@article{10272/28604,
year = {2026},
url = {https://hdl.handle.net/10272/28604},
abstract = {Context. Long-period binary systems containing a B-type hot subdwarf (sdB) and a main sequence (MS) companion are thought to originate from binary interactions involving stable mass transfer from the red giant, which is the progenitor of the sdB, to the MS companion. However, despite the recent progress in modelling their population, some of their observed properties are not fully understood. Because the determination of their orbits requires extended campaigns of high-resolution spectroscopic observations, there have only been a limited number of long-period sdB binaries with completely determined orbital parameters studied thus far.
Aims. We aim to expand the current sample of long-period sdB binaries with fully determined orbital parameters through the analysis of high-resolution spectroscopic data. In addition, we analyse the atmospheric parameters of the cool companions. Increasing the number of well-characterised systems will provide valuable insights into their formation channels and main characteristics.

Methods. A sample of 32 wide binary systems containing sdB stars was selected for the analysis of the radial velocity (RV) curves of both companions. The dataset consisted of high-resolution spectra obtained with the HERMES and UVES spectrographs. The orbital parameters were derived by simultaneously fitting Keplerian orbits to the RVs of the sdB and its companion. The atmospheric parameters of the cool companions were determined using the GSSP code, which analyses the master spectra of the systems with a grid of local thermal equilibrium (LTE) atmospheric models. An additional sample of wide sdB binaries was built by cross-matching the Gaia NSS catalogue with literature catalogues of sdB candidates and spectroscopically confirmed sdB systems. The outcomes from both samples were compared with existing theoretical models to assess their consistency with current formation and evolutionary scenarios.

Results. We obtained complete orbital solutions for 32 wide sdB binaries. The orbital period distribution of the ground-based spectroscopic sample is in reasonable agreement with population-synthesis predictions, except for two outliers. The CMD further suggests that current models overpredict systems with the coolest companions, since the observed systems with BP − RP > 0.3 are associated with companions hotter than 6000 K. The observed period-mass ratio distribution is consistent with recent population synthesis predictions and suggests that the unexplained second branch found in these models is mainly populated by old systems. Setting aside the two long-period outliers, we find the data do not support a clear increase in eccentricity with orbital period, whereas the Gaia-based candidate sample displays a discrepant behaviour, owing to selection effects and larger uncertainties.},
organization = {Grant Agency of the Czech Republic},
organization = {Fondecyt Regular program},
organization = {Australian Research Council (ARC) Centre of Excellence for Grav- itational Wave Discovery (OzGrav),},
organization = {J.V. acknowledges support from the Grant Agency of the Czech Republic (GAˇ CR 22-34467S). M.V. acknowledges funding support from the Fondecyt Regular projects 1211491 and 1250525. A.B. acknowledges support from the Australian Research Council (ARC) Centre of Excellence for Gravitational Wave Discovery (OzGrav), through project number CE230100016. This workhasmadeuseofdatafromtheEuropeanSpaceAgency(ESA)missionGaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/ web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Based on observations collected at the European Southern Observatory under ESO programs 088.D-0364, 093.D-0629, 096.D-0180, 097.D-0110, 098.D-0018, 099.D-0014, 0100.D-0082, 0101.D-0200, 0102.D0255, 0103.D-0129, 0104.D-0135, 105.20L2.001, 106.2105.001, 113.26RL.001, 114.274R.001, 115.287Y.001 and 116.28ZZ.001.},
publisher = {EDP Sciences},
keywords = {Binaries: spectroscopic},
keywords = {Stars: evolution},
keywords = {Stars: fundamental parameters},
keywords = {Subdwarfs},
title = {Wide B-type hot subdwarf binaries I. Orbital and atmospheric parameters},
doi = {10.1051/0004-6361/202659320},
author = {Molina González, Francisco and Vos, Joris and Bobrick, Alexey and Vuckovic, Maja},
}