Robust detection of quasi-periodic variability : HAWK-I mini survey of late-T dwarfs
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We present HAWK-I J-band light curves of five late-type T dwarfs (T6.5–T7.5) with a typical duration of 4 h and investigate the evidence for quasi-periodic photometric variability on intra-night time-scales. Our photometry reaches precisions in the range 7–20 mmag, after removing instrumental systematics that correlate with sky background, seeing and airmass. Based upon a Lomb–Scargle periodogram analysis, the latest object in the sample – ULAS J2321 (T7.5) – appears to show quasi-periodic variability with a period of 1.64 h and an amplitude of 3 mmag. Given the low amplitude of variability and presence of systematics in our light curves, we discuss a Bayesian approach to robustly determine if quasi-periodic variability is present in a light curve affected by red noise. Using this approach, we conclude that the evidence for quasi-periodic variability in ULAS J2321 is not significant. As a result, we suggest that studies which identify quasi-periodic variables using the false alarm probability from a Lomb–Scargle periodogram are likely to overestimate the number of variable objects, even if field stars are used to set a higher false alarm probability threshold. Instead we argue that a hybrid approach combining a false alarm probability cut, followed by Bayesian model selection, is necessary for robust identification of quasi-periodic variability in light curves with red noise.
Littlefair , S P , Burningham , B & Helling , C 2017 , ' Robust detection of quasi-periodic variability : HAWK-I mini survey of late-T dwarfs ' , Monthly Notices of the Royal Astronomical Society , vol. 466 , no. 4 , pp. 4250-4258 . https://doi.org/10.1093/mnras/stw3376
Monthly Notices of the Royal Astronomical Society
Copyright © 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. his work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at: https://doi.org/10.1093/mnras/stw3376
DescriptionSPL is supported by STFC grant ST/M001350/1. BB acknowledges financial support from the European Commision in the form of a Marie Curie International Outgoing Fellowship (PIOF-GA-2013-629435). Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 090.C-0721. ChH highlights financial support of the European Community under the FP7 by the ERC starting grant 257431.
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