Calibration of the MACHO photometry database

C. Alcock, R. A. Allsman, D. R. Alves, T. S. Axelrod, A. C. Becker, D. P. Bennett, K. H. Cook, A. J. Drake, K. C. Freeman, M. Geha, K. Griest, M. J. Lehner, S. L. Marshall, D. Minniti, B. A. Peterson, P. Popowski, M. R. Pratt, C. A. Nelson, P. J. Quinn, C. W. StubbsW. Sutherland, A. B. Tomaney, T. Vandehei, D. L. Welch

Research output: Contribution to journalArticlepeer-review

120 Citations (Scopus)

Abstract

The MACHO Project is a microlensing survey that monitors the brightnesses of ∼60 million stars in the Large Magellanic Cloud (LMC), Small Magellanic Cloud, and Galactic bulge. Our database presently contains about 80 billion photometric measurements, a significant fraction of all astronomical photometry. We describe the calibration of MACHO two-color photometry and transformation to the standard Kron-Cousins V and R system. Calibrated MACHO photometry may be properly compared with all other observations on the Kron-Cousins standard system, enhancing the astrophysical value of these data. For ∼9 million stars in the LMC bar, independent photometric measurements of ∼20,000 stars with V ≲ 18 mag in field-overlap regions demonstrate an internal precision σV = 0.021, σR = 0.019, σV-R = 0.028 mag. The accuracy of the zero point in this calibration is estimated to be ±0.035 mag for stars with colors in the range -0.1 mag < V - R < 1.2 mag. A comparison of calibrated MACHO photometry with published photometric sequences and new Hubble Space Telescope observations shows agreement. The current calibration zero-point uncertainty for the remainder of the MACHO photometry database is estimated to be ±0.10 mag in V or R and ±0.04 mag in V - R. We describe the first application of calibrated MACHO data: the construction of a color-magnitude diagram used to calculate our experimental sensitivity for detecting microlensing in the LMC.

Original languageEnglish
Pages (from-to)1539-1558
Number of pages20
JournalPublications of the Astronomical Society of the Pacific
Volume111
Issue number766
DOIs
Publication statusPublished - Dec 1999

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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