Full orbital solution and dynamical masses for a new shell-Be + sdOB binary AN Col
Abstract
AN~Col is a shell Be star that has shown transient spectral features caused by a hot, evolved companion on a months-long orbit. If confirmed, this would place it among the growing category of post-mass-transfer spun-up Be + stripped subdwarf OB-type (sdOB) binaries. Characterizing the binary orbit enables obtaining dynamical masses, to provide a rare anchor for models of binary evolution and mass transfer. We present a full 3-dimensional orbital solution, dynamical masses, and dynamical parallax, for the newly discovered Be + sdOB binary AN~Col. As a prerequisite to obtain a reliable orbital solution, we need to characterize the disk-wide density oscillation cycle that gives rise to the dominant spectroscopic cycles in order to separate the weaker periodic orbital variations. We use near-IR interferometry time series from GRAVITY to confirm the companion and to map the relative astrometric orbit. With the knowledge of the orbital period, we identify spectral lines that trace the orbit of each of the two stellar components and we measure their radial velocities to obtain a double-lined spectroscopic orbit. Combining interferometry and spectroscopy, we derive the full 3-dimensional orbital solution. The disk has completed three full oscillation cycles since 2010, with a cycle length of ~5.1 yr. The ~87.7-day orbit is compatible with edge-on orientation, but the lack of eclipses in TESS light curves limits the orbital inclination to 88.4∘ or less. The resulting masses are MBe = 8.39±0.67 Msun and MsdOB = 0.81±0.22 Msun. As in other Be + sdOB binaries, the estimated efficiency of the past mass transfer is unexpectedly high. Detection of a weak \spec{He}{ii}{4686} absorption and other \ion{He}{i} lines from the companion indicates that its effective temperature is close to 30 kK, and that it is a slow rotator. [abstract continues but no space left...]
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BibTeX
@misc{klement2026full,
title = {{Full orbital solution and dynamical masses for a new shell-Be + sdOB binary AN Col}},
author = {R. Klement and Th. Rivinius and A. C. Carciofi and A. Chaturvedi and D. R. Gies and A. C. Fonseca Silva and P. R. Querido},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.02367},
eprint = {2610.02367},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.02367},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Full orbital solution and dynamical masses for a new shell-Be + sdOB binary AN Col
AU - R. Klement
AU - Th. Rivinius
AU - A. C. Carciofi
AU - A. Chaturvedi
AU - D. R. Gies
AU - A. C. Fonseca Silva
AU - P. R. Querido
PY - 2026
DA - 2026/10/01
PB - arXiv
DO - 10.48550/arxiv.2610.02367
UR - https://arxiv.org/abs/2610.02367
AB - AN~Col is a shell Be star that has shown transient spectral features caused by a hot, evolved companion on a months-long orbit. If confirmed, this would place it among the growing category of post-mass-transfer spun-up Be + stripped subdwarf OB-type (sdOB) binaries. Characterizing the binary orbit enables obtaining dynamical masses, to provide a rare anchor for models of binary evolution and mass transfer. We present a full 3-dimensional orbital solution, dynamical masses, and dynamical parallax, for the newly discovered Be + sdOB binary AN~Col. As a prerequisite to obtain a reliable orbital solution, we need to characterize the disk-wide density oscillation cycle that gives rise to the dominant spectroscopic cycles in order to separate the weaker periodic orbital variations. We use near-IR interferometry time series from GRAVITY to confirm the companion and to map the relative astrometric orbit. With the knowledge of the orbital period, we identify spectral lines that trace the orbit of each of the two stellar components and we measure their radial velocities to obtain a double-lined spectroscopic orbit. Combining interferometry and spectroscopy, we derive the full 3-dimensional orbital solution. The disk has completed three full oscillation cycles since 2010, with a cycle length of ~5.1 yr. The ~87.7-day orbit is compatible with edge-on orientation, but the lack of eclipses in TESS light curves limits the orbital inclination to 88.4^∘ or less. The resulting masses are M_Be = 8.39±0.67 Msun and M_sdOB = 0.81±0.22 Msun. As in other Be + sdOB binaries, the estimated efficiency of the past mass transfer is unexpectedly high. Detection of a weak \spec{He}{ii}{4686} absorption and other \ion{He}{i} lines from the companion indicates that its effective temperature is close to 30 kK, and that it is a slow rotator. [abstract continues but no space left...]
ER -