Multicolor Photometry of 145 of the H [CSC]ii[/CSC] Regions in M33

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Abstract
This paper is the first in a series presenting CCD multicolor photometry for 145 H II regions, selected from 369 candidate regions from Boulesteix et al., in the nearby spiral galaxy M33. The observations, which covered the whole area of M33, were carried out with the Beijing Astronomical Observatory 60/90 cm Schmidt telescope, in 13 intermediate-band filters, covering a range of wavelengths from 3800 to 10000 Å. This procedure provides a series of maps that can be converted into a multicolor map of M33, in pixels of 17 × 17. Using aperture photometry we obtain the spectral energy distributions (SEDs) for these H II regions. We also give their identification charts. Using the relationship between the Beijing-Arizona-Taiwan-Connecticut intermediate-band system used for the observations and the UBVRI broadband system, the magnitudes in the B and V bands are then derived. Histograms of the magnitudes in V and in B-V are plotted, and the color-magnitude diagram is also given. The distribution of magnitudes in the V band shows that the apparent magnitude of almost all the regions is brighter than 18, corresponding to an absolute magnitude of -6.62 for an assumed distance modulus of 24.62, which corresponds to a single main-sequence O5 star, while the distribution of color shows that the sample is blue, with a mode close to -0.05, as would be expected from a range of typical young clusters.
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