Landolt G 163-50 + 51 field star correction

American Association of Variable Star Observers (AAVSO)
Fri, 10/28/2022 - 19:51

     In collecting data for stars in the field of the white-dwarf/M-dwarf pair G163-50 and -51, I notice that in Landolt's 2009 standards paper he has some additional lettered stars that extend the sequence among ordinary stars.  The series gives a good range in colors in a single field.  However, the photometry for the star at the coordinates and chart mark for star E are incorrect.  That star is about a magnitude brighter than Arlo's values.  The intended star is instead about 50" due south of star B on the chart.  This is confirmed by concordant values by Clem & Landolt (2013) CCD data and in Peter Stetson's 'homogeneous photometry' files.  Data rounded to 0.01 precision follow.

Landolt chart star G163-51 E   11 07 22.33 -05 16 13.9   V=13.27, B-V=0.90, U-B=0.41, V-R=0.50,R-I=0.47,V-I=0.97

GSC 4927-0266   11 07 32.84 -05 13 26.2   V=14.49, B-V=0.63, U-B=0.00, V-R=0.37, V-R=0.35, V-I=0.72

Arlo made only a single observation of the second star, so his values are not precise; there is still some uncertainty between Clem & Landolt and Stetson on the U-B color.  The LAMOST spectrum of the star shows type G2V, consistent with the UBV colors.  FWIW, the Stetson file includes the many nights of Clem & Landolt data re-reduced and merged with numerous other datasets.