HD 97950

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.

HD 97950
HST image of the HD 97950 cluster
Observation data (J2000 epoch)
Constellation	Carina
Right ascension	11^h 15^m 07.346^s[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

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.

Members

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]

Mass

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]

Age

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]

References

1. 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. 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:0712.2621. 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. 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 (1): 73. arXiv:1212.4566. Bibcode:2013ApJ...764...73P. doi:10.1088/0004-637X/764/1/73.
5. 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:1007.3284. Bibcode:2010MNRAS.408..731C. doi:10.1111/j.1365-2966.2010.17167.x.
6. 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:0710.2882. Bibcode:2008ApJ...675.1319H. doi:10.1086/524650.
7. 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 (1): 477–519. arXiv:astro-ph/0503464. Bibcode:2005ApJ...627..477M. doi:10.1086/430417.
10. 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 (1): 712–718. arXiv:1305.0851. 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 (1): L65. arXiv:1209.1598. Bibcode:2012MNRAS.427L..65R. doi:10.1111/j.1745-3933.2012.01346.x.
13. 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:1002.1961. 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–L24. arXiv:1211.5926. 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:1204.5481. Bibcode:2012ApJ...750L..44K. doi:10.1088/2041-8205/750/2/L44.

Further reading

• A comprehensive study of the young star cluster HD 97950 in NGC 3603