paper

A Multi-Color Optical Survey of the Orion Nebula Cluster. Part I: the Catalog

arXiv:0906.4336 · doi:10.1088/0067-0049/183/2/261

Abstract

We present U, B, V, I broad-band, 6200A TiO medium-band and Halpha photometry of the Orion Nebula Cluster obtained with the WFI imager at the ESO/MPI 2.2 telescope. The nearly-simultaneous observations cover the entire ONC in a field of about 34x34 arcmin. They enable us to determine stellar colors avoiding the additional scatter in the photometry induced by stellar variability typical of pre-main sequence stars. We identify 2,612 point-like sources in I band, 58%, 43% and 17% of them detected also in V, B and U, respectively. 1040 sources are identified in Halpha band. In this paper we present the observations, the calibration techniques, and the resulting catalog. We show the derived CMD of the population and discuss the completeness of our photometry. We define a spectro-photometric TiO index from the fluxes in V, I, and TiO-band. We find a correlation between the index and the spectral type valid for M-type stars, that is accurate to better than 1 spectral sub-class for M3-M6 types and better than 2 spectral subclasses for M0-M2 types. This allows us to newly classify 217 stars. We subtract from our Halpha photometry the photospheric continuum at its wavelength, deriving calibrated line excess for the full sample. This represents the largest Halpha star catalog obtained to date on the ONC. This data set enables a full re-analysis of the properties of the Pre-Main Sequence population in the Orion Nebula Cluster to be presented, in an accompanying paper.

arXiv comment15 pages, 15 figures. To be published in The Astrophysical Journal Supplement Series

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