![Schematics of a HAeBe star accreting material from its protoplanetary disc with an ongoing giant planet formation. The giant planet opens a disc gap, preventing the larger dust grains from moving inwards. The HAeBe star has a convective core (red), a radiative envelope (blue), and the stellar photosphere (yellow).-- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/09/The-refractory.png?fit=1200%2C676&ssl=1)
[astro-ph.EP] Context. Phosphorus (P) is an essential element for life on Earth and a potential tracer of planet formation history. However, there has been no detection of P-bearing molecules in protoplanetary discs so far.
Herbig Ae/Be stars constantly accrete matter from their pro- toplanetary disc, which alters the composition of the stellar photosphere due to their shallow convective, or fully radiative, envelope.
The altered surface composition reflects the composition of the accreting matter, and thus that of the inner protoplanetary disc. This accretion contamination of stellar photosphere can persist after accretion has ended in young A and B-type stars (age < 50 Myr). Aims. We aim to quantify the fraction of P locked in dust (the refractory fraction of P) compared to gas in the inner protoplanetary disc around Herbig Ae/Be stars.
Methods. We measure the stellar parameters and abundance of 5 Herbig Ae/Be stars using optical and UV spectra, to compare their P and Fe abundances. We also used a 20 Myrs old main sequence B-type star, which has P and Fe abundance estimated from optical spectrum. Fe is assumed to be completely locked in refractory reservoirs in the inner disc. A parameterised relationship between the stellar P and Fe abundance gives the fraction of P locked in refractory reservoirs.
Results. We find the refractory fraction of P in the inner protoplanetary disc to be > 96 % within 95th percentile of the posterior distribution.
Conclusions. Consistent with a previous finding in the HD 100546 system, we conclude most of the P in the inner protoplanetary disc is locked in dust, likely in refractory minerals like schreibersite or apatite.
Our result, combined with the low cosmic abundance of P, is also consistent with the lack of infrared and mm-wavelength observations of P-bearing molecules in protoplanetary discs to date.
Sandipan P. D. Borthakur (1,2,3), Mihkel Kama (4,3), Luca Fossati (1), Colin P. Folsom (3), Anna Aret (3), Christiane Helling (1,2) ((1) Space Research Institute, Austria, (2) Graz University of Technology, Austria, (3) Tartu Observatory, Estonia,(4) University College London, UK)
Comments: Accepted for publication in the A&A Letters, 9 pages (5 pages in Appendices), 11 figures, 6 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2608.29254 [astro-ph.EP] (or arXiv:2608.29254v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2608.29254
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From: Sandipan Borthakur
[v1] Sat, 29 Aug 2026 13:14:09 UTC (3,190 KB)
https://arxiv.org/abs/2608.29254
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