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NGC 2403
NGC 2403
	A Hubble Space Telescope (HST), and Subaru image of NGC 2403. NGC 2404 is visible
Observation data (J2000 epoch)
Constellation	Camelopardalis
Right ascension	07h 36m 51.298s
Declination	+65° 36′ 09.662″
Redshift	0.000445
Heliocentric radial velocity	133 ± 0 km/s
Distance	9.65 Mly (2.96 Mpc)
Apparent magnitude (V)	8.9
Characteristics
Type	SAB(s)cd
Size	~90,300 ly (27.69 kpc) (estimated)
Apparent size (V)	21.9′ × 12.3′
Other designations
	Caldwell 7, IRAS 07321+6543, UGC 3918, PGC 21396, CGCG 309-040

NGC 2403 (also known as Caldwell 7) is an intermediate spiral galaxy in the constellation Camelopardalis. It is an outlying member of the M81 Group,^[3] and is approximately 8 million light-years distant. It bears a similarity to M33, being about 50,000 light years in diameter and containing numerous star-forming H II regions.^[4] The northern spiral arm connects it to the star forming region NGC 2404.^[3] NGC 2403 can be observed using 10×50 binoculars.^[3] NGC 2404 is 940 light-years in diameter, making it one of the largest known H II regions. This H II region represents striking similarity with NGC 604 in M33, both in size and location in galaxy.

Supernovae and Supernovae Imposters

There have been four reported astronomical transients in the galaxy:

SN 1954J was first noticed by Gustav Tammann and Allan Sandage as a "bright blue irregular variable" star, which they named V12. They noted it underwent a major outburst on 2/3 November 1954, which attained a magnitude of 16 at its brightest.^[5] In 1972, Fritz Zwicky classified this event as a type V supernova.^[6] It was later determined to be a supernova imposter: a highly luminous, very massive eruptive star, surrounded by a dusty nebula, similar to the 1843 Great Eruption of η Carinae in the Milky Way.^[7]
SN 2002 kg was discovered by LOTOSS (Lick Observatory and Tenagra Observatory Supernova Searches) on 26 October 2002 and initially classified as a type IIn, or possibly the outburst of a luminous blue variable.^[8] On 24 August 2021, it was reclassified as a Gap transient.^[9]
SN 2004dj (type II-P, mag. 11.2) was discovered by Kōichi Itagaki on 31 July 2004.^[10] At the time of its discovery, it was the nearest and brightest supernova observed in the 21st century.
AT 2016ccd, initially designated as SNhunt225, is a luminous blue variable, first discovered by Catalina Real-time Transient Survey (CRTS) and Stan Howerton in December 2013. Outbursts from this star have been observed as recently as November 2021.^[11]^[12]

History

The galaxy was discovered by William Herschel in 1788. Edwin Hubble detected Cepheid variables in NGC 2403 using the Hale Telescope, making it the first galaxy beyond the Local Group within which a Cepheid was discovered.^[3] By 1963, 59 variables had been found in NGC 2403, of which 17 were eventually confirmed as Cepheids, with periods between 20 and 87 days. As late as 1950 Hubble was using a distance of just under 2 million light years for the galaxy's distance, but by 1968 the analysis of the Cepheids increased this by almost a factor of five, to within 0.2 magnitudes of the current value.

Companions

NGC 2403 has two known companions. One is the relatively massive dwarf galaxy DDO 44. It is currently being disrupted by NGC 2403, as evidenced by a tidal stream extending 82 kly (25 kpc) on both sides of DDO 44. DDO 44 is approaching NGC 2403 at a distance much closer than typical for dwarf galaxy interactions. It currently has a V-band absolute magnitude of −12.9, but its progenitor was even more luminous.^[2]

The other known companion is officially named MADCASH J074238+652501-dw, although it is nicknamed MADCASH-1. The name refers to the MADCASH (Magellanic Analog Dwarf Companions and Stellar Halos) project. MADCASH-1 is similar to typical dwarf spheroidal galaxies in the Local Group; it is quite faint, with an absolute V-band magnitude of −7.81, and has only an ancient, metal-poor population of red giant stars.^[13]

Luminous blue variables in NGC 2403

NGC 2403 has four known luminous blue variables. AT 2016ccd, NGC 2403 V14, NGC 2403 V37, and NGC 2403 V12.

