Sakurai's Object: Difference between revisions
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'''Sakurai's Object''' ('''V4334 Sgr''') is a [[star]] in the [[constellation]] of [[Sagittarius (constellation)|Sagittarius]]. It is thought to have been a [[white dwarf]] that, as a result of a [[very late thermal pulse]], swelled and became a [[red giant]].<ref name = "photoionization">{{cite journal| last1= van Hoof|first1= P. A. M.|last2= Hajduk |first2= M. |date= 2007|title = The onset of photoionization in Sakurai’s Object (V4334 Sagittarii)| journal = Astronomy & Astrophysics| volume= 471| pages = L9-L12| doi= 10.1051/0004-6361:20077932|arxiv = 0706.3857 |bibcode = 2007A&A...471L...9V }}</ref> It is located at the center of a [[planetary nebula]], which will likely lead to [[thermal instability]] during its [[shell helium flash]] phase.<ref name=ALetters/> |
'''Sakurai's Object''' ('''V4334 Sgr''') is a [[star]] located in the [[constellation]] of [[Sagittarius (constellation)|Sagittarius]]. It is thought to have been a [[white dwarf]] that, as a result of a [[very late thermal pulse]], swelled and became a [[red giant]].<ref name = "photoionization">{{cite journal| last1= van Hoof|first1= P. A. M.|last2= Hajduk |first2= M. |date= 2007|title = The onset of photoionization in Sakurai’s Object (V4334 Sagittarii)| journal = Astronomy & Astrophysics| volume= 471| pages = L9-L12| doi= 10.1051/0004-6361:20077932|arxiv = 0706.3857 |bibcode = 2007A&A...471L...9V }}</ref> It is located at the center of a [[planetary nebula]], which will likely lead to [[thermal instability]] during its [[shell helium flash]] phase.<ref name=ALetters/> |
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At the time of its discovery, astronomers believed Sakurai's Object to be a [[Nova|slow nova]] in the Sagittarius constellation, but later spectroscopic analysis suggested that the star was not a nova, but had undergone a very late thermal pulse similar to that of [[V605 Aquilae]], causing it to vastly expand.<ref name="ing">{{cite web|title=The Sakurai Object: A Case Study in Advanced Stellar Evolution|url=http://www.ing.iac.es/PR/newsletter/news2/sakurai.html|website=www.ing.iac.es|accessdate=17 January 2016}}</ref> V605 Aquilae, which was discovered in 1919, is the only other star known to have been observed during the high luminosity phase of a very late thermal pulse, and models predict that Sakurai's Object, over the next few decades, will follow a similar life cycle.<ref name="2003ApJ583-913">{{cite journal |first1= T.M. |last1= Lawlor |first2= J. |last2= MacDonald |title= Sakurai's Object, V605 Aquilae, and FG Sagittae: An Evolutionary Sequence Revealed |journal= The Astrophysical Journal |volume= 583 |pages= 913–922 |date= February 2003 |doi= 10.1086/345411|bibcode = 2003ApJ...583..913L }}</ref> |
At the time of its discovery, astronomers believed Sakurai's Object to be a [[Nova|slow nova]] in the Sagittarius constellation, but later spectroscopic analysis suggested that the star was not a nova, but had undergone a very late thermal pulse similar to that of [[V605 Aquilae]], causing it to vastly expand.<ref name="ing">{{cite web|title=The Sakurai Object: A Case Study in Advanced Stellar Evolution|url=http://www.ing.iac.es/PR/newsletter/news2/sakurai.html|website=www.ing.iac.es|accessdate=17 January 2016}}</ref> V605 Aquilae, which was discovered in 1919, is the only other star known to have been observed during the high luminosity phase of a very late thermal pulse, and models predict that Sakurai's Object, over the next few decades, will follow a similar life cycle.<ref name="2003ApJ583-913">{{cite journal |first1= T.M. |last1= Lawlor |first2= J. |last2= MacDonald |title= Sakurai's Object, V605 Aquilae, and FG Sagittae: An Evolutionary Sequence Revealed |journal= The Astrophysical Journal |volume= 583 |pages= 913–922 |date= February 2003 |doi= 10.1086/345411|bibcode = 2003ApJ...583..913L }}</ref> |
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Sakurai's Object and other similar stars are expected to end up as helium |
