| Issue |
A&A
Volume 699, July 2025
|
|
|---|---|---|
| Article Number | L1 | |
| Number of page(s) | 9 | |
| Section | Letters to the Editor | |
| DOI | https://doi.org/10.1051/0004-6361/202555495 | |
| Published online | 25 June 2025 | |
Letter to the Editor
AstroSat/UVIT Study of NGC 663: First detection of Be+sdOB systems in a young star cluster
1
INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy
2
Dipartimento di Fisica e Astronomia, Università di Firenze, Via G. Sansone 1, I-50019 Sesto Fiorentino, (Firenze), Italy
3
Indian Institute of Astrophysics, Koramangala, Bangalore 560034, India
4
Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital 263002, India
⋆ Corresponding author: snehanedhath@gmail.com
Received:
12
May
2025
Accepted:
7
June
2025
Context. Be stars are rapidly rotating stars surrounded by a disc; however, the origin of these stars remains unclear. Mass and angular momentum transfer in close binaries account for the rapid rotation of a major fraction of Be stars, as supported by the previous detection of low-mass stripped companions to these stars. The stripped companions can be helium-burning subdwarf OB-type stars (sdOBs) and white dwarfs.
Aims. The main objective of this study is to characterise the identified Be stars in the young open cluster NGC 663 and search for possible hot companions.
Methods. We present the first ultraviolet (UV) photometric study of NGC 663 using far-UV and near-UV data from UVIT/AstroSat as a part of the UOCS series (XVIII). We identified 23 previously known Be stars in the cluster. Further, we utilised the spectral energy distribution fitting technique to derive the fundamental parameters and to search for UV-bright companions of the identified Be stars.
Results. Our study reveals that 19 out of 23 Be stars show a significant UV excess, indicating the presence of hot companions. Here, we report the first detection of high-mass sdOB companions to Be stars, with 69.5% of them found in binaries within a cluster, offering direct evidence of binary interactions.
Conclusions. This study showcases the key role of binary interactions in the formation of Be stars in clusters and provides insights into massive star evolution.
Key words: binaries: general / stars: emission-line / Be / open clusters and associations: individual: NGC 663
© The Authors 2025
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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