Kavli Affiliate: Roland Vanderspek
| First 5 Authors: Masafumi Niwano, Michael M. Fausnaugh, Ryan M. Lau, Kishalay De, Roberto Soria
| Summary:
The mechanism of X-ray outbursts in Be X-ray binaries remains a mystery, and
understanding their circumstellar disks is crucial for a solution of the
mass-transfer problem. In particular, it is important to identify the Be star
activities (e.g., pulsations) that cause mass ejection and, hence, disk
formation. Therefore, we investigated the relationship between optical flux
oscillations and the infrared (IR) excess in a sample of five Be X-ray
binaries. Applying the Lomb-Scargle technique to high-cadence optical light
curves from the Transiting Exoplanet Survey Satellite (TESS), we detected
several significant oscillation modes in the 3 to 24 hour period range for each
source. We also measured the IR excess (a proxy for disk growth) of those five
sources, using J-band light curves from Palomar Gattini-IR. In four of the five
sources, we found anti-correlations between the IR excess and the amplitude of
the main flux oscillation modes. This result is inconsistent with the
conventional idea that non-radial pulsations drive mass ejections. We propose
an alternative scenario where internal temperature variations in the Be star
cause transitions between pulsation-active and mass-ejection-active states.
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