Help

discussion

Really long dip - what is it?

Started by psyham
Default_user
over 6 years ago

KID 7466500 - http://talk.planethunters.org/objects/APH23103084

I was surprised that this didn't come up in any forum searches, since it's pretty old data. I thought someone might have asked about it by now. So, what is the big dip from d113.5 to 116.2? Is it a glitch, or contamination, or an EB? If it's a transit, it's a pretty ridiculously long one.

I tried out the SkyView thing for the first time, and I think it worked ok... there appears to be a pretty big star sitting right next to the one in question.

skyview

Default_user
over 6 years ago

It's an interesting feature, and in nighthawk_black's EBs and oddities collection.

I am not an expert so don't take this on face value. There are a number of possibilities.

  1. This feature is real and maybe an eclipse in a Binary system. Personally I don't think so.

  2. It could be caused by sunspot activity, hence the dip in brightness.

  3. This is a known glitch area, esp. day 116 and 119. Those glitches don't have this shape however.

  4. It could be caused by star #2 as some form of contamination.

There are more possibilities of course but I gave it my best shot here :-)

Default_user
over 6 years ago

One of the curses of working with this data is that one never seems to find time to go back and revisit all sorts of strange things, like this target. Thanks for bumping it Psyham--I will try to find out what is going on. Cappella has listed some good possibilities; one thing that concerns me here is that the depth is very, very shallow with respect to the overall magnitude. Despite the very interesting symmetry and duration, my initial hunch is #2 or #3 in the list above.

Default_user
over 6 years ago

It turns out that on NEA the corrected pipeline data for this star no longer shows such a glaring feature near the end of Q2 in PDC_SAP flux. There is barely a hint of it in the raw SAP_FLUX, so I would chalk this one up as a pipeline introduced error. We still carry the original pipeline data on PH for the earlier quarters, so you might run into this sort of discrepancy occasionally.

Default_user
over 6 years ago

The old PDC_SAP is riddled with artefacts such as this sadly. The new one is better, though I've seen interesting events in the SAP which now get mashed up in the new PDC...

Default_user
over 6 years ago

Wow, thanks so much for looking into this everyone! I'm learning quite a bit from hanging out on the forums :) For clarification, could someone explain what PDC_SAP stands for? From the NASA Exoplanet Archive graphs it appears it represents the brightness level of the star, but I'd like to be sure.

I'm also trying to muddle my way through the NEA to see if I can find the corrected data. I punched in the KID and selected "View all time series and periodogram" for Quarter 2. Now I can see light curves, but how do I find the specific time that matches up with the Planet Hunters graph? The enumeration of the days doesn't appear to match. What does BJD mean?

Default_user
over 6 years ago

Simply put, the SAP data are the "raw" lightcurves where the data is barely processed. The PDC_SAP is the processed lightcurve where the data is detrended to remove some of the worst instrumental effects etc. The graphs on planethunters use the PDC_SAP, however while the older files on the NEA have been updated to the improved version, the data on planethunters for the first few quarters is still the old version.

As to finding the matching time, simply look at quarter 1 on NEA and the time of the first data point corresponds to 0 on planethunters. The offset is about 131.511 days IIRC. BJD = Barycentric Julian Date

Please Log In to make comments.