Astronomy:Tau Boötis

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Short description: Star in the constellation Boötes
Not to be confused with T Boötis.
τ Boötis
280px
Location of τ Boötis (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Boötes
Right ascension  13h 47m 15.7382s[1]
Declination +17° 27′ 24.810″[1]
Apparent magnitude (V) 4.50[2] (4.46 to 4.52)[3]
Characteristics
Evolutionary stage Main sequence
Spectral type F6V + M2[4]
B−V color index 0.48[2]
Variable type Suspected[3]
Astrometry
Radial velocity (Rv)−16.03±0.15[5] km/s
Proper motion (μ) RA: −468.923(95)[1] mas/yr
Dec.: +63.469(74)[1] mas/yr
Parallax (π)64.0470 ± 0.1093[1] mas
Distance50.92 ± 0.09 ly
(15.61 ± 0.03 pc)
Absolute magnitude (MV)3.38[6]
Orbit[4]
Primaryτ Boo A
Companionτ Boo B
Period (P)2,420+2,587
−947 yr
Semi-major axis (a)14.1+8.8
−3.9″
Eccentricity (e)0.87±0.04
Inclination (i)47.2+2.7
−3.7°
Longitude of the node (Ω)191.8+3.3
−4.7°
Argument of periastron (ω)
(secondary)		290.7+13
−10°
Details
τ Boo A
Mass1.35±0.03[4] M☉
Radius1.42±0.02[4] R☉
Luminosity3.06±0.16[7] L☉
Surface gravity (log g)4.26±0.06[4] cgs
Temperature6,387±44[4] K
Metallicity [Fe/H]0.25±0.03[4] dex
Rotation3.2±0.2 days[4]
Rotational velocity (v sin i)14.27±0.06[7] km/s
Age1.3+0.4
−0.6[4] Gyr
τ Boo B
Mass0.49±0.02[4] M☉
Radius0.48±0.05[4] R☉
Surface gravity (log g)4.90[8] cgs
Temperature3,580±90[4] K
Rotational velocity (v sin i)5.0[8] km/s
Other designations
τ Boo, 4 Boötis, NSV 6444, BD+18°2782, FK5 507, GC 18637, GJ 527, HD 120136, HIP 67275, HR 5185, SAO 100706, ADS 9025, CCDM 13473+1727, WDS J13473+1727A, LTT 14021[9]
Database references
SIMBADdata
A
B

Tau Boötis is a wide binary star system in the northern constellation of Boötes. Its name is a Bayer designation that is Latinised from τ Boötis, and abbreviated Tau Boo or τ Boo. This system is visible to the naked eye at a point of light with a combined apparent visual magnitude of 4.50.[2] Based on parallax measurements,[1] It is located at a distance of approximately 51 light-years (16 pc) from the Earth. This system is drifting closer to the Sun with a radial velocity of −16 km/s.[5]

The primary component is an ordinary F-type main-sequence star that is larger, brighter, and more massive than the Sun, while the secondary is a faint red dwarf. In 1999, an extrasolar planet was detected orbiting the primary star.

Stellar components

The primary component is a yellow-white F-type main-sequence star with a stellar classification of F6V. It is 35 percent more massive and 42 percent larger than the Sun. The star is radiating three[7] times the luminosity of the Sun from its photosphere at an effective temperature of 6,387 K.[4] It is about 1.3 billion years old, making it younger than the Sun.[4] Since it is more massive than the Sun, its lifespan is shorter—less than 6 billion years. This star is spinning with a projected rotational velocity of 14.3 km/s,[7] completing a rotation every three days.[4]

The primary is the first star apart from the Sun to be observed changing the polarity of its magnetic field.[10] It is listed as a suspected variable star. The magnetic activity cycle for this star shows a period of 122 days—much shorter than the solar cycle.[11]

The secondary companion is a dim, 11th magnitude red dwarf of spectral type M2.[4] It only about half the mass and radius of the Sun.[4] The stars orbit each other at a typical distance of about 220 AU (14 arcseconds) but come as close as about 28 AU during periapsis, giving its orbit a very high eccentricity of about 0.87. One orbit around the primary would take approximately 2,400 years to complete, although this period is poorly constrained.[4]

Planetary system

In 1996 the exoplanet Tau Boötis b was discovered orbiting the primary star by a team of astronomers led by R. Paul Butler.[12] It has six times the mass of Jupiter and is orbiting the star with a period of 3.3 days.[13] Tau Boötis and its planet appear to be tidally locked to each other.[14] In 2014, water vapor was discovered in the atmosphere of this hot Jupiter.[15]

There are indications of a second planet orbiting the star with a period of roughly 5,000 days; however, this could be due to an instrumental effect or a stellar magnetic activity cycle.[16] Because this is a highly eccentric binary star system, the maximum exoplanetary orbit around the primary that is dynamically stable for long periods has a semimajor axis of 4.86 au.[17]

The Tau Boötis A planetary system[13]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b 5.90+0.35−0.20[17] MJ 0.0481 ± 0.028 3.312463 ± 0.000014 0.023 ± 0.015 44.5 ± 1.5° 1.06 RJ

Naming controversy

The planet and its host star was one of the planetary systems selected by the International Astronomical Union as part of NameExoWorlds, their public process for giving proper names to exoplanets and their host star (where no proper name already exists).[18][19] The process involved public nomination and voting for the new names, and the IAU announced the new names in mid-December 2015.[20]

