Surface brightness inhomogeneity on the helium-rich hot subdwarf in the X-ray binary HD 49798

@misc{jeffery2026surface,
  title = {{Surface brightness inhomogeneity on the helium-rich hot subdwarf in the X-ray binary HD 49798}},
  author = {C. Simon Jeffery and Gavin Ramsay},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.02314},
  eprint = {2609.02314},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.02314},
}

TY  - UNPB
TI  - Surface brightness inhomogeneity on the helium-rich hot subdwarf in the X-ray binary HD 49798
AU  - C. Simon Jeffery
AU  - Gavin Ramsay
PY  - 2026
DA  - 2026/09/02
PB  - arXiv
DO  - 10.48550/arxiv.2609.02314
UR  - https://arxiv.org/abs/2609.02314
AB  - HD 49798 is an X-ray binary consisting of a hot helium-rich subdwarf primary and an accreting compact companion with an orbital period of 1.55 d. TESS observations of its optical light curve suggest short-period brightenings superimposed on a sinusoidal variation. The latter can be attributed to the tidal deformation of the primary, while frequency analysis of the additional variations shows up to eleven frequencies which form an harmonic series based on a period of 1.4 d, in excellent agreement with the stellar rotation period inferred independently from spectroscopy. These brightenings may be explained by a slowly changing and inhomogeneous temperature distribution across the surface of the hot subdwarf, such as might be associated with a magnetic field or with the presence of Rossby waves in the stellar envelope.
ER  -