TESS Overload

I just ran a script that took my machine 21 hours to complete!  It measured the brightness of about 2200 stars (identified by the IRAF task 'starfind') in a 1000x1000 pixel area (translating to 6.3 by 6.3 degrees in the sky) of Sector 1, Camera 1, CCD 1.  I did this for the entire data acquisition period, which went from day 206 to day 234 of 2018 (29 days!!).

I measured the brightness by the computing the mean and mode of a small sample box centered on the star.  The mean value is the brightness of the star plus the background.  I noticed quite a while ago that the background does change.  I need to investigate why, but for now I'm just accepting it as something that happens.  The background in my small box is estimated by computing the mode -- the most common value.  The star takes up 3 or 4 of the 49 pixels I'm sampling.  The other pixels are part of the background and will be the most common value.  To say it in stat verbage: the distribution of brightness is very non-gaussian.

So by subtracting the mode from the mean, I get a rough measurement of the brightness of the star with no varying background.

What I see it astonishing but totally expected!  I made some plots.  As I said, there are over 2000 stars, so there are 2000+ plots!  I put five plots on a single image, so that's only a little over 400 images.  Here are some examples to show the diversity.  X-axis is image number which will track time.  Every point is 30 minutes after the previous one.  The y-axis is self-scaled to whatever the data is telling gnuplot is the min and max.

2nd from the top is an eclipsing binary.

4th from the top is a very complex pattern

Top one low amp, high freq.  4th from top is complex again

And actually I'm interested in all of this for something completely in left field -- but I think is very important that no-one is talking about.

Which stars vary the least, or are closest to constant?  Do 'known' and used standard stars used in photometric measurements show any variation on these timescales?  I'm gonna see if there are any Landolt standards in this CCD's field of view.

Looking at all of these plots, there are only a handful that are totally flat (with noise, of course).  Are 'constant' stars rare?  What conditions make stars 'constant'?

All kinds of interesting questions -- and no one seems to be talking about it.

Anyhow I'm very pleased with this simple and very interesting experiment!  Except for the search for the most constant star, I have no idea where this will lead.