Sigma Orionis

(Sigma Ori)

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0.85 UTI
0.48
CN
1.0
Cdens
1.0
CC3
0.88
Clit
1.0
Cdup
N50 (P>50% members) 48
Stellar density (N50/rad) 136.0 [N/pc2]
C3 classification AA
  • CN 0.48 Poorly populated
  • Cdens 1.0 Very dense
  • CC3 1.0 Very high quality
  • Clit 0.88 Well-studied
  • Cdup 1.0 Unique
đŸ“Ĩ Members 📊 Colab đŸ”Ŧ Bayestar19 MOCAMOCA 🔍 CDS 🔍 Simbad 🔍 CDS (Îą, δ) 🔍 Simbad (Îą, δ)

Overview
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Sigma Orionis is a poorly populated, very dense object of very high C3 quality. Its parallax locates it at a very close distance, below the mid-plane, affected by low extinction. It is catalogued as a near-solar metallicity, very young cluster, but with a large variance across recent sources for the absorption, age, and metallicity parameters (see Parameters). It is well-studied in the literature.

Note: This object shares a large percentage of members with 2 later reported entries. See table with shared members information.

Liu et al. (2025)
Classified as primordial binary cluster 86 along with CWNU_1054, and as primordial binary cluster 337 along with Theia_13, and of multiple system 3 along with ASCC_18, OCSN_65, CWNU_1054 and Theia_13.

Palma et al. (2025)
Part of multiple system G229, along with OCSN_56, OCSN_65, Theia_13, CWNU_1072, CWNU_1088, ASCC_18 and OCSN_68.

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

Cavallo et al. (2024)
Gold sample.

Hunt & Reffert (2024)
Classified as open cluster. CMD class: 0.82 (50th percentile).

Data
🔍 Search references for Sigma Orionis 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– 84.697 -2.593 2.498 1.487 -0.576 28.993
Liu et al. 2025 84.71 -2.61 2.5 1.48 -0.61 24.97
Li et al. 2025 84.716 -2.582 2.48 1.577 -0.512 –
Almeida et al. 2025 84.758 -2.594 – – – –
Zhang et al. 2024 84.71 -2.61 – – – –
Swiggum et al. 2024 84.71 -2.61 2.5 1.48 -0.61 30.503
Hunt & Reffert 2024 84.71 -2.61 2.5 1.48 -0.61 24.974
Celli et al. 2024 84.716 -2.582 – – – –
Cavallo et al. 2024 84.72 -2.615 2.497 – – –
Hunt & Reffert 2023 84.71 -2.61 2.5 1.48 -0.61 24.974
He et al. 2022 84.675 -2.602 2.495 1.545 -0.485 –
Dias et al. 2021 84.758 -2.594 2.479 1.59 -0.568 -13.802
Cantat-Gaudin et al. 2020 84.716 -2.582 2.48 1.577 -0.512 –
Donor et al. 2020 84.675 -2.6 – 1.23 -0.46 30.7
Loktin & Popova 2017 84.675 -2.6 – 1.731 0.467 29.4
Dias et al. 2014 84.675 -2.6 – 3.38 -0.06 –
Gozha et al. 2012 84.675 -2.6 – – – –
Bukowiecki et al. 2011 84.662 -2.609 – – – –
Piskunov et al. 2008 84.667 -2.614 – – – –
Kharchenko et al. 2007 84.67 -2.6 – 0.4 – 29.45
Kharchenko et al. 2005 84.67 -2.61 – 3.42 -0.2 29.45
Kharchenko et al. 2003 84.7 -2.6 – 4.43 -1.52 –

💡 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] Bfrac BSS
UCC 99999– 0.4 0.165 2.25 7 -0.150 111 – –
Liu et al. 2025 0.29 0.01 – 6 – – – –
Li et al. 2025 0.30 0.15 – 7 -0.254 – – –
Almeida et al. 2025 0.30 0.17 – 10 – 109 – –
Zhang et al. 2024 – – – – -0.315(1) – – –
Swiggum et al. 2024 0.40 – – 4 – 250 – –
Hunt & Reffert 2024 – – – – – 81(1) – –
Celli et al. 2024 – – – 1 – 113 – –
Cavallo et al. 2024 0.41 1.19 – 4 0.090 – – –
Hunt & Reffert 2023 0.38 0.90 2.25 4 – – – –
He et al. 2022 – 0.15 – 3 – – – –
Spina et al. 2022 – – – – -0.150 – – –
Dias et al. 2021 0.30 0.17 – 10 -0.092 – – –
Donor et al. 2020 – – – – -0.150 – – –
Loktin & Popova 2017 0.47 0.54 – 7 – – – –
Bukowiecki et al. 2012 – – – – – 227 – –
Gozha et al. 2012 0.40 – – 13 – 76 – –
Bukowiecki et al. 2011 0.65(1) 0.35 – 16 – – – –
Piskunov et al. 2008 0.40 0.16 – 7 – – – –
Kharchenko et al. 2005 0.40 0.16 – 7 – – – –
Kharchenko et al. 2003 0.36 0.16 – – – – – –

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

Cluster % RA DEC Plx pmRA pmDE Rv UTI
UBC 205 100.0 84.71 -2.6 2.5 1.54 -0.57 29.45 0.16
OCSN 262 97.9 84.7 -2.6 2.5 1.49 -0.6 28.99 0.01

💡 Note: The % column shows the percentage of members that Sigma Orionis shares with each listed object.

Visualization
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Sigma Orionis UCC
Sigma Orionis HUNT23
Sigma Orionis CANTAT20
Galactocentric position diagram