Photometric variability in FU Ori and Z CMa as observed by MOST

TL;DR

This study uses MOST satellite data to analyze optical variability in FU Ori and Z CMa, revealing quasi-periodic features in FU Ori likely caused by disc heterogeneities, while Z CMa shows no clear periodicities.

Contribution

First detailed wavelet analysis of optical variability in FU Ori and Z CMa using MOST satellite data, identifying quasi-periodic features in FU Ori and contrasting behavior in Z CMa.

Findings

Quasi-periodic features in FU Ori suggest plasma parcels in the accretion disc.

Inner disc radius estimated at approximately 4.8 solar radii.

Z CMa shows no significant periodicities, indicating different variability mechanisms.

Abstract

Photometric observations obtained by the MOST satellite were used to characterize optical small scale variability of the young stars FU Ori and Z CMa. Wavelet analysis for FU Ori reveals the possible existence of several 2-9 d quasi-periodic features occurring nearly simultaneously; they may be interpreted as plasma parcels or other localized disc heterogeneities revolving at different Keplerian radii in the accretion disc. Their periods may shorten slowly which may be due to spiralling in of individual parcels toward the inner disc radius, estimated at 4.8+/-0.2 R_sun. Analysis of additional multicolour data confirms the previously obtained relation between variations in the B-V colour index and the V magnitude. In contrast to the FU Ori results, the oscillation spectrum of Z CMa does not reveal any periodicities with the wavelet spectrum possibly dominated by outburst of the Herbig Be component.