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The brightness variability of active stars on different timescales by robotic observations
Author(s) -
Messina S.,
Rodonò M.,
Cutispoto G.
Publication year - 2004
Publication title -
astronomische nachrichten
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.394
H-Index - 63
eISSN - 1521-3994
pISSN - 0004-6337
DOI - 10.1002/asna.200410326
Subject(s) - physics , observatory , astronomy , stars , astrophysics , citation , library science , computer science
1.1 Stellar rotation: it modulates the visibility of spotted regions and, consequently, the stellar light flux, spotted regions being cooler than surrounding photosphere (Fig. 1, left panel). Numerous observations collected within a relatively short interval of time, such that the spot pattern remains stable, allow a periodogram analysis to successfully detect with a high confidence level the period of modulation (Fig. 1, right panel). 1.2 Active region growth and decay (ARGD): the season-toseason monitoring allows us to investigate the evolution and lifetime of spot activity centers (Fig. 2, left panel). If ARGD is not properly taken into account, spurious frequencies come out from periodogram analysis, which may lead to incorrect estimates of rotational periods and to spurious variations eventually interpreted as due to surface differential rotation (Fig. 2, right panel). 1.3 Long-term cyclical modulation: the mean magnitude and, consequently, the total spotted area vary in time and cyclically in the case of VY Ari. A reliable estimate of cycle period and amplitude requires that observations are pursued over a sufficiently long time interval, in order to sample several activity cycles (Fig. 3). 1.4 Random (flaring) variability: it is the shortest-scale and unpredictable type of variability (Fig. 4).