Gliese 676

Gliese 676 A/B

Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Ara
Right ascension	17^h 30^m 11.20^s[1]
Declination	–51° 38′ 13.1″[1]
Apparent magnitude (V)	9.59
Characteristics
Spectral type	M0V[2]/M3V
Apparent magnitude (B)	11.05/14.8
Apparent magnitude (J)	6.711
Apparent magnitude (H)	6.082
Apparent magnitude (K)	5.825
B−V color index	1.46
Astrometry
Radial velocity (Rv)	−39.82±0.14[3] km/s
Proper motion (μ)	RA: −258.759±0.034[3] mas/yr Dec.: −185.119±0.025[3] mas/yr
Parallax (π)	62.5786 ± 0.0303 mas[3]
Distance	52.12 ± 0.03 ly (15.980 ± 0.008 pc)
Absolute magnitude (MV)	8.55
Details
Mass	0.631±0.017[4]/0.29[5] M☉
Radius	0.617+0.028 −0.027[4] R☉
Luminosity	0.08892±0.00220[4] L☉
Temperature	4,014+94 −90[4] K
Metallicity [Fe/H]	0.23±0.10[5] dex
Rotation	41.2±3.8 d[2]
Other designations
CD–51°10924, HIP 85647, LTT 6947/6948, NLTT 44859, NSV 8846
Database references
SIMBAD	data
Exoplanet Archive	data

Gliese 676 is a 10th-magnitude wide binary system of red dwarfs that has an estimated minimum separation of 800 AU with an orbital period of greater than 20,000 years.^[6] It is located approximately 54 light years away in the constellation Ara. In 2009, a gas giant was found in orbit around the primary star, in addition to its confirmation in 2011 there was also a strong indication of a companion; the second gas giant was characterised in 2012, along with two much smaller planets.

Planetary system

The first planet discovered, b, is a super-jovian first characterised in October 2009. The planet was formally announced in 2011,^[5] along with the first recognition of a trend not attributable to the companion star. Even after fitting a planet and a trend, it was noted that the residual velocities were still around 3.4 m/s, significantly larger than the instrumental errors of around 1.7 m/s. This tentatively implied the existence of other bodies in orbit, though nothing more could be said at the time.^[5]

The star was a test case for the HARPS-TERRA software for better reduction of data from the HARPS spectrometer in early 2012.^[7] Even with significantly lower margins of error on the data, less data was accessible than what was used in 2011. Still, the team reached a very similar conclusion to the previous team with a model of a planet and a trend. The residual velocities were still somewhat excessive, giving more weight to the existence of other bodies in the system, though still no conclusions could be made.

Between the time of the previous analysis and June 2012, the rest of the radial-velocity measurements used in 2011 were made public,^[6] allowing them to be reduced using HARPS-TERRA. These were then analysed via a Bayesian probability analysis, which was previously used to discover HD 10180 i and j, which confirmed planet b and made a first characterisation of planet c,^[8] which was previously only described as a trend. After the first two signals were introduced, the next most powerful signal was at around 35.5 days, with an analytic false alarm probability of 0.156. Through 10⁴ trials, the false alarm probability was found to be 0.44%, low enough for it to be included as a periodic, planetary signal. With a minimum mass of around 11 Earths, the planet lies at the accepted border between Super-Earths and gaseous, Neptune-like bodies of 10 Earths. After accepting the third signal, a strong peak at 3.6 days became apparent. With a false alarm probability much lower than that of the previously accepted body, it was immediately accepted. With a minimum mass of around 4.5 Earths, it is a small Super-Earth.

As of 2012^[update], this system holds the record for the widest range of masses in a single planetary system,^[6] and also shows a hierarchy reminiscent of the solar system, with the gas giants at large distances from the star while the smaller bodies are much closer-in.

