ADS Astronomy Abstract Service

Title:		Deep UBVRI photometric calibration of high-latitude fields: SA 57 (1307+30) and Hercules (1720+50)
Authors:		MAJEWSKI, S. R.; KRON, R. G.; KOO, D. C.; BERSHADY, M. A.
Affiliation:		AAObservatories of the Carnegie Inst. of Washington, Pasadena, CA, US ABYerkes Observatory, Williams Bay, WI, US ACUniversity of California, Santa Cruz, CA, US ADUniversity of California, Santa Cruz, CA, US
Journal:		Astronomical Society of the Pacific, Publications (ISSN 0004-6280), vol. 106, no. 706, p. 1258-1270
Publication Date:		12/1994
Category:		Astronomy
Origin:		STI
NASA/STI Keywords:		ASTRONOMICAL PHOTOMETRY, CALIBRATING, DWARF STARS, LATITUDE, STELLAR COLOR, BRIGHTNESS DISTRIBUTION, CHARGE COUPLED DEVICES, COLOR-COLOR DIAGRAM, COLOR-MAGNITUDE DIAGRAM, ERROR ANALYSIS, FAINT OBJECT CAMERA, PIXELS
Bibliographic Code:		1994PASP..106.1258M

Abstract

We present CCD photometric calibration sequences in the magnitude range V = 17-22 for two fields at high Galactic latitude: SA 57 (at the North Galactic Pole) and Hercules (l = 77, b = 35). Photometry to a precision of about 0.02 mag at V = 20 and, in general, better than 0.10 mag at V = 22 was obtained in the Johnson UBV as well as the Kron-Cousins R and I bands. These data are suitable for setting magnitude zero-points in catalogues of faint stars, galaxies, and QSOs, and we apply them to our own photographic catalogs in these two fields. We also note a significant deviation in the (V-R, R-I) color-color diagram for the locus of faint (V is greater than 20) M dwarfs compared to the locus provided by much brighter M dwarfs. This deviation may indicate differences in spectral properties between Population I and older populations of late dwarfs; however we do not discount the possibility that this locus for the faint stars, which appears as a saturation in V-R color with increasing R-I color, is the result of systematic photometric error.