Alessi 20

(MWSC 23; FoF 2409; OCSN 141)

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0.97 UTI
0.83
CN
1.0
Cdens
1.0
CC3
1.0
Clit
1.0
Cdup
N50 (P>50% members) 305
Stellar density (N50/rad) 35.1 [N/pc2]
C3 classification AA
  • CN 0.83 Rich
  • Cdens 1.0 Very dense
  • CC3 1.0 Very high quality
  • Clit 1.0 Very well-studied
  • Cdup 1.0 Unique
đŸ“Ĩ Members 📊 Colab đŸ”Ŧ Bayestar19 MOCAMOCA 🔍 CDS 🔍 Simbad 🔍 CDS (Îą, δ) 🔍 Simbad (Îą, δ)

Overview
ℹī¸
Alessi 20 is a rich, very dense object of very high C3 quality. Its parallax locates it at a very close distance, near 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 mass parameters (see Parameters). It is very well-studied in the literature.

Liu et al. (2025)
Classified as primordial binary cluster 19 along with OCSN_40, and of multiple system 9 along with OCSN_40 and OCSN_41.

Palma et al. (2025)
Part of multiple system G228, along with OCSN_41 and OCSN_40.

Cavallo et al. (2024)
Gold sample.

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

Data
🔍 Search references for Alessi 20 in: SciX Simbad
ℹī¸
Reference Year RA [deg] DEC [deg] Plx [mas] pmRA [mas/yr] pmDE [mas/yr] Rv [km/s]
UCC 99999– 2.541 58.71 2.329 8.135 -2.429 -10.208
Liu et al. 2025 2.64 58.76 2.34 8.12 -2.43 -9.31
Li et al. 2025 2.593 58.742 2.311 8.195 -2.341 –
Almeida et al. 2025 2.591 58.741 – – – –
Alfonso et al. 2024 2.541 58.706 2.294 8.114 -2.456 –
Zhang et al. 2024 2.643 58.757 – – – –
Hunt & Reffert 2024 2.643 58.757 2.343 8.117 -2.427 -9.305
Celli et al. 2024 2.593 58.742 – – – –
Cavallo et al. 2024 2.261 58.664 2.336 – – –
Hunt & Reffert 2023 2.643 58.757 2.343 8.117 -2.427 -9.305
Qin et al. 2023 2.64 58.77 2.33 8.12 -2.42 -10.04
Just et al. 2023 2.658 58.745 – – – –
He et al. 2022 1.905 58.624 2.333 8.019 -2.471 –
Richer et al. 2021 2.572 58.742 2.3 8.186 -2.43 –
Dias et al. 2021 2.591 58.741 2.315 8.168 -2.365 -4.979
Cantat-Gaudin et al. 2020 2.593 58.742 2.311 8.195 -2.341 –
Zhong et al. 2020 2.593 58.742 – 8.195 -2.341 -12.149
Cantat-Gaudin & Anders 2020 2.593 58.742 2.311 8.195 -2.341 –
Liu & Pang 2019 2.401 58.664 2.308 8.152 -2.404 –
Dias et al. 2019 2.592 58.742 2.311 8.195 -2.341 -4.314
Soubiran et al. 2018 2.593 58.742 – – – -5.04
Cantat-Gaudin et al. 2018 2.593 58.742 2.311 8.195 -2.341 –
Loktin & Popova 2017 2.64 58.76 – 8.73 -3.11 -11.5
Kharchenko et al. 2016 2.658 58.745 – – – –
Dias et al. 2014 2.642 58.76 – -0.39 -1.34 –
Kharchenko et al. 2013 2.667 58.748 – 6.34 -2.51 -11.5
Gozha et al. 2012 2.642 58.76 – – – –
Kharchenko et al. 2012 2.667 58.748 – 6.18 -2.37 -11.5
Piskunov et al. 2008 2.637 58.761 – – – –
Kharchenko et al. 2007 2.34 58.67 – 0.3 – -11.5
Piskunov et al. 2007 2.637 58.761 – – – –
Kharchenko et al. 2005 2.64 58.76 – 7.48 -2.61 –
Dias et al. 2002 2.642 58.76 – 8.73 -3.11 -11.5

💡 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– 0.44 0.81 1.51 10 -0.128 55 – –
Liu et al. 2025 0.44 0.31 – 29 – – – –
Li et al. 2025 0.39 0.99 – 11 -0.152 – – –
Almeida et al. 2025 0.42 1.00 – 10 – 150 – –
Alfonso et al. 2024 0.41 0.60 – 16 -0.103 – – –
Zhang et al. 2024 – – – – -0.059(1) – – –
Hunt & Reffert 2024 – – – – – 192(1) – –
Celli et al. 2024 – – – 9 – 130 – –
Cavallo et al. 2024 0.43 1.47 – 5 -0.160 – – –
Hunt & Reffert 2023 0.41 0.65 1.51 7 – – – –
Qin et al. 2023 0.65 0.99 – 9 – – – –
Just et al. 2023 – – – 38 – 17 – –
He et al. 2022 – 1.05 – 11 – – – –
Richer et al. 2021 – 1.35 – 9 – – – –
Dias et al. 2021 0.42 1.00 – 10 -0.104 – – –
Cantat-Gaudin et al. 2020 0.41 0.60 – 9 – – – –
Zhong et al. 2020 0.00 0.00 – 0 0.142 – – –
Cantat-Gaudin & Anders 2020 0.43 – – – – – – –
Liu & Pang 2019 – – – 9 -0.500 – – –
Dias et al. 2019 0.44 0.81 – 9 -0.419 – – –
Soubiran et al. 2018 0.43 – – – – – – –
Cantat-Gaudin et al. 2018 0.43 – – – – – – –
Loktin & Popova 2017 0.57 0.68 – 3 – – – –
Kharchenko et al. 2016 0.47 1.18 – 38 – – – –
Kharchenko et al. 2013 0.47 1.18 – 38 – – – –
Gozha et al. 2012 0.45 – – 3 – 23 – –
Kharchenko et al. 2012 0.47 1.18 – 39 – – – –
Piskunov et al. 2008 0.45 0.68 – 166 – 55(1) – –
Piskunov et al. 2007 0.45 0.68 – 166 – 14 – –
Kharchenko et al. 2005 0.45 0.68 – 166 – – – –
Dias et al. 2002 0.60 0.68 – 3 – – – –

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

Visualization
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Alessi 20 UCC
Alessi 20 HUNT23
Alessi 20 CANTAT20
Galactocentric position diagram