Sakurai's Object and other similar stars are expected to end up as [[helium]]-rich white dwarfs after retracing their evolution track from the "born-again" giant phase back to the white dwarf cooling track. There are few other suspected "born-again" objects, one example being [[FG Sagittae]]. Having erupted in 1995, it is expected that Sakurai's Object's final helium flash might be the well-observed one.<ref name="The Astrophysical Journal">{{cite journal|last1=Duerbeck|first1=Hilmar W.|last2=Benetti|first2=Stefano|title=Sakurai's Object—A Possible Final Helium Flash in a Planetary Nebula Nucleus|journal=The Astrophysical Journal|date=10 September 1996|volume=468|issue=2|pages=L111–L114|doi=10.1086/310241}}</ref> |
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==Observation history== |
==Observation history== |
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Revision as of 08:26, 25 January 2016
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 17h 52m 32.69s[1] |
| Declination | −17° 41′ 08.0″[1] |
| Apparent magnitude (V) | 10.90[1] |
| Characteristics | |
| Spectral type | F2Ia S...D[1] |
| Apparent magnitude (J) | 11.555 ± 0.022[1] |
| U−B color index | +0.27[2] |
| B−V color index | +0.81[2] |
| V−R color index | +0.57[2] |
| Astrometry | |
| Radial velocity (Rv) | −170 ± 30[3] km/s |
| Distance | 1800-5000[4] pc |
| Details | |
| Mass | 0.6[5] M☉ |
| Other designations | |
V4334 Sgr, V4334 Sagittarii, 2MASS J17523269-1741080, DPV 1, Sakurai's variable, PN G010.4+04.4, GSC2 S2202011182877, Sakurai's Object, AAVSO 1746-17 | |
| Database references | |
| SIMBAD | OBJECT data |
Sakurai's Object (V4334 Sgr) is a star located in the constellation of Sagittarius. It is thought to have been a white dwarf that, as a result of a very late thermal pulse, swelled and became a red giant.[4] It is located at the center of a planetary nebula, which will likely lead to thermal instability during its shell helium flash phase.[2]
At the time of its discovery, astronomers believed Sakurai's Object to be a slow nova in the Sagittarius constellation, but later spectroscopic analysis suggested that the star was not a nova, but had undergone a very late thermal pulse similar to that of V605 Aquilae, causing it to vastly expand.[6] V605 Aquilae, which was discovered in 1919, is the only other star known to have been observed during the high luminosity phase of a very late thermal pulse, and models predict that Sakurai's Object, over the next few decades, will follow a similar life cycle.[7]
Sakurai's Object and other similar stars are expected to end up as helium-rich white dwarfs after retracing their evolution track from the "born-again" giant phase back to the white dwarf cooling track. There are few other suspected "born-again" objects, one example being FG Sagittae. Having erupted in 1995, it is expected that Sakurai's Object's final helium flash might be the well-observed one.[8]
Observation history
An International Astronomical Union Circular sent on February 23, 1996 announced the discovery of a "possible 'slow' nova" of magnitude 11.4 by Yukio Sakurai, an amateur astronomer.[6] Japanese astronomer Syuichi Nakano reported the discovery, drawing attention to the fact that the object had not been visible in images from 1993 nor in Harvard–Smithsonian Center for Astrophysics records for the years 1930-1951 despite it appearing to slowly brighten over the previous year. Nakano wrote that "While the outburst [suggests] a slow or symbiotic nova, the lack of obvious emission lines one year after brightening is very unusual."[9]
Following the initial announcement, Hilmar Duerbeck et al. published a study investigating the "possible final helium flash" seen by Sakurai. In it, they noted that the location of Sakurai's Object corresponded to a faint object detected in 1976 of magnitude 21, and discussed other observations in the years 1994–1996, by which time the magnitude had increased to around 11–15.[10] By investigating the measured fluxes, angular diameter, and mass of the nebula, a distance of 5.5kpc and luminosity of 38 L☉ was determined. The researchers noted that this was in agreement with appearance and model predictions[11] and that the outburst luminosity was in the area of 3100 solar luminosities; lower than predicted by a factor of 3.
