Przybylski's Star

Przybylski's Star (pronounced /pʃɪˈbɪlskiz/ or /ʃɪˈbɪlskiz/), or HD 101065, is a rapidly oscillating Ap star at roughly 356 light-years (109 parsecs) from the Sun in the southern constellation of Centaurus. It has a unique spectrum showing over-abundances of most rare-earth elements, including some short-lived radioactive isotopes, but under-abundances of more common elements such as iron.

HD 101065

A blue band light curve for V816 Centauri, adapted from Kurtz and Wegner (1979)[1]
Observation data
Epoch J2000      Equinox J2000
Constellation Centaurus
Right ascension 11h 37m 37.04096s[2]
Declination −46° 42′ 34.8779″[2]
Apparent magnitude (V) 7.996–8.020[3]
Characteristics
Spectral type F0, F5, or G0[4] (F3 Ho)[5]
U−B color index +0.20[6]
B−V color index +0.76[6]
Variable type roAp[3][7]
Astrometry
Radial velocity (Rv)+12.4±3[8] km/s
Proper motion (μ) RA: −46.783±0.015[2] mas/yr
Dec.: +34.193±0.018[2] mas/yr
Parallax (π)9.1496 ± 0.0213 mas[2]
Distance356.5 ± 0.8 ly
(109.3 ± 0.3 pc)
Details
Mass1.4[2] M☉
Radius1.90[9] R☉
Luminosity5.55[2] L☉
Surface gravity (log g)3.97[2] cgs
Temperature6,131[2] K
Metallicity [Fe/H]−2.40[10] dex
Rotation188 years[7]
Rotational velocity (v sin i)3.50[11] km/s
Age1.5±0.1[12] Gyr
Other designations
V816 Cen, CD−46°7232, HD 101065, HIP 56709, SAO 222918[13]
Database references
SIMBADdata

History

In 1961, the Polish-Australian astronomer Antoni Przybylski discovered that this star had a peculiar spectrum that would not fit into the standard framework for stellar classification.[14][15] Przybylski's observations indicated unusually low amounts of iron and nickel in the star's spectrum, but higher amounts of unusual elements like strontium, holmium, niobium, scandium, yttrium, caesium, neodymium, praseodymium, thorium, ytterbium and uranium. In fact, at first Przybylski doubted that iron was present in the spectrum at all. Modern work shows that the iron group elements are somewhat below normal in abundance, but it is clear that the lanthanides and other exotic elements are highly over-abundant.[7]

Przybylski's Star possibly also contains many different short-lived actinide elements with actinium, protactinium, neptunium, plutonium, americium, curium, berkelium, californium, and einsteinium being theoretically detected. The longest-lived known isotope of einsteinium has a half-life of only 472 days, with astrophysicist Stephane Goriely at the Free University of Brussels (ULB) stating (in 2017) that the evidence for such actinides is not strong as “Przybylski’s stellar atmosphere is highly magnetic, stratified and chemically peculiar, so that the interpretation of its spectrum remains extremely complex [and] the presence of such nuclei remains to be confirmed.”[16] As well, the lead author of the actinide studies, Vera F. Gopka, directly admits that "the position of lines of the radioactive elements under search were simply visualized in synthetic spectrum as vertical markers because there are no atomic data for these lines except for their wavelengths (Sansonetti et al. 2004), enabling one to calculate their profiles with more or less real intensities."[17] The signature spectra of einsteinium's isotopes have since been comprehensively analyzed experimentally (in 2021),[18] though there is currently no published research confirming whether the theorized einsteinium signatures proposed to be found in the star's spectrum match the lab-determined results.

Radioactive elements that were verifiably identified in this star include technetium and promethium.[19] While the longest lived known isotopes of technetium have half lives in the millions of years, the longest lived known promethium-isotope only has a half life of 17.7 years, which requires some source constantly replenishing it for it to be still present in measurable quantities.

There have been many attempts to assign a conventional spectral class to this star. The Henry Draper Catalogue gives a class of B5. More detailed analysis when the unusual nature of the star was discovered estimated a class of F8 or G0. Later studies gave classes of F0 or F5 to G0.[4] It is considered likely to be a main sequence star with a temperature somewhat hotter than the Sun, but with its spectral lines strongly blanketed by the extreme abundances of certain metals.[20] A catalogue of chemically peculiar stars gives the type F3 Ho, indicating an Ap star with an approximate spectral class of F3 and strong holmium lines.[5]

Compared to neighboring stars, HD 101065 has a high peculiar velocity of 23.8±1.9 km/s.[21]

Hypotheses

Because of the odd properties of this star, there are numerous hypotheses about why the oddities occur. One such theory is that the star contains some long-lived nuclides from the island of stability (such as 298Fl or 304Ubn) and that the observed short-lived actinides are the daughters of these progenitors, occurring in secular equilibrium with their parents.[22][23]

