Reply To: Exoplanet Data in the BAA Database

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Dr Paul Leyland

The difficulty you may find is converting the output from HOPS into one of the file formats used by the BAA. If that is difficult, then don’t bother.

Hi Andy,

Yes, quite tricky! It’s the comparison stars that are hard to deal with. As far as I can see, exploring the various output files, the pixel co-ords of the comp stars are stored in the log.yaml file, but no details about them. I could locate them on a chart and then enter that data but it will certainly be fiddly!


How I would deal with this is to write a few scripts. It’s what I did a few years ago to upload to the BAA database.

First make sure that at least one of the images showing the target and the comparisons has an accurate WCS. If none do,, either on-line or self-hosted (my solution).

The coordinates of the target star are presumably well known, what are not are those for the comparisons but if you have a list of (x,y) coordinates and a WCS, the xy2sky program from the WCS tools utilities will produce a list of (RA,Dec) coordinates. Easily scriptable.

Given those, from I download a subset of the GAIA catalogue centred on the target and wide enough to include all the comparisons. Quarter to half the FOV is a reasonable estimate.,_DEJ&-sort=_r&-oc.form=sexa is a starting point. Customize the search fields until you have nailed down the query you want, then copy the URL for use as a prototype in subsequent searches. I tend to ask for the J2000 coordinates, either G magnitude or RP magnitude (depending on whether the images were unfiltered or V for the former, R or SR for the latter) and its error, and the G-RP value. Ask for lots of lines in tsv format.

Given that data, filter out all stars which are more than a few magnitudes brighter or fainter than the target. Reject all stars which are markedly different colour from your target. Finally, search in the remainder for stars which lie within a few arcsec of the list of coordinates you produced earlier. Remember that stars have proper motions; I have been bitten by this one before!

After all that, you have a sequence of comparison stars ready to be fed into your regular photometry program.

This is my procedure for exoplanets where good sequences do not exist at, say, AAVSO, and for asteroids where they rarely do so.

If you speak Perl, there’s a good chance that much of the scripting required can be provided. Contact me off-list if you wish to give it a try.

Good luck!