3C overlay in running catalog

[hsuyeep]

Currently, the viewing panel on the left of the running catalog page overlays the source whose running catalog is being displayed on one of a selection of surveys. For AARTFAAC, it would be beneficial to have a 3CR/4C overlay, because the lowered sensitivity does not warrant the other, higher sensitivity surveys (and being images, there is no way one can filter on source flux).

3CR/4C survey catalogs are simple text files, and can be used to overlay circles to indicate the locations of sources from the catalog. They are available at:

3CR: http://cdsarc.u-strasbg.fr/viz-bin/Cat?VIII/1A (click on the tar link on top right to get the text catalog). 4C: http://cdsarc.u-strasbg.fr/viz-bin/Cat?VIII/4#sRM-F.31 (click on the tar link on top right to get the text catalog).

[gijzelaerr]

Working on this, it looks doable. Embedding an AARTFAAC image (or a arbitrary fits file) is not that trivial though, but I imagine that can be quite awesome. I've opened a new issue for that:

https://github.com/transientskp/banana/issues/95

[gijzelaerr]

RA, DEC & flux values

https://github.com/gijzelaerr/3C-catalog/blob/master/3CR%20catalog.ipynb

[gijzelaerr]

Ok this is implemented, although there is some space for improvement for design an usability.

Peeyush can you check and make sure the coordinates make sence? We can also add more catalogs. We can even add the extracted sources in banana to aladin as an extra layer.

[gijzelaerr]

@hsuyeep please check if the coordinates are correct. If not reopen this issue.

[gijzelaerr]

@hsuyeep said he would check if this is correct.

[hsuyeep]

Hi Gijs, Sorry for the hiatus of 9 months on this.

My conclusion is that you are not precessing the 3CR coordinates from B1950 to J2000, which is the reference epoch of the VLSS/NVSS base image layer in the image thumbnail view. I looked at the monitoring source 3C380 in the database vlo_cendescandidateSB002 (http://banana.transientskp.org/master/vlo_cendescandidateSB002/runningcatalog/33825/)

The monitored coordinate of 3C380 is 18h29m31s, +48d44m47s, as obtained from the VLSS. The 3CR location is 18h28m14s,+48d41m3s (B1950). Looking at the 3CR catalog extraction code in the ipython notebook you reference above, I see that the overlay is being placed at the B1950 position of 3C380. This is off by1' in RA and ~5' in Dec. The source is almost 10' away in the overlay image. Also, precessing the B1950 coordinates gets you pretty close to the J2000 coordinates of the VLSSr 3C380 (http://www.robertmartinayers.org/tools/coordinates.html), with a deviation of ~15" in RA and ~1.5' in Dec

The VLSSr postage stamp server shows the source at the expected location very well, so not sure why it does not show up when the base image is set to VLSSr.

[gijzelaerr]

ok so solution is to run the IPython notebook again with an extra convertion to go from B1950 to J2000.

I found this one, is this correct?:

1.  change B1950.0 RA and DEC to decimal degrees
2.  work out the following formulas

     RA2000 = RA + 0.640265 + 0.278369 * sin(RA) * tan(DEC)
    DEC2000 = DEC + 0.278369 * cos(RA)

3.  convert RA back to hours, and format as Hrs, min, sec as 
    preferred.

[hsuyeep]

astropy has a conversion routine, why not use that?

[gijzelaerr]

good point!