• Source: NGC 2403

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, 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.
The northern spiral arm connects it to the star forming region NGC 2404. NGC 2403 can be observed using 10×50 binoculars. 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.




Supernova and Supernova Imposters


There have been four reported astronomical transients in the galaxy:

SN 1954J, which attained a magnitude of 16 at its brightest, was initially classified as a type V supernova. 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.
SN 2002 kg was initially classified as a type IIn, or possibly the outburst of a luminous blue variable. In 2021, it was reclassified as a Gap transient.
SN 2004dj was a type II-P which attained a magnitude of 11.2. 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.




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. 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.
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.




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.
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See also


Triangulum Galaxy-looks very similar to NGC 2403.




References






External links



Spiral Galaxy NGC 2403 at the astro-photography site of Mr. Takayuki Yoshida
NGC 2403 at ESA/Hubble

NGC 2403 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
NASA Astronomy Picture of the Day: NGC 2403 (19 February 2016)
SEDS – NGC 2403

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