The Radial Distribution of Gaia-selected Blue-straggler Candidates in the Old Open Cluster NGC 2158
- 1Yunnan Open University
- 2Guangzhou University
Abstract
We measure the projected radial distribution of blue-straggler-star (BSS) candidates in NGC 2158 using a Gaia DR3 membership catalog. The numerator and RGB/red-clump (RGB/RC) denominator are selected with the same thresholds, P mem ≥ 0.8 and RUWE < 1.2, yielding 38 BSS candidates and 197 reference stars. A boundary-free two-sample test shows that their observed radial distributions differ (two-sided KS D = 0.342, p = 8.0 × 10 ⁻⁴ ; Anderson–Darling p ≤ 0.001). The BSS candidates have a larger median radius (8 . ′ 45 versus 3 . ′ 39) and A + = − 0.26 1 − 0.110 + 0.112 , where the sign denotes a less concentrated BSS sample. However, five-fold out-of-fold tests of the archived classifier reveal strong CMD- and radius-dependent recovery: inside/outside 15′ the recovered fractions are 1/36 and 3/9 for BSS-like Hunt members, but 165/234 and 1/6 for RGB/RC-like members. Sparse outer reference templates prevent a stable inverse-completeness correction. Differential-reddening perturbations retain 14–24 outer candidates, but do not remove this dominant selection uncertainty. Two extinction-matched independent offset fields yield zero and one false full-pipeline candidate. We therefore report a significant difference in the selected catalog, not an intrinsic outer BSS excess. Spectroscopic membership and a selection function calibrated with independent, deeper photometry are required for a dynamical interpretation.
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BibTeX
@article{迟2026radial,
title = {{The Radial Distribution of Gaia-selected Blue-straggler Candidates in the Old Open Cluster NGC 2158}},
author = {Huanbin 焕斌 Chi 迟 and Jinli Lv},
journal = {The Astronomical Journal},
year = {2026},
month = oct,
doi = {10.3847/1538-3881/aea094},
url = {https://iopscience.iop.org/article/10.3847/1538-3881/aea094},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - The Radial Distribution of Gaia-selected Blue-straggler Candidates in the Old Open Cluster NGC 2158
AU - Huanbin 焕斌 Chi 迟
AU - Jinli Lv
PY - 2026
DA - 2026/10/01
JO - The Astronomical Journal
DO - 10.3847/1538-3881/aea094
UR - https://iopscience.iop.org/article/10.3847/1538-3881/aea094
AB - We measure the projected radial distribution of blue-straggler-star (BSS) candidates in NGC 2158 using a Gaia DR3 membership catalog. The numerator and RGB/red-clump (RGB/RC) denominator are selected with the same thresholds, P mem ≥ 0.8 and RUWE < 1.2, yielding 38 BSS candidates and 197 reference stars. A boundary-free two-sample test shows that their observed radial distributions differ (two-sided KS D = 0.342, p = 8.0 × 10 ⁻⁴ ; Anderson–Darling p ≤ 0.001). The BSS candidates have a larger median radius (8 . ′ 45 versus 3 . ′ 39) and A + = − 0.26 1 − 0.110 + 0.112 , where the sign denotes a less concentrated BSS sample. However, five-fold out-of-fold tests of the archived classifier reveal strong CMD- and radius-dependent recovery: inside/outside 15′ the recovered fractions are 1/36 and 3/9 for BSS-like Hunt members, but 165/234 and 1/6 for RGB/RC-like members. Sparse outer reference templates prevent a stable inverse-completeness correction. Differential-reddening perturbations retain 14–24 outer candidates, but do not remove this dominant selection uncertainty. Two extinction-matched independent offset fields yield zero and one false full-pipeline candidate. We therefore report a significant difference in the selected catalog, not an intrinsic outer BSS excess. Spectroscopic membership and a selection function calibrated with independent, deeper photometry are required for a dynamical interpretation.
SN - 0004-6256
SN - 1538-3881
ER -