54 Piscium

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54 Piscium
LuhmanTstarSpitzer (54 Psc).jpg
54 Piscium A and the brown dwarf 54 Piscium B (circled).
Observation data
Epoch J2000.0       Equinox J2000.0
Constellation Pisces
Right ascension 00h 39m 21.80551s [1]
Declination +21° 15′ 01.7161″ [1]
Apparent magnitude  (V)5.88 [2]
Characteristics
Spectral type K0V [3] / T7.5V
U−B color index +0.57 [2]
B−V color index +0.85 [2]
Variable type Suspected
Astrometry
Radial velocity (Rv)−34.2 [4]  km/s
Proper motion (μ)RA: −462.056 [1]   mas/yr
Dec.: −369.814 [1]   mas/yr
Parallax (π)89.7891 ± 0.0581  mas [1]
Distance 36.32 ± 0.02  ly
(11.137 ± 0.007  pc)
Absolute magnitude  (MV)5.65 [5]
Details
54 Psc A
Mass 0.76 [6]   M☉
Radius 0.944±0.033 [3]   R☉
Luminosity 0.52 [7]   L☉
Surface gravity (log g)4.61 [8]   cgs
Temperature 5,062±88 [3]   K
Metallicity [Fe/H]–0.15 [8]   dex
Rotation 40.2±4.0 d [9]
Age 6.4 [10]   Gyr
54 Psc B
Mass 0.051±0.014 [11]   M☉
Radius 0.082±0.006 [11]   R☉
Temperature 810±50 [11]   K
Other designations
54 Psc, NSV  245, BD+20°85, FK5  276, GJ  27, HD  3651, HIP  3093, HR  166, SAO  74175, LHS  1116, LTT  10224 [12]
Database references
SIMBAD data

54 Piscium is an orange dwarf star approximately 36 light-years away in the constellation of Pisces. In 2003, an extrasolar planet was confirmed to be orbiting the star, and in 2006, a brown dwarf was also discovered orbiting it.

Contents

Stellar components

The Flamsteed designation 54 Piscium originated in the star catalogue of the British astronomer John Flamsteed, first published in 1712. It has an apparent magnitude of 5.86, allowing it to be seen with the unaided eye under suitable viewing conditions. The star has a classification of K0V, with the luminosity class V indicating this is a main sequence star that is generating energy at its core through the thermonuclear fusion of hydrogen into helium. The effective temperature of the photosphere is about 5,062 K, [3] giving it the characteristic orange hue of a K-type star. [13]

It has been calculated that the star may have 76 percent [6] of the Sun's mass and 46 percent of the luminosity. The radius has been directly determined by interferometry to be 94 percent that of the Sun's radius using the CHARA array. [3] The rotational period of 54 Piscium is about 40.2 days. [9] The age of the star is about 6.4 billion years, based on chromospheric activity and isochronal analysis. [10] There is some uncertainty in the scientific press concerning the higher ratio of elements heavier than hydrogen compared to those found in the Sun; what astronomers term the metallicity. Santos et al. (2004) report the logarithm of the abundance ratio of iron to hydrogen, [Fe/H], to be 0.12  dex, [14] whereas Cenarro et al. (2007) published a value of –0.15 dex. [8]

Long term observation of this star's magnetic activity levels suggests that it is entering a Maunder minimum period, which means it may undergo an extended period of low starspot numbers. It has a Sun-like activity cycle that has been decreasing in magnitude. As of 2010, the most recent period of peak activity was 1992–1996, which showed a lower level of activity than the previous peak in 1976–1980. [9]

An artist's impression of brown dwarf 54 Piscium B and the planet 54 Piscium b. LuhmanTStarCompanion (54 Psc).jpg
An artist's impression of brown dwarf 54 Piscium B and the planet 54 Piscium b.

