Pi Mensae

Pi Mensae (π Men), also known as HD 39091, is a yellow dwarf star[3] in the constellation of Mensa. This star has a high proper motion. The apparent magnitude is 5.67, which can be visible to the naked eye in exceptionally dark, clear skies. It is nearly 60 ly away. The star is slightly larger than the Sun in terms of mass, size, luminosity, temperature, and metallicity and is about 730 million years younger. It hosts two planets.

Pi Mensae
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Mensa
Right ascension  05h 37m 09.89s [1]
Declination –80° 28′ 08.8″ [1]
Apparent magnitude (V) +5.65[2]
Characteristics
Spectral type G0 V[3]
U−B color index 0.11[2]
B−V color index 0.60[2]
V−R color index 0.31
R−I color index 0.29
Variable type none
Astrometry
Radial velocity (Rv)+10.9[4] km/s
Proper motion (μ) RA: 312.01±0.24[1] mas/yr
Dec.: 1,050.38±0.26[1] mas/yr
Parallax (π)54.7052 ± 0.0671[5] mas
Distance59.62 ± 0.07 ly
(18.28 ± 0.02 pc)
Absolute magnitude (MV)+4.35±0.01[6]
Details[7]
Mass1.11±0.01 M☉
Radius1.15±0.01 R☉
Luminosity1.532±0.004 L☉
Surface gravity (log g)4.35±0.01 cgs
Temperature6,013±18 K
Metallicity [Fe/H]0.09[8] dex
Rotational velocity (v sin i)2.96[8] km/s
Age3.4±0.6 Gyr
Other designations
π Men, CD−80° 195, CPD−80° 161, GJ 9189, HD 39091, HIP 26394, HR 2022, SAO 258421, LFT 429, LHS 208, LTT 2359, TOI 144
Database references
SIMBADdata
ARICNSdata

Planetary system

On October 15, 2001, an extrasolar planet was found orbiting the star.[9] Pi Mensae b is one of the most massive planets ever discovered, and has a very eccentric orbit that takes approximately 2,151 days (5.89 years) to complete. Because of its eccentricity, and being a massive brown dwarf that passes through the habitable zone, it would have disrupted the orbits of any Earth-like planets, and possibly thrown them into the star, or out into the interstellar medium.

Incorporating more accurate Hipparcos data yields a mass range for the companion to be anywhere from 10.27 to 29.9 times that of Jupiter, confirming its substellar nature with the upper limit of mass putting it in the brown dwarf range.[10] The companion b was confirmed to be a brown dwarf with the accurate mass measurement in 2020.[11] Pi Mensae was ranked 100th on the list of top 100 target stars for the planned (but now canceled) Terrestrial Planet Finder mission to search for Earth-like planets.

On September 16, 2018, a preprint was posted to arXiv detailing the discovery of a super-Earth on a 6.27-day orbit around the star, the first exoplanet detection by the Transiting Exoplanet Survey Satellite (TESS) submitted for publication.[12]. This was confirmed two days latter by [13] where the attention was called that the system is amenable for future planet atmospheric studies.

In 2020, an analysis with Gaia DR2 and Hipparcos astrometry showed that planets b and c are located on orbits mutually inclined by 49°-131° (1 sigma), which causes planet c to not transit most of the time, and acquire large misalignments with its host star's spin axis.[14]

The c is likely formed on wide orbit, and then migrated inward under gravitational influence of the brown dwarf b.[15]

The Pi Mensae planetary system[12][16][11][15]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
c 4.5±0.7 M⊕ 0.06839 ± 0.00050 6.2679 ± 0.00046 0.15+0.14
−0.08		 87.456 ± 0.08° 1.874+0.048
−0.051 R⊕
b 14.1+0.5
−0.4 MJ		 3.28±0.04 2093.07 ± 1.73 0.642±0.001 — —
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See also

