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==Discovery==
==Discovery==
WR 30a was discovered in a photographic survey in the constellation Carina using the [[Cerro_Tololo_Inter-American_Observatory#Tenant_telescopes|Curtis-Schmidt Telescope]] at the [[Cerro Tololo Inter-American Observatory]]. It was listed as MS4 out of nine new discoveries.<ref name=macconnell/>
WR 30a was discovered in a photographic survey in the constellation Carina using the [[Cerro_Tololo_Inter-American_Observatory#Tenant_telescopes|Curtis-Schmidt Telescope]] at the [[Cerro Tololo Inter-American Observatory]]. It was listed as MS4 out of nine new discoveries, classified only as "WR::".<ref name=macconnell/>

WR 30a was entered into the sixth catalogue of galactic WR stars at the last minute with the designation WR 29a and a spectral class of "WR + ABS".<ref name=wr6/><ref name=gosset/> A review of Wolf-Rayet stars in 1984 reported that WR30a had a [[right ascension]] greater than [[WR 30]] and should correctly be numbered 30a rather than 29a.<ref name=ls1/> The name was corrected in the seventh edition of the catalogue.<ref name=wr/>

Still in 1984, WR 30a was studied spectroscopically and assigned a WC4 class.<ref name=ls2/> Another 1984 study noted dilution of some emission lines, and suggested the presence of a binary companion of approximate spectral type O4.<ref name=moffat/> The WO spectral classification had already been defined, but neither paper considered WR 30a to show sufficiently high excitation lines or strong oxygen lines to merit that classification. A WO spectral class was eventually assigned, with relatively weak O{{smallcaps|vi}} emission but confirmed by the lack of C{{smallcaps|iii}} emission. A WO5 class was temporarily assigned to account for the unusually low excitation,<ref name=kingsburgh/> but it was confirmed at WO4 when quantitative criteria for the WO sub-classes were defined.<ref name=crowther/>

The identification of the companion remained only as an approximate O4 until 2001, when detailed spectroscopy assigned an O5((f)) class. This is based on the existence of narrow N{{smallcaps|iii}} lines, and the identification of He{{smallcaps|ii}} emission. The luminosity class could not be determined with certainty, but a supergiant can be ruled out and the line widths suggest a giant class is most likely.<ref name=gosset/>


==System==
==System==
Line 72: Line 78:
name=gosset/>
name=gosset/>


The stars do not eclipse eachother, but they are deformed by the gravity and show small brightness variations during the orbit. These brightness variations are regular and consistent over long periods, so the orbital period is known accurately. The inclination can be estimated from the mass function and the [[Colliding-wind binary|colliding wind]]s. The eccentricity is small and the most accurate model of spectral line profile variations during the orbit gives an eccentricity of 0.2. The semi-major axis of the orbit is {{solar radius|35.4}}, with the WO star moving in an ellipse of smi-major axis {{solar radius|30}} and the more massive O companion in an ellipse of semi-major axis {{solar radius|5.4}}. The separation of the stars varies from {{solar radius|28}} to {{solar radius|42}}.<ref name=f-g/>
The stars do not eclipse eachother, but they are deformed by the gravity and show small brightness variations during the orbit. These brightness variations are regular and consistent over long periods, so the orbital period is known accurately. The inclination can be estimated from the mass function and the [[Colliding-wind binary|colliding wind]]s. The eccentricity is small and the most accurate model of spectral line profile variations during the orbit gives an eccentricity of 0.2. The [[semi-major axis]] of the orbit is {{solar radius|35.4}}, with the WO star moving in an ellipse of semi-major axis {{solar radius|30}} and the more massive O companion in an ellipse of semi-major axis {{solar radius|5.4}}. The separation of the stars varies from {{solar radius|28}} to {{solar radius|42}}.<ref name=f-g/>


Although the hot secondary star produces what would typically be considered a fast stellar wind, it is entirely overpowered by the wind from the primary star. The shock front where the winds collide is approximately a cone around the O star with a half angle of 50°. The apex of the shock cone is estimated to lie at {{solar radius|25}} from the WO stars and {{solar radius|10}} from the O star. {{solar radius|10}} is comparable to the radius of a typical non-supergiant O5 star so that its own wind is forced back against the surface of the star.<ref name=f-g/>
Although the hot secondary star produces what would typically be considered a fast stellar wind, it is entirely overpowered by the wind from the primary star. The [[shock front]] where the winds collide is approximately a cone around the O star with a half angle of 50°. The apex of the shock cone is estimated to lie at {{solar radius|25}} from the WO stars and {{solar radius|10}} from the O star. {{solar radius|10}} is comparable to the radius of a typical non-supergiant O5 star so that its own wind is forced back against the surface of the star.<ref name=f-g/>


==Variability==
==Variability==
Line 117: Line 123:


