Help

discussion

Patterns v transits

Started by Gene ius
koi
Default_user
about 7 years ago

How do you tell the difference between a pattern (Irregular, regular pulsating) and a transit? What causes the pattern if not a transit?

Default_user
about 7 years ago

It can be a lot of things. The two main ones are that the star itself is intrinsically variable (starspots that spin in and out of view at the star rotates, for example, or quite a few stars literally pulsate -- Cepheids and Delta Scuti variables, to name two), and that Kepler itself is messing up the curve (either in the initial measurements, or the post-measurement data processing that they do is notorious for really screwing up the results from certain CCDs in the satellite's camera).

Basically I look at any suspicious bump this way:

1 - Is it symmetrical? Transits are even on the way down and the way up.

2 - Are the sides angled? A planet transit, except in certain peculiar circumstances, has a very sharp down drop and back up again, close to 90 degrees. If the sides are angled it's possible it's a planet, but it's a strike against it.

3 - Does it have a flat bottom or a pointy one? Unless it's very quick, a planet transit has a flat one. Pointy might mean an eclipsing binary, though, so it might be worth following up for different reasons.

4 - Is it periodic? Short transits show up several times in the same curve, and are evenly spaced. Wider transits imply a longer "year" for a planet and so will be more widely spaced, so I give it the benefit of the doubt in that case. But as soon as it lets me I go and check the other quarters for evenly spaced dips spread across them!

5 - Are the dips alternating in depth, bigger and smaller? That's an eclipsing binary. Not what we're after, though still interesting. Planet transits are all the same depth, within reason.

6 - Is the dip really deep? Anything more than 1% drop in light on the scale at the left of the curve is a bad sign, more than 5% means it's absolutely not a planet.

It's one amazing planet candidate if it passes all six, and I'm still hopeful if it passes five. Four or less and I get more and more worried -- I might mark it, might not depending on my gut feeling having looked at a lot of the Kepler-team confirmed transits (click this hash tag #KOI and then the Objects link on that page if you want to look at a bunch yourself). Two or less and I'm figuring "Nah".

Please Log In to make comments.