References
  1. van Leeuwen, F. (2007). "HIP 26394". Hipparcos, the New Reduction. Retrieved 2010-02-28.
  2. Johnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99). Bibcode:1966CoLPL...4...99J.
  3. Gray, R. O.; et al. (July 2006). "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample". The Astronomical Journal. 132 (1): 161–170. arXiv:astro-ph/0603770. Bibcode:2006AJ....132..161G. doi:10.1086/504637.
  4. Valenti, Jeff A.; Fischer, Debra A. (July 2005). "Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs". The Astrophysical Journal Supplement Series. 159 (1): 141–166. Bibcode:2005ApJS..159..141V. doi:10.1086/430500.
  5. 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.
  6. Holmberg, J.; et al. (July 2009), "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics", Astronomy and Astrophysics, 501 (3): 941–947, arXiv:0811.3982, Bibcode:2009A&A...501..941H, doi:10.1051/0004-6361/200811191.
  7. Bonfanti, A.; et al. (2015). "Revising the ages of planet-hosting stars". Astronomy and Astrophysics. 575. A18. arXiv:1411.4302. Bibcode:2015A&A...575A..18B. doi:10.1051/0004-6361/201424951.
  8. Delgado Mena, E.; et al. (April 2015), "Li abundances in F stars: planets, rotation, and Galactic evolution", Astronomy & Astrophysics, 576: 24, arXiv:1412.4618, Bibcode:2015A&A...576A..69D, doi:10.1051/0004-6361/201425433, A69.
  9. Jones; et al. (2002). "A probable planetary companion to HD 39091 from Anglo-Australian Planet Search". Monthly Notices of the Royal Astronomical Society. 333 (4): 871–875. arXiv:astro-ph/0112084. Bibcode:2002MNRAS.333..871J. doi:10.1046/j.1365-8711.2002.05459.x. (web Preprint)
  10. Reffert, S.; Quirrenbach, A. (2011). "Mass constraints on substellar companion candidates from the re-reduced Hipparcos intermediate astrometric data: nine confirmed planets and two confirmed brown dwarfs". Astronomy & Astrophysics. 527. id.A140. arXiv:1101.2227. Bibcode:2011A&A...527A.140R. doi:10.1051/0004-6361/201015861.
  11. A precise architecture characterization of the π Men planetary system, 2020, arXiv:2007.06410
  12. Huang, Chelsea Xu; et al. (2018). "TESS Discovery of a Transiting Super-Earth in the π Mensae System". The Astrophysical Journal Letters. arXiv:1809.05967.
  13. Gandolfi, D.; Barragan, O.; Livingston, J.; Fridlund, M.; Justesen, A. B.; Redfield, S.; Fossati, L.; Mathur, S.; Grziwa, S.; Cabrera, J.; Garcia, R. A.; Persson, V.; van Eylen, V.; Hatzes, A. P.; Hidalgo, D.; Bugnet, L.; Cochran, W. D.; Csizmadia, Sz.; Deeg, H.; Eigmueller, Ph.; Endl, M.; Erikson, E.; Esposito, M.; Guenther, E.; Korth, J.; Luque, R.; Montanes-Rodriguez, P.; Nespral, D.; Nowak, G.; Paetzold, M.; Prieto-Arranz, J. (2019). "TESS's first planet: a super-Earth transiting the naked-eye star Pi Mensae". Astronomy & Astrophysics. 619 (1): L10. Bibcode:2018A&A...619L..10G. doi:10.1051/0004-6361/201834289.
  14. Evidence for a high mutual inclination between the cold Jupiter and transiting super Earth orbiting π Men, 2020, arXiv:2007.01871
  15. Orbital misalignment of the super-Earth π Men c with the spin of its star, 2020, arXiv:2007.11564
  16. Butler; et al. (2006). "Catalog of Nearby Exoplanets". The Astrophysical Journal. 646 (1): 505–522. arXiv:astro-ph/0607493. Bibcode:2006ApJ...646..505B. doi:10.1086/504701.

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