AG Carinae

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AG Carinae
A closer look at Hubble's 31st anniversary snapshot (51484874537).jpg
AG Car (Hubble Space Telescope image)
Observation data
Epoch J2000       Equinox J2000
Constellation Carina
Right ascension 10h 56m 11.57814s [1]
Declination −60° 27′ 12.8107″ [1]
Apparent magnitude  (V)6.96 [2] (5.7–9.0) [3]
Characteristics
Spectral type LBV [4]
U−B color index −0.58 [2]
B−V color index +0.61 [2]
Variable type LBV [5]
Astrometry
Proper motion (μ)RA: −4.808 [1]   mas/yr
Dec.: +1.955 [1]   mas/yr
Parallax (π)0.1925 ± 0.0165  mas [1]
Distance 17,000 ± 1,000  ly
(5,200 ± 400  pc)
Absolute magnitude  (MV)~−8 (at minimum) [4]
Details
Mass 55 [6]   M☉
Radius 50 [7] –552 [8]   R☉
Luminosity 600,000–900,000 [9] [lower-alpha 1]   L☉
Temperature 8,000–26,000 [7]   K
Rotation 13±2 [10] days
Rotational velocity (v sin i)220±50 [10]  km/s
Other designations
CD–59°3430, HD  94910, HIP  53461, SAO  251185, WR  31b, AAVSO  1052–69
Database references
SIMBAD data

AG Carinae (AG Car) is a star in the constellation Carina. It is classified as a luminous blue variable (LBV) and is one of the most luminous stars in the Milky Way. The great distance (20,000 light-years) and intervening dust mean that the star is not usually visible to the naked eye; its apparent brightness varies erratically between magnitude 5.7 and 9.0.

Contents

Description

This image showcases the details of the ionised hydrogen and ionised nitrogen emissions from the nebula (seen here in red). A Closer Look at Hubble's 31st Anniversary Snapshot.jpg
This image showcases the details of the ionised hydrogen and ionised nitrogen emissions from the nebula (seen here in red).

The star is surrounded by a nebula of ejected material at 0.4–1.2 pc from the star. The nebula contains around 15 M☉, all lost from the star around 10,000 years ago. There is an 8.8-parsec-wide empty cavity in the interstellar medium around the star, presumably cleared by fast winds earlier in the star's life. [4] [6]

AG Carinae is apparently in a transitional phase between a massive class O blue supergiant and a Wolf–Rayet star, where it is highly unstable and suffers from erratic pulsations, occasional larger outbursts, and rare massive eruptions. The spectral type varies between WN11 at visual minimum and an early A hypergiant at maximum. [4] At visual minimum the star is about 65 R☉ and 20,000–24,000 K, while at maximum it is over 400 R☉ and 8,000 K. The temperature varies at different minima. [7] [12]

One study calculated that the bolometric luminosity of AG Carinae decreases during its S Doradus-type outbursts, unlike most LBVs which remain at approximately constant luminosity. The luminosity drops from around 1.5 million L☉ at visual minimum to around 1 million L☉ at visual maximum, possibly due to the energy required to expand a considerable fraction of the star. [4]

Evolutionary models of the star suggest that it had a low rotation rate for much of its life, but current observations show fairly rapid rotation. [6]

Models of LBV progenitors of type IIb supernovae list AG Carinae as matching the final stellar spectrum prior to core collapse, although the models are for stars with 20 to 25 times the mass of the Sun while AG Carinae is thought to be considerably more massive. [13] The initial mass of the star would have been around 100 M☉ and is now thought to be 55–70 M☉. [4] [6]

Distance controversy

Parallaxes from data release 1 (DR1) of the Gaia mission suggest a much closer distance to AG Carinae and its neighbour Hen 3-519 than previously accepted, around 2,000 parsecs. Then both stars would be less luminous than LBVs and it is argued that they would be former red supergiants whose unusual characteristics are the result of binary evolution. [14]

The earlier Hipparcos parallax for AG Carinae had a margin of error larger than the parallax itself and so gave little information about its distance. [15] The distance of 6,000 parsecs is based on assumptions about the properties of LBVs, models of interstellar extinction, and kinematical measurements. [4] The Gaia DR1 parallax, derived from the combination of the first year of Gaia measurements with Tycho astrometry, is 0.40±0.22  mas . The Gaia team recommend that a further 0.3 mas systematic error is allowed for (i.e. added to the formal margin of error). [16] A 2017 study argues that the 0.3 mas systematic margin of error can be ignored and that the implied distance to AG Carinae is 2.50±1.41  kpc . [14]

