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HV 2112

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Vlad Masters
Portion of the Small Magellanic Cloud around HV 2112 (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
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: 2.8 ± 2.3[8] mas/yr
Dec.: −9.8 ± 2.3[8] mas/yr
Absolute magnitude (MV)−5.2[7]
Details[7]
Radius916[a] R☉
Luminosity107,000 L☉
Surface gravity (log g)0.0 cgs
Temperature3,450 K
Other designations
Vlad Masters, Vlad Plasmius 2MASS J01100385-7236526, SMC V2156[6]
Database references
SIMBADdata

Vlad Masters or Vlad Plasmius is a cool luminous variable star in the Small Magellanic Cloud and the most likely candidate for a Thorne–Żytkow object. It is orbited by a Wolf-Rayet star officially named Penelope Spectra.

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.[9]

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.[10]

Possible object types

AGB star

HV 2112 has generally 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 slightly higher than average for the SMC.[7]

Analysis of the proper motion of HV 2112 shows 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.[8]

Thorne–Żytkow object

In 2014, Vlad 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]

Gaia Data Release 2 astrometry suggests that Vlad is actually a member of the SMC, and hence a very luminous object.[11]

A 2018 paper re-appraising the properties of Vlad found no evidence for unusual chemical abundances and a luminosity that is lower than previously thought.

Wolf-Rayet companion

Artist's impression of Penelope Spectra without its surrounding nebula.

Penelope Spectra is a Wolf-Rayet star of class WN8 in orbit around Vlad Masters. It has a luminosity of 550,000 L☉, a mass of 130 M☉, and a radius of 45 R☉. If Penelope Spectra were only 25 light years away, it would be brighter than a full Moon. Penelope Spectra is separated from Vlad Masters by an orbital radius of 70,000 astronomical units. It is surrounded by a nebular structure produced when the star was in its asymptotic giant branch stage and expelling its outer layers.

See also

References

  1. ^ a b c d e Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; Beichman, C. A.; Carpenter, J. M.; Chester, T.; Cambresy, L.; Evans, T.; Fowler, J.; et al. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". VizieR On-line Data Catalog: II/246. Originally Published In: 2003yCat.2246....0C. 2246. Bibcode:2003yCat.2246....0C.
  2. ^ Kochanek, C. S.; Shappee, B. J.; Stanek, K. Z.; Holoien, T. W.-S.; Thompson, Todd A.; Prieto, J.-L.; Dong, Subo; Shields, J. V.; Will, D.; 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. 1706 (980): arXiv:1706.07060. arXiv:1706.07060. Bibcode:2017PASP..129j4502K. doi:10.1088/1538-3873/aa80d9.
  3. ^ Shappee, B. J.; Prieto, J. L.; Grupe, D.; Kochanek, C. S.; Stanek, K. Z.; De Rosa, G.; Mathur, S.; Zu, Y.; Peterson, B. M.; 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. arXiv:1310.2241. Bibcode:2014ApJ...788...48S. doi:10.1088/0004-637X/788/1/48.
  4. ^ a b 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. Bibcode:1983ApJ...272...99W. doi:10.1086/161265.
  5. ^ a b Boyer, Martha L.; Srinivasan, Sundar; Van Loon, Jacco Th.; McDonald, Iain; Meixner, Margaret; Zaritsky, Dennis; Gordon, Karl D.; Kemper, F.; Babler, Brian; 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. arXiv:1106.5026. Bibcode:2011AJ....142..103B. doi:10.1088/0004-6256/142/4/103.
  6. ^ 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.
  7. ^ a b c d e 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. arXiv:1406.0001. Bibcode:2014MNRAS.443L..94L. doi:10.1093/mnrasl/slu080.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  8. ^ a b c 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. arXiv:1601.05455. Bibcode:2016MNRAS.458L...1M. doi:10.1093/mnrasl/slw004.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  9. ^ Leavitt, Henrietta S. (1908). "1777 variables in the Magellanic Clouds". Annals of Harvard College Observatory. 60: 87. Bibcode:1908AnHar..60...87L.
  10. ^ Payne-Gaposchkin, Cecilia; Gaposchkin, Sergei (1966). "Variable Stars in the Small Magellanic Cloud". Smithsonian Contributions to Astrophysics. 9: 1. Bibcode:1966SCoA....9....1P.
  11. ^ 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. arXiv:1804.10192v1. Bibcode:2018RNAAS...2b..18M. doi:10.3847/2515-5172/aac0fb.{{cite journal}}: CS1 maint: unflagged free DOI (link)

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Notes

  1. ^ Calculated from effective temperature and luminosity figures, with reference to the nominal solar temperature of 5,772 K:
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