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benmontet / k2-characterization

Stellar/planet properties and confirmation of some K2 planets
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201555883 and the like? #13

Closed timothydmorton closed 9 years ago

timothydmorton commented 9 years ago

We are saying that we know 201555883 is a period-epoch match with a known EB (201569483). How deep is the EB signal? What is the relationship on the detector b/w these two stars? Are they close by? On the same CCD column? How closely are they matched?

Details are important because my FPPs say "planet."

And have we checked for other period-epoch collisions among our detected signals?

benmontet commented 9 years ago

The EV is ~10% deep. They don't necessarily make sense as being closely matched/on the same column/a 180 degree rotation.

I emailed the K2 team about this and Jeff Coughlin just got back, I'll cc you in the loop on the reply.

There are no other collisions between planet-like signals in C1 (either planetary or EBs). I did not yet check for collisions between nearby known EBs that are not being downlinked and our catalogue.

On Tue, Mar 10, 2015 at 6:06 AM, timothydmorton notifications@github.com wrote:

We are saying that we know 201555883 is a period-epoch match with a known EB (201569483). How deep is the EB signal? What is the relationship on the detector b/w these two stars? Are they close by? On the same CCD column? How closely are they matched?

Details are important because my FPPs say "planet."

And have we checked for other period-epoch collisions among our detected signals?

— Reply to this email directly or view it on GitHub https://github.com/benmontet/k2-characterization/issues/13.

timothydmorton commented 9 years ago

How far away is the EB from our candidate?

benmontet commented 9 years ago

Not close enough to interfere directly by PSF overlap. The EB is near the edge of the detctor, and the candidate is several modules away (see figure). 2_fov

timothydmorton commented 9 years ago

maybe try an ephemeris match using this: http://www.astrouw.edu.pl/asas/?page=acvs

benmontet commented 9 years ago

Nothing within 15 degrees found with that tool. Also doesn't find the 10% deep one that we have in K2. It continuously surprises me how many EBs we don't know about around reasonably bright stars, given how deep they are!

benmontet commented 9 years ago

So I don't really know what to do with this one. I don't particularly have the confidence to say "this is definitely an artifact, we just have no idea how" after talking to Tom and Jeff. But it has to be, right? What's the expected number of objects with the same period, phase, and duration? This is the Serial podcast all over again.

I propose we leave it in limbo in our formal tally. In the subsection currently titled "instrumental false positive" I'll note that it formally passes your test, but because of this weirdness that isn't captured by your scheme, we note the possibility that it might be a FP and recommend follow-up both to confirm this system and better understand a potential artifact inherent to Kepler.

Any opposed to that plan?

dfm commented 9 years ago

I'd be inclined to say that it's definitely an artifact but I don't have the argument fully. One reason why I'm concerned is that the star is very variable so our systematics model has to pick up more shit than it's supposed to. This means that maybe there's some residual signal from the EB in the basis and somehow the model has to weight that basis very highly to pick up the variability... this is surprising again because it requires a large number of coincidences but there's nothing formal protecting us against it!

Also: this is a pretty marginal transit in a noisy light curve and the in-transit noise appears to be lower than the out-of-transit noise. Let me explore this in more detail...