IK Tauri


IK Tauri
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Taurus
Right ascension 03h 53m 28.87s[1]
Declination +11° 24′ 21.7″[1]
Apparent magnitude (V) 10.8 - 16.5[2]
Evolutionary stage Asymptotic giant branch
Spectral type M6e - M10e[2]
Apparent magnitude (K) −1.24[3]
U−B color index −0.04[3]
B−V color index +3.64[3]
Variable type Mira[2]
Radial velocity (Rv)~46[4] km/s
Proper motion (μ) RA: 32.806±0.799[5] mas/yr
Dec.: −22.820±0.663[5] mas/yr
Parallax (π)3.5114 ± 0.3496[5] mas
Distance930 ± 90 ly
(280 ± 30 pc)
Mass1 - 1.5[6] M
Radius608 ± 66[6] R
Luminosity8,724±1,921[6] L
Surface gravity (log g)–0.95[6] cgs
Temperature2,234±86[6] K
Other designations
IK Tau, NML Tauri, 2MASS J03532886+1124216, IRAS 03507+1115, AAVSO 0347+11
Database references

IK Tauri or NML Tauri is a Mira variable star located about 280 parsecs (910 ly) from the Sun in the zodiac constellation of Taurus.[6]


In 1965, Neugebauer, Martz, and Leighton, astronomers with the California Institute of Technology, reported the discovery of two extremely cool stars. At the time, the temperatures of these extremely red objects were estimated to be around 1,000 K.[7]

In the absence of other designations, these were named after the initials of their discoverers as NML Cygni and NML Tauri.[8][9] It was identified as a Mira variable in 1967.[10] The name NML Tauri fell into disuse after the star received its variable star designation of IK Tauri.[11]


IK Tauri varies approximately every 470 days between extreme visual magnitudes of 10.8 and 16.5.[2] It was classified as a Mira variable soon after discovery on the basis of its spectrum showing strong hydrogen emission and its very large visual amplitude.[10] During each cycle, the spectrum of the star also varies, consistently reaching M10 near minimum and only M6-M8 at maximum.[2]


IK Tauri pulsates strongly every 470 days, being coolest and largest at minimum brightness. The bolometric luminosity varies less dramatically and is estimated to be 8,724 L. The temperature is calculated to be only 2,234 K, and the radius is calculated to be 608 R.

IK Tauri has strong maser emission from its extended atmosphere and circumstellar material.[12] The circumstellar material is rich in dust, with alumina close to the star and silicates further out. The two types of dust form separate shells, one within twice the star's radius and one more than three times its radius. The densest region of dust is at 6-8 times IK Tauri's radius.[13]

Although IK Tauri is far below naked eye visibility, even at maximum brightness, this is due to the low temperature and strong extinction at visual wavelengths. In the infrared, it is brighter than prominent stars such as Rigel (K-band magnitude +0.18[3]) and comparable to Sirius (K-band magnitude −1.35[3]).[13]


As a Mira variable, IK Tauri is an asymptotic giant branch (AGB) star, originally around 1.5 M.[14] It has exhausted its core hydrogen and helium, is not massive enough to ignite its carbon-oxygen core, and is now alternately fusing in concentric hydrogen and helium shells. As the inert core grows and the hydrogen shell nears the surface, mass loss becomes very high, and the star becomes highly obscured visually, an infrared star.[15] It will then quickly lose its entire atmosphere, creating a planetary nebula and leaving behind a white dwarf.