In Gaia Data Release 2, the parallax is 0.1532±0.0291 mas, suggesting a distance around 6,500 pc. [17] A 2019 observation yields a most likely distance of 4,650 pc. [9] Gaia Early Data Release 3 gives a parallax of 0.1925±0.0165 mas, although with a non-trivial level of excess astrometric noise where there was none in Gaia DR2. [1]

Light curve

AAVSO light curve of luminous blue variable AG Car from 1 Jan 1940 to 23 Nov 2010. Up is brighter and down is fainter. AG-Car-Lightcurve-AAVSO.png
AAVSO light curve of luminous blue variable AG Car from 1 Jan 1940 to 23 Nov 2010. Up is brighter and down is fainter.

Notes

  1. ↑ Smith et al. 2019 stated that assuming the 4.65 kpc distance, the luminosity of AG Car would be 40% lower than the 1–1.5 million L☉ which was based on the 6 kpc distance.

Related Research Articles

<span class="mw-page-title-main">S Doradus</span> Star in the Large Magellanic Cloud

S Doradus is one of the brightest stars in the Large Magellanic Cloud (LMC), a satellite galaxy of the Milky Way, located roughly 160,000 light-years away. The star is a luminous blue variable, and one of the most luminous stars known, having a luminosity varying widely above and below 1,000,000 times the luminosity of the Sun, although it is too far away to be seen with the naked eye.

<span class="mw-page-title-main">Luminous blue variable</span> Type of star that is luminous, blue, and variable in brightness

Luminous blue variables (LBVs) are massive evolved stars that show unpredictable and sometimes dramatic variations in their spectra and brightness. They are also known as S Doradus variables after S Doradus, one of the brightest stars of the Large Magellanic Cloud. They are considered to be rare.

<span class="mw-page-title-main">P Cygni</span> Variable star in the constellation Cygnus

P Cygni is a variable star in the constellation Cygnus. The designation "P" was originally assigned by Johann Bayer in Uranometria as a nova. Located about 5,300 light-years from Earth, it is a hypergiant luminous blue variable (LBV) star of spectral type B1-2 Ia-0ep that is one of the most luminous stars in the Milky Way.

<span class="mw-page-title-main">V354 Cephei</span> Star in the constellation Cepheus

V354 Cephei is a red supergiant star located within the Milky Way. It is an irregular variable located over 8,900 light-years away from the Sun. It has an estimated radius of 685 solar radii. If it were placed in the center of the Solar System, it would extend to between the orbits of Mars and Jupiter.

<span class="mw-page-title-main">RS Puppis</span> Variable star in the constellation Puppis

RS Puppis is a Cepheid variable star around 6,000 ly away in the constellation of Puppis. It is one of the biggest and brightest known Cepheids in the Milky Way galaxy and has one of the longest periods for this class of star at 41.5 days.

<span class="mw-page-title-main">Cygnus OB2-12</span> Blue hypergiant star

Cygnus OB2 #12 is an extremely luminous blue hypergiant with an absolute bolometric magnitude of −10.9, among the most luminous stars known in the galaxy. This makes the star nearly two million times more luminous than the Sun, although estimates were even higher when the star was first discovered. It is now known to be a binary, with the companion approximately a tenth as bright. A very approximate initial estimate of the orbit gives the total system mass as 120 M☉ and the period as 30 years.

<span class="mw-page-title-main">HR Carinae</span> Star in the constellation Carina

HR Carinae is a luminous blue variable star located in the constellation Carina. It is surrounded by a vast nebula of ejected nuclear-processed material because this star has a multiple shell expanding atmosphere. This star is among the most luminous stars in the Milky Way. It has very broad emission wings on the Balmer lines, reminiscent from the broad lines observed in the spectra of O and Wolf–Rayet stars. A distance of 5 kpc and a bolometric magnitude of −9.4 put HR Car among the most luminous stars of the galaxy.

