[vsnet-chat 1369] Re: [vsnet-chart 108], comparison of GSPC and USNO-based V mags

[Taichi Kato <tkato>]

Re: [vsnet-chart 108], comparison of GSPC and USNO-based V mags

  Moved from vsnet-chart 108:

Brian Skiff wrote:

>      The new Hercules CV is located about 1 degree north of GSPC sequence
> P334.  I compared Kato's 'mv' for the sequence stars between mag. 12.5 and 15.0
> and find a negligible offset.  This suggests an ensemble of stars near 
> the CV wil give magnitudes fairly close to standard V once corrected by
> Kato-san's prescription.  Just one or two stars will not work, since even in
> the sample of five stars in the sequence, one was off by almost two full
> magnitudes, whereas the others were within +/- 0.15.  Thus use several stars
> and reject the outliers.  I also checked the USNO-A2.0 and found the
> magnitudes have a slightly larger offset (following correction), but still
> okay.

  I have checked all GSPC stars against USNO A1.0.  The result is at:

  http://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/others/GSPC/gspc.cmp

  The table is like:

                      GSPC data                     USNO A1.0 data
            =============================== ==================================
               R.A.     Decl.     V    B-V    A1.0 number      r    b   V_exp
            =============================== ==================================
GSPC_P001-A 180808.92 +884923.0  8.22  1.07 USNO1725.587440    7.4  9.3  8.11 
GSPC_P001-B 191448.68 +884657.3 10.47  0.42 duplicate
GSPC_P001-C 180555.85 +884200.9 11.17  0.53 USNO1725.586277   11.1 12.3 11.55 
GSPC_P001-D 180847.46 +883731.5 11.82  0.51 USNO1725.587796   12.0 12.6 12.22 
GSPC_P001-E 181940.56 +884339.1 12.48  1.27 USNO1725.593605   12.5 14.6 13.28 
GSPC_P001-F 184304.94 +884135.1 13.07  0.60 USNO1725.606735   13.3 14.6 13.78 
GSPC_P001-G 183520.34 +884235.7 13.08  1.40 USNO1725.602213   13.2 15.2 13.95 *
GSPC_P002-P 004241.58 +851412.8  9.55  0.50 duplicate
GSPC_P002-Q 004404.71 +850607.7 10.76  0.62 duplicate
GSPC_P002-R 004620.22 +851307.9 11.79  0.53 USNO1725.37108    12.2 13.0 12.50 
GSPC_P002-S 004659.64 +852349.4 12.88  0.69 USNO1725.37667    13.0 14.4 13.52 
GSPC_P002-T 004429.17 +851509.4 13.95  1.01 USNO1725.35596    13.6 15.7 14.38 
GSPC_P002-U 004746.98 +851253.7 14.98  0.97 USNO1725.38371    14.8 16.5 15.43 
GSPC_P002-V 005105.89 +851506.9 15.97  0.70 USNO1725.41149    15.9 17.1 16.35 
GSPC_P002-W 004617.55 +851454.9 16.98  1.06 USNO1725.37064    16.5 18.1 17.10 
GSPC_P003-A 030614.63 +843801.2  8.83  0.22 USNO1725.140767   10.6  9.4 10.15 *
GSPC_P003-B 030029.87 +843851.5  9.98  0.38 no_id
GSPC_P003-C 030720.57 +843104.5 10.74  0.56 USNO1725.141486   11.3 11.6 11.41 
GSPC_P003-D 030045.68 +842116.0 11.53  1.08 USNO1725.137159   11.5 13.3 12.17 
GSPC_P003-E 030511.44 +842403.8 13.31  0.68 USNO1725.140086   13.1 15.1 13.85 
GSPC_P003-F 030554.82 +842804.8 14.85  0.88 USNO1725.140560   14.0 16.6 14.97 

  The entry V_exp is calculated by V = r + 0.375(b-r), the symbol '*'
following this indicates USNO A1.0 flags it with uncertain magnitudes.

  USNO A1.0 stars are selected within 6 arcsec of the GSPC positions.

  Hope this table would help further assesement.

Regards,
Taichi Kato

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