NGC 1624-2 is a massive O-type star located in the star cluster NGC 1624, in the constellation of Perseus, about 16,800 light years away. NGC 1624-2 is notable for being most strongly magnetised O-type star known,[6] with a magnetic field strength of 20 kG, or about 20,000 times the Sun's magnetic field strength.[5] It hosts a large and dense magnetosphere, formed from the interaction between its very strong magnetic field and its dense, radiatively-driven stellar wind, which also absorbs up to 95% of x-rays generated from around the star.[5]

NGC 1624-2

NGC 1624-2 is the brightest star at the centre of NGC 1624 on the left of this image spanning about one degree.
Observation data Epoch J2000      Equinox J2000
Constellation	Perseus
Right ascension	04h 40m 37.276s[1]
Declination	50° 27′ 41.04″[1]
Apparent magnitude (V)	11.57[2]
Characteristics
Evolutionary stage	O-type star
Spectral type	O7f?cp[3]
U−B color index	−0.57[2][4]
B−V color index	0.9[2]
Astrometry
Proper motion (μ)	RA: 0.025[1] mas/yr Dec.: 0.108[1] mas/yr
Parallax (π)	−0.3521 ± 0.1716 mas[1]
Distance	5,152.3[5] pc
Details
Mass	34[5] M☉
Radius	10[5] R☉
Luminosity	126,000[5] L☉
Surface gravity (log g)	3.55[1] cgs
Temperature	35,000[5] K
Metallicity [Fe/H]	+0.07[1] dex
Rotation	315.98 d[6]
Rotational velocity (v sin i)	<3[5] km/s
Other designations
TYC 3350-255-1, ALS 18660, 2MASS J04403728+5027410
Database references
SIMBAD	data

Properties

NGC 1624-2 is a very massive, young, blue star no more than 4 million years old. It is an Of?p star a type of highly magnetic star that has unusual emission lines of multiply-ionized carbon and nitrogen. In NGC 1624-2, the carbon emission is particularly extreme. The luminosity class is uncertain because of the unusual spectrum; it is most commonly given as V (main sequence), but has also been given as I (supergiant).[7]

Analysis of its spectral energy distribution with CHORIZOS modelling yields an effective temperature of 35,000 K, a luminosity of 125,900 L_☉ (10^5.1 L_☉) and a radius of about 10 R_☉. Assuming a log g of 4.0 yields a mass of 34 M_☉, but evolutionary models tend towards a current mass of 28 M_☉, given the results from the modelling. However, this assumes that NGC 1624-2 is a normal star, while it is not, so it should only be taken as an indication of its true mass. NGC 1624-2 is currently losing mass at a rate of 10^−6.8 M_☉/year, through a stellar wind with a terminal velocity of 2,875 km/s.[5]

Rotation

NGC 1624-2 rotates very slowly, only once every 316 days.[6] This slow rotation is typical for very magnetic O-type stars as their magnetic fields slow down their rotation in a process known as magnetic braking, where angular momentum is quickly shed by the stellar wind via the strong magnetic field, which also minimises mass loss throughout the main sequence.[5][6]

References