Candidate O I 7774 Å Absorption from an Escaping Rock-Vapor Outflow of BD+05 4868 Ab

@misc{walker2026candidate,
  title = {{Candidate O I 7774 Å Absorption from an Escaping Rock-Vapor Outflow of BD+05 4868 Ab}},
  author = {Kody M. Walker and James C. Wallace II},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.04986},
  eprint = {2610.04986},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.04986},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - Candidate O I 7774 Å Absorption from an Escaping Rock-Vapor Outflow of BD+05 4868 Ab
AU  - Kody M. Walker
AU  - James C. Wallace II
PY  - 2026
DA  - 2026/10/04
PB  - arXiv
DO  - 10.48550/arxiv.2610.04986
UR  - https://arxiv.org/abs/2610.04986
AB  - Disintegrating rocky planets provide a rare opportunity to probe material escaping directly from intensely irradiated planetary surfaces. We present time-resolved, low-resolution (R≃600) optical spectroscopy and complementary ground-based photometry of BD+05 4868 Ab. The in-transit spectra exhibit an additional unresolved absorption feature near the O I triplet at 7771.94, 7774.17, and 7775.39 Angstroms relative to the out-of-transit baseline. The feature has an equivalent width of W_λ≃1.4±0.2 Angstroms, a maximum differential depth of approximately 9%, and an apparent width of 13-16 Angstroms, comparable to the instrumental resolution. We interpret the feature as candidate O I absorption from an oxygen-bearing mineral-vapor outflow. The 3s ^5S^∘_2 lower level of the triplet lies 9.146 eV above the ground state and cannot be appreciably populated in LTE at the reported planetary temperature, requiring non-LTE excitation. A one-zone forward model in which photoionization, O^+ recombination, radiative cascade, and radiative trapping populate the excited state reproduces the measured equivalent width and instrumentally broadened line profile. The model favors an atomic component with a projected extent larger than the narrow condensed-dust layer and permits gas-to-dust mass-loss ratios of order a few for representative ionizing irradiation. Stellar O I line-profile variations remain the principal alternative at the present spectral resolution. We therefore identify escaping O I as the preferred physical interpretation while retaining the designation candidate O I. High-resolution, phase-resolved spectroscopy can directly test this interpretation by resolving the individual triplet components.
ER  -