The first infrared observations were published in 1998, in which both near and far infrared spectroscopy was presented. The collected data showed Sakurai's Object brightening over the year of observations as expected and the researchers found that circumstellar dust was present at a temperature of ~680K.[12] Further infrared data, taken using the United Kingdom Infrared Telescope, was published in 2000 in which findings of the changing absorption lines were discussed.[13][14]
Sakurai's Object is modeled to increase in temperature in the next few decades to match the current state of V605, the only other star known to have been observed in a similar state.[7]
Properties
Sakurai's Object is classed as a post-asymptotic giant branch star which has, following a brief period on the white dwarf cooling track, undergone a helium shell flash (also known as a very late thermal pulse).[15] The star is thought to have a mass of around 0.6 M☉.[5]
Dust cloud
During the second half of 1998 an optically thick dust shell obscured Sakurai's Object, causing a rapid decrease in visibility of the star, until in 1999 it disappeared from optical wavelength observations altogether.[16] Infrared observations showed that the dust cloud around the star is primarily carbon in an amorphous form.[17] In 2009 it was discovered that the dust shell is strongly asymmetrical, as a disc with a major axis oriented at an angle of 134°, and inclination of around 75°. The disc is thought to be growing more opaque due to the fast spectral evolution of the source towards lower temperatures.[18][19]
Planetary nebula
Sakurai's Object is surrounded by a planetary nebula created following the star's red giant phase around 8300 years ago.[20] It has been determined that the nebula has a diameter of 44 arcseconds and expansion velocity of roughly 32 km/s.[21]
Significance in astronomical research
It is expected that promising research in the evolution of ancient stars will spring forth from this unusual star.[22] There is also a question why the born again stars Sakurai's Object and V605 Aquilae have a significantly shorter timeframe of evolution. While Sakurai's Object and V605 Aquilae have been shown to undergo born-again behavior for less than 10 years, while FG Sagittae has undergone it for 120 years. It can be answered provisionally by theorizing that Sakurai's object is only evolving to the asymptotic giant branch of stars for the first time, while FG Sagittae is doing it the second time.[23]
See also
References
- ^ a b c d e "SIMBAD Database entry for V4334 Sgr". SIMBAD. Retrieved April 19, 2013.
- ^ a b c d "UBV photometry of Sakurai's object in 1996 and remarks about its evolutionary status". Astronomy Letters. 23 (5): 709. September 1997. Retrieved 16 January 2016.
- ^ Eyres, S. P. S.; Geballe, T. R.; Tyne, V. H.; Evans, A.; Smalley, B.; Worters, H. L. (May 2004). "Warm high-velocity CO in the wind of Sakurai's Object (= V4334 Sgr)". Monthly Notices of the Royal Astronomical Society. 350 (1): L9–L12. doi:10.1111/j.1365-2966.2004.07808.x.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ a b van Hoof, P. A. M.; Hajduk, M. (2007). "The onset of photoionization in Sakurai's Object (V4334 Sagittarii)". Astronomy & Astrophysics. 471: L9–L12. arXiv:0706.3857. Bibcode:2007A&A...471L...9V. doi:10.1051/0004-6361:20077932.
- ^ a b Herwig, Falk (2011). "Convective-reactive proton-12C combustion in Sakurai's Object (V4334 Sagittarii) and implications for the evolution and yields from the first generations of stars". The Astrophysical Journal. 727: 89. arXiv:1002.2241. Bibcode:2011ApJ...727...89H. doi:10.1088/0004-637X/727/2/89.
- ^ a b "The Sakurai Object: A Case Study in Advanced Stellar Evolution". www.ing.iac.es. Retrieved 17 January 2016.
- ^ a b Lawlor, T.M.; MacDonald, J. (February 2003). "Sakurai's Object, V605 Aquilae, and FG Sagittae: An Evolutionary Sequence Revealed". The Astrophysical Journal. 583: 913–922. Bibcode:2003ApJ...583..913L. doi:10.1086/345411.
