WR 7

HD 56925

WR7 at the centre of NGC 2359
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Canis Major
Right ascension	07^h 18^m 29.1311^s[1]
Declination	−13° 13′ 01.514″[1]
Apparent magnitude (V)	11.56[2]
Characteristics
Spectral type	WN4-s[3]
U−B color index	−0.47[4]
B−V color index	+0.28[4]
Astrometry
Proper motion (μ)	RA: −3.601[1] mas/yr Dec.: −2.998[1] mas/yr
Parallax (π)	0.2096 ± 0.0268 mas[1]
Distance	approx. 16,000 ly (approx. 4,800 pc)
Absolute magnitude (MV)	−3.8[5]
Details
Mass	13[3] M☉
Radius	1.26[3] R☉
Luminosity	229,000[3] L☉
Temperature	112,200[3] K
Other designations
WR 7, HIP 35378, HD 56925, 2MASS J07182912-1313015.
Database references
SIMBAD	data

WR 7 (HD 56925) is a Wolf–Rayet star in the constellation of Canis Major. It lies at the centre of a complex bubble of gas which is shocked and partially ionised by the star's radiation and winds.

The distance is uncertain, with estimates between 3.5 kiloparsecs (11,410 light-years) and 6.9 kiloparsecs (22,500 light-years). Assuming a distance of 4.8 kiloparsecs (15,600 light-years), this star is calculated to be 229,000 times brighter than the Sun, 13 times more massive, and 1.26 times larger with a surface temperature of 112,200 K. This makes it currently the second smallest known WN star in the galaxy, after WR 2.

Stars of its kind are characterised by a rapid loss of stellar mass, driven by chemically enriched high-speed stellar winds. It is estimated that it loses mass at the rate of 7x10⁻⁵ solar masses each year through winds of 1,545 km/s.^[6]

The ring nebula NGC 2359 is excited by the ionising radiation of WR7. It is also known as Thor's Helmet or the Duck Nebula. The ring is approximately 4pc across and prominent at wavelengths from radio to X-ray.^[6][7]

References

1. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
2. Zacharias, N.; Finch, C. T.; Girard, T. M.; Henden, A.; Bartlett, J. L.; Monet, D. G.; Zacharias, M. I. (2012). "VizieR Online Data Catalog: UCAC4 Catalogue (Zacharias+, 2012)". VizieR On-line Data Catalog: I/322A. Originally Published in: 2012yCat.1322....0Z; 2013AJ....145...44Z. 1322. Bibcode:2012yCat.1322....0Z.
3. Sota, A.; Maíz Apellániz, J.; Morrell, N. I.; Barbá, R. H.; Walborn, N. R.; Gamen, R. C.; Arias, J. I.; Alfaro, E. J.; Oskinova, L. M. (2019). "The Galactic WN stars revisited. Impact of Gaia distances on fundamental stellar parameters". Astronomy & Astrophysics. A57: 625. arXiv:1904.04687. Bibcode:2019A&A...625A..57H. doi:10.1051/0004-6361/201834850. S2CID 104292503.
4. Reed, B. Cameron (1998). "UBVβ Database for Case-Hamburg Northern and Southern Luminous Stars". The Astrophysical Journal Supplement Series. 115 (2): 271–275. Bibcode:1998ApJS..115..271R. doi:10.1086/313088. S2CID 120773004.
5. Crowther, Paul A.; Rate, Gemma (2020). "Unlocking Galactic Wolf–Rayet stars with Gaia DR2 – I. Distances and absolute magnitudes". Monthly Notices of the Royal Astronomical Society. 493 (1): 1512–1529. arXiv:1912.10125. Bibcode:2020MNRAS.493.1512R. doi:10.1093/mnras/stz3614. S2CID 209444955.
6. Cappa, C. E.; Goss, W. M.; Niemela, V. S.; Ostrov, P. G. (1999). "A Study of Neutral and Ionized Gas of the Wolf-Rayet Ring Nebula NGC 2359". The Astronomical Journal. 118 (2): 948. Bibcode:1999AJ....118..948C. doi:10.1086/300995. S2CID 123709946.
7. Zhekov, S. A. (2014). "X-rays from wind-blown bubbles: An XMM-Newton detection of NGC 2359". Monthly Notices of the Royal Astronomical Society. 443 (1): 12–18. arXiv:1406.2463. Bibcode:2014MNRAS.443...12Z. doi:10.1093/mnras/stu1138. S2CID 118510853.

External links

• NASA Astronomy Picture of the Day: NGC 2359: Thor's Helmet (15 February 2014)
• NASA Astronomy Picture of the Day: Thor's Helmet (5 June 2010)
• NASA Astronomy Picture of the Day: The Seagull and the Duck (19 March 2010)
• NGC 2359 Thor's Helmet^[usurped] Images of the Universe
• Galactic Wolf–Rayet Catalogue
• NGC 2359 Thor's Helmet - Duck Nebula (HaR)GB Astrobin