Astronomy:HV 2112
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| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| Constellation | Tucana |
| Right ascension | 01h 10m 03.858s[1] |
| Declination | −72° 36′ 52.62″[1] |
| Apparent magnitude (V) | 12.7 to below 16.7[2][3] |
| Characteristics | |
| Spectral type | M5.5 II (M3e – M7.5[4]) |
| Apparent magnitude (J) | 10.020[1] |
| Apparent magnitude (H) | 9.100[1] |
| Apparent magnitude (K) | 8.723[1] |
| U−B color index | +0.33[5] |
| B−V color index | +1.80[5] |
| Variable type | Mira?[6] |
| Astrometry | |
| Radial velocity (Rv) | 157[7] km/s |
| Proper motion (μ) | RA: 1.116±0.073[8] mas/yr Dec.: −1.291±0.067[8] mas/yr |
| Parallax (π) | −0.2029 ± 0.0446[8] mas |
| Absolute magnitude (MV) | −5.2[7] |
| Details | |
| Mass | ~5[9] M☉ |
| Radius | 675 - 1,193[9][lower-alpha 1] R☉ |
| Luminosity | 50,100 - 81,300[9] L☉ |
| Surface gravity (log g) | 0.0[7] cgs |
| Temperature | 2,500 - 3,750[9] K |
| Metallicity [Fe/H] | -2.18[10] dex |
| Other designations | |
| Database references | |
| SIMBAD | data |
HV 2112 is a cool luminous variable star in the Small Magellanic Cloud. Until 2018, it was considered to be the most likely candidate for a Thorne–Żytkow object, but it is now thought to be an asymptotic giant branch star.
Discovery
HV 2112 was first reported as a variable star in 1908, by Henrietta Leavitt. At the time it was identified as Harvard no. 2112. No period was given, but it was reported to be "probably long". The magnitude range was given as 13.7 to fainter than 16.5, from photographic plates.[12]
In 1966, analysis of Magellanic Cloud variable stars showed that HV 2112 had a photographic magnitude range from 13.0 to below 17.8. It was classified as a long-period variable, now known as a Mira variable, on the basis of its large amplitude and reasonably regular light variations.[13]
Possible object types
AGB star
HV 2112 had historically been treated as a very luminous asymptotic giant branch (AGB) star, a red giant that has exhausted its core helium and is in the last stages of its evolution. Large-amplitude class-M variables and stars with spectral types later than about M5 are almost always AGB stars rather than red supergiants. These stars have a theoretical maximum luminosity and, at the distance of the SMC, HV 2112 was typically calculated to be slightly more luminous than this limit at around 60,000 L☉.[4]
More modern calculations gave higher values for the luminosity of HV 2112 above 100,000 L☉, which is unambiguously too luminous to be an AGB star. These calculations included an interstellar extinction value of 0.4 magnitudes which is higher than average for massive stars in the SMC. However, it is not exceptional for red supergiants, which are believed to show additional extinction due to circumstellar dust near the star.[7]
Analysis of the proper motion of HV 2112 in 2016 reported that it is unusually large for an SMC star, although the radial velocity is consistent with other SMC objects. The proper motion of around 10 mas/year would indicate a space velocity of 3,100 km/sec at the distance of the SMC, well above its escape velocity. A more likely explanation of such a proper motion would be that HV 2112 lies about 3,000 parsecs away in our own galaxy. It would then be around 1,000 L☉ rather than 100,000 L☉ and so a typical AGB star. The over-abundance of heavy elements would then be explained as pollution from an unseen companion, producing an extrinsic S-type star.[14] Other analyses of the proper motion show much smaller velocities, consistent with an object in the SMC[15][16]
Thorne–Żytkow object
In 2014, HV 2112 was identified as a possible Thorne–Żytkow object (TZO) using the Magellan Clay telescope in Chile. To find candidate TZOs, Emily Levesque used the Apache Point Observatory to examine 24 red supergiant stars in the Milky Way, and the Magellan Clay telescope to look at 16 in the Large Magellanic Cloud and 22 in the Small Magellanic Cloud. The star was thought to contain unusually high levels of the elements lithium, molybdenum and rubidium that are expected only to be produced by TZOs.[7]
A 2018 paper re-appraising the properties of HV 2112 found no evidence for unusual chemical abundances and a luminosity that is lower than previously thought. This suggests that the star is unlikely to be a TZO, and is much more likely an intermediate mass AGB star.[9]
Binary star
HV 2112 is listed in the OGLE catalogue as an unresolved multiple star. The proper motions and radial velocity are consistent with other SMC objects, while the parallax is negative but acceptably close to the expected value for such a distant object.[17]
See also
References
- ↑ 1.0 1.1 1.2 1.3 1.4 Cutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; Beichman, Charles A.; Carpenter, John M.; Chester, Thomas; Cambresy, Laurent; Evans, Tracey E. et al. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". CDS/ADC Collection of Electronic Catalogues 2246: II/246. Bibcode: 2003yCat.2246....0C. http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=II/246.
- ↑ Kochanek, C. S.; Shappee, B. J.; Stanek, K. Z.; Holoien, T. W.-S.; Thompson, Todd A.; Prieto, J.-L.; Dong, Subo; Shields, J. V. et al. (2017). "The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0". Publications of the Astronomical Society of the Pacific 129 (980): 104502. doi:10.1088/1538-3873/aa80d9. Bibcode: 2017PASP..129j4502K.
