Asteroid 576 Emanuela occulting a mag 6.4 star

[StephenM]

Hi all,

I captured my first asteroid occultation last night. As previewed in the July issue of AS&T (p.58), Emanuela passed in front of the star HIP 94645 at about 6:54:30 pm. I drove to a spot just a few km south of the Amberley air force base, and set up my Canon 50D and 70-200mm telephoto lens, capturing a series of 1 sec exposures at f/4 and 3200 iso. Based on these images, the occultation lasted for about 7.5 seconds.

Here's a short star trail image consisting of about 1 minute of 1 sec exposures stacked using star trails. You can clearly see the gap in the trail of HIP 94645, where the star disappeared behind the asteroid.

There's also a 4 mg animation of the occultation here:

http://farm3.staticflickr.com/2880/9368057247_9770728149_o.gif

Hopefully a few other people measured the occultation as well, so that we can get an measurement of the asteroid's size and shape!

Cheers,
Stephen

[RichardJ]

Hi Stephen,

Congratulations on a lovely capture and image.

RichardJ

[von Tom]

Fantastic work Stephen, very well executed. Well done!

Tom

[StephenM]

Thanks very much Richard and Tom!

This was good timing, because I'm giving a talk at the kids' school in a couple of weeks, about contributions that amateur astronomers can make to research, and measuring the size and shape of asteroids (by recording occultations) is one of the topics I'll cover :)

Cheers,
Stephen:eyepop:

[StephenM]

Here's a better star trail image, starting 10 sec before the occultation and finishing 10 sec after.

Thanks for looking.

Cheers,
Stephen

[Larryp]

Well done, Stephen!

[Matt Wastell]

That is an excellent sequence - thanks for sharing Stephen.

[AstroJunk]

Great stuff - that makes 6 positive chords. I was a 'Miss' just north.

If you haven't yet, check out: http://www.asteroidoccultation.com/observations/DriftScan/Index.htm

[AstroJunk]

Oh, and by the way, this is the first multichord event for this asteroid and clearly shows the nature of its profile so you can expect to get your name published as a result on that photo :thumbsup:

Next up 10 Hygeia at 3am on Sun 11 Aug - perfectly placed for Astrofest, but a more challenging 10th mag.

[StephenM]

Thanks very much Laurie!



Thanks a lot Matt! It was a fun event to capture!





Thanks very much for the info Jonathon! That's great to hear that there are at least 6 successful chords, and that this is the first time that multiple chords have been obtained for this asteroid! :)

I know my timing estimate is not very accurate due to the method I used, but how difficult would it be to see how my chord fits on the shape determination that you posted? I estimated 7.5 seconds because the first one second exposure shows a dimming of the star, and the next 7x1 sec exposures show no star. I'd be interested to see how it compares to the "proper" video-based measurements!

Thanks and cheers,
Stephen

[AstroJunk]

I'll help you make an official report over the next few days. We should be able to accurately determine the length of the occultation to a high degree of precision and that is still a very useful observation. Of course knowing the exact time is even better, but duration only observations are fine.

Using video, its possible to determine the time of an event like this one to one fiftieth of a second, but software tools allow drift occultation's like yours to get a precision not too far off.

Can you PM me your exact lat/long and your email so we can get your draft observation plotted!

[StephenM]

Thanks Jonathan, I've sent you a PM with the details.

Cheers,
Stephen

[Lee]

Great stuff.... and scientifically useful too....

[Derek Klepp]

Stephen I was just reading about this in the Astro mag and realized what you,d done .A great piece of Science.
Derek