Not much is known about AT 2016ccd, besides that it is a luminous blue variable. AT 2016ccd has a magnitude of 18-19.95, so it is quite dim. NGC 2403 V14 is more well known then AT 2016ccd. NGC 2403 V14 has a size of 1,260.2 solar radii, it has a mass of 24 solar masses and has a temperature of 7,041 K. NGC 2403 V14 has a magnitude of 12.9. NGC 2403 V37 is not well known, it is believed to be a luminous blue variable with a magnitude of 12.9. NGC 2403 V12 is an unknown luminous blue variable with a magnitude of 6.5. [1] [2] [3] [4]

References

^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ "NASA/IPAC Extragalactic Database". Results for NGC 2403. Retrieved 2006-11-21.
^ ^a ^b Carlin, Jeffrey L.; Garling, Christopher T.; Peter, Annika H. G.; Crnojević, Denija; Forbes, Duncan A.; Hargis, Jonathan R.; Mutlu-Pakdil, Burçin; Pucha, Ragadeepika; Romanowsky, Aaron J.; Sand, David J.; Spekkens, Kristine; Strader, Jay; Willman, Beth (2019). "Tidal Destruction in a Low-mass Galaxy Environment: The Discovery of Tidal Tails around DDO 44". The Astrophysical Journal. 886 (2): 109. arXiv:1906.08260. Bibcode:2019ApJ...886..109C. doi:10.3847/1538-4357/ab4c32. S2CID 195218404.
^ ^a ^b ^c ^d Kepple, George Robert; Glen W. Sanner (1998). The Night Sky Observer's Guide. Vol. 1. Willmann-Bell, Inc. p. 73. ISBN 978-0-943396-58-3.
^ Ho, Luis C.; Filippenko, Alexei V.; Sargent, Wallace L. W. (October 1997). "A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies". Astrophysical Journal Supplement. 112 (2): 315–390. arXiv:astro-ph/9704107. Bibcode:1997ApJS..112..315H. doi:10.1086/313041. S2CID 17086638.
^ Tammann, G. A.; Sandage, Allan (1968). "The Stellar Content and Distance of the Galaxy NGC 2403 IN the M81 Group". The Astrophysical Journal. 151: 825. Bibcode:1968ApJ...151..825T. doi:10.1086/149487.
^ Kowal, C. T.; Sargent, W. L. W.; Searle, L.; Zwicky, F. (1972). "The 1971 Palomar Supernova Search". Publications of the Astronomical Society of the Pacific. 84 (502): 844. Bibcode:1972PASP...84..844K. doi:10.1086/129392.
^ Van Dyk, Schuyler D.; Filippenko, Alexei V.; Chornock, Ryan; Li, Weidong; Challis, Peter M. (2005). "Supernova 1954J (Variable 12) in NGC 2403 Unmasked". Publications of the Astronomical Society of the Pacific. 117 (832): 553–562. arXiv:astro-ph/0503324. Bibcode:2005PASP..117..553V. doi:10.1086/430238.
^ Green, Daniel W. E. (January 15, 2003). "Central Bureau for Astronomical Telegrams, Circular No. 8051". Retrieved 14 August 2024.
^ "SN 2002 kg". Transient Name Server. IAU. Retrieved 14 August 2024.
^ "SN 2004dj". Transient Name Server. IAU. Retrieved 14 August 2024.
^ Bishop, David (9 November 2021). "LBV AT2016ccd in NGC 2403". Rochester Astronomy. Retrieved 31 August 2024.
^ "AT 2016ccd". Transient Name Server. IAU. Retrieved 31 August 2024.
^ Carlin, Jeffrey L.; Mutlu-Pakdil, Burçin; Crnojević, Denija; Garling, Christopher T.; Karunakaran, Ananthan; Peter, Annika H. G.; Tollerud, Erik; Forbes, Duncan A.; Hargis, Jonathan R.; Lim, Sungsoon; Romanowsky, Aaron J.; Sand, David J.; Spekkens, Kristine; Strader, Jay (2021). "Hubble Space Telescope Observations of Two Faint Dwarf Satellites of Nearby LMC Analogs from MADCASH". The Astrophysical Journal. 909 (2): 211. arXiv:2012.09174. Bibcode:2021ApJ...909..211C. doi:10.3847/1538-4357/abe040. S2CID 229297953.