[vsnet-chart 224] NGC 2442 T&B sequence

[Brian Skiff <bas@lowell.edu>]

     Kato-san's chart for NGC 2442 based on USNO-A1.0 stars almost certainly
has a severe scale error at the faint end---those mag. 22 stars simply are not
that faint!  I show below the rough (0.1-mag.) sequence shown on the
Thompson & Bryan chart for the galaxy.  I also show the two fainter stars of
the GSPC sequence for the relevant sky survey plate, and USNO-A1.0 (not A2.0)
magnitudes for the stars.  As is fairly evident, in this magnitude range the
A1.0 blue magnitudes are not too far from standard B magnitudes, albeit noisy.
However, the red magnitudes are about 0.5 mag. too faint compared to Cousins R
near the galaxy and a full magnitude in error (too faint) in the GSPC sequence
region.  (The A1.0 blue mags are about 0.5 too bright compared to the GSPC
stars.)  
     CCD observers are probably best off using the T&B series, especially if
you can get all or most of the stars in the frame and use a mean offset from
all available stars to adjust the zero-point.

\Brian



T&B        RA  (2000)  Dec        GSC      V     B-V    USNO-A1.0 mags
111      7 35 13.7  -69 36 34  9183-1629  11.1
123      7 35 37.5  -69 30 52  9183-1042  12.3
137      7 35 10.9  -69 38 28  9183-1246  13.7          mr=14.0, mb=14.4
143      7 35 13.0  -69 29 57  9183-0955  14.3          mr=13.7, mb=14.4
151      7 37 02.9  -69 32 36             15.1          mr=15.3, mb=16.2
159      7 36 54.2  -69 30 21             15.9          mr=16.0, mb=16.9

S059-F   7 59 54.5  -70 16 36  9184-0980  13.29  1.45   mr=13.3, mb=14.1
S059-G   8 00 12.3  -70 13 52  9197-0645  14.44  0.60   mr=14.9, mb=14.6

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