Report for Asteroid Rotation Observing day on 18th June 2007

Aim

As asteroids rotate they reflect various amounts of light due to their uneven surface. From this variation it is possible to work out the rotation period of the asteroid. The technique works well, but we have never previously tried it with FT North; it was highly experimental because there were two variables we have never tested before.

The first was whether the CCD was sensitive enough to detect such small variations in the light intensity from a rotating asteroid. The second was whether the software we were recommending (Astrometrica) could measure the brightness with enough accuracy to show the variation (if the CCD could detect the change in the first place).

So the aim of the day was to observe two asteroids of different rotation periods and see if we could produce a light curve which is comparable to exisiting data from professional bodies.

The first asteroid we observed was (216) Kleopatra. We imaged this asteroid from 0600 - 1030 UTC. We collaborated with users in Hawaii to take images in the early hours of the night and the UK schools continued the observations from 0900 UTC.

Kleopatra has a known period of about 5.4 hours and varies somewhere between 0.8 and 1.4 magnitudes.

The second asteroid was 1997 QD2. This has a shorter period of about 2 hours and its light intensity varies by a smaller amount than (216) Kleopatra. It would be more difficult therefore to obtain a light curve for this asteroid.

All observations were taken with the R filter.

Comments

Observations

Kleopatra was a very slow mover so we were able to use the same RA and Dec for the entire observing run. This helped in that we could use the same comparison stars to calculate the magnitude of the asteroid.

1997 QD2 moved faster and we had to move the telescope slightly but not enough to have to use different comparison stars during the observing run for this asteroid.

This observing day was run with our Focus Group schools only and they are all well accustomed to the RTI.

Weather

The one aspect that could have made this day very hard was if the weather was bad. Fortunately the seeing conditions were photometric so the data was of really good quality.

Analysis

Kleopatra was observed first so that was where we started the analysis. Astrometrica automatically identifies the stars in an image and compares them with the online USNO catalogue. It then uses the known measured magnitudes of the reference stars to calculate the magnitude of the asteroid.

This was carried out for each image, and the time the images were taken was recorded. A light curve was then plotted.

Here is the final light curve of (216) Kleopatra (click for larger view):

Here is a light curve of the same asteroid from Smithsonian/NASA Astrophysics Data System (ADS):

The second asteroid, 1997 QD2 unfortunately passed in front of a star during the time we were observing it. This therefore made measuring the asteroid almost impossible, and I expect additional light from the star drowned out the subtle changes in the asteroid's light.

Evaluation

I am quite excited by what we managed to achieve on this observing day - we see a variation of the asteroid's reflected light in a pattern that is similar to the known data above.

To confirm, we will need to do some follow-up work where we record the magnitude of a comparison star to see if it remains constant. If it varies by the same amount as the asteroid then we have proved nothing.

User Contributions

Most schools are going through an exam period at the moment so teachers and students are extra busy. I've been contacted via several schools saying that they do intend to analyse their images when the exam pressure is over.

We will then be able to replace the curves above with data analysed by the schools who took part.

User Comments

Monmouth School carried out the observing in front of an audience of 10 year olds from another local school who all found the experience very interesting and exciting.

Monmouth School have also produced this flash movie of the moving asteroid.

From the teacher:

"This movie of Kleopatra was assembled from 23 frames taken over a thirty minute period. Each frame was exposed for ten seconds with a red filter.

Asteroid 216 Kleopatra was discovered in 1880 and is about 200km long and 85km wide. Radar reflections reveal that it is metallic and shaped rather like a dog bone although this cannot be discerned from these images.

Kleopatra moves slowly in the movie as it orbits between Mars and Jupiter. A transient streak also appears in the movie and may be the track of an artificial Earth satellite caught on one of the frames."