It was suggested that stellar wind from a close neutron star companion could produce the observed radioactive elements, but subsequent radial velocity measurements appeared to exclude this possibility.[24] More recently it has been proposed that a companion may be present but impossible to observe with radial velocity methods if it orbits in the plane of sky. In that scenario it may still be detected because it would also produce deuterium,[25] but so far no deuterium has been found spectroscopically.[26]

Przybylski's star has occasionally attracted attention as a SETI candidate[24] because it aligns with speculation that a technological species may salt the photosphere of its star with unusual elements, either to signal its presence[27][28] or to dispose of nuclear waste.[29]

Properties

With a mass of about 1.5 M☉ and an age of around 1.5 billion years, HD 101065 is calculated to be right at the end of its main sequence life. It shines with a bolometric luminosity of about 5.6 L☉ at an effective temperature of 6,131 K. It has a very slow projected rotational velocity for a hot main sequence star of just 3.5 km/s. Observations of its magnetic field suggest a possible rotation period of about 188 years, although this is considered a minimum likely value.[7] A metallicity index ([Fe/H]) of −2.40 has been published, suggesting levels of metals just a few percent of the Sun's, but this single value does not adequately represent the chemical makeup shown in the star's unique spectrum. Levels of some other metals as derived from the spectrum are thousands of times higher than in the Sun.[11] Also, because the chemical peculiarities of Ap stars are largely due to stratification of elements allowed by very slow rotation, the published metallicity also probably does not represent the proportion of heavy elements in the whole star.[7]

HD 101065 is the prototype star of the rapidly oscillating Ap star (roAP) variable star class. In 1978, it was discovered to pulsate photometrically with a period of 12.15 min.[30]

A potential companion had also been detected, a 14th-magnitude star (in infrared) 8 arc seconds away. This could have meant a separation of just 1,000 AU (0.02 light-years);[31] however, Gaia Data Release 2 suggests that while those two stars appear to us as separated by a very close angle, the actual distance separating us from this second star is 890±90 light-years, which is more than twice the distance to Przybylski's Star.[32]

