WR 31a
{{Short description|Wolf Rayet star in the constellation Carina}}
{{Use dmy dates|date=July 2017}}
{{Starbox begin
| name = WR 31a
}}
{{Starbox image
| image = 280px
| caption = WR 31a is surrounded by a blue bubble nebula created by a powerful stellar wind impacting material expelled during earlier stages of the star's life.
| credit = ESA/Hubble & NASA; Acknowledgement: Judy Schmidt
}}
{{Starbox observe
| epoch = J2000.0
| constell = Carina
}}
{{Starbox character
| type = Wolf–Rayet
| appmag_1_passband = B
| appmag_1 = {{val|11.64|0.10}}
| appmag_2_passband = V
| appmag_2 = {{val|10.85|0.08}}
| appmag_3_passband = R
| appmag_3 = {{val|10.56|0.02}}
| appmag_4_passband = G
| appmag_4 = {{val|10.033|0.004}}
| appmag_5_passband = J
| appmag_5 = {{val|7.323|0.024}}
| appmag_6_passband = H
| appmag_6 = {{val|6.72|0.05}}
| appmag_7_passband = K
| appmag_7 = {{val|6.097|0.021}}
| appmag_8_passband = g
| appmag_8 = {{val|11.53|0.32}}
| r-i = 0.5
| v-r = 0.29
| b-v = 0.79
| j-h = 0.603
| j-k = 1.226
| variable = cLBV
}}
{{Starbox astrometry
| radial_v =
| parallax = 0.1152
| p_error = 0.0131
| dist_ly =
| dist_pc =
}}
{{Starbox detail
| source =
| radius = {{val|29.8|11.9|6.1}}
| luminosity = {{nowrap|1,820,000}}
| temperature = {{nowrap|30,200 (1985–1992)}} {{nowrap|27,500 (1991)}}
| metallicity_fe =
| gravity =
| age =
}}
{{Starbox catalog
| names = {{nowrap|WR 31a,}} {{nowrap|Hen 3-519,}} {{nowrap|He 3-519,}} {{nowrap|2MASS J10535958-6026444,}} {{nowrap|GSC 08958-01166,}} {{nowrap|GSC2 S1113013697,}} {{nowrap|UCAC2 5308747,}} {{nowrap|UCAC4 148-066854,}} {{nowrap|IRAS 10520-6010,}} {{nowrap|TYC 8928-1166-1,}} {{nowrap|AAVSO 1050–59,}} {{nowrap|MSX5C G288.9347-00.8046}}
}}
{{Starbox reference
| Simbad = WR_31a
}}
{{Starbox end}}
WR 31a, commonly referred to as Hen 3-519, is a Wolf–Rayet (WR) star in the southern constellation of Carina that is surrounded by an expanding Wolf–Rayet nebula. It is not a classical old stripped-envelope WR star, but a young massive star which still has some hydrogen left in its atmosphere.
History of observations
WR 31a was first published in 1952 as one of six peculiar emission line stars, but not given a designation at that time. It was described as having numerous P Cygni type lines with unusually broad emission components.{{cite journal |bibcode=1952ApJ...115..133H |title=Six Peculiar Hα-Emission Stars |journal=Astrophysical Journal |volume=115 |pages=133 |last1=Henize |first1=Karl G. |year=1952 |doi=10.1086/145522|doi-access=free }} A year later it was listed as being associated with nebulosity, at the time thought to be a planetary nebula.
In 1976, it was included in a catalogue of southern emission-line stars, the third catalogue of emission objects compiled by Karl Gordon Henize. The designation {{nowrap|Hen 3-519}}, sometimes {{nowrap|He 3-519}}, was adopted as the most common identifier for this star.{{cite journal |bibcode=1976ApJS...30..491H |title=Observations of southern emission-line stars |journal=Astrophysical Journal Supplement Series |volume=30 |pages=491 |last1=Henize |first1=K. G. |year=1976 |doi=10.1086/190369|doi-access=free }} In 2001, it was listed in The Seventh Catalogue of Galactic Wolf-Rayet stars as entry 31a, but it is still frequently called {{nowrap|Hen 3-519}}.
In 1994, WR 31a was first described as a candidate luminous blue variable (cLBV) after a detailed spectrographic study with the Anglo-Australian Telescope.
