[vsnet-alert 9907] re DA55 aka QSO B0133 +47

[da55 at Safe-mail.net]

first off, just as an aside, CBET 1249 seems to have decided it's called QSO 0133+476, however, QSO B0133+47 is the primary simbad ID, and strictly by the ol' IAU nomenclature rules the B _must_ be included in the coord part.

Anyway...

CPJ uttered :-

"If anybody is aware of a better sequence I would be interested"

Hiya Chris

Well, on a better than nothing level, some aeons ago I matched thousands of r'_CMT and 2MASS J-Ks against equal lots of V from loneos.phot and got V=r'-0.60(J-Ks)-0.03 r' 9..15, J-Ks 0..1 standard deviation 0.06.

The two sixteenth mag stars you mention lie outside this range somewhat in terms of faintness, but are well within the colour range, so although not exactly assured, they may well give better values to be going on with.  Each has two r' observations both having standard deviation 0.163, which is likely more to reflect the quality of the magnitudes than any real variation (note the QSO standard deviation for two observations, which undoubtedly will be on the same dates, is 0.732).  That's still going to be better than USNO A2.0 colours.  The 2MASS colours for these stars have quoted errors of better than 0.05 for J and better than 0.08 for Ks in both cases.

So, in the first instance you've

14CMC J013659.1+475112

RA 2000  01h36m59.19s
Dec2000 +47d51'12.3"

JD 2451264 + 1298

r'  15.961  sd  0.163

2/2  observations

J   14.757
H   14.418
Ks  14.392

and

14CMC J013657.0+475125

RA 2000 01h36m57.09s
Dec2000 +47d51'25.6"

JD 2451264 + 1298

r'  16.020  sd  0.163

2/2  observations

J   14.811
H   14.420
Ks  14.341

in RA order, and which shows the two aren't particularly red, yellowish to orange by the looks, from J-Ks, and also gives you some reasonable quality red magnitudes.

If you want to take it further to get an approximate V you can then use the above formula but not quote it as exact in any way, remembering the above mentioned caveats (not that they'll be bad, but folk tend to take catalogue values too damn literal).

So in order of RA you've got V = 16.15 and 16.27 respectively (double check my arithmetic, that's why I've quoted all mags above) which I'd be guesstimate to be good to about 0.2 mags unless we're really being unlucky, which might be something you're happier with.

Interestingly that makes stuff about 0.4 to 0.5 mags fainter than in V estimated from USNO A2.0 derived V via the old Kato/Henden route people usually use (I can't remember which one of them it was now, I think AAH did one for USNO A1.0 and KT extended it to USNO A2.0), and kind of fits with what you are saying about your usual limiting mag and your current result.

Cheers

John