Needle in a haystack?
I’ve mentioned before just how difficult it is to find extrasolar planets. I’ve also made little secret of the fact that I’m a huge fan of the SuperWASP experiment which adds lenses to professional standard CCD cameras, essentially getting rid of the telescope in order to monitor a huge area of sky for faint dips in the light coming from a star which might indicate the passage of a planet in front of it. The technique works well - one of the leading teams announced the discovery of the largest known planet this way yesterday. (Largest - not most massive. That had me confused for a bit).
I know have a new appreciation for quite how difficult this is. Scrolling through the list of new papers, I saw that Clarkson et al. had published the first tranche of superWASP data, and the numbers in the abstract made me stop dead. They had worked hard to obtain 141,895 lightcurves (each of them tracing the brightness of a single star over time). Buried within this set were 2688 - that’s less than 2% - which have transit-like features. They then looked at those few thousand light curves by eye, and end up with 44 (0.03% of the original sample) which were worth following up further.
What next? Job done? Nope! Another 24 are removed to leave only events which are statistically significant, leaving 20. The next task is to search through everything that’s known about those 20 stars, a process which ruled most of them out. Finally, after a huge amount of work, we’re left with 0.003% of the original sample - 4 stars which might, just might, have planets orbiting them. Wow!
on August 8th, 2007 at 9:11 am
I never realised it was so tenuous. Well done them! It is a great project, isn’t it? I really love the idea and of course the name.
“Well its better than WASP…”
“What about SuperWASP, boss?”
“You sir, are a genius!”
on August 8th, 2007 at 8:03 pm
Once the “small matter” of identifying the planets from all the possibles is complete, it is fascinating to see just how obvious these transiting planets are. Detection of most of the ones discovered to date are within reach of modestly equipped amateurs. One rival group of transit hunters (XO) is using a group of experienced amateurs to help sift the wheat from the chaff and I gather the SuperWASP team are considering a similar approach.
Robin
on August 9th, 2007 at 2:06 pm
The calibration is also a huge job, especially with such a large field of view. The point spread function will get distorted significantly towards the edges. To get significant numbers of transits, you have to have reliable photometry where the systematic errors are a few millimagnitudes at most. Only then can you start searching for your needles.
on August 21st, 2007 at 4:50 am
Chris - I just listened to Don Pollacco presenting this material at a talk at the JENAM conference. Actually they are finding fewer candidates than they expected and believe their filtering is too harsh .. so there are more to come !
on October 31st, 2007 at 12:23 pm
[...] Excellent news! I’ve written before about SuperWASP’s planet search, and I’m pleased to say that they’ve just announced their second round of successes. Three new planets are announced today, detected by the small dip in their parent stars’ brightness as the planet passes in front of it. WASP-3 was discovered by the first set of cameras, on the island of La Palma in the Canaries, but WASP-4 and WASP-5 are the first discoveries from the new station in South Africa. These are fairly typical ‘hot Jupiters’, large planets extremely close to their parent stars. As I’ve said before, WASP is based on a brilliantly simple idea and is an extremely ambitious, but low budget, project and I’m really happy it’s continuing to get new results. [...]