MAGIC's interferometric diameters of θ Ophiuchi and β CMa and comparison with asteroseismic modelling
Abstract
β Cephei type stars are massive (8−25M⊙) and known to have several pulsation modes with periods typically of a few hours. Despite a better understanding of their physics since 1992, the inner structure of these stars involves key stellar physics processes that are still uncertain. Asteroseismology offers insights into these variable stars by analysing pulsation modes, helping to probe their inner layers and understand their structure and mixing processes. We measure the angular diameter of two β Cephei stars, θ Oph and β CMa, using the MAGIC Stellar Intensity Interferometer and compare them, together with the Gaia and Hipparcos parallaxes, to the predictions of the asteroseismic model. The latter are based on Levenberg-Marquardt local minimisation of stellar evolution model parameters to fit observed pulsation modes. In the case of θ Oph, the observed angular diameters are compatible with the asteroseismic model. For β CMa, the radius derived from the angular diameter and the Hipparcos parallax is in tension, at the 2.5σ level, with the asteroseismic prediction. We show that this tension mirrors a pre-existing conflict between independent spectroscopic determinations of the surface gravity of the star, that percent-level systematics of the stellar models are quantitatively insufficient to explain it, and that it most likely points to a bias of the Hipparcos parallax. In the frame of this paper, the statistical uncertainty on the interferometric results is similar to the systematic uncertainty on the parallaxes. With the already implemented addition in early 2024 of the first Large-Sized Telescope (CTAO-North LST-1) to the setup, the uncertainty in the angular diameter of these stars is expected to decrease by an order of magnitude, allowing to further constrain stellar evolution models and parallaxes.
Related
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- Diameters and Temperatures VII: High-angular resolution measurements of Solar-type stars with the CHARA Array
BibTeX
@misc{abe2026magics,
title = {{MAGIC's interferometric diameters of $θ$ Ophiuchi and $β$ CMa and comparison with asteroseismic modelling}},
author = {K. Abe and J. Abhir and A. Abhishek and V. A. Acciari and A. Aguasca-Cabot and I. Agudo and I. Albanese and T. Aniello and C. Arauner and A. Arbet Engels and C. Arcaro and T. T. H. Arnesen and A. Babić and C. Bakshi and U. Barres de Almeida and J. A. Barrio and L. Barrios-Jiménez and I. Batković and J. Becerra González and E. Bernardini and J. Bernete and A. Berti and J. Besenrieder and C. Bigongiari and A. Biland and O. Blanch and Z . Bošnjak and E. Bronzini and I. Burelli and A. Campoy-Ordaz and A. Carosi and R. Carosi and M. Carretero-Castrillo and A. J. Castro-Tirado and D. Cerasole and G. Ceribella and A. Cerviño and Y. Chen and G. Chon and A. Cifuentes Santos and J. L. Contreras and J. Cortina and S. Covino and P. Da Vela and F. Dazzi and A. De Angelis and B. De Lotto and C. Delgado Mendez and F. Di Pierro and R. Di Tria and A. Dinesh and D. Dominis Prester and D. Dorner and M. Doro and L. Eisenberger and D. Elsaesser and L. Foffano and F. Frías García-Lago and Y. Fukazawa and S. García Soto},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.04650},
eprint = {2611.04650},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.04650},
}
RIS
TY - UNPB
TI - MAGIC's interferometric diameters of θ Ophiuchi and β CMa and comparison with asteroseismic modelling
AU - K. Abe
AU - J. Abhir
AU - A. Abhishek
AU - V. A. Acciari
AU - A. Aguasca-Cabot
AU - I. Agudo
AU - I. Albanese
AU - T. Aniello
AU - C. Arauner
AU - A. Arbet Engels
AU - C. Arcaro
AU - T. T. H. Arnesen
AU - A. Babić
AU - C. Bakshi
AU - U. Barres de Almeida
AU - J. A. Barrio
AU - L. Barrios-Jiménez
AU - I. Batković
AU - J. Becerra González
AU - E. Bernardini
AU - J. Bernete
AU - A. Berti
AU - J. Besenrieder
AU - C. Bigongiari
AU - A. Biland
AU - O. Blanch
AU - Z . Bošnjak
AU - E. Bronzini
AU - I. Burelli
AU - A. Campoy-Ordaz
AU - A. Carosi
AU - R. Carosi
AU - M. Carretero-Castrillo
AU - A. J. Castro-Tirado
AU - D. Cerasole
AU - G. Ceribella
AU - A. Cerviño
AU - Y. Chen
AU - G. Chon
AU - A. Cifuentes Santos
AU - J. L. Contreras
AU - J. Cortina
AU - S. Covino
AU - P. Da Vela
AU - F. Dazzi
AU - A. De Angelis
AU - B. De Lotto
AU - C. Delgado Mendez
AU - F. Di Pierro
AU - R. Di Tria
AU - A. Dinesh
AU - D. Dominis Prester
AU - D. Dorner
AU - M. Doro
AU - L. Eisenberger
AU - D. Elsaesser
AU - L. Foffano
AU - F. Frías García-Lago
AU - Y. Fukazawa
AU - S. García Soto
PY - 2026
DA - 2026/11/03
PB - arXiv
DO - 10.48550/arxiv.2611.04650
UR - https://arxiv.org/abs/2611.04650
AB - β Cephei type stars are massive (8−25M_⊙) and known to have several pulsation modes with periods typically of a few hours. Despite a better understanding of their physics since 1992, the inner structure of these stars involves key stellar physics processes that are still uncertain. Asteroseismology offers insights into these variable stars by analysing pulsation modes, helping to probe their inner layers and understand their structure and mixing processes. We measure the angular diameter of two β Cephei stars, θ Oph and β CMa, using the MAGIC Stellar Intensity Interferometer and compare them, together with the Gaia and Hipparcos parallaxes, to the predictions of the asteroseismic model. The latter are based on Levenberg-Marquardt local minimisation of stellar evolution model parameters to fit observed pulsation modes. In the case of θ Oph, the observed angular diameters are compatible with the asteroseismic model. For β CMa, the radius derived from the angular diameter and the Hipparcos parallax is in tension, at the 2.5σ level, with the asteroseismic prediction. We show that this tension mirrors a pre-existing conflict between independent spectroscopic determinations of the surface gravity of the star, that percent-level systematics of the stellar models are quantitatively insufficient to explain it, and that it most likely points to a bias of the Hipparcos parallax. In the frame of this paper, the statistical uncertainty on the interferometric results is similar to the systematic uncertainty on the parallaxes. With the already implemented addition in early 2024 of the first Large-Sized Telescope (CTAO-North LST-1) to the setup, the uncertainty in the angular diameter of these stars is expected to decrease by an order of magnitude, allowing to further constrain stellar evolution models and parallaxes.
ER -