References
  1. Kurtz, Don; Wegner, Gary (September 1979). "The nature of Przybylski's star: an Ap star model inferred from the light variations and temperature". The Astrophysical Journal. 232: 510–519. Bibcode:1979ApJ...232..510K. doi:10.1086/157310.
  2. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  3. 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: B/gcvs. Bibcode:2009yCat....102025S.
  4. Skiff, B. A. (October 2014). "General Catalogue of Stellar Spectral Classifications". Vizier Online Data Catalog. Bibcode:2014yCat....1.2023S.
  5. Renson, P.; Manfroid, J. (2009). "Catalogue of Ap, Hg Mn and Am stars". Astronomy and Astrophysics. 498 (3): 961. Bibcode:2009A&A...498..961R. doi:10.1051/0004-6361/200810788.
  6. Wegner, G. (1976). "On the reddening and the effective temperature of HD 101065". Monthly Notices of the Royal Astronomical Society. 177: 99–108. Bibcode:1976MNRAS.177...99W. doi:10.1093/mnras/177.1.99.
  7. Hubrig, S.; Järvinen, S. P.; Madej, J.; Bychkov, V. D.; Ilyin, I.; Schöller, M.; Bychkova, L. V. (2018). "Magnetic and pulsational variability of Przybylski's star (HD 101065)". Monthly Notices of the Royal Astronomical Society. 477 (3): 3791. arXiv:1804.07260. Bibcode:2018MNRAS.477.3791H. doi:10.1093/mnras/sty889. S2CID 55698015.
  8. Gontcharov, G. A (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. S2CID 119231169.
  9. Shulyak, D.; Ryabchikova, T.; Kildiyarova, R.; Kochukhov, O. (2010). "Realistic model atmosphere and revised abundances of the coolest Ap star HD 101065". Astronomy and Astrophysics. 520: A88. arXiv:1004.0246. Bibcode:2010A&A...520A..88S. doi:10.1051/0004-6361/200913750. S2CID 53538833.
  10. Przybylski, A. (January 1977). "Is iron present in the atmosphere of HD 101065". Monthly Notices of the Royal Astronomical Society. 178 (2): 71–84. Bibcode:1977MNRAS.178...71P. doi:10.1093/mnras/178.2.71.
  11. Ghazaryan, S.; Alecian, G.; Hakobyan, A. A. (2018). "New catalogue of chemically peculiar stars, and statistical analysis". Monthly Notices of the Royal Astronomical Society. 480 (3): 2953. arXiv:1807.06902. Bibcode:2018MNRAS.480.2953G. doi:10.1093/mnras/sty1912.
  12. Mkrtichian, D. E.; Hatzes, A. P.; Saio, H.; Shobbrook, R. R. (2008). "The detection of the rich p-mode spectrum and asteroseismology of Przybylski's star". Astronomy & Astrophysics. 490 (3): 1109–1120. Bibcode:2008A&A...490.1109M. doi:10.1051/0004-6361:200809890.
  13. "V* V816 Cen". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2008-06-06.
  14. Przybylski, A.; Kennedy, P. Morris (August 1963). "The Spectrum of HD 101065". Publications of the Astronomical Society of the Pacific. 75 (445): 349–353. Bibcode:1963PASP...75..349P. doi:10.1086/127965.
  15. Powell, C. S.; Wright, J. (30 June 2017). "The Strangest (and Second-Strangest) Star in the Galaxy". Discover. Retrieved 12 December 2022.
  16. Jesse Empsak (23 March 2017). "Oddball star could be home to long-sought superheavy elements". New Scientist. Retrieved 29 May 2022.
  17. Gopka, V. F.; Yushchenko, Alexander V.; Shavrina, Angelina V.; Mkrtichian, David E.; Hatzes, Artie P.; Andrievsky, Sergey M.; Chernysheva, Larissa V. (2005). "On the radioactive shells in peculiar main sequence stars: the phenomenon of Przybylski's star". Proceedings of the International Astronomical Union. 2004: 734–742. doi:10.1017/S174392130500966X. S2CID 122474778.
  18. Nothhelfer, S.; Albrecht-Schönzart, Th.E.; Block, M.; Chhetri, P.; Düllmann, Ch.E.; Ezold, J.G.; Gadelshin, V.; Gaiser, A.; Giacoppo, F.; Heinke, R.; Kieck, T.; Kneip, N.; Laatiaoui, M.; Mokry, Ch.; Raeder, S.; Runke, J.; Schneider, F.; Sperling, J.M.; Studer, D.; Thörle-Pospiech, P.; Trautmann, N.; Weber, F.; Wendt, K. (2022). "Nuclear structure investigations of 253−255Es by laser spectroscopy". Physical Review C. 105. doi:10.1103/PhysRevC.105.L021302. S2CID 246603539.
  19. Gopka, V. F.; Yushchenko, A. V.; Yushchenko, V. A.; Panov, I. V.; Kim, Ch. (15 May 2008). "Identification of absorption lines of short half-life actinides in the spectrum of Przybylski's star (HD 101065)". Kinematics and Physics of Celestial Bodies. 24 (2): 89–98. Bibcode:2008KPCB...24...89G. doi:10.3103/S0884591308020049. S2CID 120526363.
  20. Cowley, C. R.; Ryabchikova, T.; Kupka, F.; Bord, D. J.; Mathys, G.; Bidelman, W. P. (2000). "Abundances in Przybylski's star". Monthly Notices of the Royal Astronomical Society. 317 (2): 299–309. Bibcode:2000MNRAS.317..299C. doi:10.1046/j.1365-8711.2000.03578.x.
  21. Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x, S2CID 118629873
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  24. Jason T. Wright (2018). "Exoplanets and SETI". In Hans J. Deeg; Juan Antonio Belmonte (eds.). Handbook of Exoplanets. Springer, Cham. pp. 3405–3412. arXiv:1707.02175. doi:10.1007/978-3-319-55333-7_186. ISBN 978-3-319-55332-0. S2CID 119228548.
  25. Andrievsky, S.M. (2022). "An Enigma of the Przybylski Star". Odessa Astronomical Publications. 35: 13–17. Bibcode:2022OAP....35...13A. doi:10.18524/1810-4215.2022.35.268673. S2CID 254907782.
  26. Andrievsky, S.M.; Kovtyukh, V.V. (February 2023). "Probing the Przybylski star for Deuterium". Astronomische Nachrichten. 344 (3). arXiv:2302.02487. Bibcode:2023AN....34420133A. doi:10.1002/asna.20220133. S2CID 256615832.
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  28. Iosif S. Shklovskii; Carl Sagan (1966). Intelligent Life in the Universe. Holden-Day. pp. 406–407.
  29. D.P. Whitmire; D.P. Wright (April 1980). "Nuclear waste spectrum as evidence of technological extraterrestrial civilizations". Icarus. 42 (1): 149–156. Bibcode:1980Icar...42..149W. doi:10.1016/0019-1035(80)90253-5.
  30. Kurtz, D. W. (1978). "12.15 Minute Light Variations in Przybylski's Star, HD 101065". Information Bulletin on Variable Stars. 1436: 1. Bibcode:1978IBVS.1436....1K.
  31. Schöller, M.; Correia, S.; Hubrig, S.; Kurtz, D. W. (2012). "Multiplicity of rapidly oscillating Ap stars". Astronomy & Astrophysics. 545: A38. arXiv:1208.0480. Bibcode:2012A&A...545A..38S. doi:10.1051/0004-6361/201118538. S2CID 119311263.
  32. 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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