New distance measures for classifying X-ray astronomy data into stellar classes
EntityUAM. Departamento de Matemáticas
PublisherSpringer-Verlag GmbH Germany, part of Springer Nature
10.1007/s11634-018-0309-2Advances in Data Analysis and Classification 18 January (2018): 1-29
ISSN1862-5347 (print); 1862-5355 (online)
Funded byResearch by A.B. and J.C. was supported by the Spanish MEyC grants MTM2013-44045- P and MTM2016-78751-P. K.G. acknowledges the support from the Chandra ACIS Team contract SV4-74018 (G. Garmire & L. Townsley, PIs), issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory on behalf of NASA under contract NAS8-03060
ProjectGobierno de España. MTM2013-44045- P; Gobierno de España. MTM2016-78751-P.
SubjectsClassification; Exponential distribution; Photon interarrival time; Wasserstein distance; X-ray astronomy; Zolotarev metric; Matemáticas
NoteThe final publication is available at Springer via http://dx.doi.org/10.1007/s11634-018-0309-2
Rights© 2018 Springer-Verlag GmbH Germany, part of Springer Nature
The classification of the X-ray sources into classes (such as extragalactic sources, background stars,...) is an essential task in astronomy. Typically, one of the classes corresponds to extragalactic radiation, whose photon emission behaviour is well characterized by a homogeneous Poisson process. We propose to use normalized versions of the Wasserstein and Zolotarev distances to quantify the deviation of the distribution of photon interarrival times from the exponential class. Our main motivation is the analysis of a massive dataset from X-ray astronomy obtained by the Chandra Orion Ultradeep Project (COUP). This project yielded a large catalog of 1616 X-ray cosmic sources in the Orion Nebula region, with their series of photon arrival times and associated energies. We consider the plug-in estimators of these metrics, determine their asymptotic distributions, and illustrate their finite-sample performance with a Monte Carlo study. We estimate these metrics for each COUP source from three different classes. We conclude that our proposal provides a striking amount of information on the nature of the photon emitting sources. Further, these variables have the ability to identify X-ray sources wrongly catalogued before. As an appealing conclusion, we show that some sources, previously classified as extragalactic emissions, have a much higher probability of being young stars in Orion Nebula.
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