WR 148
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 20h 41m 21.54644s[1] |
| Declination | +52° 35′ 15.1565″[1] |
| Apparent magnitude (V) | 10.3[2] |
| Characteristics | |
| Spectral type | WN8h + B3IV/BH[3] |
| Apparent magnitude (J) | 8.759[4] |
| Apparent magnitude (K) | 8.318[5] |
| U−B color index | −0.45[6] |
| B−V color index | +0.57[6] |
| Variable type | Unique[2] |
| Astrometry | |
| Radial velocity (Rv) | −134[7] km/s |
| Proper motion (μ) | RA: −7.63[1] mas/yr Dec.: −1.78[1] mas/yr |
| Parallax (π) | −0.25 ± 1.16[1] mas |
| Distance | 8,280[8] pc |
| Absolute magnitude (MV) | −7.22[3] |
| Orbit[9] | |
| Period (P) | 4.32[8] days |
| Semi-major axis (a) | 7.5 ± 0.2 R☉ |
| Eccentricity (e) | 0.079±0.030 |
| Semi-amplitude (K1) (primary) | 87.7 ± 2.4 km/s |
| Semi-amplitude (K2) (secondary) | 36.2 ± 9.4 km/s |
| Details[3] | |
| WR | |
| Mass | 44 M☉ |
| Radius | 26.5 R☉ |
| Luminosity | 1,600,000 L☉ |
| Temperature | 39,800 K |
| Other designations | |
| Database references | |
| SIMBAD | data |
WR 148 is a spectroscopic binary in the constellation Cygnus consisting of a Wolf-Rayet star and an unknown massive companion. The secondary may be a black hole, or an early B subgiant that is not visible for some reason. It is one of the most luminous stars known.
WR 148 shows a classic WN8h spectrum, but with the addition of weak central absorption on some of the emission lines.[9] NIII and NIV emission lines are stronger than NV, and HeI lines are stronger than HeII, The Balmer series hydrogen lines and some other lines have P Cygni profiles.[10]
WR 148 is erratically variable on timescales ranging from seconds to years, but it shows consistent brightness and radial velocity variations with a period of 4.32 days. There is little doubt that it is a binary system, due to the regular variations and the presence of hard x-ray radiation from colliding winds, but the secondary has never been observed. The absorption cores might be due to a faint B class companion, but the radial velocity changes of the absorption components are smaller than those of the emission lines, making this unlikely. Alternatives include a very massive companion that would almost certainly have to be a black hole to remain invisible, or an unacceptably small mass for the primary star. The absorption nay also arise in circumstellar material.[9]
Because of its erratic changes in apparent magnitude at so many frequencies WR 148 is classified in the General Catalogue of Variable Stars as a unique type of variable, not a member of any of the defined classes.[2] The shape of the light curve is unusual and has been modelled as being produced by an extended secondary object which may be an ionised cavity in the dense wind of the primary star, produced as the secondary orbits at a distance comparable to the radius of the primary star.[9]
WR 148 is found unusually far from the galactic plane for a Wolf-Rayet star, at 500 - 800 pc. Young massive stars such as WN8h WR stars are members of the thin disc population, on average only 60 pc from the galactic plane. It is suggested that WR 148 is a runaway from a supernova explosion.[9]
References
- 1 2 3 4 5 Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
- 1 2 3 Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
- 1 2 3 Hamann, W.-R.; Gräfener, G.; Liermann, A. (2006). "The Galactic WN stars. Spectral analyses with line-blanketed model atmospheres versus stellar evolution models with and without rotation". Astronomy and Astrophysics. 457 (3): 1015. arXiv:astro-ph/0608078. Bibcode:2006A&A...457.1015H. doi:10.1051/0004-6361:20065052.
- ↑ Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; Beichman, C. A.; Carpenter, J. M.; Chester, T.; Cambresy, L.; Evans, T.; Fowler, J.; Gizis, J.; Howard, E.; Huchra, J.; Jarrett, T.; Kopan, E. L.; Kirkpatrick, J. D.; Light, R. M.; Marsh, K. A.; McCallon, H.; Schneider, S.; Stiening, R.; Sykes, M.; Weinberg, M.; Wheaton, W. A.; Wheelock, S.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". VizieR On-line Data Catalog: II/246. Originally published in: 2003yCat.2246....0C. 2246. Bibcode:2003yCat.2246....0C.
- ↑ Van Der Hucht, K. A. (2006). "New Galactic Wolf-Rayet stars, and candidates. An annex to the VIIth Catalogue of Galactic Wolf-Rayet Stars". Astronomy and Astrophysics. 458 (2): 453. arXiv:astro-ph/0609008. Bibcode:2006A&A...458..453V. doi:10.1051/0004-6361:20065819.
- 1 2 Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
- ↑ 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.
- 1 2 Zhekov, Svetozar A. (2012). "X-rays from colliding stellar winds: The case of close Wolf-Rayet+O binary systems". Monthly Notices of the Royal Astronomical Society. 422 (2): 1332. arXiv:1202.1386. Bibcode:2012MNRAS.422.1332Z. doi:10.1111/j.1365-2966.2012.20706.x.
- 1 2 3 4 5 Marchenko, Sergey V.; Moffat, Anthony F. J.; Lamontagne, Robert; Tovmassian, Gaghik H. (1996). "The Wolf-Rayet Star HD 197406, with Its Strongly Ionizing Close Companion". Astrophysical Journal. 461: 386. Bibcode:1996ApJ...461..386M. doi:10.1086/177067.
- ↑ Smith, Lindsey F.; Shara, Michael M.; Moffat, Anthony F. J. (1996). "A three-dimensional classification for WN stars". Monthly Notices of the Royal Astronomical Society. 281: 163. Bibcode:1996MNRAS.281..163S. doi:10.1093/mnras/281.1.163.