- ^ Duerbeck, Hilmar W.; Benetti, Stefano (10 September 1996). "Sakurai's Object—A Possible Final Helium Flash in a Planetary Nebula Nucleus". The Astrophysical Journal. 468 (2): L111–L114. doi:10.1086/310241.
- ^ Green, Daniel (February 23, 1996). "IAUC 6322: NOVALIKE Var IN Sgr". International Astronomical Union.
- ^ Duerbeck, Hilmar; Benetti, Stefano (September 10, 1996). "Sakurai's Object - A possible Final Helium Flash in a Planetary Nebula Nucleus". The Astrophysical Journal. 468: L111-L114. Bibcode:1996ApJ...468L.111D. doi:10.1086/310241.
- ^ Iben, I. (1983). "On the Evolution of Those Nuclei of Planetary-Nebulae That Experience a Final Helium Shell Flash". Astrophysical Journal. 264: 605–612. Bibcode:1983ApJ...264..605I. doi:10.1086/160631.
- ^ S. Eyres (1998). "Infrared Spectroscopy of Sakurai's Object". Monthly Notices of the Royal Astronomical Society. 298: L37–L41. Bibcode:1998MNRAS.298L..37E. doi:10.1046/j.1365-8711.1998.01898.x.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ Geballe, T. R.; Eyres, S. (2002). "The Infrared Evolution of Sakurai's Object". Astrophysics and Space Science. 279: 39–49. arXiv:astro-ph/0102043. Bibcode:2002Ap&SS.279...39G. doi:10.1023/a:1014683521291.
- ^ Tyne, V.; Eyres, S. (2000). "The continuing saga of Sakurai's object (V4334 Sgr): dust production and helium line emission". Monthly Notices of the Royal Astronomical Society. 315: 595–599. Bibcode:2000MNRAS.315..595T. doi:10.1046/j.1365-8711.2000.03412.x.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ Worters, H.; Rushton, M. (2009). "Sakurai's Object: characterizing the near-infrared CO ejecta between 2003 and 2007". Monthly Notices of the Royal Astronomical Society. 393: 108–112. Bibcode:2009MNRAS.393..108W. doi:10.1111/j.1365-2966.2008.14135.x.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ Pavlenko, Y.V.; Geballe, T.R. (2002). "Models of infrared spectra of Sakurai's Object (V4334 Sgr) in 1997". Astronomy & Astrophysics. 390: 621–626. arXiv:astro-ph/0205528. Bibcode:2002A&A...390..621P. doi:10.1051/0004-6361:20020732.
- ^ Tyne, V (2002). "Modelling the dust cloud around Sakurai's Object". Astrophysics and Space Science. 279: 139–147. Bibcode:2002Ap&SS.279..139T. doi:10.1023/A:1014672712630.
- ^ Tyne, V (2002). "Sakurai's Object (V4334 Sgr): evolution of the dust shell from 1999 to 2001". Monthly Notices of the Royal Astronomical Society. 334: 875–882. Bibcode:2002MNRAS.334..875T. doi:10.1046/j.1365-8711.2002.05561.x.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ Chesneau, O.; Clayton, G. (2009). "A dense disk of dust around the born-again Sakurai's object". Astronomy & Astrophysics. 493: L17–L20. arXiv:0811.3295. Bibcode:2009A&A...493L..17C. doi:10.1051/0004-6361:200811173.
- ^ Hajduk, M. (2008). "Studying the old planetary nebula of V4334 Sgr". Astronomical Society of the Pacific Conference Series. 391: 163–164.
- ^ Pollacco, Don (2002). "Modelling the Planetary Nebula". Astrophysics and Space Science. 279: 129–137. Bibcode:2002Ap&SS.279..129P. doi:10.1023/a:1014620711722.
- ^ Pollacco, Don. "The Sakurai Object: A Case Study in Advanced Stellar Evolution". Isaac Newton Group of Telescopes. Retrieved 16 January 2016.
- ^ Lawlor, T.M.; MacDonald, J. "Sakurai's Object, V605 Aquilae, and FG Sagittae: An Evolutionary Sequence Revealed". SAO/NASA ADS Astronomy Abstract Service. The Astrophysical Journal, Volume 583, Issue 2, pp. 913-922. Retrieved 16 January 2016.
