Astronomy:Super-AGB star

From HandWiki
Short description: Stars that have properties between Asymptotic Giant Branch stars and red supergiants
Colour-Magnitude Diagram showing evolutionary tracks for stars in the super-AGB mass range

A super-AGB star is a star with a mass intermediate between those that end their lives as a white dwarf and those that end with a core collapse supernova, and properties intermediate between asymptotic giant branch (AGB) stars and red supergiants. They have initial masses of 7.5–9.25 M☉ in stellar-evolutionary models, but have exhausted their core hydrogen and helium, left the main sequence, and expanded to become large, cool, and luminous.

HR diagram

Super-AGB stars occupy the top-right of the Hertzsprung–Russell diagram (HR diagram), and have cool temperatures between 3,000 and 4,000 K, which is similar to normal AGB stars and red supergiant stars (RSG stars).[1] These cool temperatures allow molecules to form in their photospheres and atmospheres.[2] Super-AGB stars emit most of their light in the infra-red spectrum because of their extremely cool temperatures.

The Chandrasekhar limit and their life

A super-AGB star's core may grow to (or past) the Chandrasekhar mass because of continued hydrogen (H) and helium (He) shell burning, ending as core-collapse supernovae.[1][3] The most massive super-AGB stars (at around 9 M☉) are theorized to end in electron capture supernovae. The error in this determination due to uncertainties in the third dredge-up efficiency and AGB mass-loss rate could lead to about a doubling of the number of electron-capture supernovae, which also supports the theory that these stars make up 66% of the supernovae detected by satellites. These stars are at a similar stage in life to red giant stars, such as Aldebaran, Mira, and Chi Cygni, and are at a stage where they start to brighten, and their brightness tends to vary, along with their size and temperature.


List of super-AGB candidates

Candidate Right ascension Declination Location Discovery Notes Refs
HV 2112  01h 10m 03.87s −72° 36′ 52.6″ Small Magellanic Cloud 2014 [4][5]
MSX SMC 055  00h 50m 07.2s −73° 31′ 25.1″ Small Magellanic Cloud 2009 Considered to be a likely super-AGB star candidate[6] [6]
VX Sagittarii  18h 08m 04.04831s −22° 13′ 26.6327″ Sagittarius 1904 Commonly classified as an unusually cool red supergiant or red hypergiant.[7][8] [9]

References

  1. ↑ 1.0 1.1 Groenewegen, M. A. T.; Sloan, G. C. (2018). "Luminosities and mass-loss rates of Local Group AGB stars and red supergiants". Astronomy & Astrophysics 609: A114. doi:10.1051/0004-6361/201731089. Bibcode: 2018A&A...609A.114G. 
  2. ↑ Levesque, Emily M.; Massey, Philip; Olsen, K. A. G.; Plez, Bertrand; Josselin, Eric; Maeder, Andre; Meynet, Georges (2005). "The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not as Cool as We Thought". The Astrophysical Journal 628 (2): 973–985. doi:10.1086/430901. Bibcode: 2005ApJ...628..973L. 
  3. ↑ Poelarends, A. J. T.; Herwig, F.; Langer, N.; Heger, A. (2008). "The Supernova Channel of Super-AGB Stars". The Astrophysical Journal 675 (1): 614–625. doi:10.1086/520872. Bibcode: 2008ApJ...675..614P. 
  4. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named tout
  5. ↑ Goldman, Steven R.; Van Loon, Jacco Th.; Gómez, José F.; Green, James A.; Zijlstra, Albert A.; Nanni, Ambra; Imai, Hiroshi; Whitelock, Patricia A. et al. (2018). "A dearth of OH/IR stars in the Small Magellanic Cloud". Monthly Notices of the Royal Astronomical Society 473 (3): 3835–3853. doi:10.1093/mnras/stx2601. 
  6. ↑ 6.0 6.1 Groenewegen, M. A. T.; Sloan, G. C.; Soszyński, I.; Petersen, E. A. (2009). "Luminosities and mass-loss rates of SMC and LMC AGB stars and red supergiants". Astronomy & Astrophysics 506 (3): 1277–1296. doi:10.1051/0004-6361/200912678. Bibcode: 2009A&A...506.1277G. 
  7. ↑ Lockwood, G. W.; Wing, R. F. (1982). "The light and spectrum variations of VX Sagittarii, an extremely cool supergiant" (in en). Monthly Notices of the Royal Astronomical Society 198 (2): 385–404. doi:10.1093/mnras/198.2.385. ISSN 0035-8711. Bibcode: 1982MNRAS.198..385L. 
  8. ↑ Xu, Shuangjing; Zhang, Bo; Reid, Mark J; Menten, Karl M; Zheng, Xingwu; Wang, Guangli (2018). "The Parallax of the Red Hypergiant VX Sgr with Accurate Tropospheric Delay Calibration". The Astrophysical Journal 859 (1): 14. doi:10.3847/1538-4357/aabba6. Bibcode: 2018ApJ...859...14X. 
  9. ↑ Tabernero, Hugo M.; Dorda Laforet, Ricardo; Negueruela Díez, Ignacio; Marfil, Emilio Gómez (2021). "The nature of VX Sagitarii". Astronomy & Astrophysics 646: A98. doi:10.1051/0004-6361/202039236. Bibcode: 2021A&A...646A..98T. 

attribution contains text copied from Asymptotic giant branch available under CC-BY-SA-3.0



Retrieved from "https://handwiki.org/wiki/index.php?title=Astronomy:Super-AGB_star&oldid=3942850"