WR 1

This article is about the star. For the nuclear reactor, see WR-1.

WR 1 is a Wolf-Rayet star located around 10,300 light years away from Earth in the constellation of Cassiopeia. It is only slightly more than twice the size of the sun, but due to a temperature over 100,000 K it is over 758,000 times as luminous as the sun.

WR 1

A visual band light curve for V863 Cassiopeiae, adapted from Chené et al. (2008).[1] The data were taken from November 2003 to February 2004, and different cycles are shown with different colors.
Observation data Epoch J2000      Equinox J2000
Constellation	Cassiopeia[2]
Right ascension	00h 43m 28.39717s[3]
Declination	+64° 45′ 35.3847″[3]
Apparent magnitude (V)	10.54[4]
Characteristics
Evolutionary stage	Wolf-Rayet
Spectral type	WN4-s[5]
U−B color index	−0.24[6]
B−V color index	+0.37[6]
Variable type	WR[4]
Astrometry
Proper motion (μ)	RA: −2.878[3] mas/yr Dec.: −0.702[3] mas/yr
Parallax (π)	0.3092±0.0139 mas[3]
Distance	10,500 ± 500 ly (3,200 ± 100 pc)
Absolute magnitude (MV)	−4.9[7]
Details
Mass	27[5] M☉
Radius	2.26[5] R☉
Luminosity	760,000[5] L☉
Temperature	112,200[5] K
Rotational velocity (v sin i)	6.5[8] km/s
Other designations
V863 Cas, BD+63°83, HD 4004, HIP 3415
Database references
SIMBAD	data

Although WR 1 has been recognised as a Wolf-Rayet star since the 19th century,^[9] the WR 1 designation does not indicate that it was the first to be discovered. Ordered by right ascension, WR 1 is the first star in the Seventh Catalogue of galactic Wolf-Rayet stars.^[10]

WR 1 is a member of the nitrogen sequence of WR stars and has a spectrum with He_II lines much stronger than He_I lines, and N_V emission more than twice the strength of N_III, leading to the assignment of a WN4 spectral type. The spectrum has particularly wide He_II, leading to the equivalent classifications of WN4-b (for broad) or WN4-s (for strong). The spectrum also includes C_IV and N_IV, but no hydrogen lines at all,^[11][12] indicating that WR 1 has already expelled all of its hydrogen through its powerful solar winds.

In 1986, Anthony F. J. Moffat and Michael M. Shara announced their discovery that WR 1 is a variable star.^[13] It was given its variable star designation, V863 Cassiopeiae, in 2001.^[14] The total amplitude of the variations is only 0.09 magnitudes at visual wavelengths. The variations are well-defined with a period of 16.9 days, but the light curve is not sinusoidal and its shape may vary.^[15] The variations have been ascribed to a dense asymmetric stellar wind and co-rotating interacting regions in ejected material.^[8]

It has been suggested that the variability and an infrared excess could be due to a cool companion, but WR 1 is now considered to be a single star.^[12] The WN-b subclass of Wolf-Rayet star are generally thought to be all single, in contrast with the WN-A subclass which have narrow emission on a stronger continuum and are thought to be binary systems with a more conventional hot luminous star.^[11]

WR 1 is a possible member of the Cassiopeia OB7 association^[10] at a distance of around 1,800 pc,^[5] although its Gaia parallax suggests it is more distant.^[3] Interstellar extinction is calculated to be 2.1 magnitudes, and at 1,820 pc the bolometric luminosity would be 758,600 L_☉. A temperature of 112,200 K is derived from fitting the spectrum, giving a radius of 2.26 R_☉.^[5]