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We present a catalogue of candidate Hα emission and absorption line sources and blue objects in the Galactic Bulge Survey (GBS) region.We use a point source catalogue of the GBS fields (two strips of (l × b) = (6° × 1°) centred at b = 1. ° 5 above and below the Galactic Centre), covering the magnitude range 16 ≤ r' ≤ 22.5. We utilize (r' - i', r' - Hα) colour-colour diagrams to select Hα emission and absorption line candidates, and also identify blue objects (compared to field stars) using the r' - i' colour index. We identify 1337 Hα emission line candidates and 336 Hα absorption line candidates. These catalogues likely contain a plethora of sources, ranging from active (binary) stars, early-type emission line objects, cataclysmic variables (CVs) and low-mass X-ray binaries (LMXBs) to background active galactic nuclei (AGN). The 389 blue objects we identify are likely systems containing a compact object, such as CVs, planetary nebulae and LMXBs. Hot subluminous dwarfs (sdO/B stars) are also expected to be found as blue outliers. Cross-matching our outliers with the GBS X-ray catalogue yields 16 sources, including 7 (magnetic) CVs and 1 qLMXB candidate among the emission line candidates and 1 background AGN for the absorption line candidates. One of the blue outliers is a high-state AM CVn system. Spectroscopic observations combined with the multiwavelength coverage of this area, including X-ray, ultraviolet and (time-resolved) optical and infrared observations, can be used to further constrain the nature of individual sources.

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Monthly Notices of the Royal Astronomical Society

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