J/AJ/116/1789 J/AJ/116/1789 VI Photometry of NGC 188 T von Hippel A Sarajedini Astron. J. 116 1789 1998 1998AJ....116.1789V Clusters, open Photometry We present V and I broad-band photometry on the Johnson-Kron-Cousins (Landolt 1992) system for the central 6.7' x 6.7' field of the old open cluster NGC 188. Only objects with a probability of >= 95% of being stellar based on SExtractor (Bertin & Arnouts 1996) analysis of 0.7" I-band images are presented. The resulting photometry of 750 sources spans the range from V = 14 (just above the turn-off) to V = 26. We estimate the external accuracy (tie to the Landolt system) to be <= 0.01 mag for the brightest stars (V < 17) and <= 0.032 mag for the fainter stars blueward of V-I = 2. Stars redder than V-I = 2 required an extrapolation of our standard star solution. Equatorial coordinates for equinox J2000 and epoch 1996.10 were kindly derived by Imants Platais, Yale University, using 160 reference stars from the HST Guide Star Catalog. The standard error of the coordinates is 0.14", primarily limited by the accuracy of GSC star positions.

IAU IAU designation The IDs are based on the IAU standard system and include the name of our collaboration, WOCS (WIYN Open Cluster Study), followed by J for J2000 coordinates, and then the coordinates themselves in RA+Dec notation. For example, our first object is WOCS J0049562+851236 with coordinates RA=00:49:56.29 and Dec=+85:12:36.2 (J2000). ------------------------------------------------------------------------------- References: "UBVRI photometric standard stars in the magnitude range 11.5-16.0 around the celestial equator.", 1992, Landolt, A.U., AJ, 104, 340 "SExtractor: Software for source extraction.", 1996, Bertin, E., Arnouts, S., 1996, A&AS, 117, 393 --- RAh Right Ascension hours (J2000) h RAm Right Ascension minutes (J2000) min RAs Right Ascension seconds (J2000) s DEd Declination degrees (J2000) deg DEm Declination minutes (J2000) arcmin DEs Declination seconds (J2000) arcsec X CCD X position pix Y CCD Y position pix V V magnitude mag u_V IRAF estimated V magnitude error mag o_V number of V-bandpass measurements --- I I magnitude mag u_I IRAF estimated I magnitude error mag o_I number of I-band measurements --- prob stellar classification probability % Ted von Hippel NOAO modified by James E. Gass SSDOO/ADC 1998Oct27 J_AJ_116_1789.xml