Andromeda I

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This article is about the galaxy. For the star, see ι Andromedae.
"Andromeda 1" redirects here. For the star, see 1 Andromedae.
For other uses, see And 1.
Andromeda I
Andromeda I Hubble WikiSky.jpg
Andromeda I by HST
Observation data (J2000 epoch)
Constellation Andromeda
Right ascension 00h 45m 39.8s[1]
Declination +38° 02′ 28″[1]
Redshift -368 ± 11 km/s[1]
Distance 2.40 ± 0.08 Mly (735 ± 23 kpc)[2][3][4]
Type dSph
Apparent dimensions (V) 2′.5 × 2′.5[1]
Apparent magnitude (V) 13.6[1]
Notable features satellite galaxy of M31
Other designations
And I,[2] Anon 0043+37,[1] PGC 2666[1]
See also: Galaxy, List of galaxies

Andromeda I is a dwarf spheroidal galaxy(dSph)[5] about 2.40[4] million light-years away in the constellation Andromeda. Andromeda I is part of the Local group of galaxies and a satellite galaxy of the Andromeda Galaxy (M31). It is roughly 3.5 degrees south and slightly east of M31.[6] As of 2005, it is the closest known dSph companion to M31[7] at an estimated projected distance of ~40[4] kpc or ~150,000[6] light-years.

Andromeda I was discovered by Sidney van den Bergh[8] in 1970 with the Mount Palomar Observatory 48-inch telescope.[5] Further study of Andromeda I was done by the WFPC2 camera of the Hubble Space Telescope. This found that the horizontal branch stars, like other dwarf spheroidal galaxies were predominantly red.[9] From this, and the abundance of blue horizontal branch stars, along with 99 RR Lyrae stars detected in 2005,[7] lead to the conclusion there was an extended epoch of star formation. The estimated age is approximately 10 Gyr. The Hubble telescope also found a globular cluster in Andromeda I, being the least luminous galaxy where such a cluster was found.[10]

See also[edit]


  1. ^ a b c d e f g "NASA/IPAC Extragalactic Database". Results for Andromeda I. Retrieved 2008-01-21. 
  2. ^ a b 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 
  4. ^ a b c McConnachie, A. W.; Irwin, M. J.; Ferguson, A. M. N.; Ibata, R. A. et al. (May 2004), "Determining the location of the tip of the red giant branch in old stellar populations: M33, Andromeda I and II", Monthly Notices of the Royal Astronomical Society 350 (1): 250, arXiv:astro-ph/0401453, Bibcode:2004MNRAS.350..243M, doi:10.1111/j.1365-2966.2004.07637.x 
  5. ^ a b van den Bergh, Sydney (January 1972), "Search for Faint Companions to M31", Astrophysical Journal 171: L31, Bibcode:1972ApJ...171L..31V, doi:10.1086/180861 
  6. ^ a b Andromeda I, Students for the Exploration and Development of Space (SEDS), July 25, 2001 
  7. ^ a b Pritzl, Barton J.; Armandroff, Taft E.; Jacoby, George H.; Da Costa, G. S. (May 2005), "The Dwarf Spheroidal Companions to M31: Variable Stars in Andromeda I and Andromeda III", The Astronomical Journal 129 (5): 2232–2256, arXiv:astro-ph/0501083, Bibcode:2005AJ....129.2232P, doi:10.1086/428372 
  8. ^ McConnachie, A. W.; Irwin, M. J.; Ferguson, A. M. N.; Ibata, R. A. et al. (2005), "Distances and metallicities for 17 Local Group galaxies", Monthly Notices of the Royal Astronomical Society 356 (4): 979–997, arXiv:astro-ph/0410489, Bibcode:2005MNRAS.356..979M, doi:10.1111/j.1365-2966.2004.08514.x. 
  9. ^ Da Costa, G. S.; Armandroff, T. E.; Caldwell, Nelson; Seitzer, Patrick (December 1996), "The Dwarf Spheroidal Companions to M31: WFPC2 Observations of Andromeda I", Astronomical Journal 112: 2576, arXiv:astro-ph/9610083, Bibcode:1996AJ....112.2576D, doi:10.1086/118204 
  10. ^ Grebel, E. K.; Dolphin, A. E.; Guhathakurta, P. (September 18–23, 2000), "Discovery of a Globular Cluster in M31's Dwarf Spheroidal Companion Andromeda I", Astronomische Gesellschaft Abstract Series (Bremen) 17, Bibcode:2000AGM....17..P61G  |chapter= ignored (help)

External links[edit]

Coordinates: Sky map 00h 45m 39.8s, +38° 02′ 28″