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Description
The VST Photometric H{alpha} Survey of the Southern Galactic Plane and Bulge (VPHAS+) is surveying the southern Milky Way in u, g, r, i and H{alpha} at ~1arcsec angular resolution. Its footprint spans the Galactic latitude range -5{deg}<b<+5{deg} at all longitudes south of the celestial equator. Extensions around the Galactic Centre to Galactic latitudes +/-10{deg} bring in much of the Galactic bulge. This European Southern Observatory public survey, begun on 2011 December 28, reaches down to ~20th magnitude (10{sigma}) and will provide single-epoch digital optical photometry for ~300 million stars. The observing strategy and data pipelining are described, and an appraisal of the segmented narrow-band H{alpha} filter in use is presented. Using model atmospheres and library spectra, we compute main-sequence (u-g), (g-r), (r-i) and (r-H{alpha}) stellar colours in the Vega system. We report on a preliminary validation of the photometry using test data obtained from two pointings overlapping the Sloan Digital Sky Survey. An example of the (u-g, g-r) and (r-H{alpha}, r-i) diagrams for a full VPHAS+ survey field is given. Attention is drawn to the opportunities for studies of compact nebulae and nebular morphologies that arise from the image quality being achieved. The value of the u band as the means to identify planetary-nebula central stars is demonstrated by the discovery of the central star of NGC 2899 in survey data. Thanks to its excellent imaging performance, the VLT Survey Telescope (VST)/OmegaCam combination used by this survey is a perfect vehicle for automated searches for reddened early-type stars, and will allow the discovery and analysis of compact binaries, white dwarfs and transient sources.
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