  1. ^ a b Cutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; Beichman, Charles A.; Carpenter, John M.; Chester, Thomas; Cambresy, Laurent; Evans, Tracey E.; Fowler, John W.; Gizis, John E.; Howard, Elizabeth V.; Huchra, John P.; Jarrett, Thomas H.; Kopan, Eugene L.; Kirkpatrick, J. Davy; Light, Robert M.; Marsh, Kenneth A.; McCallon, Howard L.; Schneider, Stephen E.; Stiening, Rae; Sykes, Matthew J.; Weinberg, Martin D.; Wheaton, William A.; Wheelock, Sherry L.; Zacarias, N. (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.
  2. ^ a b c d e 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.
  3. ^ a b c d e Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237: 0. Bibcode:2002yCat.2237....0D.
  4. ^ Feast, Michael W.; Whitelock, Patricia A. (2000). "Mira kinematics from Hipparcos data: A Galactic bar to beyond the Solar circle". Monthly Notices of the Royal Astronomical Society. 317 (2): 460. arXiv:astro-ph/0004107. Bibcode:2000MNRAS.317..460F. doi:10.1046/j.1365-8711.2000.03629.x.
  5. ^ a b c 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.
  6. ^ a b c d e f Adam, C.; Ohnaka, K. (2019). "Exploring the innermost dust formation region of the oxygen-rich AGB star IK Tauri with VLT/SPHERE-ZIMPOL and VLTI/AMBER". Astronomy & Astrophysics. 628: A132. arXiv:1907.05534. Bibcode:2019A&A...628A.132A. doi:10.1051/0004-6361/201834999. S2CID 196470928.
  7. ^ Neugebauer, G.; Martz, D. E.; Leighton, R. B. (1965). "Observations of Extremely Cool Stars" (PDF). Astrophysical Journal. 142: 399. Bibcode:1965ApJ...142..399N. doi:10.1086/148300.
  8. ^ Kruszewski, A. (1968). "Infrared Objects: Wavelength Dependence of Polarization". Publications of the Astronomical Society of the Pacific. 80 (476): 560. Bibcode:1968PASP...80..560K. doi:10.1086/128685.
  9. ^ Wyckoff, S.; Wehinger, P. (1973). "Revised period and minimum-light spectrum of NML Tauri". Astrophysical Journal. 186: 989. Bibcode:1973ApJ...186..989W. doi:10.1086/152562.
  10. ^ a b Wing, Robert F.; Spinrad, Hyron; Kuhi, L. V. (1967). "Infrared Stars". Astrophysical Journal. 147: 117. Bibcode:1967ApJ...147..117W. doi:10.1086/148985.
  11. ^ Wing, R. F.; Lockwood, G. W. (1973). "The period and spectral range of IK Tauri". Astrophysical Journal. 184: 873. Bibcode:1973ApJ...184..873W. doi:10.1086/152376.
  12. ^ Cotton, W. D.; Ragland, S.; Danchi, W. C. (2011). "Polarized Emission from SiO Masers in IK Tauri". The Astrophysical Journal. 736 (2): 96. Bibcode:2011ApJ...736...96C. doi:10.1088/0004-637X/736/2/96.
  13. ^ a b Gobrecht, D.; Cherchneff, I.; Sarangi, A.; Plane, J. M. C.; Bromley, S. T. (2016). "Dust formation in the oxygen-rich AGB star IK Tauri". Astronomy & Astrophysics. 585: A6. arXiv:1509.07613. Bibcode:2016A&A...585A...6G. doi:10.1051/0004-6361/201425363. S2CID 59360552.
  14. ^ Decin, L.; De Beck, E.; Brünken, S.; Müller, H. S. P.; Menten, K. M.; Kim, H.; Willacy, K.; De Koter, A.; Wyrowski, F. (2010). "Circumstellar molecular composition of the oxygen-rich AGB star IK Tauri. II. In-depth non-LTE chemical abundance analysis". Astronomy and Astrophysics. 516: A69. arXiv:1004.1914. Bibcode:2010A&A...516A..69D. doi:10.1051/0004-6361/201014136. S2CID 55743965.
  15. ^ Wilson, W. J.; Barrett, A. H. (1972). "Characteristics of OH emission from infrared stars". Astronomy and Astrophysics. 17: 385. Bibcode:1972A&A....17..385W.