NGC 221

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NGC 221, also known as Messier 32, is an elliptical galaxy located in the constellation Andromeda. It is a satellite galaxy of the Andromeda Galaxy.

NGC 221
Observation data: 2000.0 epoch
Constellation Andromeda
Right ascension 0h 42m
Declination +40° 52ˡ
Redshift -0.00068
Distance 2.4 - 2.9 million light years
Type Galaxy
Apparent dimensions 8ˡ.7 X 6ˡ.5
Apparent magnitude +9.0
Other designations Messier 32

Discovery and observational data

NGC 221 can be found 22' south of the nucleus of the Andromeda Galaxy as an elongated, bright galaxy. LeGentil discovered the object in 1749 while French comet hunter Charles Messier recorded it in 1757. Seven years later he included the galaxy in his catalogue of clusters and nebulae as number 32.

With an apparent magnitude of +9, NGC 221 is one of the brightest galaxies on the Messier list. Through modest amateur telescopes it is readily visible when observing the Andromeda Galaxy.

NGC 221 seems to be superimposed on the outer regions of its parent galaxy and studies indicate that it is in the foreground in relation to its larger neighbor.

There have not been any recorded observations of supernovae in NGC 221. In 1998 a nova was recorded about 53ˡˡ south and west of the galaxy's nucleus. It reached magnitude +16.5 on September 1, 1998.

Physical data

The elliptical companion of the Andromeda Galaxy is classified as being of type E2, indicating its slightly elongated shape as seen from Earth. Its distance is variously given as 2.4 tot 2.9 million light years and it is moving toward Earth at a speed of roughly 200 km/s giving it a negative redshift (blueshift) of -0.00068. The estimated distance to NGC 221 and its apparent size translate into a diameter of the galaxy of about 8.000 light years while its mass is calculated at some 3 X 109 solar masses.[1]

Walter Baade, observing at the Mount Wilson Observatory in 1944, was the first to resolve NGC 221 into individual stars of which the brightest were found to be of photographic magnitude +21.3 [2] Most of the stars in the galaxy were found to be older population II stars as is usual for elliptical galaxies although NGC 221's spectrum does reveal a higher concentration of heavy elements compared to similar objects.[3]

NGC 221's nucleus is rather large in relation to the total size of the galaxy. One likely reason for this is that its parent galaxy, Messier 31, through gravitational interactions with NGC 221, stripped the smaller galaxy of parts of its outer envelope of stars. The absence of globular clusters associated with NGC 221 also provides evidence of this.[1]

References

  1. 1.0 1.1 Frommert and Kronberg, SEDS, online at http://seds.lpl.arizona.edu/messier/m/m032.html
  2. Walter Baade, The resolution of Messier 32, NGC 205, and the central region of the Andromeda Nebula printed in the Astrophysical Journal, 1944
  3. IAU circular 7004, September 1, 1998, online at http://www.cfa.harvard.edu/iauc/07000/07004.html#Item2