UPK 21

0.59 UTI

0.66

C_N

0.38

C_dens

0.75

C_C3

0.57

C_lit

1.0

C_dup

N_m (P>50%) 81

Core radius and density 2.0 [pc], 1.9 [pc^-2]

C3 classification AB

C_N 0.66 Moderately populated
C_dens 0.38 Loose
C_C3 0.75 High quality
C_lit 0.57 Moderately studied
C_dup 1.0 Unique

📥 Members 📊 Colab 🔬 Bayestar19

MOCA 🔍 CDS 🔍 Simbad 🔍 CDS (α, δ) 🔍 Simbad (α, δ)

Overview

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UPK 21 is a moderately populated, loose object of high C3 quality. Its parallax locates it at a close distance, below the mid-plane, affected by moderate extinction. It is catalogued as a near-solar metallicity, intermediate-age cluster, but with a large variance across recent sources for the age and metallicity parameters (see Parameters). It is moderately studied in the literature.

Close Moderate extinction Near-solar metallicity Intermediate age

Li et al. (2026)
Tidal & Core radii: r_t=38+/-44.2 [pc], r_c=0.26+/-0.05 [pc]; stars within r_t: N~73

Palma et al. (2025)
Classified as optical pair (not dynamically associated) P166, along with Ruprecht_145.

Almeida et al. (2025)
Mass determination: intermediate fit. Isochrone match: good fit. Silver sample.

Cavallo et al. (2024)
Gold sample.

Hunt & Reffert (2024)
Classified as open cluster. CMD class: 0.99 (50th percentile).

Hunt & Reffert (2023)
Classified as open cluster. CMD class: 0.99 (50th percentile).

Data

🔍 Search references for UPK 21 in: SciX Simbad

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Reference	Year	RA [deg]	DEC [deg]	Plx [mas]	pmRA [mas/yr]	pmDE [mas/yr]	Rv [km/s]
UCC	99999–	282.904	-15.157	1.684	7.866	0.671	-25.045
Li et al.	2026	282.88	-15.22	–	–	–	–
Li et al.	2025	282.895	-15.15	1.667	7.839	0.721	–
Almeida et al.	2025	282.89	-15.165	–	–	–	–
Alfonso et al.	2024	282.932	-15.116	1.645	7.879	0.666	–
Hunt & Reffert	2024	282.92	-15.174	1.679	7.797	0.694	-23.852
Cavallo et al.	2024	282.985	-14.911	1.682	–	–	–
Hunt & Reffert	2023	282.92	-15.174	1.679	7.797	0.694	-23.852
Almeida et al.	2023	282.843	-15.159	–	–	–	–
Tarricq et al.	2022	282.911	-15.203	1.672	7.84	0.671	–
Jadhav & Subramaniam	2021	282.895	-15.15	–	–	–	–
Dias et al.	2021	282.89	-15.165	1.679	7.831	0.756	-25.27
Cantat-Gaudin et al.	2020	282.895	-15.15	1.667	7.839	0.721	–
Cantat-Gaudin & Anders	2020	282.903	-15.16	1.686	7.813	0.749	–
Sim et al.	2019	282.938	-15.191	–	7.82	0.73	–

💡 Note: The UCC values are estimated from its identified members.

Reference	Year	Dist [kpc]	Av [mag]	DAv [mag]	Age [Myr]	[Fe/H] [dex]	Mass [Msun]	B_frac	BSS
UCC	99999–	0.58	1.43	1.6	825	0.141	148	0.5	0
Li et al.	2025	0.48	1.21	–	1324	-0.239	–	–	–
Almeida et al.	2025	0.59	1.48	–	731	–	116	–	–
Alfonso et al.	2024	0.58	0.81	–	1090	0.141	–	–	–
Hunt & Reffert	2024	0.56	1.43	1.60	467	–	90⁽¹⁾	–	–
Cavallo et al.	2024	0.58	1.93	–	355	-0.170	–	–	–
Hunt & Reffert	2023	0.56	1.43	1.60	467	–	–	–	–
Almeida et al.	2023	0.58	1.45	–	759	0.198	195⁽¹⁾	0.50	–
Tarricq et al.	2022	0.57	–	–	1230	–	–	–	–
Jadhav & Subramaniam	2021	0.58	0.81	–	1148	–	179	–	0⁽¹⁾
Dias et al.	2021	0.59	1.48	–	731	0.141	–	–	–
Cantat-Gaudin et al.	2020	0.58	0.81	–	1148	–	–	–	–
Cantat-Gaudin & Anders	2020	0.58	–	–	–	–	–	–	–
Sim et al.	2019	0.59	–	–	891	–	–	–	–

(N): Indicates that there are N extra values assigned to this parameter in the corresponding reference.

Visualization

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