[vsnet-alert 10908] Re: re FWD ATEL 1892

[Brian Skiff]

     ASAS-3 shows V=14.03 for this star, though the uncertainty
is large.  This is consistent with the V=13.99 derived from CMC14,
however.  So again NOMAD is ~0.7 mag too bright.  Not good!

\Brian


On Mon, 2009-01-05 at 21:54 +0000, qso at Safe-mail.net wrote:
> ATEL 1892 informs :-
> 
> "The V-band magnitudes of the object were obtained with a comparison star located at RA=12:39:30.08, Dec=+04:39:53.2 (V=13.320; NOMAD)."
> 
> Hmmm, around mag 13 is a bit bright for SDSS usage in any conversion.
> 
> I'll have to dig out me own, mindnumbingly unpublished and unpeer reviewed, CMC14 conversion then, V = r' + 0.60(J-Ks)-0.03 where r' is from CMC14 and J and Ks from 2MASS.
> 
> That gives the V mag of the calibration star as 13.99, and the two observations quoted in ATEL 1892 then would become 16.4 and 16.8 ish, errors still around 0.1.
> 
> Swift doesn't say when exactly on Jan 2nd the U band was measured, so the potential U_swift-V_cmc ~ +0.4 from the Kanata measure on Jan 2.8 might include some decay in V.
> 
> If the calibration star is V 13.99, that is.
> 
> Incidentally, a bit noisy this relatively faint, but the NSVS data suggest the calibration star is constant enough.
> 
> http://skydot.lanl.gov/nsvs/star.php?num=13207748&mask=15636
> 
> Cheers
> 
> John