HD 74156

HD 74156 is a yellow dwarf star (spectral type G0V) in the constellation of Hydra, 210 light years from the Solar System.[1] It is known to be orbited by two giant planets.

HD 74156
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Hydra
Right ascension 08h 42m 25.122s[1]
Declination +04° 34′ 41.15″[1]
Apparent magnitude (V) +7.614[2]
Characteristics
Spectral type G0V
U−B color index ?
B−V color index 0.581[2]
V−R color index 0.4
R−I color index 0.2
Variable type “None”
Astrometry
Radial velocity (Rv)+3.7 km/s
Proper motion (μ) RA: 24.83±0.64[1] mas/yr
Dec.: −200.90±0.46[1] mas/yr
Parallax (π)15.52 ± 0.54[1] mas
Distance210 ± 7 ly
(64 ± 2 pc)
Absolute magnitude (MV)+3.57 ± 0.15
Details
Mass1.24[2] M☉
Radius1.64 ± 0.19[2] R☉
Luminosity (bolometric)3.037 ± 0.485[2] L☉
Surface gravity (log g)4.4 ± 0.15[2] cgs
Temperature5960 ± 100[2] K
Metallicity [Fe/H]+0.13[2] dex
Rotational velocity (v sin i)4.3[2] km/s
Age3.7 ± 0.4[2] Gyr
Other designations
HIP 42723, SAO 117040, BD+05 2035
Database references
SIMBADdata

Star

This star is 24% more massive and 64% larger than our Sun. The total luminosity is 2.96 times that of our Sun and its temperature 5960 K.[2] The age of the star is estimated at approximately 3.7 billion years,[2] with metallicity 1.35 times that of the Sun based on its abundance of iron.

Planetary system

In April 2001, two giant planets were announced orbiting the star.[3][4] The first planet HD 74156 b orbits the star at a distance closer than Mercury is to our Sun, in an extremely eccentric orbit. The second planet HD 74156 c is a long-period, massive planet (at least 8 times the mass of Jupiter), which orbits the star in an elliptical orbit with a semimajor axis of 3.90 astronomical units.[2]

The HD 74156 planetary system[5]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b >1.778±0.020 MJ 0.2916±0.0033 51.6385±0.0015 0.6380±0.0061 — —
c >7.997±0.095 MJ 3.820±0.044 2448.9±5.5 0.3829±0.0080 — —

Claims of a third planet

Given the two-planet configuration of the system under the assumption that the orbits are coplanar and have masses equal to their minimum masses, an additional Saturn-mass planet would be stable in a region between 0.9 and 1.4 AU between the orbits of the two known planets.[6] Under the "packed planetary systems" hypothesis, which predicts that planetary systems form in such a way that the system could not support additional planets between the orbits of the existing ones, the gap would be expected to host a planet.

In September 2007, a third planet with a mass at least 0.396 Jupiter masses was announced to be orbiting between planets b and c with an eccentric orbit.[7] The planet, orbiting in a region of the planetary system previously known to be stable for additional planets, was seen as a confirmation of the "packed planetary systems" hypothesis.[8] However, Roman V. Baluev has cast doubt on this discovery, suggesting that the observed variations may be due to annual errors in the data.[9] A subsequent search using the Hobby-Eberly Telescope also failed to confirm the planet,[10] and further data obtained using HIRES instrument strongly contradicts its existence.[2]

See also

References
  1. van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.Vizier catalog entry
  2. Meschiari, Stefano; et al. (2011). "The Lick-Carnegie Survey: Four New Exoplanet Candidates". The Astrophysical Journal. 727 (2). 117. arXiv:1011.4068. Bibcode:2011ApJ...727..117M. doi:10.1088/0004-637X/727/2/117.
  3. "Exoplanets: The Hunt Continues!" (Press release). Garching, Germany: European Southern Observatory. April 4, 2001. Retrieved December 27, 2012.
  4. Naef, D.; et al. (2004). "The ELODIE survey for northern extra-solar planets III. Three planetary candidates detected with ELODIE". Astronomy and Astrophysics. 414 (1): 351–359. arXiv:astro-ph/0310261. Bibcode:2004A&A...414..351N. doi:10.1051/0004-6361:20034091.
  5. Feng, Y. Katherina; et al. (2015). "The California Planet Survey IV: A Planet Orbiting the Giant Star HD 145934 and Updates to Seven Systems with Long-period Planets". The Astrophysical Journal. 800 (1). 22. arXiv:1501.00633. Bibcode:2015ApJ...800...22F. doi:10.1088/0004-637X/800/1/22.
  6. Sean N. Raymond; Rory Barnes (2005). "Predicting Planets in Known Extrasolar Planetary Systems. II. Testing for Saturn Mass Planets". The Astrophysical Journal. 619 (1): 549–557. arXiv:astro-ph/0404211. Bibcode:2005ApJ...619..549R. doi:10.1086/426311.
  7. Jacob L. Bean; et al. (2008). "Detection of a Third Planet in the HD 74156 System Using the Hobby-Eberly Telescope". The Astrophysical Journal. 672 (2): 1202–1208. arXiv:0709.1656. Bibcode:2008ApJ...672.1202B. doi:10.1086/523701.
  8. Barnes, Rory; et al. (2008). "The Successful Prediction of the Extrasolar Planet HD 74156 d". The Astrophysical Journal Letters. 680 (1): L57–L60. arXiv:0804.4496. Bibcode:2008ApJ...680L..57B. doi:10.1086/589712.
  9. Baluev, Roman V. (2008). "Accounting for velocity jitters in planet search surveys". Monthly Notices of the Royal Astronomical Society. 393 (3): 969–978. arXiv:0712.3862. Bibcode:2009MNRAS.393..969B. doi:10.1111/j.1365-2966.2008.14217.x.
  10. Wittenmyer, Robert A.; Endl, Michael; Cochran, William D.; Levison, Harold F.; Henry, Gregory W. (2009). "A Search for Multi-Planet Systems Using the Hobby-Eberly Telescope". The Astrophysical Journal Supplement. 182 (1): 97–119. arXiv:0903.0652. Bibcode:2009ApJS..182...97W. doi:10.1088/0067-0049/182/1/97.

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