Observations of high-frequency variability in the chromospherically active star V390 Aurigae

Abstract

V390 Aurigae is a rapidly rotating, chromospherically active late-type giant. The X-ray emission from the corona of V390 Aur, observed by the XMM–Newton space observatory, indicates intense flaring activity on this star. Multisite, coordinated high-speed UBVRI photometry of V390 Aur and a reference star was carried out in years 2002–2009 at the Peak Terskol, Crimean and Belogradchik observatories, aimed at finding persistent variability on millisecond-to-subsecond time-scales. We find that variability is peaked at f ∼ 1 Hz, gradually subsiding in the range 0.1–10 Hz, with the peak rms amplitude of 0.005 mag in the UBV bands. We conclude that the light curves of V390 Aur contain microflares that may be responsible for the observed activity on subsecond time-scales, with a relative power of fluctuations reaching (2.1–3.0) × 10−5 in the UBV bands.