NGC 7742

NGC 7742^[1]

A Hubble Space Telescope (HST) image of NGC 7742.
Credit: NASA/ESA/STScI/AURA.
Observation data Epoch J2000
Constellation	Pegasus
Right ascension	23h 44m 15.7s[2]
Declination	+10° 46′ 02″[2]
Apparent dimension (V)	1.778 × 1.698 moa[3]
Apparent magnitude (V)	12.35[2]
Characteristics
Type	SA(r)b,[2] LINER/HII[2]
Astrometry
Helio Radial velocity	1663 ± 1[2]km/s
Redshift	0.005547 ± 0.000003[2]
Galactocentric Velocity	1809 ± 6[2] km/s
Distance	72.4 ± 6.2 Mly (22.2 ± 1.9 Mpc)
Other designations
UGC 12760,[2] MCG +02-60-010,[2] UZC J234415.8+104601,[2] 2MASX J23441571+1046015[2]
Database references
SIMBAD	Search NGC 7742 data
See also: Galaxy, List of galaxies

NGC 7742 is a face-on unbarred spiral galaxy in the constellation Pegasus.

The galaxy is unusual in that it contains a ring but no bar.^[4] Typically, bars are needed to produce a ring structure. The bars' gravitational forces move gas to the ends of the bars, where it forms into the rings seen in many barred spiral galaxies. In this galaxy, however, no bar is present, so this mechanism cannot be used to explain the formation of the ring. O. K. Sil'chenko and A. V. Moiseev proposed that the ring was formed partly as the result of a merger event in which a smaller gas-rich dwarf galaxy collided with NGC 7742. As evidence for this, they point to the unusually bright central region, the presence of highly-inclined central gas disk, and the presence of gas that is counterrotating (or rotating in the opposite direction) with respect to the stars.^[4]

See also

• NGC 7217 - a face-on spiral galaxy with identical characteristics
• Sombrero Galaxy - a similar galaxy with a dust ring

References

1. ^ Filho,, M. E.; Barthel, P. D.; Ho, L. C. (October 2002). "The Nature of Composite LINER/H_II Galaxies, Part II". The Astrophysical Journal Supplement (The University of Chicago Press) 142 (2): 223–238. arXiv:astro-ph/0205196. Bibcode 2002ApJS..142..223F. doi:10.1086/341786. ISSN 0067-0049. 
2. ^ ^{a b c d e f g h i j k l} "NASA/IPAC Extragalactic Database". Results for NGC 7742. http://nedwww.ipac.caltech.edu/. Retrieved 2006-08-20. 
3. ^ "Centre de Données astronomiques de Strasbourg". Results for NGC 7742. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=ngc7742. Retrieved 2008-07-09. 
4. ^ ^{a b} O. K. Sil'chenko, A. V. Moiseev (2006). "Nature of Nuclear Rings in Unbarred Galaxies: NGC 7742 and NGC 7217". Astronomical Journal 131 (3): 1366–1346. arXiv:astro-ph/0512431. Bibcode 2006AJ....131.1336S. doi:10.1086/499945. 

External links

• NGC 7742 at ESA/Hubble
• NGC 7742 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images

Coordinates: 23^h 44^m 15.7^s, +10° 46′ 02″