Ground-Based Spectroscopic Detection of Iron-Bearing Material in the Dust Tail of BD+05 4868 Ab

Short-period disintegrating exoplanets provide a rare opportunity to probe rocky planet interiors through the composition of their escaping dust tails. BD+05 4868 Ab represents an extreme case: a Mercury-mass planet on a 30.5hr orbit rapidly losing mass and producing a prominent comet-like dust tail. Here we present ground-based low-resolution spectroscopy and multi-site transit photometry obtained with 0.4–0.6m telescopes. We detect a weak absorption feature near 7770 angstroms (Wλ = 0.5 angstroms at 3σ significance) that appears only during predicted dust-tail transit phases and is absent in out-of-transit spectra, suggesting enhanced opacity from iron-bearing material such as Fe oxides or Fe-rich silicates. Complementary photometry reveals asymmetric transit profiles with gradual ingress, structured in transit variations, and extended egress (∆teg = 2.9hr), validating the Hon et al. (2025) model with Ltail = 14R⋆ (∼ 2 Roche-lobe radii). These results provide initial ground-based evidence for iron bearing components in BD+05 4868 Ab’s escaping dust and demonstrate composition constraints achievable with small-aperture telescopes.