A fast-rotating blue straggler star in the tidal tail of the open cluster NGC 752

¹ Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, PR China
e-mail: lichunyan@shao.ac.cn; chenli@shao.ac.cn
² School of Astronomy and Space Science, University of Chinese Academy of Sciences, No. 19A, Yuquan Road, Beijing 100049, PR China
³ Yunnan Observatories, Chinese Academy of Sciences, 396 Yangfangwang, Guandu District, Kunming 650216, PR China
⁴ International Centre of Supernovae, Yunnan Key Laboratory, Kunming 650216, PR China
⁵ Shanghai Science and Technology Museum, No. 2000 Century Avenue, Pudong New Area, Shanghai 200127, PR China

Received: 30 January 2024
Accepted: 28 March 2024

Abstract

Context. NGC 752 is a well-known Galactic open cluster of intermediate age. In recent works, a very long and asymmetric tail was revealed. A blue straggler star (BSS) at the periphery of the tidal tail of the cluster was subsequently identified.

Aims. We aim to perform a detailed analysis of the newly detected BSS based on the available comprehensive spectroscopic and photometric data. We also explored this BSS’s possible formation pathway and age limitation based on the collected spectroscopic and photometric data.

Methods. We reconfirmed the membership of the newly determined BSS of NGC 752, supplemented by Gaia DR3 radial velocity data. Moreover, we also estimated the projected rotational velocity and the mass of the BSS from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope low-resolution spectra and multiband photometric data from various catalogs, respectively.

Results. The newly discovered BSS is confirmed as a genuine member of NGC 752. The lack of ultraviolet excess in the spectral energy distribution and no significant variations in the light curve imply that this BSS is likely a single star (mass = 1.86_−0.94^+3.62 M_⊙) formed through stellar mergers. The fast rotation velocity (v sin i = 206.9 ± 4.9 km s⁻¹) of the BSS may provide constraints on its age (less than a hundred million years), but more formation details require further investigation.