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Dwarf galaxy in the constellation Andromeda From Wikipedia, the free encyclopedia
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 | |
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![]() Andromeda I by the 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] |
Apparent magnitude (V) | 13.6[1] |
Characteristics | |
Type | dSph |
Apparent size (V) | 2.5′ × 2.5′[1] |
Notable features | satellite 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]
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