<ref name=macconnell>{{cite journal|bibcode=1970PASP...82...80M|title=Faint New Wolf-Rayet Stars in Carina|journal=Publications of the Astronomical Society of the Pacific|volume=82|pages=80|author1=MacConnell|first1=Darrell J.|last2=Sanduleak|first2=N.|year=1970|doi=10.1086/128887}}</ref>
<ref name=macconnell>{{cite journal|bibcode=1970PASP...82...80M|title=Faint New Wolf-Rayet Stars in Carina|journal=Publications of the Astronomical Society of the Pacific|volume=82|pages=80|author1=MacConnell|first1=Darrell J.|last2=Sanduleak|first2=N.|year=1970|doi=10.1086/128887}}</ref>

<ref name=wr6>{{cite journal|bibcode=1981SSRv...28..227V|title=The Sixth Catalogue of galactic Wolf-Rayet stars, their past and present|journal=Space Science Reviews|volume=28|issue=3|pages=227|author1=Van Der Hucht|first1=K. A.|last2=Conti|first2=P. S.|last3=Lundstrom|first3=I.|last4=Stenholm|first4=B.|year=1981|doi=10.1007/BF00173260}}</ref>

<ref name=ls1>{{cite journal|bibcode=1984A&AS...58..163L|title=Wolf-Rayet stars in open clusters and associations|journal=Astronomy and Astrophysics Supplement Series (ISSN 0365-0138)|volume=58|pages=163|author1=Lundstrom|first1=I.|last2=Stenholm|first2=B.|year=1984}}</ref>

<ref name=ls2>{{cite journal|bibcode=1984A&A...138..311L|title=Spectroscopy of five Wolf-Rayet star candidates including a Wolf-Rayet star in the galactic bulge|journal=Astronomy and Astrophysics (ISSN 0004-6361)|volume=138|pages=311|author1=Lundstrom|first1=I.|last2=Stenholm|first2=B.|year=1984}}</ref>

<ref name=kingsburgh>{{cite journal|bibcode=1995A&A...295...75K|title=Properties of the WO Wolf-Rayet stars|journal=Astronomy and Astrophysics (ISSN 0004-6361)|volume=295|pages=75|author1=Kingsburgh|first1=R. L.|last2=Barlow|first2=M. J.|last3=Storey|first3=P. J.|year=1995}}</ref>

<ref name=crowther>{{cite journal|bibcode=1998MNRAS.296..367C|title=Quantitative classification of WC and WO stars|journal=Monthly Notices of the Royal Astronomical Society|volume=296|issue=2|pages=367|author1=Crowther|first1=P. A.|last2=De Marco|first2=Orsola|last3=Barlow|first3=M. J.|year=1998|doi=10.1046/j.1365-8711.1998.01360.x}}</ref>


}}
}}

Revision as of 20:14, 16 June 2016

WR 30a
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Carina
Right ascension 10h 51m 38.93s[1]
Declination −60° 56′ 35.2″[1]
Apparent magnitude (V) 12.73[2]
Characteristics
Evolutionary stage Wolf-Rayet star
Spectral type WO4 + O5((f))[3]
U−B color index −0.22[4]
B−V color index +1.04[4]
Variable type WR[2]
Astrometry
Distance7,770[5] pc
Absolute magnitude (MV)−6.0[6] (−3.0 + −5.9)
Orbit
PrimaryWR
CompanionO
Period (P)4.619 days[5]
Semi-major axis (a)35.4 R☉[7]
Eccentricity (e)0.2[7]
Inclination (i)20 ± 5[7]°
Semi-amplitude (K1)
(primary)		189[4] km/s
Semi-amplitude (K2)
(secondary)		25[7] km/s
Details
WR
Mass7.5-9.7[7] M☉
Luminosity195,000[8] L☉
Temperature129,500[8] K
O
Mass40-60[7] M☉
Other designations
WR 29a, V574 Carinae, GSC 08958-04143, MS4
Database references
SIMBADdata

WR 30a is a massive spectroscopic binary in the constellation Carina. The primary is an extremely rare star on the WO oxygen sequence.

Discovery

WR 30a was discovered in a photographic survey in the constellation Carina using the Curtis-Schmidt Telescope at the Cerro Tololo Inter-American Observatory. It was listed as MS4 out of nine new discoveries, classified only as "WR::".[9]

WR 30a was entered into the sixth catalogue of galactic WR stars at the last minute with the designation WR 29a and a spectral class of "WR + ABS".[10][4] A review of Wolf-Rayet stars in 1984 reported that WR30a had a right ascension greater than WR 30 and should correctly be numbered 30a rather than 29a.[11] The name was corrected in the seventh edition of the catalogue.[1]