However, the IAU annulled the vote for the system, as the winning names ("Shri Ram Matt" for the star and "Bhagavatidevi" for the planet)[19] were judged not to conform with the IAU rules for naming exoplanets due to the political activities of the namesake people.[21] The names garnered the majority of the votes cast for the system, and made up a significant proportion of all votes cast as part of the contest.[19]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  2. ↑ 2.0 2.1 2.2 Mallik, Sushma V. (December 1999). "Lithium abundance and mass". Astronomy and Astrophysics 352: 495–507. Bibcode: 1999A&A...352..495M. 
  3. ↑ 3.0 3.1 Samus, N. N. et al. (2017). "General Catalogue of Variable Stars". Astronomy Reports. 5.1 61 (1): 80–88. doi:10.1134/S1063772917010085. Bibcode: 2017ARep...61...80S.  Search for: NSV 6444.
  4. ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 Justesen, A. B.; Albrecht, S. (2019). "Constraining the orbit of the planet-hosting binary τ Boötis". Astronomy & Astrophysics (EDP Sciences) 625: A59. doi:10.1051/0004-6361/201834368. ISSN 0004-6361. Bibcode: 2019A&A...625A..59J. 
  5. ↑ 5.0 5.1 Nidever, David L. et al. (2013). "Radial Velocities for 889 Late-Type Stars". The Astrophysical Journal Supplement Series 141 (2): 503–522. doi:10.1086/340570. Bibcode: 2002ApJS..141..503N. 
  6. ↑ Reiners, Ansgar (January 2006). "Rotation- and temperature-dependence of stellar latitudinal differential rotation". Astronomy and Astrophysics 446 (1): 267–277. doi:10.1051/0004-6361:20053911. Bibcode: 2006A&A...446..267R. 
  7. ↑ 7.0 7.1 7.2 7.3 Borsa, F. et al. (2015). "The GAPS programme with HARPS-N at TNG. VII. Putting exoplanets in the stellar context: Magnetic activity and asteroseismology of τ Bootis A". Astronomy and Astrophysics 578: A64. doi:10.1051/0004-6361/201525741. Bibcode: 2015A&A...578A..64B. 
  8. ↑ 8.0 8.1 Lindgren, Sara et al. (February 2016). "Metallicity determination of M dwarfs". Astronomy & Astrophysics 586: A100. doi:10.1051/0004-6361/201526602. ISSN 0004-6361. Bibcode: 2016A&A...586A.100L. 
  9. ↑ "Tau Boo". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=Tau+Boo. 
  10. ↑ Donati, J.-F. et al. (2008). "Magnetic cycles of the planet-hosting star Tau Boötis". Monthly Notices of the Royal Astronomical Society 385 (3): 1179–1185. doi:10.1111/j.1365-2966.2008.12946.x. Bibcode: 2008MNRAS.385.1179D. 
  11. ↑ Mittag, M. et al. (April 2017). "Four-month chromospheric and coronal activity cycle in τ Boötis". Astronomy & Astrophysics 600: 9. doi:10.1051/0004-6361/201629156. A119. Bibcode: 2017A&A...600A.119M. 
  12. ↑ Butler, R. Paul et al. (1997). "Three New 51 Pegasi Type Planets". The Astrophysical Journal Letters 474 (2): L115–L118. doi:10.1086/310444. Bibcode: 1997ApJ...474L.115B. 
  13. ↑ 13.0 13.1 Butler, R. P. et al. (2006). "Catalog of Nearby Exoplanets". The Astrophysical Journal 646 (1): 505–522. doi:10.1086/504701. Bibcode: 2006ApJ...646..505B. 
  14. ↑ Walker, G. A. H. et al. (2008). "MOST detects variability on tau Bootis possibly induced by its planetary companion". Astronomy and Astrophysics 482 (2): 691–697. doi:10.1051/0004-6361:20078952. Bibcode: 2008A&A...482..691W. 
  15. ↑ Lockwood, Alexandra C. et al. (March 2014). "Near-IR Direct Detection of Water Vapor in Tau Boötis b". The Astrophysical Journal Letters 783 (2): id. L29. doi:10.1088/2041-8205/783/2/L29. Bibcode: 2014ApJ...783L..29L. 
  16. ↑ Howard, Andrew W.; Fulton, Benjamin J. (2016). "Limits on Planetary Companions from Doppler Surveys of Nearby Stars". Publications of the Astronomical Society of the Pacific 128 (969): 114401. doi:10.1088/1538-3873/128/969/114401. Bibcode: 2016PASP..128k4401H. 
  17. ↑ 17.0 17.1 Jaime, Luisa G. et al. (December 2012). "Regions of dynamical stability for discs and planets in binary stars of the solar neighbourhood". Monthly Notices of the Royal Astronomical Society 427 (4): 2723–2733. doi:10.1111/j.1365-2966.2012.21839.x. Bibcode: 2012MNRAS.427.2723J. 
  18. ↑ "NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars". International Astronomical Union. 9 July 2014. http://www.iau.org/news/pressreleases/detail/iau1404/. 
  19. ↑ 19.0 19.1 19.2 "The ExoWorlds". NameExoWorlds. International Astronomical Union. n.d.. http://nameexoworlds.iau.org/statistics. 
  20. ↑ "The Process". NameExoWorlds. International Astronomical Union. 30 November 2015. http://nameexoworlds.iau.org/process. 
  21. ↑ "Final Results of NameExoWorlds Public Vote Released". International Astronomical Union. 15 December 2015. http://www.iau.org/news/pressreleases/detail/iau1514/. 

Coordinates: Sky map 13h 47m 15.7s, +17° 27′ 25″



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