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Population-based identification of H α-excess sources in the Gaia DR2 and IPHAS catalogues

Fratta, M; Scaringi, S; Drew, JE; Monguió, M; Knigge, C; Maccarone, TJ; Court, JMC; Iłkiewicz, KA; Pala, AF; Gandhi, P; Gänsicke, B

Population-based identification of H α-excess sources in the Gaia DR2 and IPHAS catalogues Thumbnail


JE Drew

M Monguió

C Knigge

TJ Maccarone

JMC Court

KA Iłkiewicz

AF Pala

P Gandhi

B Gänsicke


We present a catalogue of point-like H α-excess sources in the Northern Galactic Plane. Our catalogue is created using a new technique that leverages astrometric and photomeric information from Gaia to select H α-bright outliers in the INT Photometric H α Survey of the Northern Galactic Plane (IPHAS), across the colour–absolute magnitude diagram. To mitigate the selection biases due to stellar population mixing and to extinction, the investigated objects are first partitioned with respect to their positions in the Gaia colour–absolute magnitude space, and Galactic coordinates space, respectively. The selection is then performed on both partition types independently. Two significance parameters are assigned to each target, one for each partition type. These represent a quantitative degree of confidence that the given source is a reliable H α-excess candidate, with reference to the other objects in the corresponding partition. Our catalogue provides two flags for each source, both indicating the significance level of the H α-excess. By analysing their intensity in the H α narrow band, 28 496 objects out of 7474 835 are identified as H α-excess candidates with a significance higher than 3. The completeness fraction of the H α outliers selection is between 3 and 5 per cent. The suggested 5σ conservative cut yields a purity fraction of 81.9 per cent.


Fratta, M., Scaringi, S., Drew, J., Monguió, M., Knigge, C., Maccarone, T., …Gänsicke, B. (2021). Population-based identification of H α-excess sources in the Gaia DR2 and IPHAS catalogues. Monthly Notices of the Royal Astronomical Society, 505(1), 1135-1152.

Journal Article Type Article
Acceptance Date Apr 27, 2021
Online Publication Date May 21, 2021
Publication Date 2021-07
Deposit Date Aug 18, 2021
Publicly Available Date Aug 19, 2021
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 505
Issue 1
Pages 1135-1152


Accepted Journal Article (9.5 Mb)

Copyright Statement
© 2021 The Author(s).<br /> Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative<br /> Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium,<br /> provided the original work is properly cited.

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