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NGC 1624-2 is a massive O-type star located in the star cluster NGC 1624, in the constellation of Perseus, about 16,800 light years away. NGC 1624-2 is notable for being most strongly magnetised O-type star known,[6] with a magnetic field strength of 20 kG, or about 20,000 times the Sun's magnetic field strength.[5] It hosts a large and dense magnetosphere, formed from the interaction between its very strong magnetic field and its dense, radiatively-driven stellar wind, which also absorbs up to 95% of x-rays generated from around the star.[5]

Properties

NGC 1624-2 is a very massive, young, blue star no more than 4 million years old. It is an Of?p star a type of highly magnetic star that has unusual emission lines of multiply-ionized carbon and nitrogen. In NGC 1624-2, the carbon emission is particularly extreme. The luminosity class is uncertain because of the unusual spectrum; it is most commonly given as V (main sequence), but has also been given as I (supergiant).[7]

Analysis of its spectral energy distribution with CHORIZOS modelling yields an effective temperature of 35,000 K, a luminosity of 125,900 L☉ (105.1 L☉) and a radius of about 10 R☉. Assuming a log g of 4.0 yields a mass of 34 M☉, but evolutionary models tend towards a current mass of 28 M☉, given the results from the modelling. However, this assumes that NGC 1624-2 is a normal star, while it is not, so it should only be taken as an indication of its true mass. NGC 1624-2 is currently losing mass at a rate of 10−6.8 M☉/year, through a stellar wind with a terminal velocity of 2,875 km/s.[5]

Rotation

NGC 1624-2 rotates very slowly, only once every 316 days.[6] This slow rotation is typical for very magnetic O-type stars as their magnetic fields slow down their rotation in a process known as magnetic braking, where angular momentum is quickly shed by the stellar wind via the strong magnetic field, which also minimises mass loss throughout the main sequence.[5][6]

References

  1. ^ a b c d e f g Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. ^ a b c Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000-03-01). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H. ISSN 0004-6361.
  3. ^ Sota, A.; Maíz Apellániz, J.; Morrell, N. I.; Barbá, R. H.; Walborn, N. R.; Gamen, R. C.; Arias, J. I.; Alfaro, E. J. (2014-03-01). "The Galactic O-Star Spectroscopic Survey (GOSSS). II. Bright Southern Stars". The Astrophysical Journal Supplement Series. 211 (1): 10. arXiv:1312.6222. Bibcode:2014ApJS..211...10S. doi:10.1088/0067-0049/211/1/10. ISSN 0067-0049. S2CID 118847528.
  4. ^ Reed, B. Cameron (2003-05-01). "Catalog of Galactic OB Stars". The Astronomical Journal. 125 (5): 2531–2533. Bibcode:2003AJ....125.2531R. doi:10.1086/374771. ISSN 0004-6256. S2CID 121285799.
  5. ^ a b c d e f g h i j Wade, G. A.; Maíz Apellániz, J.; Martins, F.; Petit, V.; Grunhut, J.; Walborn, N. R.; Barbá, R. H.; Gagné, M.; García-Melendo, E.; Jose, J.; Moffat, A. F. J.; Nazé, Y.; Neiner, C.; Pellerin, A.; Penadés Ordaz, M. (2012-09-01). "NGC 1624-2: a slowly rotating, X-ray luminous Of?cp star with an extraordinarily strong magnetic field". Monthly Notices of the Royal Astronomical Society. 425 (2): 1278–1293. arXiv:1206.2834. Bibcode:2012MNRAS.425.1278W. doi:10.1111/j.1365-2966.2012.21523.x. ISSN 0035-8711. S2CID 53360606.
  6. ^ a b c d David-Uraz, A.; Petit, V.; Shultz, M. E.; Fullerton, A. W.; Erba, C.; Keszthelyi, Z.; Seadrow, S.; Wade, G. A. (2021-02-01). "New observations of NGC 1624-2 reveal a complex magnetospheric structure and underlying surface magnetic geometry". Monthly Notices of the Royal Astronomical Society. 501 (2): 2677–2687. arXiv:2010.07482. Bibcode:2021MNRAS.501.2677D. doi:10.1093/mnras/staa3768. ISSN 0035-8711.
  7. ^ Skiff, B. A (2014). "VizieR Online Data Catalog: Catalogue of Stellar Spectral Classifications (Skiff, 2009-2016)". VizieR On-line Data Catalog: B/Mk. Originally Published in: Lowell Observatory (October 2014). 1. Bibcode:2014yCat....1.2023S.
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