Still in 1984, WR 30a was studied spectroscopically and assigned a WC4 class.[12] Another 1984 study noted dilution of some emission lines, and suggested the presence of a binary companion of approximate spectral type O4.[6] The WO spectral classification had already been defined, but neither paper considered WR 30a to show sufficiently high excitation lines or strong oxygen lines to merit that classification. A WO spectral class was eventually assigned, with relatively weak Ovi emission but confirmed by the lack of Ciii emission. A WO5 class was temporarily assigned to account for the unusually low excitation,[13] but it was confirmed at WO4 when quantitative criteria for the WO sub-classes were defined.[14]

The identification of the companion remained only as an approximate O4 until 2001, when detailed spectroscopy assigned an O5((f)) class. This is based on the existence of narrow Niii lines, and the identification of Heii emission. The luminosity class could not be determined with certainty, but a supergiant can be ruled out and the line widths suggest a giant class is most likely.[4]

System

WR 30a is a close spectrocopic binary containing a WO4 star and a non-supergiant O5 star. They orbit eachother every 4.916 days.[5] Although spectral lines from both stars can be detected and orbital radial velocity variations measured, the orbit is still poorly known. The primary has highly broadened emission lines which are difficult to measure accurately, and the secondary has a relatively low orbital speed due to its high mass. Measurements of different spectral lines and different portions of line profiles lead to different results. Some components of the spectrum are produced by stellar winds not moving at orbital velocity with the stars.[4]

The stars do not eclipse eachother, but they are deformed by the gravity and show small brightness variations during the orbit. These brightness variations are regular and consistent over long periods, so the orbital period is known accurately. The inclination can be estimated from the mass function and the colliding winds. The eccentricity is small and the most accurate model of spectral line profile variations during the orbit gives an eccentricity of 0.2. The semi-major axis of the orbit is 35.4 R☉, with the WO star moving in an ellipse of semi-major axis 30 R☉ and the more massive O companion in an ellipse of semi-major axis 5.4 R☉. The separation of the stars varies from 28 R☉ to 42 R☉.[7]

Although the hot secondary star produces what would typically be considered a fast stellar wind, it is entirely overpowered by the wind from the primary star. The shock front where the winds collide is approximately a cone around the O star with a half angle of 50°. The apex of the shock cone is estimated to lie at 25 R☉ from the WO stars and 10 R☉ from the O star. 10 R☉ is comparable to the radius of a typical non-supergiant O5 star so that its own wind is forced back against the surface of the star.[7]

Variability

WR 30a shows regular and continuous brightness variations of 0.02 magnitudes with a stable period of 4.6 days. These are ascribed to the orbital motion and to the deformed shapes of the two stars. In addition, the system shows occasional very rapid brightness of up to 0.2 magnitudes. These brightness changes have only been seen at visual wavelengths and last for only a few hours. At blue wavelengths the variations are either not seen, or sometimes a small opposite brightness change. They are not predictable but there is a possible period around three days. The cause of these brightness changes is completely unknown.[15]

Features

The primary star, of spectral classification WO4, is one of the very few known oxygen-sequence Wolf-Rayet stars, just four in the Milky Way galaxy and five in external galaxies. Modelling the atmosphere gives a luminosity around 195,000 L☉. It is a very small dense star, with a radius less than the sun's but with a mass nearly 10 solar masses. Very strong stellar winds, with a terminal velocity of 4,500 kilometers per second are causing WR 93b to lose over 10−5 M☉/year.[4] For comparison, the Sun loses (2-3) x 10−14 solar masses per year due to its solar wind, several hundred million times less than WR 30a.

The secondary star has an O5 spectral class. It is not a supergiant, but could be a main sequence or giant star. Some emission is detected in the spectrum, indicating a strong stellar wind.

WR 30a is a very strong x-ray source. This is expected for a colliding-wind binary, but the source of the x-rays has not been conclusively determined. They may have a thermal or non-thermal origin.[5]

Evolutionary status

WO Wolf-Rayet stars are the last evolutionary stage of the most massive stars before exploding as supernovae, possibly with a gamma-ray burst.[16] It is very likely that WR 30a is on its last stages of nuclear fusion, near or beyond the end of helium burning.[17]

