Variability at the Edge: Optical Near/IR Rapid Cadence Monitoring of Newly Outbursting FU Orionis Object HBC 722

Abstract

We present the detection of day-timescale periodic variability in the r-band lightcurve of newly outbursting FU Orionis-type object HBC 722, taken from > 42 nights of observation with the CQUEAN instrument on the McDonald Observatory 2.1m telescope. The optical/near-IR lightcurve of HBC 722 shows a complex array of periodic variability, clustering around 5.8 day (0.044 mag amplitude) and 1.28 day (0.016 mag amplitude) periods, after removal of overall baseline variation. We attribute the unusual number of comparable strength signals to a phenomenon related to the temporary increase in accretion rate associated with FUors. We consider semi-random "flickering", magnetic braking/field compression and rotational asymmetries in the disk instability region as potential sources of variability. Assuming the 5.8 day period is due to stellar rotation and the 1.28 day period is indicative of Keplerian rotation at the inner radius of the accretion disk (at 2 R(star)), we derive a B-field strength of 2.2-2.7 kG, slightly larger than typical T Tauri stars. If instead the 5.8 day signal is from a disk asymmetry, the instability region has an outer radius of 5.4 R(star), consistent with models of FUor disks. Further exploration of the time domain in this complicated source and related objects will be key to understanding accretion processes.

18 pages, 4 figures, accepted to ApJ Part 1

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Cited by in corpus (14)

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• High Resolution Optical and NIR Spectra of HBC 722
• Inferring possible magnetic field strength of accreting inflows in EXor-type objects from scaled laboratory experiments
• Insights into the inner regions of the FU Orionis disc
• X-ray emission from an FU Ori star in early outburst: HBC 722
• Photometric and spectroscopic variability of the FUor star V582 Aurigae
• A multi-epoch, multi-wavelength study of the classical FUor V1515 Cyg approaching quiescence
• Photometric and spectroscopic study of the EXor-like eruptive young star Gaia19fct
• Color Variability of HBC 722 in the Post-Outburst Phases
• LkH$\alpha$ 225 (V1318 Cyg) South in Outburst
• The FUor star V2493 Cyg (HBC 722) -- eleven years at maximum brightness
• Gaia20bdk -- a new FUor in Sh 2-301 Star Forming Region