HD 97950

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HD 97950
NGC 3603b.jpg
HST image of the HD 97950 cluster
Observation data (J2000 epoch)
Constellation Carina
Right ascension 11h 15m 07.346s[1]
Declination −61° 15′ 38.52″[1]
Distance 25 kly (7.6 kpc[2])
Apparent magnitude (V) 9.03[3]
Physical characteristics
Mass 19,000[4] M
Radius 120"[4]
Notable features Main cluster in NGC 3603
Other designations HD 97950, NGC 3603YC, CD-60°3452, CPD-60° 2732, HIP 54948, MR 38, WR 43
See also: Open cluster, List of open clusters

HD 97950, is a multiple star system and part of a super star cluster within the NGC 3603 H II region. It was catalogued as a single star although it was always known to be a compact cluster. It is now resolved into a massive multiple star at the centre of one of the densest clusters in the galaxy.

Only the six lettered stars A-F at the core of the cluster are typically referred to as components of HD 97950, while the remaining stars of the cluster and surrounding area are usually numbered as members of NGC 3603. The cluster itself is still called the HD 97950 cluster as well as the NGC 3603 young cluster (NGC 3603YC). There are no other notable groupings of stars in NGC 3603 and the HD 97950 cluster is often loosely referred to as simply NGC 3603.


The core of the cluster, with A1/2/3 at the very centre, and B and C to its left

The main components are designated A1, A2, A3, B, and C, of which A1 and C are known to be spectroscopic binaries. A1a, A1b, and C are all WN6h Wolf-Rayet Stars, amongst the most massive and luminous known.[5]

There are several dozen early O class stars (O3 and O4) in the cluster, mostly main sequence stars. There are just a handful of giants and supergiants including: one prominent early B supergiant, Sher 25; a highly luminous O3.5 supergiant, Sher 18; and an interesting carbon-rich O9.7 supergiant, Sher 23.

Over 7,500 stars have been identified in the cluster, with the least massive being smaller than the sun and the most massive over 100 M. Stars less than about 4 M have not yet reached the main sequence.[6]

Prominent stars, ordered by distance from the cluster centre[7]
[8] [7] Other names Spectral type[6] mV[2] MV[7] Temperature (K)[2][9] Luminosity (L)[2]
A1a[5] 30 WR 43a WN6h 11.18 −7.8 42,000 2,500,000
A1b[5] WN6h 40,000 1,500,000
A2 31 O3V 12.53 −6.9 46,500
A3 26 O3III 13.09 −6.4 46,500
29 O4V 13.68[7] −5.2 44,000
27 O4V 13.07[7] −5.8 44,000
25 O4V 13.01[7] −5.9 44,000
B[5] 23 WR 43b WN6h 11.33 −7.9 42,000 2,900,000
40 O3V 13.33 −5.7 46,500 780,000
33 O5V+OB?[2] 13.69 −5.8
41 O4V 14.24 −5.1 44,000 236,000
42 O3III 12.99 −6.1 46,500 1,030,000
37 O6.5V+? 14.16 −5.0
C[5] 18 WR 43c WN6h 11.89 −7.3 44,000 2,200,000
D 49 O4V 12.64[7] −6.3 44,000
50 O5V 12.74[7] −6.2 41,000
52 O4V 13.68[7] −5.2 44,000
38 O3V 13.21 −5.9 46,500 540,000
E 19 O5.5III(f) 12.83[7] −6.1 41,000
F 39 O5V 11.86[7] −6.1 41,000
16 O3V 13.53 −5.4 46,500 711,000
43 O4V 13.87[7] −5.0 44,000
14 O4V 13.88[7] −5.0 44,000
59 O4V 13.65[7] −5.3 44,000
60 O4V 13.60[7] −5.3 44,000
62 O4V 13.09 −5.6 44,000
58 O5.5V 13.09 −5.1 39,500
G 61 O5V 12.74[7] −6.0 41,000
51 O4V(f) 13.33[7] −5.6 44,000
9 O4V 13.71 −5.2 44,000
7 O4V 13.58[10] −5.4 44,000
22 O5III(f) 13.23[10] −5.8 41,000
1 Sher 23 OC9.7Ia[2] 12.70 −6.3 30,250 449,000
2 Sher 22 O3III(f)[2] 13.21 −5.6 46,500 863,000
5 Sher 25 B1Iab[2] 12.23 −6.5 22,000 649,000
48 Sher 18 O3.5If[2] 12.65 −6.4 39,500 1,790,000
24 O4V[2] 12.72 −6.2 44,000
MTT 25 O3V[2] 12.61[10] −6.2 46,500
20 O4V 13.98[7] 44,000
17 O4V 14.10 44,000
45 O8V-III 14.14 −4.7[2] 33,750 124,000
57 O4V 13.98[7] 44,000
10 O4V 14.17 −5.1[2] 44,000 258,000
MTT 58[11] O2If*/WN6 14.76 −5.7 855,000
WR 42e[12] O2If*/WN6 14.53 −6.3 1,300,000

