Accretion Funnel Reconfiguration during an Outburst in a Young Stellar Object: EX Lupi
The Astrophysical Journal(2024)
Abstract
EX Lupi, a low-mass young stellar object, went into an accretion-driven
outburst in March of 2022. The outburst caused a sudden phase change of
112^∘ ± 5^∘ in periodically oscillating multiband
lightcurves. Our high resolution spectra obtained with HRS on SALT also
revealed a consistent phase change in the periodically varying radial
velocities, along with an increase in the radial velocity amplitude of various
emission lines. The phase change and increase of radial velocity amplitude
morphologically translates to a change in the azimuthal and latitudinal
location of the accretion hotspot over the stellar surface, which indicates a
reconfiguration of the accretion funnel geometry. Our 3D MHD simulations
reproduce the phase change for EX Lupi. To explain the observations we explored
the possibility of forward shifting of the dipolar accretion funnel as well as
the possibility of an emergence of a new accretion funnel. During the outburst,
we also found evidence of the hotspot's morphology extending azimuthally,
asymmetrically with a leading hot edge and cold tail along the stellar
rotation. Our high cadence photometry showed that the accretion flow has
clumps. We also detected possible clumpy accretion events in the HRS spectra,
that showed episodically highly blue-shifted wings in the Ca II IRT and Balmer
H lines.
MoreTranslated text
Key words
Young stellar objects,FU Orionis stars,Burst astrophysics
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