Which of the two lightcurves shown above contains a planetary transit? If you’ve been following my blog then you’ll know the answer is the one on the right, since that’s the Kepler-5b graph from my last post about planetary transits! The graph on the left shows a detached eclipsing binary, which is consists of two stars orbiting eachother at a great enough distance that they are two distinct objects – as they orbit their centre of mass, the stars pass in front of eachother and reduce the total light coming from the system, which manifests as the dips in the lightcurve. So in that case, the transit is caused by a star and not a planet.
Tag Archive for 'transits'
One of the questions that comes up quite frequently on the planethunters.org forums is “what does a planetary transit look like”? That’s been partially answered by this post by Matt Giguere on the PH blog, but I’ve come across some more examples that planethunters might find useful.
You may remember that in January 2010, the Kepler team announced the discovery of the first five exoplanets from Kepler data. The lightcurves for the stars that these planets orbit are actually available online, and they’re available in a text format that makes it easy to import into a spreadsheet program! So, this is what the lightcurves for the transits of these confirmed planets look like! (click on them to see a larger image):
Over the past week I’ve been having a whale of a time looking at lightcurves at http:/www.planethunters.org (I’m on there as EDG) – well, actually I seem to be spending more time discussing them and trying to figure them out! I’ve learned a few things in the process that might be useful to other planet hunters out there:
Making sense of Eclipsing Binaries
I’ve learned a lot about the light curves of eclipsing binaries (EBs) this week, which consist of two stars orbiting eachother with one star passing in front of the other as seen from our perspective (which changes the light curve). If you’re looking through the data and want to see what the lightcurves for these EBs look like, then check out pages 18-22 of this Kepler paper (right-click the link and select “save as” to save it), which shows some typical examples of detached, semi-detached, over-contact, ellipsoid, and irregular binaries (there’s an explanation on page 17 for what these types mean – “detached” means that the stars are far enough away to be distinct from eachother, “semi-detached” means that one star has overflowed its roche lobe and is distorted, and “over-contact” means that the two stars are close enough to share a common envelope (i.e. both have overflowed their roche lobes). A dead giveaway for detached eclipsing binaries is that there may be two dips on the lightcurve, but one is shorter than the other.
Continue reading ‘Planethunters: Making sense of the lightcurves’