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,<ref name="NSOG" /> and is approximately 8 million light-years distant.

Observation history

The galaxy was discovered by German-British astronomer William Herschel on 1 November 1788.<ref name="selig" /> 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.<ref name="NSOG" /> 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.

Characteristics

File:A Galaxy of Birth and Death.jpg

A Galaxy of Birth and Death

NGC 2403 bears a similarity to M33, containing numerous star-forming H II regions, but being a little bit larger at approximately 90,000 light-years in diameter compared to the 61,100 light-year diameter of M33.<ref name="hoetal1997" /> It is a flocculent spiral galaxy, with short, patchy arms.<ref name=Kostiuk>Template:Cite journal</ref> The northern spiral arm connects it to the star forming region NGC 2404.<ref name="NSOG" /> NGC 2403 can be observed using 10×50 binoculars.<ref name="NSOG" /> 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.<ref name=Tammann /> In 1972, Fritz Zwicky classified this event as a Type V supernova.<ref name=Zwicky /> 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.<ref name=VanDyk />
• 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.<ref name=IAUC8051 /> On 24 August 2021, it was reclassified as a Gap transient.<ref name=TNS-2002kg />
• SN 2004dj (Type II-P, mag. 11.2) was discovered by Kōichi Itagaki on 31 July 2004.Template:R At the time of its discovery, it was the nearest and brightest supernova observed in the 21st century, and is now listed as the brightest supernova of 2004.Template:R
• ATTemplate:Nbsp2016ccd, 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.Template:R

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 Template:Cvt 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.<ref name=jeffrey />

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.<ref name=Carlin2021 />

See also

• Triangulum Galaxy - looks very similar to NGC 2403.
• List of NGC objects (2001–3000)

External links

• Spiral Galaxy NGC 2403 at the astro-photography site of Mr. Takayuki Yoshida
• NGC 2403 at ESA/Hubble
• Template:WikiSky
• Template:APOD
• SEDS – NGC 2403