An Halpha survey of infrared bow-shocks around OB-type stars
Abstract
Bow shocks (BSs) around massive stars are commonly identified in mid-infrared (MIR) surveys. In contrast, systematic optical investigations of these structures remain scarce with only a few possible detections reported so far. We performed a targeted Halpha imaging survey of 78 IR BS candidates compiled from literature catalogues. Observations were obtained with multiple ground-based facilities and complemented with archival MIR images from Spitzer and WISE. For the detected bow structures, geometrical parameters were measured, and the bows were classified based on the parameters of their central stars, the measured stand-off distances and adopted plausible ISM conditions Clear arc-shaped Halpha nebulae are detected in 15 objects, with one additional BS discovered serendipitously. A further 35 objects exhibit diffuse Halpha emission associated with complex background structures, while 28 show no detectable Halpha emission. The Halpha and IR morphologies generally trace the same large-scale structures, although most of the IR arcs lie slightly closer to the star and appear broader than their optical counterparts. We find that several systems are consistent with radiation-supported BSs, bow waves or dust waves, while others remain compatible with classical wind-supported BSs. This survey demonstrates that a fraction of IR BS candidates around OB stars also exhibit detectable ionised gas structures in Halpha, and both stellar wind momentum and radiation pressure can contribute to shaping these structures. No correlation is found between the detection of an Halpha BS and the stellar parameters, and the overlap in objects observed in Halpha and in the radio regime was too small for firm conclusions. Future spectroscopic observations will be required to determine the physical conditions and kinematics of the ionised gas and to further constrain the nature of these BS systems.
Versions
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BibTeX
@misc{saddal2026halpha,
title = {{An Halpha survey of infrared bow-shocks around OB-type stars}},
author = {Kuljeet Singh Saddal and Michaela Kraus and Dieter H. Nickeler and Tiina Liimets and Sergey Karpov and Olga V. Maryeva},
howpublished = {arXiv},
year = {2026},
month = jul,
doi = {10.48550/arxiv.2607.24544},
eprint = {2607.24544},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.24544},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - An Halpha survey of infrared bow-shocks around OB-type stars
AU - Kuljeet Singh Saddal
AU - Michaela Kraus
AU - Dieter H. Nickeler
AU - Tiina Liimets
AU - Sergey Karpov
AU - Olga V. Maryeva
PY - 2026
DA - 2026/07/27
PB - arXiv
DO - 10.48550/arxiv.2607.24544
UR - https://arxiv.org/abs/2607.24544
AB - Bow shocks (BSs) around massive stars are commonly identified in mid-infrared (MIR) surveys. In contrast, systematic optical investigations of these structures remain scarce with only a few possible detections reported so far. We performed a targeted Halpha imaging survey of 78 IR BS candidates compiled from literature catalogues. Observations were obtained with multiple ground-based facilities and complemented with archival MIR images from Spitzer and WISE. For the detected bow structures, geometrical parameters were measured, and the bows were classified based on the parameters of their central stars, the measured stand-off distances and adopted plausible ISM conditions Clear arc-shaped Halpha nebulae are detected in 15 objects, with one additional BS discovered serendipitously. A further 35 objects exhibit diffuse Halpha emission associated with complex background structures, while 28 show no detectable Halpha emission. The Halpha and IR morphologies generally trace the same large-scale structures, although most of the IR arcs lie slightly closer to the star and appear broader than their optical counterparts. We find that several systems are consistent with radiation-supported BSs, bow waves or dust waves, while others remain compatible with classical wind-supported BSs. This survey demonstrates that a fraction of IR BS candidates around OB stars also exhibit detectable ionised gas structures in Halpha, and both stellar wind momentum and radiation pressure can contribute to shaping these structures. No correlation is found between the detection of an Halpha BS and the stellar parameters, and the overlap in objects observed in Halpha and in the radio regime was too small for firm conclusions. Future spectroscopic observations will be required to determine the physical conditions and kinematics of the ionised gas and to further constrain the nature of these BS systems.
ER -