Return to Home Page
From John Greaves: === This thing isn't at vizier yet, but seeing as NPM1, NPM2 and SPM2 were deposited at vizier, I suppose this one will be too. Meanwhile, http://phoenix.astro.yale.edu/pub/spm/spmcat/spm3/spm_3_1.aareadme shows that it has photographic plate V and B measures, down to magnitude 17 or so, for a Southern sky strip of millions of stars. People tend to use USNO A2.0 for these magnitudes, which usually gives a big error when converted to V, and the situation is worse in the Southern Hemisphere as the blue and red plates are not necessarily from the same source. Anyway, a quick test against the usual benchmark of Brian Skiff's loneos.phot managed a mere ~500 hits. Attached is a graph of the loneos V and SPM3.1 V differences as y axis against loneos V as x axis for the 12 to 17.5 V range. The mags seem to match to the +/- 0.2 mark, which is better than USNO A2.0 expectations of about +/- 0.5 The catalogue actually carries estimated errors in the photometry quoted in hundredths of a mag. The B-V situation wasn't as healthy, with scatter up to +/- 0.4 Remember, as usual, this is an astrometric catalogue, not a photometric one, but I reckon this should be used where possible, and V from CMC13 r' and 2MASS J-Ks (which has errors around +/- 0.1) for more Northern stuff (Dec -3 to 30 degrees) in preference to USNO A2.0 derived V mags for the faint range. Unfortunately, neither are on vizier at the moment, which is the problem, but there ya go. For colour decisions there is something on VizieR, the 2MASS all sky release. Just don't use anything with J-Ks > 0.8, about M0, or > 0.6, about K0, if you're cautious. Cheers John
Return to the Powerful Daisaku Nogami
vsnet-adm@kusastro.kyoto-u.ac.jp