Measurements of its parallax, published in 2017 as a result of the Gaia mission, suggested a much closer (6,500 light-year; 2,000 parsec) distance to {{nowrap|WR 31a}} as well as to its neighbor, the luminous blue variable AG Carinae. It was thought that, if this distance was confirmed by Gaia{{'s}} second data release (DR2) in 2018, this would mean both stars were much less luminous than previously thought, and both may instead be former red supergiant stars.{{cite journal |title=The Canonical Luminous Blue Variable AG Car and Its Neighbor Hen 3-519 are Much Closer than Previously Assumed |journal=The Astronomical Journal |first1=Nathan |last1=Smith |first2=Keivan G. |last2=Stassun |volume=153 |issue=3 |at=125 |date=March 2017 |doi=10.3847/1538-3881/aa5d0c |bibcode=2017AJ....153..125S |arxiv=1610.06522|s2cid=119296636 |doi-access=free }} However, Gaia Data Release 2 returned a parallax of {{val|0.0418|0.0299|ul=mas}}; using Bayesian inference, Smith et al. (2018) calculated its distance to be {{val|31,200|8,500|6,000|fmt=commas|ul=ly}} ({{val|9,570|2,600|1,850|fmt=commas|ul=pc}}).{{cite journal |title=On the Gaia DR2 distances for Galactic Luminous Blue Variables |arxiv=1805.03298 |first1=Nathan |last1=Smith |first2=Mojgan |last2=Aghakhanloo |first3=Jeremiah W. |last3=Murphy |first4=Keivan G. |last4=Stassun |first5=Maria R. |last5=Drout |first6=Jose H. |last6=Groh |journal=Monthly Notices of the Royal Astronomical Society |year=2019 |volume=488 |issue=2 |pages=1760–1778 |display-authors=1 |doi=10.1093/mnras/stz1712 |doi-access=free |bibcode=2019MNRAS.488.1760S |s2cid=119267371 }} Gaia Data Release 3 lists a parallax of {{val|0.1152|0.0156|u=mas}}, again indicating a large distance. A statistical analysis leads to a distance of {{val|7,315|993|935|ul=pc|fmt=commas}}.
Blue bubble
WR 31a is surrounded by a shell of ionised gas nearly {{convert|8|ly|pc|spell=in}} wide. The Hubble Space Telescope (HST) has captured a striking image of the nebula, rendering it as a thin blue bubble. In this false colour image, the blue colours represents red visible light (605 nm), while orange-red colours represent near infrared radiation at 814 nm.{{cite web |url=https://www.nasa.gov/image-feature/goddard/2016/hubbles-blue-bubble |title=Hubble's Blue Bubble |work=NASA |access-date=1 March 2016|date=2016-02-26 }} Some media sources have wrongly claimed this deep-sky object was recently discovered by the HST,{{cite web |url=http://www.inquisitr.com/2841239/hubble-captures-blue-bubble-star-20-times-bigger-a-million-times-brighter-than-sun/ |title=Hubble Captures "Blue Bubble' Star—20 Times Bigger, a Million Times Brighter than the Sun's |work=Inquisitr |date=29 February 2016 |access-date=2 March 2016}} but this nebula was originally found by Ellen Dorrit Hoffleit in 1953 and designated as the planetary nebula Hf 39.{{cite journal |bibcode=1953AnHar.119...37H |title=A preliminary survey of nebulosities and associated B-stars in Carina |journal=Annals of Harvard College Observatory |volume=119 |pages=37 |last1=Hoffleit |first1=Dorrit |year=1953}} Other planetary nebula catalogue names include ESO 128-18 and Wray 15-682.
Since 2013, the nebula has been considered not as a planetary nebula, but rather as a much larger expanding gas shell, formally classified as a Wolf–Rayet nebula or WR nebula.{{cite journal |doi=10.1093/mnras/sts393 |title=A catalogue of integrated Hα fluxes for 1258 Galactic planetary nebulae |journal=Monthly Notices of the Royal Astronomical Society |volume=431 |issue=1 |pages=2–26 |year=2013 |last1=Frew |first1=D. J. |last2=Bojicic |first2=I. S. |last3=Parker |first3=Q. A. |doi-access=free |bibcode=2013MNRAS.431....2F |arxiv=1211.2505|s2cid=119174103 }} Its observed expansion velocity is {{convert|365|km/s|mi/s|abbr=on}}, and is estimated to be some {{convert|2.4|pc|ly}} across.{{Cite journal |arxiv=1503.06878 |last1=Toalá |first1=J. A. |title=WISE morphological study of Wolf-Rayet nebulae |journal=Astronomy & Astrophysics |volume=578 |pages=A66 |last2=Guerrero |first2=M. A. |last3=Ramos-Larios |first3=G. |last4=Guzmán |first4=V. |year=2015 |doi=10.1051/0004-6361/201525706 |bibcode=2015A&A...578A..66T|s2cid=55776698 }} The dynamical age of the nebula is estimated at 18,000 years and the total mass of ionised gas at {{solar mass|2–3}}.
