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SN 1885A

Supernova event of August 1885 in the Andromeda Galaxy

Supernova 1885

The visual band light curve of S Andromedae, adapted from Patchett et al. (1985)[1]
Event type	Supernova
Type Ia
Date	c. 2.5 million years ago (discovered 20 August 1885 by Ernst Hartwig)
Constellation	Andromeda
Right ascension	00h42m 43.11s
Declination	+41° 16′ 04.2′′
Epoch	J2000.0
Galactic coordinates	121.1702 -21.5741
Distance	c. 2.5 million ly
Host	Andromeda Galaxy
Colour (B-V)	+1.3 ~ +0.6[2]
Notable features	First and only supernova observed in Andromeda; first extragalactic supernova observed; closest type Ia observed
Peak apparent magnitude	+6
Other designations	SN 1885A, HR 182, 2MASS J00424312+4116032, BD+40 147a, S And, TIC 438234291, AAVSO 0037+40, EV* M31 V0894
Preceded by	SN 1604 (observed), Cassiopeia A (unobserved, c. 1680), G1.9+0.3 (unobserved, c. 1868)
Followed by	SN 1895B
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SN 1885A (also S Andromedae) was a supernova in the Andromeda Galaxy, the only one seen in that galaxy so far by astronomers. It was the first supernova ever seen outside the Milky Way,^[3] though it was not known at the time how far away it was. It is also known as "Supernova 1885".

The supernova appears to have been seen first on August 17, 1885, by French astronomer Ludovic Gully during a public stargazing event.^[4] Gully thought it was scattered moonlight in his telescope and did not follow up on this observation. Irish amateur astronomer Isaac WardinBelfast claimed to have seen the object on August 19, 1885, but did not immediately publish its existence.^[5][6]

The independent detection of the supernova by Ernst HartwigatDorpat (Tartu) ObservatoryinEstonia on August 20, 1885, however, was communicated in a telegram on August 31, 1885, once Hartwig had verified in more ideal circumstances that the feature was not caused by reflected moonlight.^[7][8] The telegram prompted widespread observations of the event,^[9] and prompted Isaac Ward, Ludovic Gully, and several others to publish their earlier observations (the first reports on S Andromedae appeared before Hartwig's discovery letter which followed his telegram, since the letter was initially lost by Astronomische Nachrichten and only reprinted in a later issue). The history of the discovery is summarized by K.G. Jones^[10] and de Vaucouleurs and Corwin.^[2] Both studies doubt that Ward really saw the event since his estimated magnitude is significantly off from the later reconstructed light curve,^[2] and conclude that Hartwig should be considered as the discoverer of the supernova.

SN 1885A reached magnitude 5.85 on 21 August 1885, and faded to magnitude 14 six months later.^[2] It was reddish in color and declined rapidly in brightness, which is unusual for type Ia supernovae. Some astronomers observed the spectrum of the star visually (no photographic spectral observations were made in that time). These observations were made at the limit of visibility, but they were considered to be in good agreement with each other and with modern data on typical supernovae of type Ia; SN 1885A has thus been assigned to this type.^[2] Studies led by Dovi Poznanski and by Hagai Perets suggest that SN 1885A belongs to a new subclass of Type I supernovae, along with SN 2002bj and SN 1939B.^[11][12]

The supernova occurred 16″ from the relatively bright nucleus of the galaxy. This made detection of its remnant difficult — early attempts were unsuccessful. In 1988, R. A. Fesen and others used the 4-meter Mayall telescopeatKitt Peak to discover the iron-rich remnant of the explosion.^[13] Further observations were made with the Hubble Space Telescope in 1999.^[14] The spectrum of the remnant shows the presence of iron, calcium and manganese, which were likely created during the explosion. There is some evidence for spherical symmetry in the explosion; this would mean that this type Ia supernova was not triggered by merging.^[15]

• Light curve Archived 2017-10-22 at the Wayback Machine on the Open Supernova Catalog
• "S Andromedae: Supernova 1885 in M31". Students for the Exploration and Developments of Space. Retrieved 2005-08-12.
• "Supernova 1885A - S Andromedae". Archived from the original on February 19, 2001. Retrieved August 12, 2005.
• "S And". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved October 9, 2018.