The number of WNh and early O stars exceeds any known cluster in the galaxy. The Quintuplet and Arches clusters each have around 20 young massive stars and may have masses comparable to the HD 97950 cluster, but they contain no O3 or WN6 stars at all. The rich red supergiant clusters such as Westerlund 1 are too old to contain such stars, although may be even more massive. R136 in the Large Magellanic Cloud contains stars more massive than any in HD 97950, as well as large numbers of early O stars, and the cluster as a whole may be ten times as massive.[13]

It has been proposed that the star WR 42e, found 2.6 arcmin from the centre of the cluster, and J1117−6120, an O6V runaway a quarter of a degree away on the other side of the cluster, were both ejected in a 3-body interaction. Two of the stars then merged to form the extremely massive and luminous WR 42e.[14]


The HD 97950 cluster has a total photometric mass of 10,000 - 16,000 M,[6] and a dynamical mass of 19,000 M.[4] The constituent stars have apparently dynamical segregated with the more massive stars predominantly found at the centre of the cluster.[4] The centre of the cluster has a density of 60,000 M pc−3, ten times the Orion Nebula and comparable to R136.[6]


Fitting the main sequence, and pre-main sequence gives a cluster age of 1 million years or less. There is no clear main sequence turnoff, although the most massive stars are modelled best with an age of 2.5 million years, but are compatible with an age around one million years.[6] A small number of stars, for example Sher 25, apparently show much greater ages and it has been suggested that there is either ongoing star formation, or an earlier burst of star formation.[2] Other studies have estimated ages up to 2 million years, but the existence of the most massive and luminous stars provide a hard upper limit of 2.5 million years on the possible age.[15]

This is one of the youngest clusters in the galaxy. The Arches cluster is around 2.5 million years old, the Quintuplet cluster nearly double that, and the various red supergiant clusters obviously even older. Even R136 is thought to be near to 2 million years old. Trumpler 14 in the Carina Nebula is thought to be as little as 300,000 - 500,000 years old, but is much less massive.[13]