See also

References

  1. ^ a b c van der Hucht, Karel A. (2001). "The VIIth catalogue of galactic Wolf–Rayet stars". New Astronomy Reviews. 45 (3): 135–232. Bibcode:2001NewAR..45..135V. doi:10.1016/S1387-6473(00)00112-3. ISSN 1387-6473.
  2. ^ a b 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.
  3. ^ Tramper, F.; Straal, S. M.; Sanyal, D.; Sana, H.; de Koter, A.; Gräfener, G.; Langer, N.; Vink, J. S.; de Mink, S. E.; Kaper, L. (2015). "Massive stars on the verge of exploding: The properties of oxygen sequence Wolf-Rayet stars". Astronomy & Astrophysics. 581 (110): A110. arXiv:1507.00839v1. Bibcode:2015A&A...581A.110T. doi:10.1051/0004-6361/201425390.
  4. ^ a b c d e f g Gosset, E.; Royer, P.; Rauw, G.; Manfroid, J.; Vreux, J.-M. (2001). "A first detailed study of the colliding wind WR+O binary WR 30a". Monthly Notices of the Royal Astronomical Society. 327 (2): 435. Bibcode:2001MNRAS.327..435G. doi:10.1046/j.1365-8711.2001.04755.x.
  5. ^ a b c d Zhekov, Svetozar A.; Skinner, Stephen L. (2015). "X-rays from the oxygen-type Wolf-Rayet binary WR 30a". Monthly Notices of the Royal Astronomical Society. 452: 872. arXiv:1506.04634. Bibcode:2015MNRAS.452..872Z. doi:10.1093/mnras/stv1343.
  6. ^ a b Moffat, A. F. J.; Seggewiss, W. (1984). "The Wolf-Rayet spectrum of MS 4 = WR 29a". Astronomy and Astrophysics Supplement Series (ISSN 0365-0138). 58: 117. Bibcode:1984A&AS...58..117M.
  7. ^ a b c d e f g h Falceta-Gonçalves, D.; Abraham, Z.; Jatenco-Pereira, V. (2008). "Modelling the line variations from the wind-wind shock emissions of WR30a". Monthly Notices of the Royal Astronomical Society. 383: 258. arXiv:0710.0662. Bibcode:2008MNRAS.383..258F. doi:10.1111/j.1365-2966.2007.12526.x.
  8. ^ a b Nugis, T.; Lamers, H. J. G. L. M. (2000). "Mass-loss rates of Wolf-Rayet stars as a function of stellar parameters". Astronomy and Astrophysics. 360: 227. Bibcode:2000A&A...360..227N.
  9. ^ MacConnell, Darrell J.; Sanduleak, N. (1970). "Faint New Wolf-Rayet Stars in Carina". Publications of the Astronomical Society of the Pacific. 82: 80. Bibcode:1970PASP...82...80M. doi:10.1086/128887.
  10. ^ Van Der Hucht, K. A.; Conti, P. S.; Lundstrom, I.; Stenholm, B. (1981). "The Sixth Catalogue of galactic Wolf-Rayet stars, their past and present". Space Science Reviews. 28 (3): 227. Bibcode:1981SSRv...28..227V. doi:10.1007/BF00173260.
  11. ^ Lundstrom, I.; Stenholm, B. (1984). "Wolf-Rayet stars in open clusters and associations". Astronomy and Astrophysics Supplement Series (ISSN 0365-0138). 58: 163. Bibcode:1984A&AS...58..163L.
  12. ^ Lundstrom, I.; Stenholm, B. (1984). "Spectroscopy of five Wolf-Rayet star candidates including a Wolf-Rayet star in the galactic bulge". Astronomy and Astrophysics (ISSN 0004-6361). 138: 311. Bibcode:1984A&A...138..311L.
  13. ^ Kingsburgh, R. L.; Barlow, M. J.; Storey, P. J. (1995). "Properties of the WO Wolf-Rayet stars". Astronomy and Astrophysics (ISSN 0004-6361). 295: 75. Bibcode:1995A&A...295...75K.
  14. ^ Crowther, P. A.; De Marco, Orsola; Barlow, M. J. (1998). "Quantitative classification of WC and WO stars". Monthly Notices of the Royal Astronomical Society. 296 (2): 367. Bibcode:1998MNRAS.296..367C. doi:10.1046/j.1365-8711.1998.01360.x.
  15. ^ Paardekooper, S. J.; Van Der Hucht, K. A.; Van Genderen, A. M.; Brogt, E.; Gieles, M.; Meijerink, R. (2003). "New type of brightness variations of the colliding wind WO4 + O5((f)) binary WR 30a". Astronomy and Astrophysics. 404 (2): L29. Bibcode:2003A&A...404L..29P. doi:10.1051/0004-6361:20030574.
  16. ^ Groh, Jose H.; Meynet, Georges; Georgy, Cyril; Ekstrom, Sylvia (2013). "Fundamental properties of core-collapse Supernova and GRB progenitors: Predicting the look of massive stars before death". Astronomy & Astrophysics. 558: A131. arXiv:1308.4681v1. Bibcode:2013A&A...558A.131G. doi:10.1051/0004-6361/201321906.
  17. ^ Groh, Jose (2014). "The evolution of massive stars and their spectra I. A non-rotating 60 Msun star from the zero-age main sequence to the pre-supernova stage". Astronomy & Astrophysics. 564: A30. arXiv:1401.7322. Bibcode:2014A&A...564A..30G. doi:10.1051/0004-6361/201322573.
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