We present a catalogue of point-source Halpha emission line objects selected from the INT/WFC Photometric H$alpha$ Survey of the Northern Galactic Plane (IPHAS). The catalogue covers the magnitude range 13 < r < 19.5 and includes northern hemisphere
sources in the Galactic latitude range -5 < b < 5 degress. It is derived from ~1500 square degress worth of imaging data, which represents 80 percent of the final IPHAS survey area. The electronic version of the catalogue will be updated once the full survey data becomes available. In total, the present catalogue contains 4853 point sources that exhibit strong photometric evidence for Halpha emission. We have so far analyzed spectra for ~300 of these sources, confirming more than 95 percent of them as genuine emission-line stars. A wide range of stellar populations are represented in the catalogue, including early-type emission line stars, active late-type stars, interacting binaries, young stellar objects and compact nebulae. The spatial distribution of catalogue objects shows overdensities near sites of recent or current star formation, as well as possible evidence for the warp of the Galactic plane. Photometrically, the incidence of Halpha emission is bimodally distributed in r-i. The blue peak is made up mostly of early-type emission line stars, whereas the red peak may signal an increasing contribution from other objects, such as young/active low-mass stars. We have cross-matched our Halpha-excess catalogue against the emission-line star catalogue of Kohoutek & Wehmeyer, as well as against sources in SIMBAD. We find that fewer than 10 per cent of our sources can be matched to known objects of any type. Thus IPHAS is uncovering an order of magnitude more faint (r > 13) emission line objects than were previously known in the Milky Way.
We report the discovery of 11 new cataclysmic variable (CV) candidates by the Isaac Newton Telescope (INT) Photometric H alpha Survey of the northern Galactic plane (IPHAS). Three of the systems have been the subject of further follow-up observations
. For the CV candidates IPHAS J013031.90+622132.4 and IPHAS J051814.34+294113.2, time-resolved optical spectroscopy has been obtained and radial-velocity measurements of the H alpha emission-line have been used to estimate their orbital periods. A third CV candidate (IPHAS J062746.41+ 014811.3) was observed photometrically and found to be eclipsing. All three systems have orbital periods above the CV period-gap of 2-3 h. We also highlight one other system, IPHAS J025827.88+635234.9, whose spectrum distinguishes it as a likely high luminosity object with unusual C and N abundances.