Properties
WR 31a itself, the highly luminous central star of the nebula, is invisible to the naked-eye at magnitude 10.85V. It has a spectral classification of WN11h, indicating a WR star with strong N{{smallcaps|ii}} emission but no N{{smallcaps|iii}} emission, and with hydrogen features visible in the spectrum. The spectral classification WN11 was created for this star and AG Carinae since they did not fit into any existing spectral type and appeared to constitute an extension of the WR nitrogen sequence to cooler temperatures.{{cite journal |bibcode=1994A&A...281..833S |title=A study of the luminous blue variable candidate He 3-519 and its surrounding nebula |journal=Astronomy and Astrophysics |volume=281 |issue=3 |pages=833–854 |last1=Smith |first1=L. J. |last2=Crowther |first2=P. A. |last3=Prinja |first3=R. K. |year=1994}} The progenitor's mass of the central star is estimated to have been about 45 times that of the Sun,{{cite journal |bibcode=2015MNRAS.447..598S |arxiv=1406.7431 |title=Luminous blue variables are antisocial: Their isolation implies that they are kicked mass gainers in binary evolution |journal=Monthly Notices of the Royal Astronomical Society |volume=447 |issue=1 |pages=598–617 |last1=Smith |first1=Nathan |last2=Tombleson |first2=Ryan |year=2015 |doi=10.1093/mnras/stu2430|doi-access=free |s2cid=119284620 }} and this massive star will likely explode as a supernova in the future.{{cite web |url=https://www.spacetelescope.org/images/potw1608a/ |title=Blue bubble in Carina |work=NASA |access-date=2 March 2016}}
The spectrum of WR 31a shows P Cygni profiles, most strongly on the dominant H{{smallcaps|i}}, He{{smallcaps|i}}, and N{{smallcaps|ii}} lines. These profiles may show dramatic changes on a timescale of weeks, with the absorption components of the lines sometimes disappearing completely.
Variability
File:WR31aLightCurve.png light curve for WR 31a, plotted from ASAS-SN data]]
No significant brightness changes have been detected in WR 31a, but it has been listed as a candidate luminous blue variable because of its luminosity, temperature, and mass loss properties. Van Genderen catalogued it as a dormant or ex-LBV because of the lack of characteristic LBV variations.{{cite journal |bibcode=2001A&A...366..508V |title=S Doradus variables in the Galaxy and the Magellanic Clouds |journal=Astronomy and Astrophysics |volume=366 |issue=2 |pages=508–531 |last1=Van Genderen |first1=A. M. |year=2001 |doi=10.1051/0004-6361:20000022|doi-access=free }}[http://vizier.cfa.harvard.edu/viz-bin/VizieR-6?-out.form=%2bH&-source=33660508&-out.all&-corr=PFK=Name&-out.max=9999&Name==He3-519 Vizie database entry] Possible small brightness changes have been seen in All Sky Automated Survey (ASAS) data,{{cite journal |bibcode=2002AcA....52..397P |arxiv=astro-ph/0210283 |title=The All Sky Automated Survey. Catalog of Variable Stars. I. 0 h – 6 h Quarter of the Southern Hemisphere |journal=Acta Astronomica |volume=52 |pages=397–427 |last1=Pojmanski |first1=G. |year=2002}} WR 31a is included as a variable star in the International Variable Star Index,{{cite web |url=https://www.aavso.org/vsx/index.php?view=detail.top&revid=256789 |title=Hen 3-519 |publisher=American Association of Variable Star Observers |work=International Variable Star Index |access-date=30 September 2016 |date=4 January 2010}} although not in the General Catalogue of Variable Stars.{{cite journal |bibcode=2009yCat....102025S |title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007–2013) |journal=VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S |volume=1 |display-authors=etal |last1=Samus |first1=N. N. |last2=Durlevich |first2=O. V. |year=2009}}
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References
{{Reflist|refs=
{{cite Gaia DR3|5338229115839425664}}
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{{Stars of Carina}}
{{DEFAULTSORT:WR 31a}}
Category:Carina (constellation)