[BAA Comets] Astrometrica 4.10.0.431 and UCAC-4 R magnitudes

[denis buczynski]

Hi Nick/allI have upgraded to the latest version of Astrometrica 4.10.0.431 but I don't see the Gaia DR1 catalogue in the list available in catalogue settings. The only new one I see is URAT-1. Am I missing something?Denis


      From: Nick James <ndj at nickdjames.com>
 To: BAA Comets discussion list <comets-disc at britastro.org> 
 Sent: Tuesday, 7 March 2017, 7:38
 Subject: [BAA Comets] Astrometrica 4.10.0.431 and UCAC-4 R magnitudes
   
I've just moved from Astrometrica version 4.9.1.420 to in 
order to take advantage of its abilty to use the Gaia DR1 catalogue for 
astrometry. I'm still using UCAC-4 for photometry and I use the R band 
option since this is the closest match to my unfiltered CCD.

I was surprised to see that the new version produces R magnitudes that 
are around 0.25 mag brighter than the old one for the same image and 
configuration. Richard Miles has explained that this is a real change. 
Astrometrica used to use the Sloan r' magnitude from UCAC-4 directly as 
Cousins Rc but it now correctly applies a transformation which, on 
everage, corresponds to Rc = r' - 0.24 mag.

Other catalogues containing r' mags (CMC-14, CMC-15) were handled 
correctly so this change only applies to UCAC-4 R mags.

I recommend that you move to this new release however be prepared for a 
zero point shift of around 0.25 mags if you are using UCAC-4 R as your 
photometry reference.

Nick.

_______________________________________________
Comets-disc mailing list
Comets-disc at lists.britastro.org
http://lists.britastro.org/mailman/listinfo/comets-disc