WR 2

WR 2
Observation data
Epoch J2000      Equinox J2000
Constellation Cassiopeia
Right ascension 01h 05m 23.01436s[1]
Declination +60° 25′ 18.9652″[1]
Apparent magnitude (V) 11.33[2]
Characteristics
Evolutionary stage Wolf-Rayet
Spectral type WN2-w[3]
B−V color index +0.16[2]
Astrometry
Proper motion (μ) RA: −12.80[1] mas/yr
Dec.: −7.18[1] mas/yr
Parallax (π)4.46 ± 3.31 mas[1]
Distance2,510[4] pc
Absolute magnitude (MV)−2.43[3]
Details
Mass16[3] M☉
Radius0.89[3] R☉
Luminosity282,000[3] L☉
Temperature141,000[3] K
Rotational velocity (v sin i)500[5] km/s
Age4.0[6] Myr
Other designations
HD 6327, WR 2, HIP 5100
Database references
SIMBADdata

WR 2 is a Wolf-Rayet star located around 8,000 light years away from Earth in the constellation of Cassiopeia, in the stellar association Cassiopeia OB1.[7] It is smaller than the Sun, but due to a temperature over 140,000 K it is 282,000 times as luminous as the Sun. With a radius of 89% that of the Sun, it is the smallest known WN star in the Milky Way.[3]

WR 2 is considered to be a member of the nitrogen sequence of WR stars, but completely lacks lines of NIII, NIV, NV, and HeI. Its spectrum is dominated by broad rounded emission lines of HeII, leading to the classification of WN2-b (for broad).[8] It is now given the spectral type of WN2-w (for weak), due to the relative strength of the continuum and lack of extremely intense emission lines. It is the only galactic WN2 star known.[3] Weak-lined Wolf-Rayet stars often have hot luminous companions which dilute the emission. WR 2 does have a companion, but it is much fainter than the primary and not thought to be the cause of the weak-lined spectrum.[5]

WR 2 is the smallest and hottest WN star known in the galaxy. Its unusual rounded emission lines are thought to be due to extremely fast rotation, although the exact rotation rate is not known. Estimates range from 500 km/s to approximately the breakup rate for the star of 1,900 km/s.[9][3][5] The high temperature also leads to a very fast stellar wind of 1,800 km/s,[3] although the overall rate of mass loss is one of the lowest for any Wolf-Rayet star.[10] The combination of a massive Wolf-Rayet star and rapid rotation is likely to result in a gamma-ray burst when the star explodes as a supernova.[9]

X-rays have been detected from WR 2 although they may not be due to colliding winds as is common for massive stars.[10]

  1. ^ a b c d e Cite error: The named reference hipparcos was invoked but never defined (see the help page).
  2. ^ a b Cite error: The named reference tycho2 was invoked but never defined (see the help page).
  3. ^ a b c d e f g h i j Cite error: The named reference hamann was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference hucht was invoked but never defined (see the help page).
  5. ^ a b c Cite error: The named reference shenar was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference tetzlaff was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference lundstrom1984 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference smith was invoked but never defined (see the help page).
  9. ^ a b Cite error: The named reference sander was invoked but never defined (see the help page).
  10. ^ a b Cite error: The named reference skinner was invoked but never defined (see the help page).