Andromeda I

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
Andromeda I by the HST
Observation data (J2000 epoch)
ConstellationAndromeda
Right ascension 00h 45m 39.8s[1]
Declination+38° 02′ 28″[1]
Redshift-368 ± 11 km/s[1]
Distance2.40 ± 0.08 Mly (735 ± 23 kpc)[2][3][4]
Apparent magnitude (V)13.6[1]
Characteristics
TypedSph
Apparent size (V)2′.5 × 2′.5[1]
Notable featuressatellite galaxy of M31
Other designations
And I,[2] Anon 0043+37,[1] PGC 2666[1]

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

References
  1. "NASA/IPAC Extragalactic Database". Results for Andromeda I. Retrieved 2008-01-21.
  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
  4. 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. 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. Andromeda I, Students for the Exploration and Development of Space (SEDS), July 25, 2001, archived from the original on November 30, 2004
  7. 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", Abstracts of Contributed Talks and Posters presented at the Annual Scientific Meeting of the Astronomische Gesellschaft, Astronomische Gesellschaft Abstract Series, 17, Bremen, Bibcode:2000AGM....17..P61G



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