Fundamentals of Differential and All-Sky Aperture Photometry Analysis for an Open Cluster

This article provides detailed description on the fundamentals of aperture photometry analysis. The differential and all-sky aperture photometry techniques are described thoroughly to depict the difference between the two techniques and their selection for determining the stars' magnitudes and their respective magnitude errors. The crucial calibration parameters required for the all-sky photometry analysis such as atmospheric extinction-coefficient, air-mass, zero point, color term and color index are discussed comprehensively with their extraction from the Sloan Digital Sky Survey (SDSS) archive. The all-sky aperture photometry technique is applied on the stars of the open cluster NGC 2420 to determine their calibrated magnitudes and magnitude errors in the g, r, and i bands. The images required for the analysis are extracted from data release DR12 of SDSS III archive. Herein, the photometry analysis is performed by the Makali'i: SUBARU Image Processor, a Windows-based software. This software has a simple yet effective GUI and it provides the starlight minus the background sky light value with a single click. This article would aid in providing the insight into the physics of aperture photometry by manually scanning the astronomical images. In addition, the g, r, and i magnitudes are transformed to B, V, and R band magnitudes of Johnson-Cousins UBVRI photometric system. The color magnitude diagrams for both standard photometry systems are also provided.