<span class="mw-page-title-main">Hypergiant</span> Rare star with tremendous luminosity and high rates of mass loss by stellar winds

A hypergiant (luminosity class 0 or Ia+) is a very rare type of star that has an extremely high luminosity, mass, size and mass loss because of its extreme stellar winds. The term hypergiant is defined as luminosity class 0 (zero) in the MKK system. However, this is rarely seen in literature or in published spectral classifications, except for specific well-defined groups such as the yellow hypergiants, RSG (red supergiants), or blue B(e) supergiants with emission spectra. More commonly, hypergiants are classed as Ia-0 or Ia+, but red supergiants are rarely assigned these spectral classifications. Astronomers are interested in these stars because they relate to understanding stellar evolution, especially star formation, stability, and their expected demise as supernovae.

Zeta<sup>1</sup> Scorpii Star in the constellation Scorpius.

Zeta1 Scorpii is a B-type hypergiant star in the constellation of Scorpius. It has an apparent visual magnitude which varies between 4.66 and 4.86. It is a member of the Scorpius OB1 association, and the open star cluster NGC 6231, also known as the "Northern jewel box" cluster. Around 36 times as massive as the Sun, it is also one of the most luminous stars known in the Galaxy, with an estimated bolometric luminosity of around 850,000 times that of the Sun and a radius 103 times that of the Sun.

<span class="mw-page-title-main">V602 Carinae</span> Star in the constellation Carina

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<span class="mw-page-title-main">HD 168607</span> Star in the constellation Sagittarius

HD 168607 is a blue hypergiant and luminous blue variable (LBV) star located in the constellation of Sagittarius, easy to see with amateur telescopes. It forms a pair with HD 168625, also a blue hypergiant and possible luminous blue variable, that can be seen at the south-east of M17, the Omega Nebula.

<span class="mw-page-title-main">V1429 Aquilae</span> Star in the constellation Aquila

V1429 Aquilae is a candidate luminous blue variable multiple star system located in the constellation of Aquila. It is often referred to by its Mount Wilson Observatory catalog number as MWC 314. It is a hot luminous star with strong emission lines in its spectrum.

<span class="mw-page-title-main">AS 314</span> Protoplanetary nebula in the constellation Scutum

AS 314, also known as V452 Scuti, is a protoplanetary nebula once believed to be a white hypergiant star or luminous blue variable located in the constellation of Scutum. It has an apparent magnitude of 9.85 and can be seen with small telescopes.

<span class="mw-page-title-main">HD 316285</span> Star in the constellation Sagittarius

HDE 316285 is a blue supergiant star in the constellation Sagittarius. It is a candidate luminous blue variable and lies about 6,000 light years away in the direction of the Galactic Center.

<span class="mw-page-title-main">WR 31a</span> Wolf Rayet star in the constellation Carina

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.

<span class="mw-page-title-main">V528 Carinae</span> Star in the constellation Carina

V528 Carinae is a variable star in the constellation Carina.

<span class="mw-page-title-main">BO Carinae</span> Star in the constellation Carina

BO Carinae, also known as HD 93420, is an irregular variable star in the constellation Carina.

<span class="mw-page-title-main">R71 (star)</span> Star in the Large Magellanic Cloud

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<span class="mw-page-title-main">V1936 Aquilae</span> Blue supergiant star in the constellation Aquila

V1936 Aquilae is a blue supergiant and candidate Luminous blue variable located in the nebula Westerhout 51, in the constellation Aquila, about 20,000 light years away. The star was originally identified as a massive star in 2000, and was thought to be an O-type supergiant. However, subsequent analyses have shown it to be not O but B-type, as well as being possibly an LBV.

HD 37836 is a candidate luminous blue variable located in the Large Magellanic Cloud and one of the brightest stars in its galaxy.