In 2016, the true mass of Gliese 676 Ab was measured via astrometry.^[8] A 2022 study revised this mass estimate, along with measuring the true mass of Gliese 676 Ac.^[9] There are two Super-Jupiter planets: "b" with a period of 1051 days (2.9 years) and a mass of 5.79 M_J, and "c" with a period of 13900 days (38.1 years) and a mass of 13.49 M_J, which is at the borderline between planets and brown dwarfs.^[9]

The Gliese 676 A planetary system^[6]^[8]^[9]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
d	≥4.4±0.3 M🜨	0.0413±0.0014	3.6005±0.0002	0.262+0.090 −0.101	—	—
e	≥8.1±0.7 M🜨	0.187±0.007	35.39+0.03 −0.04	0.125+0.119 −0.087	—	—
b	5.792+0.469 −0.477 MJ	1.735+0.056 −0.060	1051.4±0.4	0.319±0.003	48.919+3.312 −2.781°	—
c	13.492+1.046 −1.127 MJ	9.726+0.629 −0.793	13921.4+1238.4 −1518.2	0.295+0.033 −0.049	33.690+1.362 −1.324°	—

See also

• Gliese 581
• Gliese 876

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. S2CID 18759600. Archived from the original on 2019-12-07. Retrieved 2012-11-04. Vizier catalog entry Archived 2022-05-31 at the Wayback Machine
2. Suárez Mascareño, A.; et al. (September 2015), "Rotation periods of late-type dwarf stars from time series high-resolution spectroscopy of chromospheric indicators", Monthly Notices of the Royal Astronomical Society, 452 (3): 2745–2756, arXiv:1506.08039, Bibcode:2015MNRAS.452.2745S, doi:10.1093/mnras/stv1441, S2CID 119181646.
3. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
4. Pineda, J. Sebastian; Youngblood, Allison; France, Kevin (September 2021). "The M-dwarf Ultraviolet Spectroscopic Sample. I. Determining Stellar Parameters for Field Stars". The Astrophysical Journal. 918 (1): 23. arXiv:2106.07656. Bibcode:2021ApJ...918...40P. doi:10.3847/1538-4357/ac0aea. S2CID 235435757. 40.
5. Forveille, Thierry; Bonfils, Xavier; Lo Curto, Gaspare; Delfosse, Xavier; Udry, Stéphane; Bouchy, François; Lovis, Christophe; Mayor, Michel; Moutou, Claire; Naef, Dominique; Pepe, Francesco (February 2011). "The HARPS search for southern extra-solar planets: XXVIII. Two giant planets around M0 dwarfs". Astronomy & Astrophysics. 526: A141. arXiv:1012.1168. Bibcode:2011A&A...526A.141F. doi:10.1051/0004-6361/201016034. ISSN 0004-6361.
6. Anglada-Escudé, Guillem; Tuomi, Mikko (2012). "A planetary system with gas giants and super-Earths around the nearby M dwarf GJ 676A. Optimizing data analysis techniques for the detection of multi-planetary systems" (PDF). Astronomy. 548: A58. arXiv:1206.7118. Bibcode:2012A&A...548A..58A. doi:10.1051/0004-6361/201219910. S2CID 17115882.^{[permanent dead link‍]}
7. Anglada-Escudé, Guillem; Butler, R. Paul (2012). "The HARPS-TERRA Project. I. Description of the Algorithms, Performance, and New Measurements on a Few Remarkable Stars Observed by HARPS". The Astrophysical Journal Supplement Series. 200 (2): 15. arXiv:1202.2570. Bibcode:2012ApJS..200...15A. doi:10.1088/0067-0049/200/2/15. S2CID 118528839.
8. Sahlmann, J.; Lazorenko, P. F.; Ségransan, D.; Astudillo-Defru, N.; Bonfils, X.; Delfosse, X.; Forveille, T.; Hagelberg, J.; Lo Curto, G.; Pepe, F.; Queloz, D.; Udry, S.; Zimmerman, N. T. (2016), "The mass of planet GJ 676A b from ground-based astrometry", Astronomy & Astrophysics, 595: A77, arXiv:1608.00918, doi:10.1051/0004-6361/201628854, S2CID 118480445
9. Feng, Fabo; Butler, R. Paul; et al. (August 2022). "3D Selection of 167 Substellar Companions to Nearby Stars". The Astrophysical Journal Supplement Series. 262 (21): 21. arXiv:2208.12720. Bibcode:2022ApJS..262...21F. doi:10.3847/1538-4365/ac7e57. S2CID 251864022.