  1. ^ a b Zacharias, N.; et al. (2003). "The Second U.S. Naval Observatory CCD Astrograph Catalog (UCAC2)". CDS/ADC Collection of Electronic Catalogues. 1289. Bibcode:2003yCat.1289....0Z. 
  2. ^ a b c d e f g h i j k l m n Melena, Nicholas W.; Massey, Philip; Morrell, Nidia I.; Zangari, Amanda M. (2008). "The Massive Star Content of NGC 3603". The Astronomical Journal. 135 (3): 878–891. arXiv:0712.2621free to read. Bibcode:2008AJ....135..878M. doi:10.1088/0004-6256/135/3/878. 
  3. ^ Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237: 0. Bibcode:2002yCat.2237....0D. 
  4. ^ a b c d Pang, Xiaoying; Grebel, Eva K.; Allison, Richard J.; Goodwin, Simon P.; Altmann, Martin; Harbeck, Daniel; Moffat, Anthony F. J.; Drissen, Laurent (2013). "On the Origin of Mass Segregation in NGC 3603". The Astrophysical Journal. 764: 73. arXiv:1212.4566free to read. Bibcode:2013ApJ...764...73P. doi:10.1088/0004-637X/764/1/73. 
  5. ^ a b c d e Crowther, P. A.; Schnurr, O.; Hirschi, R.; Yusof, N.; Parker, R. J.; Goodwin, S. P.; Kassim, H. A. (2010). "The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 M stellar mass limit". Monthly Notices of the Royal Astronomical Society. 408 (2): 731–751. arXiv:1007.3284free to read. Bibcode:2010MNRAS.408..731C. doi:10.1111/j.1365-2966.2010.17167.x. 
  6. ^ a b c d e Harayama, Y.; Eisenhauer, F.; Martins, F. (2008). "The Initial Mass Function of the Massive Star-forming Region NGC 3603 from Near-Infrared Adaptive Optics Observations". The Astrophysical Journal. 675 (2): 1319–1342. arXiv:0710.2882free to read. Bibcode:2008ApJ...675.1319H. doi:10.1086/524650. 
  7. ^ a b c d e f g h i j k l m n o p q r s Moffat, Anthony F. J.; Drissen, Laurent; Shara, Michael M. (1994). "NGC 3603 and its Wolf-Rayet stars: Galactic clone of R136 at the core of 30 Doradus, but without the massive surrounding cluster halo". Astrophysical Journal. 436: 183. Bibcode:1994ApJ...436..183M. doi:10.1086/174891. 
  8. ^ Van Den Bos, W. H. (1928). "Another nebulous multiple star". Bulletin of the Astronomical Institutes of the Netherlands. 4: 261. Bibcode:1928BAN.....4..261V. 
  9. ^ Massey, Philip; Puls, Joachim; Pauldrach, A. W. A.; Bresolin, Fabio; Kudritzki, Rolf P.; Simon, Theodore (2005). "The Physical Properties and Effective Temperature Scale of O-Type Stars as a Function of Metallicity. II. Analysis of 20 More Magellanic Cloud Stars and Results from the Complete Sample". The Astrophysical Journal. 627: 477–519. arXiv:astro-ph/0503464free to read. Bibcode:2005ApJ...627..477M. doi:10.1086/430417. 
  10. ^ a b c Melnick, J.; Tapia, M.; Terlevich, R. (1989). "The galactic giant H II region NGC 3603". Astronomy and Astrophysics. 213: 89. Bibcode:1989A&A...213...89M. 
  11. ^ Roman-Lopes, A. (2013). "An O2 If*/WN6 star caught in the act in a compact H II region in the starburst cluster NGC 3603". Monthly Notices of the Royal Astronomical Society. 433: 712–718. arXiv:1305.0851free to read. Bibcode:2013MNRAS.433..712R. doi:10.1093/mnras/stt762. 
  12. ^ Roman-Lopes, A. (2012). "A Galactic O2 If*/WN6 star possibly ejected from its birthplace in NGC 3603". Monthly Notices of the Royal Astronomical Society: Letters. 427: L65. arXiv:1209.1598free to read. Bibcode:2012MNRAS.427L..65R. doi:10.1111/j.1745-3933.2012.01346.x. 
  13. ^ a b Portegies Zwart, Simon F.; McMillan, Stephen L. W.; Gieles, Mark (2010). "Young Massive Star Clusters". Annual Review of Astronomy and Astrophysics. 48: 431–493. arXiv:1002.1961free to read. Bibcode:2010ARA&A..48..431P. doi:10.1146/annurev-astro-081309-130834. 
  14. ^ Gvaramadze, V. V.; Kniazev, A. V.; Chené, A. -N.; Schnurr, O. (2012). "Two massive stars possibly ejected from NGC 3603 via a three-body encounter". Monthly Notices of the Royal Astronomical Society: Letters. 430: L20. arXiv:1211.5926free to read. Bibcode:2013MNRAS.430L..20G. doi:10.1093/mnrasl/sls041. 
  15. ^ Kudryavtseva, Natalia; Brandner, Wolfgang; Gennaro, Mario; Rochau, Boyke; Stolte, Andrea; Andersen, Morten; Da Rio, Nicola; Henning, Thomas; Tognelli, Emanuele; Hogg, David; Clark, Simon; Waters, Rens (2012). "Instantaneous Starburst of the Massive Clusters Westerlund 1 and NGC 3603 YC". The Astrophysical Journal Letters. 750 (2): L44. arXiv:1204.5481free to read. Bibcode:2012ApJ...750L..44K. doi:10.1088/2041-8205/750/2/L44. 

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