In 2006, a direct image of 54 Piscium showed that there was a brown dwarf companion to 54 Piscium A. [6] 54 Piscium B is thought to be a "methane brown dwarf" of the spectral type "T7.5V". The luminosity of this substellar object suggests that it has a mass of 0.051 that of the Sun (50 times the mass of Jupiter) and 0.082 times the Sun's radius. Similar to Gliese 570 D, this brown dwarf is thought to have a surface temperature of about 810 K (537 °C). [11]

When 54 Piscium B was directly imaged by NASA's Spitzer Space Telescope, it was shown that the brown dwarf had a projected separation of around 476 astronomical units from the primary star. [11] 54 Piscium B was the first brown dwarf to be detected around a star with an already known extrasolar planet (based on radial velocity surveys).

Planetary system

The star rotates at an inclination of 83+7
−56 degrees relative to Earth. [9]

On January 16, 2003, a team of astronomers (led by Geoff Marcy) announced the discovery of an extrasolar planet (named 54 Piscium b) around 54 Piscium. [15] [16] The planet has been estimated to have a mass of only 20 percent that of Jupiter (making the planet around the same size and mass of Saturn).

The planet orbits its sun at a distance of 0.28 astronomical units (which would be within the orbit of Mercury), which takes approximately 62 days to complete. It has been assumed that the planet shares the star's inclination and so has real mass close to its minimum mass; [17] however, several "hot Jupiters" are known to be oblique relative to the stellar axis. [18]

The planet has a high eccentricity of about 0.65. The highly elliptical orbit suggested that the gravity of an unseen object farther away from the star was pulling the planet outward. That cause was verified with the discovery of the brown dwarf within the system.

The orbit of an Earth-like planet would need to be centered within 0.68 AU [19] (around the orbital distance of Venus), which in a Keplerian system means a 240-day orbital period. In a later simulation with the brown dwarf, 54 Piscium b's orbit "sweeps clean" most test particles within 0.5 AU, leaving only asteroids "in low-eccentricity orbits near the known planet's apastron distance, near the 1:2 mean-motion resonance". Also, observation has ruled out Neptune-class or heavier planets with a period of one year or less; which still allows for Earth-sized planets at 0.6 AU or more. [20]

A two planet fit to the radial velocities with two circular planets in a 2:1 orbital resonance is possible [21] however it does not significantly improve the solution, and therefore does not justify the additional complexity. [22]

The 54 Piscium planetary system [22]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b ≥0.228±0.011  MJ 0.295±0.02962.250±0.0040.645±0.02——

See also

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References

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  10. 1 2 Mamajek, Eric E.; Hillenbrand, Lynne A. (November 2008). "Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics". The Astrophysical Journal. 687 (2): 1264–1293. arXiv: 0807.1686 . Bibcode:2008ApJ...687.1264M. doi:10.1086/591785. S2CID   27151456.
  11. 1 2 3 4 5 Luhman, K. L.; et al. (2007). "Discovery of Two T Dwarf Companions with the Spitzer Space Telescope". The Astrophysical Journal. 654 (1): 570–579. arXiv: astro-ph/0609464 . Bibcode:2007ApJ...654..570L. doi:10.1086/509073. S2CID   11576708.
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  18. ↑ Roberto Sanchis-Ojeda; Josh N. Winn; Daniel C. Fabrycky (2012). "Starspots and spin-orbit alignment for Kepler cool host stars". Astronomische Nachrichten. 334 (1–2): 180–183. arXiv: 1211.2002 . Bibcode:2013AN....334..180S. doi:10.1002/asna.201211765. S2CID   38743202.
  19. ↑ This based upon square root of the star's luminosity relative to the Sun, per the inverse-square law.
  20. ↑ Wittenmyer, Robert A.; Endl, Michael; Cochran, William D.; Levison, Harold F. (2007). "Dynamical and Observational Constraints on Additional Planets in Highly Eccentric Planetary Systems". The Astronomical Journal . 134 (3): 1276–1284. arXiv: 0706.1962 . Bibcode:2007AJ....134.1276W. doi:10.1086/520880. S2CID   14345035.
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  22. 1 2 Wittenmyer, Robert A.; et al. (2019). "Truly eccentric – I. Revisiting eight single-eccentric planetary systems". Monthly Notices of the Royal Astronomical Society. 484 (4): 5859–5867. arXiv: 1901.08471 . Bibcode:2019MNRAS.484.5859W. doi: 10.1093/mnras/stz290 . S2CID   118915974.
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