NGC 691
Unbarred spiral galaxy with multiple rings in Aries.
NGC 691 is an unbarred spiral galaxy in the constellation Aries, roughly 120 million light-years from Earth. Its apparent size suggests it spans about 130,000 light-years across. William Herschel discovered it on November 13, 1786.
The galaxy has a multiple ring structure, with three distinct rings detected in infrared light, measuring 1.03, 1.67, and 2.79 arcminutes in diameter. In H-alpha images, NGC 691 appears patchy. Its total star formation rate is estimated at about 0.6 solar masses per year.
NGC 691 is the leading member of the NGC 691 group, which also includes IC 163, NGC 678, NGC 680, NGC 694, IC 167, and NGC 697.
One supernova has been observed in this galaxy: SN 2005W. Yoji Hirose discovered it on February 1, 2005, using unfiltered CCD frames with a 0.35-meter Schmidt-Cassegrain reflector. It was located 56 arcseconds east and 1 arcsecond south of the galaxy's center, with an apparent magnitude of 15.2 at discovery. Spectroscopic observations identified it as a Type Ia supernova about a week before maximum brightness. Its peak magnitude was 14.3, reached on February 10, 2005.
Quick Facts
- Epoch
- J2000
- Ra
- 01 · 50 · 41.7
- Dec
- +21 · 45 · 36
- Dist Ly
- 119 ± 14 Mly (36.5 ± 4.3 Mpc)
- Z
- 0.008889 ± 0.000013
- H Radial V
- 2,665 ± 5 km/s
- Appmag V
- 11.5
- Constellation Name
- Aries
- Names
- UGC 1305, CGCG 482-023, MCG +04-05-019, PGC 6793
Facts from the source article.
Lore & Background
NGC 691 was discovered by William Herschel on November 13, 1786. It is an unbarred spiral galaxy located approximately 120 million light years from Earth, with an estimated diameter of about 130,000 light years. The galaxy exhibits a multiple ring structure, with three rings identified in the infrared, having diameters of 1.03, 1.67, and 2.79 arcminutes. When imaged in H-alpha, the galaxy appears patchy. The total star formation rate of NGC 691 is estimated to be about 0.6 solar masses per year.
NGC 691 is the foremost member of a galaxy group known as the NGC 691 group. Other members of this group include IC 163, NGC 678, NGC 680, NGC 694, IC 167, and NGC 697. One supernova has been observed in NGC 691: SN 2005W, discovered by Yoji Hirose in unfiltered CCD frames taken on February 1.442 UT with a 0.35-m f/6.8 Schmidt-Cassegrain reflector. The supernova was located 56" east and 1" south of the center of NGC 691 and at discovery had an apparent magnitude of 15.2. Spectrographic observations indicated it was a Type Ia supernova about a week before maximum, reaching a peak magnitude of 14.3 on February 10.759.
Reader's Guide
NGC 691 holds significance as the foremost member of the NGC 691 group, a collection of galaxies that includes IC 163, NGC 678, NGC 680, NGC 694, IC 167, and NGC 697. Its multiple ring structure, with three distinct rings observed in the infrared, provides insight into the dynamical processes within unbarred spiral galaxies. The detection of a Type Ia supernova, SN 2005W, in NGC 691 contributes to the study of such stellar explosions, with its discovery by amateur astronomer Yoji Hirose highlighting the role of citizen science in astronomical observations. The galaxy's patchy appearance in H-alpha imaging and its star formation rate of about 0.6 solar masses per year offer clues about its ongoing stellar birth activity. As a relatively nearby spiral at about 120 million light years, NGC 691 serves as a useful target for studying ring structures and supernova events in a group environment.
Did You Know?
- NGC 691 has three recognized rings in the infrared, with diameters of 1.03, 1.67, and 2.79 arcminutes.
- The supernova SN 2005W in NGC 691 was discovered by Yoji Hirose using a 0.35-m Schmidt-Cassegrain reflector.
More in NGC Objects 1-24
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