Binary-object spectral-synthesis in 3D (BOSS-3D): Modelling Hαemission in the enigmatic multiple system LB-1

L. Hennicker*, N. D. Kee, T. Shenar, J. Bodensteiner, M. Abdul-Masih, I. El Mellah, H. Sana, J. O. Sundqvist

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Context. To quantitatively decode the information stored within an observed spectrum, detailed modelling of the physical state and accurate radiative transfer solution schemes are required. The accuracy of the model is then typically evaluated by comparing the calculated and observed spectra. In the analysis of stellar spectra, the numerical model often needs to account for binary companions and 3D structures in the stellar envelopes. The enigmatic binary (or multiple) system LB-1 constitutes a perfect example of such a complex multi-D problem. Thus far, the LB-1 system has been indirectly investigated by 1D stellar-atmosphere codes and by spectral disentangling techniques, yielding differing conclusions about the nature of the system (e.g., a B-star and black-hole binary with an accretion disc around the black hole or a stripped-star and Be-star binary system have been proposed). Aims. To improve our understanding of the LB-1 system, we directly modelled the phase-dependent Hα line profiles of this system. To this end, we developed and present a multi-purpose binary-object spectral-synthesis code in 3D (BOSS-3D). Methods. BOSS-3D calculates synthetic line profiles for a given state of the circumstellar material. The standard pz-geometry commonly used for single stars is extended by defining individual coordinate systems for each involved object and by accounting for the appropriate coordinate transformations. The code is then applied to the LB-1 system, considering two main hypotheses, a binary containing a stripped star and Be star, or a B star and a black hole with a disc. Results. Comparing these two scenarios, neither model can reproduce the detailed phase-dependent shape of the Hα line profiles. A satisfactory match with the observations, however, is obtained by invoking a disc around the primary object in addition to the Be-star disc or the black-hole accretion disc. Conclusions. The developed code can be used to model synthetic line profiles for a wide variety of binary systems, ranging from transit spectra of planetary atmospheres, to post-asymptotic giant branch binaries including circumstellar and circumbinary discs and massive-star binaries with stellar winds and disc systems. For the LB-1 system, our modelling provides strong evidence that each object in the system contains a disc-like structure.

Original languageEnglish
Article numberA17
JournalAstronomy and Astrophysics
Volume660
DOIs
StatePublished - 1 Apr 2022
Externally publishedYes

Funding

FundersFunder number
Belgian Research Foundation Flanders
SPAWN ERC863412
National Science Foundation
H2020 Marie Skłodowska-Curie Actions101024605
European Commission
European Research Council
Fonds Wetenschappelijk OnderzoekG0H9218N, G0F8H6N
Horizon 2020772225

    Keywords

    • Binaries: spectroscopic
    • Methods: numerical
    • Radiative transfer
    • Stars: black holes
    • Stars: emission-line, Be

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