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Differential Photometry In Practice

21 Jul 2017, 15:52 UTC
Differential Photometry In Practice
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Photometry shows the changes in luminosity taking place in a star, which in M stars are mainly due to stellar activity. They can be shown as rotational modulation in the light curves as a consequence of the presence of starspots or any other co-rotating structure in the stellar surface. They can also be shown as sporadic and strong flares or simply as larger of smaller stellar activity episodes. Coordinated photometry simultaneously acquired with radial velocity (RV) measurements, collected with high-resolution spectrographs, is important to discard spurious signals (instrumental and/or stellar activity) in the interpretation of the spectroscopic data.
The differential photometry technique consists in obtaining measurements on the main target (the expected variable star, V) and one or more reference stars (the comparison stars, Ci). Then, the magnitude differences V-C1, C2-C1, etc., relative to the main comparison star C1, can be determined and the changes in luminosity of V are revealed. The rest of the comparison stars (C2, C3, etc) are used as check stars, to make sure that the variability that we are measuring comes effectively from the main target V, and not from C1.
Star field centred in Proxima Centuri. Selected comparison stars are labeled from C1 ...

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