NGC 2403
| NGC 2403 | |
|---|---|
| File:NGC2403-Subaru-HST-L.jpg 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[1] |
| Declination | +65° 36′ 09.662″[1] |
| Redshift | 0.000445[1] |
| Heliocentric radial velocity | 133 ± 0 km/s[1] |
| Distance | 9.65 Mly (2.96 Mpc)[2] |
| Apparent magnitude (V) | 8.9[1] |
| Characteristics | |
| Type | SAB(s)cd[1] |
| Size | ~90,300 ly (27.69 kpc) (estimated)[1] |
| Apparent size (V) | 21.9′ × 12.3′[1] |
| Other designations | |
| Caldwell 7, IRAS 07321+6543, UGC 3918, PGC 21396, CGCG 309-040[1] | |
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.
Observation history
[edit | edit source]The galaxy was discovered by German-British astronomer William Herschel on 1 November 1788.[4] 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.
Characteristics
[edit | edit source]
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.[5] It is a flocculent spiral galaxy, with short, patchy arms.[6] 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
[edit | edit source]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.[7] In 1972, Fritz Zwicky classified this event as a Type V supernova.[8] 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.[9]
- 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.[10] On 24 August 2021, it was reclassified as a Gap transient.[11]
- SN 2004dj (Type II-P, mag. 11.2) was discovered by Kōichi Itagaki on 31 July 2004.[12][13] 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.[14]
- 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.[15][16]
Companions
[edit | edit source]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.[17]
See also
[edit | edit source]- Triangulum Galaxy - looks very similar to NGC 2403.
- List of NGC objects (2001–3000)
References
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External links
[edit | edit source]
- 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
