XP-TEAL: Gaia XP tool for emission and absorption lines

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Abstract
Context. With Gaia ’s third Data Release (DR3), low-resolution BP/RP (XP) spectra became available for more than 219 million sources. In previous work, we developed a fast method for detecting absorption and emission lines while measuring their equivalent widths directly from the XP spectral coefficients. Aims. We conduct a systematic search for H α emitters in the Gaia DR3 XP spectra. Methods. We measured the equivalent width of the Balmer H α line for all sources with Gaia XP spectra and selected an initial sample of 556 100 sources depicting an H α emission-like feature at 2 σ level or above. Using a semi-supervised classifier complemented by manual spectral labelling, we removed sources that merely masqueraded as emission-line stars. Results. We find that 95% of the initial candidates are most likely cool M-type stars, where a molecular absorption band gives rise to a local maximum that can mimic H α emission. Subsequently, 28 394 sources were flagged as bona fide H α emitters using the Gaia DR3 XP spectra. The majority are Be-like candidates (26 287), M-type emission-line stars (717), Herbig Ae/Be candidates (525), quasi-stellar objects (204), Wolf–Rayet stars (177), cataclysmic variables (51), and carbon stars (18), among other sources. Our equivalent widths and stellar classifications agree well with results from higher-resolution studies and recent Gaia XP spectra-based catalogues. Ground-based spectroscopic follow-up for some of the newly found H α emitters reinforces our confidence in the catalogue.

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