WR 46

WR 46 (DI Crucis) is a Wolf-Rayet star in the constellation of the Southern Cross of apparent magnitude +10.8. It is located at 55 arcmin north of Theta2 Crucis. The star is a member of the distant stellar association OB4 Cru, and is around 2,900 parsecs or 9,300 light years from the Solar System.

WR 46
WR 46 (location circled) in the constellation Crux
Observation data
Epoch J2000      Equinox J2000
Constellation Crux
Right ascension  12h 05m 18.72028s[1]
Declination −62° 03′ 10.1280″[1]
Apparent magnitude (V) 10.83[2]
Characteristics
Spectral type WN3p-w[3]
U−B color index -0.84[2]
B−V color index -0.03[2]
Variable type Irregular[4]
Astrometry
Radial velocity (Rv)4.00[5] km/s
Proper motion (μ) RA: -5.625[6] mas/yr
Dec.: 0.304[6] mas/yr
Parallax (π)0.3501 ± 0.0343[6] mas
Distance9,300 ± 900 ly
(2,900 ± 300 pc)
Absolute magnitude (MV)−2.56[3]
Details
Mass14[3] M☉
Radius1.36[3] R☉
Luminosity263,000[3] L☉
Temperature112,200[3] K
Other designations
HD 104994, HIP 58954, DI Crucis, CD-61°3331, GSC 08978-02316, 2MASS J12051871-6203101, AAVSO 1200-61
Database references
SIMBADdata

Features

WR 46 has spectral type WN3, with peculiarities in the spectrum including unusually broad emission lines. Its spectrum is characterized by the presence of strong lines of NV and HeII and the absence of hydrogen lines. It is known as a weak-lined WNE star because of the high temperature but relatively weak emission strength.[4]

The physical parameters of WR 46 are all estimates from assumptions about the distance and models for stars of its type, complicated by the suspicion that there is a companion star. The effective temperature is over 110,000K, the luminosity greater than 200,000 times the solar luminosity (L☉), the mass around 14 times that of the Sun (M☉) and a radius of 1.36 times the solar radius (R☉). The terminal velocity of the stellar wind reaches 2450 km/s with a total mass loss rate of 4 × 10−6 M☉ per year.

WR 46 is a known source of X-rays, an aspect that was discovered by the Einstein Observatory.[7] The X-ray luminosity between 0.2 and 10.0 keV is 7.7 × 1032 erg/s. Its X-ray spectrum is dominated by a soft component but there is also a hard component above 3 keV (a hard tail).

Variability

WR 46 exhibits complex variability on relatively short time scales of a few hours. In the past there have been regular but intermittent changes in the radial velocity, multiple periods and photometric variation at some wavelengths, particularly ultraviolet. It has been proposed that this short-term behavior is due to non-radial pulsations, fast rotational modulation, or the presence of a lower-mass companion.[8] Theories that are now discounted include WR 46 being a Super soft X-ray source[9] or a V Sagittae star,[10]

The radial velocity changes of the spectral lines originating most deeply within the stellar wind show clear radial velocity variations with a period of 7.9 hours. However the lines do not change their shape or intensity, which would be expected from a pulsating star[11] Non-radial pulsations have been proposed, with multiple pulsation periods of varying amplitude accounting for the apparently irregular brightness changes.[4]

Binary star

WR 46 has been suspected to be a binary system with an OB companion. The orbital period of the system has been reported at 0.311 days[9] and 0.329 days.[12] Most recent research refutes the idea of a companion, instead favoring the single WN star theory.[13]

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References
  1. 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.
  2. Reed, B. Cameron (2003). "Catalog of Galactic OB Stars". The Astronomical Journal. 125 (5): 2531–2533. Bibcode:2003AJ....125.2531R. doi:10.1086/374771. ISSN 0004-6256.
  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". arXiv:1904.04687 [astro-ph.SR].
  4. Hénault-Brunet, V.; St-Louis, N.; Marchenko, S. V.; Pollock, A. M. T.; Carpano, S.; Talavera, A. (2011). "New Constraints on the Origin of the Short-Term Cyclical Variability of the Wolf-Rayet Star Wr 46". The Astrophysical Journal. 735: 13. arXiv:1104.4497. Bibcode:2011ApJ...735...13H. doi:10.1088/0004-637X/735/1/13.
  5. Pourbaix, D.; Tokovinin, A. A.; Batten, A. H.; Fekel, F. C.; Hartkopf, W. I.; Levato, H.; Morrell, N. I.; Torres, G.; Udry, S. (2004). "SB9: The ninth catalogue of spectroscopic binary orbits". Astronomy and Astrophysics. 424 (2): 727–732. arXiv:astro-ph/0406573. Bibcode:2004A&A...424..727P. doi:10.1051/0004-6361:20041213. ISSN 0004-6361.
  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. Pollock, A. M. T. (1987). "The Einstein view of the Wolf-Rayet stars". The Astrophysical Journal. 320: 283. Bibcode:1987ApJ...320..283P. doi:10.1086/165539.
  8. Zhekov, S. 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.
  9. Bibcode: 1995IAUS..163..245N
  10. Steiner, J. E.; Diaz, M. P. (1998). "The V Sagittae Stars". Publications of the Astronomical Society of the Pacific. 110 (745): 276. Bibcode:1998PASP..110..276S. doi:10.1086/316139.
  11. Marchenko, Sergey V.; Arias, Julia; Barbá, Rodolfo; Balona, Luis; Moffat, Anthony F. J.; Niemela, Virpi S.; Shara, Michael M.; Sterken, Christiaan (2000). "The Puzzle of HD 104994 (WR 46)". The Astronomical Journal. 120 (4): 2101–2113. Bibcode:2000AJ....120.2101M. doi:10.1086/301580. ISSN 0004-6256.
  12. Marchenko, S. V.; Arias, J.; Barbá, R.; Balona, L.; Moffat, A. F. J.; Niemela, V. S.; Shara, M. M.; Sterken, C. (2000). "The Puzzle of HD 104994 (WR 46)". The Astronomical Journal. 120 (4): 2101. Bibcode:2000AJ....120.2101M. doi:10.1086/301580.
  13. Gosset, E.; De Becker, M.; Nazé, Y.; Carpano, S.; Rauw, G.; Antokhin, I. I.; Vreux, J. -M.; Pollock, A. M. T. (2011). "XMM-Newtonobservation of the enigmatic object WR 46". Astronomy & Astrophysics. 527: A66. Bibcode:2011A&A...527A..66G. doi:10.1051/0004-6361/200912510.
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