- ↑ Shappee, B. J.; Prieto, J. L.; Grupe, D.; Kochanek, C. S.; Stanek, K. Z.; De Rosa, G.; Mathur, S.; Zu, Y. et al. (2014). "The Man behind the Curtain: X-Rays Drive the UV through NIR Variability in the 2013 Active Galactic Nucleus Outburst in NGC 2617". The Astrophysical Journal 788 (1): 48. doi:10.1088/0004-637X/788/1/48. Bibcode: 2014ApJ...788...48S.
- ↑ 4.0 4.1 Wood, P. R.; Bessell, M. S.; Fox, M. W. (1983). "Long-period variables in the Magellanic Clouds – Supergiants, AGB stars, supernova precursors, planetary nebula precursors, and enrichment of the interstellar medium". Astrophysical Journal 272: 99. doi:10.1086/161265. Bibcode: 1983ApJ...272...99W.
- ↑ 5.0 5.1 Boyer, Martha L.; Srinivasan, Sundar; Van Loon, Jacco Th.; McDonald, Iain; Meixner, Margaret; Zaritsky, Dennis; Gordon, Karl D.; Kemper, F. et al. (2011). "Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud (SAGE-SMC). II. Cool Evolved Stars". The Astronomical Journal 142 (4): 103. doi:10.1088/0004-6256/142/4/103. Bibcode: 2011AJ....142..103B.
- ↑ 6.0 6.1 Samus, N. N. 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.
- ↑ 7.0 7.1 7.2 7.3 7.4 Levesque, Emily (1 September 2014). "Discovery of a Thorne-̇Żytkow object candidate in the Small Magellanic Cloud". Monthly Notices of the Royal Astronomical Society: Letters 443: L94–L98. doi:10.1093/mnrasl/slu080. Bibcode: 2014MNRAS.443L..94L.
- ↑ 8.0 8.1 8.2 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode: 2018A&A...616A...1G. Gaia DR2 record for this source at VizieR.
- ↑ 9.0 9.1 9.2 9.3 9.4 Beasor, Emma; Davies, Ben; Cabrera-Ziri, Ivan; Hurst, Georgia (2 July 2018). "A critical re-evaluation of the Thorne-Żytkow object candidate HV 2112". Monthly Notices of the Royal Astronomical Society 479 (3): 3101. doi:10.1093/mnras/sty1744. Bibcode: 2018MNRAS.479.3101B.
- ↑ Anders, F.; Khalatyan, A.; Chiappini, C.; Queiroz, A. B.; Santiago, B. X.; Jordi, C.; Girardi, L.; Brown, A. G. A. et al. (2019). "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18". Astronomy and Astrophysics 628: A94. doi:10.1051/0004-6361/201935765. Bibcode: 2019A&A...628A..94A.
- ↑ "HV 2112". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=HV+2112.
- ↑ Leavitt, Henrietta S. (1908). "1777 variables in the Magellanic Clouds". Annals of Harvard College Observatory 60: 87. Bibcode: 1908AnHar..60...87L.
- ↑ Payne-Gaposchkin, Cecilia; Gaposchkin, Sergei (1966). "Variable Stars in the Small Magellanic Cloud". Smithsonian Contributions to Astrophysics 9: 1–205. doi:10.5479/si.00810231.9.1. Bibcode: 1966SCoA....9....1P.
- ↑ MacCarone, Thomas J.; De Mink, Selma E. (2016). "Large proper motion of the Thorne-Żytkow object candidate HV 2112 reveals its likely nature as foreground Galactic S-star". Monthly Notices of the Royal Astronomical Society: Letters 458 (1): L1. doi:10.1093/mnrasl/slw004. Bibcode: 2016MNRAS.458L...1M.
- ↑ Worley, C. Clare; Irwin, Mike. J.; Tout, Christopher A.; Żytkow, Anna N.; Fraser, Morgan; Izzard, Robert G. (2016). "The proper motion of HV2112: A TŻO candidate in the SMC". Monthly Notices of the Royal Astronomical Society: Letters 459 (1): L31–L35. doi:10.1093/mnrasl/slw034. Bibcode: 2016MNRAS.459L..31W.
- ↑ McMillan, Paul J; Church, Ross P (2018). "Gaia DR2 confirms that candidate Thorne-Żytkow object HV 2112 is in the SMC". Research Notes of the AAS 2 (2): 18. doi:10.3847/2515-5172/aac0fb. Bibcode: 2018RNAAS...2...18M.
- ↑ González-Fernández, Carlos; Dorda, Ricardo; Negueruela, Ignacio; Marco, Amparo (2015). "A new survey of cool supergiants in the Magellanic Clouds". Astronomy & Astrophysics 578: A3. doi:10.1051/0004-6361/201425362. Bibcode: 2015A&A...578A...3G.
Notes
- ↑ Calculated from effective temperature and luminosity figures, with reference to the nominal solar temperature of 5,772 K: [math]\displaystyle{ \sqrt{(5772/3750)^4 * 81,283} = 675.4\ R\odot }[/math] [math]\displaystyle{ \sqrt{(5772/2500)^4 * 50,119} = 1,193.4\ R\odot }[/math]
External links
- "First Thorne-Zytkow Object Found 200,000 Light-Years Away". 5 June 2014. http://www.sci-news.com/astronomy/science-thorne-zytkow-object-01970.html.
- Eller, Cynthia (30 June 2014). "Kip Thorne discusses first discovery of Thorne-Zytkow object". http://phys.org/news/2014-06-kip-thorne-discusses-discovery-thorne-zytkow.html.
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