CCD 41 in dad_dr2

Question

It seems like CCD 41 is being reported a lot for DES observations in dad_dr2 (I haven't checked other observations). I did a few spot checks, and sometimes the ra_obs, dec_obs coordinates were not contained in CCD 41. It looks like 199/203 observations are listed as CCD 41. Example query below:

select * from dad_dr2.movobs o, dad_dr2.movds d where d.dataset = o.dataset and d.pi = 'Frieman' and o.ccd = 41

Answer 1

Hi Alex,

I am not a member of the Data Lab team and was not aware of this help mechanism.  As a publisher in the DL I assume this would eventually come to me.  This behavior came as a surprise to me and I first verified it in my master copy.  After wracking my brains about this I realized the CCD field is spurious for any dataset that begins with MOV.  I’ve used various methods as I’ve tried to exploit the DECam archive for serendipitous asteroid detections.  The MOV class of datasets was done by making single images of the DECam field (from the archived stacks I think) and then doing the difference detection on that.  In this case there is no info about the CCD but the part that converts detections into database records ends up with something that is meaningless.  This is also why the x/y fields are generally large numbers (i.e. not within 2048x4096).

In principle you should be able to do the inverse of what you mention:  given an ra and dec and observation invert to CCD coordinates.  However, I know that would not be generally easy.

I can try a help you with your goals if you want since the number from DES data is relatively small.  Do you want cutouts or something like that?  I could probably also create something that would do the inverse mapping so you could get CCD + coordinates.

Thanks for pointing this problem out.

Yours, Frank

Comments

Hi Frank,

I was using your catalog to prepare a tutorial on asteroid detection, and I just needed to identify the exposures containing asteroids. Your catalog was great for this, and I just wanted to point out this "feature" that I found.

Best,
Alex

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I post this here because these tutorials might be useful to others.  Frank

Hi Alex,

Yes I totally agree that the database can be a really good teaching tool.  I used this in a tutorial for advanced high school students (Teen Astronomy Cafe).  You might find the attached links useful.  These depend only on two available tools - aladin and topcat.

TAC Part 1: http://dec01.tuc.noao.edu/NHPPS_DATA/Allen/doc/TAC1802/Part1.html
TAC Part 2: http://dec01.tuc.noao.edu/NHPPS_DATA/Allen/doc/TAC1802/Part2.html

Yours,
Frank

On Mar 12, 2019, at 9:14 PM, Alex Drlica-Wagner <kadrlica@gmail.com> wrote:

Hi Frank,

I was actually preparing a short tutorial on asteroid detection using
catalogs from the DES single-epoch supernova visits. I was just using
your asteroid catalog to "cheat" and choose exposures where I knew the
students would be able to find bright-ish asteroids. Your catalog  has
already proven very successful for this (much easier that trying to
find Planet 9...).

I don't think I need any help from your side, I just wanted to make
sure you were aware of this "feature". I had also noticed the large
x/y values, but I assumed they could be relative to CRPIX rather than
the single CCD, though your answer makes more sense.

Best,
Alex

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I posted the wrong links (internal vs. external).  The correct links are:

TAC Part 1: https://www.noao.edu/noao/staff/fvaldes/TAC1802/Part1.html
TAC Part 2: https://www.noao.edu/noao/staff/fvaldes/TAC1802/Part2.html

Frank