The Radial Distribution of Gaia-selected Blue-straggler Candidates in the Old Open Cluster NGC 2158
Year: 2026
Type: article
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.
Source: The Astronomical Journal
Authors: Huanbin 焕斌 Chi 迟, Jinli Lv
Institutions: Guangzhou University, Yunnan Open University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
Awards: G6050541297, G6090385840
OpenAlex ID: W7215094254