RSGC1

RSGC1 (Red Supergiant Cluster 1) is a young massive open cluster in to the Milky Way galaxy. It was discovered in 2006 in the data generated by several infrared surveys, named for the unprecedented number of red supergiant members.[3] The cluster is located in the constellation Scutum at the distance of about 6.6 kpc from the Sun. It is likely situated at the intersection of the northern end of the Long Bar of the Milky Way and the inner portion of the Scutum–Centaurus Arm—one of its two major spiral arms.[4]

RSGC1
Spitzer image of RSGC1
Observation data (J2000 epoch)
Constellation	Scutum
Right ascension	18^h 36^m 29^s[1]
Declination	−06° 52′ 48″[1]
Distance	22.0 ± 2.9kly (6.60 ± 0.89kpc[2])
Apparent magnitude (V)	not visible[2]
Apparent dimensions (V)	~1.5′[3][1]
Physical characteristics
Mass	~3 × 10^4[2] M☉
Radius	1.5 ± 0.3 pc[2]
Estimated age	12 ± 2 my[2][1]

The age of RSGC1 is estimated at 10–14 million years. The cluster is heavily obscured and has not been detected in the visible light. It lies close to other groupings of red supergiants known as Stephenson 2, RSGC3, Alicante 7, Alicante 8, and Alicante 10. The mass of RSGC1 is estimated at 30 thousand solar masses, which makes it one of the most massive open clusters in the Galaxy.[2]

The observed red supergiants with the mass of about 16–20 solar masses are type II supernova progenitors.[2] Over 200 main sequence stars have been detected with masses over 8 M_☉, which allows the distance to be determined from main sequence fitting. Fourteen red supergiant members have been identified.[1]

Prominent supergiants[2][5]

Star	Spectral type	Magnitude (K band)	Temperature (effective, K)	Absolute magnitude	Luminosity (L☉)	Radius (R☉)
F01	M5	4.962	3,300[5]-3,450[2]	−11.75	257,000[5]-263,000[2]	1,435[2]-1,551[5]
F02	M2	5.029	3,600[5]-3,660[2]	−11.92	363,000[2][5]	1,498[2]-1,549[5]
F03	M5	5.333	3,200[5]-3,450[2]	−11.28	166,000[5]-174,000[2]	1,168[2]-1,326[5]
F04	M1	5.342	3,752[2]-3,900[5]	−11.24	174,000[5]-209,000[2]	914[5]-1,082[2]
F05	M4	5.535	3,535[2]-3,600[5]	−11.36	166,000[5]-195,000[2]	1,047[5]-1,177[2]
F06	M5	5.613	3,300[5]-3,450[2]	−10.70	100,000[2][5]	885[2]-967[5]
F07	M3	5.631	3,600[5]-3,605[2]	−10.81	78,000[5]-126,000[2]	718[5]-910[2]
F08	M3	5.654	3,605[2]-3,700[5]	−11.33	200,000[2][5]	1,088[5]-1,146[2]
F09	M6	5.670	3,100[5]-3,399[2]	−10.92	117,000[2]-126,000[5]	986[2]-1,231[5]
F10	M3	5.709	3,500[5]-3,605[2]	−10.86	123,000[5]-132,000[2]	931[2]-954[5]
F11	M5	5.722	3,535[2]-3,600[5]	−11.03	138,000[5]-145,000[2]	955[5]-1,015[2]
F12[3]	M0	5.864	3,200[5]	−10.70	95,000[5]-200,000[2]	1,003[5]
F13	K2	5.957	4,015[2]-4,100[5]	−11.39	251,000[5]-282,000[2]	993[5]-1,098[2]
F14	M3	6.167	3,500[5]-3,605[2]	−10.25	47,000[5]-74,000[2]	590[5]-697[2]
F15	G0	6.682	6,850[2]	−10.07	229,000[2]	340[2]

References

1. Froebrich, D.; Scholz, A. (2013). "The main sequence of three red supergiant clusters". Monthly Notices of the Royal Astronomical Society. 436 (2): 1116–1122. arXiv:1308.6436. Bibcode:2013MNRAS.436.1116F. doi:10.1093/mnras/stt1633. ISSN 0035-8711.
2. Davies, B.; Figer, D. F.; Law, C. J.; Kudritzki, R. P.; Najarro, F.; Herrero, A.; MacKenty, J. W. (2008). "The Cool Supergiant Population of the Massive Young Star Cluster RSGC1". The Astrophysical Journal. 676 (2): 1016–1028. arXiv:0711.4757. Bibcode:2008ApJ...676.1016D. doi:10.1086/527350.
3. Figer, D. F.; MacKenty, J. W.; Robberto, M.; Smith, K.; Najarro, F.; Kudritzki, R. P.; Herrero, A. (2006). "Discovery of an Extraordinarily Massive Cluster of Red Supergiants". The Astrophysical Journal. 643 (2): 1166–1179. arXiv:astro-ph/0602146. Bibcode:2006ApJ...643.1166F. doi:10.1086/503275.
4. Davies, B.; Figer, D. F.; Kudritzki, R. P.; MacKenty, J.; Najarro, F.; Herrero, A. (2007). "A Massive Cluster of Red Supergiants at the Base of the Scutum‐Crux Arm". The Astrophysical Journal. 671: 781. arXiv:0708.0821. Bibcode:2007ApJ...671..781D. doi:10.1086/522224.
5. Fok, Thomas K. T.; Nakashima, Jun-ichi; Yung, Bosco H. K.; Hsia, Chih-Hao; Deguchi, Shuji (2012-11-20). "Maser Observations of Westerlund 1 and Comprehensive Considerations on Maser Properties of Red Supergiants Associated with Massive Clusters". The Astrophysical Journal. 760 (1): 65. doi:10.1088/0004-637X/760/1/65. hdl:10722/181706. ISSN 0004-637X.