDC@yahoogroups.com

Inviato: Domenica 20 settembre 2009, 1:39:09

Oggetto: [Astro_IIDC] Eros Light Curve Data Captured


Hi folks;

Seeing was mediocre last night (light haze, faintest visible star Mag 3.9) and my HEQ5 (POS) mount was acting up again (binding then loose then binding), but I managed to capture 4.75 hours of images of the Asteroid Eros. I shot 141 two minute exposures continuously between 03:39:42.17 to 08:17:42.17UTC on September 19, 2009. I had Astro IIDC guiding on a Mag 7.31 star for the entire time. I used the 16 bit cooled Grasshopper camera for capture and the clear AstroDon Luma filter (it has IR cut). Flats and Darks were applied to the movie data before processing.

I used the "Measure Differential Photometrics. ." in Astro IIDC to track and measure the changes in magnitude over those 4.75 hours for Eros, a constant star (TYC552-977- 1 Mag 11.93 ) and a check star (USNO J2150444+052355 Mag 11.93). I was getting an average MSR error for the Eros measurements Eros of +/- 0.023 magnitude, and +/- 0.034 magnitude for the the constant and check star. That's really good for being on the edge of a large light polluted urban area.

Here is the resulting light curve (plotted up in AppleWorks):

http://groups. yahoo.com/ group/Astro_ IIDC/files/ Other/Eros_ Lightcurve_ 20090919_ MJA.png

All of this work (capture, guiding, processing) was done solely on a Mac too in Astro IIDC and in old trusty AppleWorks for the plotting of the Graph.

The curve shows that it went from first low to second low (approximately 0.7 magnitudes) in about 138 minutes (peak to peak) or 152 minutes (using start of the flattening of the down curve).

I initially though this was a bit "odd", because Eros is supposed to do a complete rotation every 5.27 hours or 316 minute intervals. However Eros is shaped like a peanut or banana, so it is presenting it's widest side to us about every half rotation which is 158 minutes. That is in pretty good agreement with my higher end 152 minute peak to peak estimate.

Also, assuming the asteroid reflectivity is constant, this also means the ratio of the long to short axis is approximately 1.45 to 1.9 times depending on peak to peak change of 0.4 to 0.7 magnitudes.

According to :

http://nineplanets. org/eros. html

Eros measures 33x13x13 km, so it has a ratio of 2.5 times long to short axis. This is actually pretty close to my off the cuff estimate using the 4 hours of data I collected.

I would need a lot more curve data spread over multiple nights before I can draw any hard conclusions, but this was an interesting first experiment.

One thing I should mention was that I did not collect good data for the Asteroid because I over exposed it and some pixels saturated the CCD (reaching 65535). I'll likely try again using 1 minute exposures next time, after I get this @#$#$% HEQ5 mount RA gearing straightened out again. I can't quite record a complete rotation because it disappear behind the edge of a building on the west side.

I will eventually crop the original movie down and post it so you can see Erso slowly move over time (about 1 arc second per minute).

TTYL..

Milton Aupperle