[vsnet-alert 10906] re FWD ATEL 1892

[qso at Safe-mail.net]

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I'll have to dig out me own, mindnumbingly unpublished and unpeer reviewed, CMC14 conversion then, V = r' + 0.60(J-Ks)-0.03 where r' is from CMC14 and J and Ks from 2MASS.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