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Sextans B

Sextans B
Sextans B, imaged by the 4-meter Telescope at Kitt Peak National Observatory
Observation data (J2000 epoch)
ConstellationSextans
Right ascension10h 00m 00.1s[1]
Declination+05° 19′ 56″[1]
Redshift301 ± 1 km/s[1]
Distance4.44 ± 0.23 Mly (1.36 ± 0.07 Mpc)[2][3]
Apparent magnitude (V)11.9[1]
Characteristics
TypeImIV–V[1]
Size~8,900 ly (2.73 kpc) (estimated)[1]
Apparent size (V)5.1′ × 3.5′[1]
Other designations
DDO 70, UGC 5373, MCG +01-26-005, PGC 28913, CGCG 036-012

Sextans B (also known as UGC 5373 and DDO 70) is an irregular galaxy that may be part of the Local Group, or lie just beyond it. The earliest known reference to this galaxy is from a 1954 paper by Edison Pettit in The Astrophysical Journal, where it was listed as "Wilson Dwarf".[4]

Sextans B is 4.44 million light-years away from Earth and thus is one of the most distant members of the Local Group, if it is indeed a member. It forms a pair with its neighbouring galaxy Sextans A.[5] It is a type Ir IV–V galaxy according to the galaxy morphological classification scheme.[6] Sextans B may also be gravitationally associated with the galaxies NGC 3109 and the Antlia Dwarf.[7]

Sextans B has a uniform stellar population,[8] but the interstellar medium in it may be inhomogeneous.[9] Its mass is estimated to be about 2×108 times the mass of the Sun, of which 5.5×107 is in the form of atomic hydrogen.[8] Star formation in the galaxy seems to have proceeded in distinct periods of low intensity, separated by shorter periods of no activity.[8] The existence of Cepheid variables in the galaxy implies that Sextans B contains at least some young stars.[6] The metallicity of Sextans B is very low, with a value of approximately Z = 0.001.[8] Sextans B is receding from the Milky Way with a speed of approximately 300 kilometres per second (190 mi/s),[9] and probably lies just outside the edge of the Local Group, so as its neighbour Sextans A.[10]

Five planetary nebulae have been identified in Sextans B, which is one of the smallest galaxies where planetary nebulae have been observed. These appear point-like and can be identified by their spectral emission lines.[11] It also contains a massive globular cluster.[12]

Although no supernovae have been observed in Sextans B, the galaxy is close enough for classical novae to be detected. The first confirmed nova in this galaxy was discovered by ATLAS at magnitude 18.553 on 10 November 2024, and designated AT 2024aawe.[13]

References

  1. ^ a b c d e f g "NASA/IPAC Extragalactic Database". Results for Sex B. Retrieved 2006-12-13.
  2. ^ I. D. Karachentsev; V. E. Karachentseva; W. K. Hutchmeier; D. I. Makarov (2004). "A Catalog of Neighboring Galaxies". Astronomical Journal. 127 (4): 2031–2068. Bibcode:2004AJ....127.2031K. doi:10.1086/382905.
  3. ^ Karachentsev, I. D.; Kashibadze, O. G. (2006). "Masses of the local group and of the M81 group estimated from distortions in the local velocity field". Astrophysics. 49 (1): 3–18. Bibcode:2006Ap.....49....3K. doi:10.1007/s10511-006-0002-6. S2CID 120973010.
  4. ^ Pettit, Edison (1954). "Magnitudes and Color Indices of Extragalactic Nebulae Determined Photoelectrically". The Astrophysical Journal. 120: 413. Bibcode:1954ApJ...120..413P. doi:10.1086/145932.
  5. ^ Sandage, Allan; Carlson, George (July 1985). "The brightest stars in nearby galaxies. V – Cepheids and the brightest stars in the dwarf galaxy Sextans B compared with those in Sextans A". Astronomical Journal. 90: 1019–1026. Bibcode:1985AJ.....90.1019S. doi:10.1086/113809.
  6. ^ a b van den bergh, Sidney (2000). The galaxies of the Local Group. University of Cambridge. p. 265. ISBN 978-0-521-65181-3.
  7. ^ van den Bergh, Sidney (1999). "Stellar Content of Local Group Galaxies – An Introduction". The Stellar Content of Local Group Galaxies. 192: 3. Bibcode:1999IAUS..192....3V.
  8. ^ a b c d Tosi, M; Greggio, L.; Marconi, G.; Focardi, P. (September 1991). "Star formation in dwarf irregular galaxies – Sextans B". Astronomical Journal. 102: 951–974. Bibcode:1991AJ....102..951T. doi:10.1086/115925.
  9. ^ a b Kniazev, Alexei Y.; Grebel, Eva K.; Pustilnik, Simon A.; Pramskij, Alexander G.; Zucker, Daniel B. (October 2005). "Spectrophotometry of Sextans A and B: Chemical Abundances of H II Regions and Planetary Nebulae". Astronomical Journal. 130 (4): 1558–1573. arXiv:astro-ph/0502562. Bibcode:2005AJ....130.1558K. doi:10.1086/432931. S2CID 14176608.
  10. ^ Alloin, Danielle M.; Gieren, Wolfgang (2000). Stellar candles for the extragalactic distance scale. University of Cambridge. p. 265. ISBN 978-3-540-20128-1.
  11. ^ Magrini, L.; Corradi, R. L. M.; Walton, N. A.; Zijlstra, A. A.; Pollacco, D. L.; Walsh, J. R.; Perinotto, M.; Lennon, D. J.; Greimel, R. (2002). "The Local Group Census: Planetary nebulae in Sextans B". Astronomy & Astrophysics. 386 (3): 869–873. arXiv:astro-ph/0202516. Bibcode:2002A&A...386..869M. doi:10.1051/0004-6361:20020296. S2CID 16954005.
  12. ^ Sharina, M.E.; Puzia, T. H.; Krylatyh, A. S. (September 2009). "A globular cluster in the dwarf galaxy Sextans B". Astrophysical Bulletin. 62 (3): 209–216. arXiv:0704.3908. Bibcode:2007AstBu..62..209S. doi:10.1134/S1990341307030029. S2CID 119588326.
  13. ^ "AT 2024aawe". Transient Name Server. IAU. Retrieved 12 November 2024.
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