References

  1. 1 2 3 4 5 6 Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics . 649: A1. arXiv: 2012.01533 . Bibcode:2021A&A...649A...1G. doi: 10.1051/0004-6361/202039657 . S2CID   227254300. (Erratum:  doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  2. 1 2 3 Nicolet, B. (1978). "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System". Astronomy and Astrophysics Supplement Series. 34: 1–49. Bibcode:1978A&AS...34....1N.
  3. ↑ Watson, C. L. (2006). "The International Variable Star Index (VSX)". The Society for Astronomical Sciences 25th Annual Symposium on Telescope Science. Held May 23–25. 25: 47. Bibcode:2006SASS...25...47W.
  4. 1 2 3 4 5 6 7 Groh, J. H.; Hillier, D. J.; Damineli, A.; Whitelock, P. A.; Marang, F.; Rossi, C. (2009). "On the Nature of the Prototype Luminous Blue Variable Ag Carinae. I. Fundamental Parameters During Visual Minimum Phases and Changes in the Bolometric Luminosity During the S-Dor Cycle". The Astrophysical Journal. 698 (2): 1698–1720. arXiv: 0904.2363 . Bibcode:2009ApJ...698.1698G. doi:10.1088/0004-637X/698/2/1698. S2CID   1391092.
  5. ↑ Samus, N. N.; Durlevich, O. V.; Kazarovets, R. V. (1997). "The General Catalog of Variable Stars (GCVS)". Baltic Astronomy. 6 (2): 296. Bibcode:1997BaltA...6..296S. doi: 10.1515/astro-1997-0229 .
  6. 1 2 3 4 Vamvatira-Nakou, C.; Hutsemekers, D.; Royer, P.; Cox, N. L. J.; Naze, Y.; Rauw, G.; Waelkens, C.; Groenewegen, M. A. T. (2015). "The Herschel view of the nebula around the luminous blue variable star AG Carinae". Astronomy & Astrophysics. 1504: 3204. arXiv: 1504.03204 . Bibcode:2015A&A...578A.108V. doi:10.1051/0004-6361/201425090. S2CID   119160088.
  7. 1 2 3 Stahl, O.; Jankovics, I.; Kovács, J.; Wolf, B.; Schmutz, W.; Kaufer, A.; Rivinius, Th.; Szeifert, Th. (2001). "Long-term spectroscopic monitoring of the Luminous Blue Variable AG Carinae". Astronomy and Astrophysics. 375: 54–69. Bibcode:2001A&A...375...54S. doi: 10.1051/0004-6361:20010824 .
  8. ↑ https://ui.adsabs.harvard.edu/abs/1998A%26ARv...8..145D/abstract
  9. 1 2 Groh, Jose H.; Stassun, Keivan G.; Drout, Maria R.; Murphy, Jeremiah W.; Aghakhanloo, Mojgan; Smith, Nathan (2019). "On the Gaia DR2 distances for Galactic luminous blue variables". Monthly Notices of the Royal Astronomical Society. 488 (2): 1760–1778. arXiv: 1805.03298 . Bibcode:2019MNRAS.488.1760S. doi:10.1093/mnras/stz1712. S2CID   119267371.
  10. 1 2 Groh, J. H.; Hillier, D. J.; Damineli, A. (July 2011). "On the Nature of the Prototype Luminous Blue Variable AG Carinae. II. Witnessing a Massive Star Evolving Close to the Eddington and Bistability Limits". The Astrophysical Journal. 736 (1): 46. arXiv: 1105.0814 . Bibcode:2011ApJ...736...46G. doi:10.1088/0004-637X/736/1/46. S2CID   117109500.
  11. ↑ "A Closer Look at Hubble's 31st Anniversary Snapshot" . Retrieved September 28, 2021.
  12. ↑ Groh, J. H.; Damineli, A.; Hillier, D. J. (2008). P. Benaglia (ed.). "LBVs and the nature of the S Dor cycles: The case of AG Carinae". Massive Stars: Fundamental Parameters and Circumstellar Interactions. 33: 132. arXiv: astro-ph/0702612 . Bibcode:2008RMxAC..33..132G.
  13. ↑ Groh, J. H.; Meynet, G.; Ekström, S. (2013). "Massive star evolution: luminous blue variables as unexpected supernova progenitors". Astronomy & Astrophysics. 550: 4. arXiv: 1301.1519 . Bibcode:2013A&A...550L...7G. doi:10.1051/0004-6361/201220741. S2CID   119227339. L7.
  14. 1 2 Smith, N.; Stassun, K. G. (2017). "The Canonical Luminous Blue Variable AG Car and Its Neighbor Hen 3-519 are Much Closer than Previously Assumed". The Astronomical Journal. 153 (3): 7. arXiv: 1610.06522 . Bibcode:2017AJ....153..125S. doi: 10.3847/1538-3881/aa5d0c . S2CID   119296636. 125.
  15. ↑ Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv: 0708.1752 . Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID   18759600.
  16. ↑ Gaia Collaboration (2016). "VizieR Online Data Catalog: Gaia DR1 (Gaia Collaboration, 2016)". VizieR On-line Data Catalog: I/337. Originally Published in: Astron. Astrophys. 1337. Bibcode:2016yCat.1337....0G. doi:10.26093/cds/vizier.1337.
  17. ↑ 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.
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