WR 124

WR 124 is a Wolf–Rayet star in the constellation of Sagitta surrounded by a ring nebula of expelled material known as M1-67.[8] It is one of the fastest runaway stars in the Milky Way with a radial velocity around 200 km/s. It was discovered by Paul W. Merrill in 1938, identified as a high-velocity Wolf–Rayet star.[9] It is listed in the General Catalogue of Variable Stars as QR Sagittae with a range of 0.08 magnitudes.[4]

WR 124

Hubble Space Telescope image of nebula M1-67 around Wolf–Rayet star WR 124
Observation data
Epoch J2000      Equinox J2000
Constellation Sagitta
Right ascension  19h 11m 30.876s[1]
Declination +16° 51′ 38.168″[1]
Apparent magnitude (V) 11.50 ± 0.11[2]
Characteristics
Spectral type WN8h[3]
B−V color index 0.69[2]
Variable type Eruptive (WR)[4]
Astrometry
Radial velocity (Rv)190 ± 7.4[5] km/s
Proper motion (μ) RA: −2.645±0.050[6] mas/yr
Dec.: −5.534±0.049[6] mas/yr
Parallax (π)0.1153 ± 0.0365[6] mas
Distanceapprox. 28,000 ly
(approx. 9,000 pc)
Absolute magnitude (MV)-7.22[3]
Details
Mass33[3] M☉
Radius26.5[3] R☉
Luminosity1,000,000[3] L☉
Temperature39,800[3] K
Age8.6[7] Myr
Other designations
Merrill's Star, QR Sagittae, HIP 94289, GSC 01586-00411, Sh 2-80, Hen 2-427
Database references
SIMBADdata

Distance

A 2010 study of WR 124 directly measured the expansion rate of the M1-67 nebula expelled from the star using Hubble Space Telescope camera images taken 11 years apart, and compared that to the expansion velocity measured by the Doppler shift of the nebular emission lines.[7] This yielded a distance of 3.35 kpc, which is less than previous studies, and the resulting luminosity of 150,000 times the Sun (L☉) is much lower than previously calculated. The luminosity is also lower than predicted by models for a star of this spectral class. Previous studies had found distances of 5 kpc[8] to 8.4 kpc,[3] with corresponding luminosities of 338,000–1,000,000 L☉, as expected for a typical WN8h which is a very young star just moving away from the main sequence. The Gaia satellite measured the distance to WR 124 from its parallax, giving a distance of 6,203+1,621
−1,123 pc.[6][10]

Physical characteristics

With an assumed visual absolute magnitude of -7.22 and 3.1 magnitudes of extinction, WR 124 would be 8.5 kpc away. The temperature of around 40,000K means that most of its energy is emitted at ultraviolet wavelengths, the bolometric luminosity is 1,000,000 L☉ and the radius is 26 R☉. The mass is calculated from evolutionary models to be 33 M☉.[3]

WR 124 is measured to still be about 15% hydrogen with most of the remaining mass being helium. A young highly massive and luminous WN8h star would still be burning hydrogen in its core, but a less luminous and older star would be burning helium in its core.[11] The result of modelling the star purely from its observed characteristics is a luminosity of 1,000,000 L☉ and a mass of 33 M☉, corresponding to a relatively young hydrogen-burning star at around 8 kpc.[3] In either case, it has only a few hundred thousand years before it explodes as a type Ib or Ic supernova.

The mass loss rate is 10−5 M☉–10−4 M☉ per year, depending on the distance and properties determined for the star.[8]

Nebula

WR 124 is surrounded by an intensely hot nebula formed from the star's extreme stellar wind.[8] The nebula M1-67 is expanding at a rate of over 150,000 km/h (93,000 mph) and is nearly 6 light-years across, leading to the dynamical age of 20,000 years. M1-67 has little internal structure, though large clumps of material have been detected, some of which have 30 times the mass of Earth and stretch out up to 150 billion km (93 billion mi). If placed in the Solar System, one of these clumps would span the distance from the Sun to Saturn.

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References
  1. Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27. Bibcode:2000A&A...355L..27H. doi:10.1888/0333750888/2862.
  3. Hamann, W.-R.; Gräfener, G.; Liermann, A. (2006). "The Galactic WN stars". Astronomy and Astrophysics. 457 (3): 1015. arXiv:astro-ph/0608078. Bibcode:2006A&A...457.1015H. doi:10.1051/0004-6361:20065052.
  4. Kukarkin, B. V.; Kholopov, P. N.; Pskovsky, Y. P.; Efremov, Y. N.; Kukarkina, N. P.; Kurochkin, N. E.; Medvedeva, G. I. (1971). "The third edition containing information on 20437 variable stars discovered and designated till 1968". General Catalogue of Variable Stars: 0. Bibcode:1971GCVS3.C......0K.
  5. Kharchenko, N. V.; Scholz, R.-D.; Piskunov, A. E.; Röser, S.; Schilbach, E. (2007). "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ˜55000 stars and mean radial velocities of 516 Galactic open clusters and associations". Astronomische Nachrichten. 328 (9): 889. arXiv:0705.0878. Bibcode:2007AN....328..889K. doi:10.1002/asna.200710776.
  6. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  7. Marchenko, S. V.; Moffat, A. F. J.; Crowther, P. A. (2010). "Population I Wolf–Rayet Runaway Stars: The Case of Wr124 and Its Expanding Nebula M1-67". The Astrophysical Journal. 724 (1): L90–L94. arXiv:1011.0785. Bibcode:2010ApJ...724L..90M. doi:10.1088/2041-8205/724/1/L90.
  8. Crowther, Paul A.; Pasquali, A.; De Marco, Orsola; Schmutz, W.; Hillier, D. J.; De Koter, A. (1999). "Wolf–Rayet nebulae as tracers of stellar ionizing fluxes. I. M1-67". Astronomy and Astrophysics. 350: 1007. arXiv:astro-ph/9908200. Bibcode:1999A&A...350.1007C.
  9. Merrill, P. W. (1938). "A Wolf–Rayet Star with High Velocity". Publications of the Astronomical Society of the Pacific. 50 (298): 350. Bibcode:1938PASP...50..350M. doi:10.1086/124982.
  10. Bailer-Jones, C. A. L.; Rybizki, J.; Fouesneau, M.; Mantelet, G.; Andrae, R. (2018). "Estimating Distance from Parallaxes. IV. Distances to 1.33 Billion Stars in Gaia Data Release 2". The Astronomical Journal. 156 (2): 58. arXiv:1804.10121. Bibcode:2018AJ....156...58B. doi:10.3847/1538-3881/aacb21.
  11. Meynet, G.; Maeder, A. (2003). "Stellar evolution with rotation". Astronomy and Astrophysics. 404 (3): 975–990. arXiv:astro-ph/0304069. Bibcode:2003A&A...404..975M. doi:10.1051/0004-6361:20030512.
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