Gliese 176

Gliese 176

Observation data Epoch J2000.0       Equinox J2000.0
Constellation	Taurus
Right ascension	04h 42m 55.7750s [1]
Declination	+18° 57′ 29.396″ [1]
Apparent magnitude  (V)	9.95 [2]
Characteristics
Spectral type	M2V [3]
B−V color index	1.523±0.025 [4]
Variable type	None [5]
Astrometry
Radial velocity (Rv)	26.4105±0.0004 [3] km/s
Proper motion (μ)	RA: +656.647 [1] mas/yr Dec.: −1116.594 [1] mas/yr
Parallax (π)	105.4275±0.0210  mas [1]
Distance	30.937 ± 0.006  ly (9.485 ± 0.002  pc)
Absolute magnitude  (MV)	10.10±0.06 [3]
Details
Mass	0.485±0.012 [6]   M☉
Radius	0.474±0.015 [6]   R☉
Luminosity	0.03516±0.00032 [6]   L☉
Temperature	3,632+58 −56 [6]   K
Metallicity [Fe/H]	−0.1±0.2 [3]   dex
Rotation	40.00±0.11 [3] days
Rotational velocity (v sin i)	≤0.8 [3]  km/s
Age	8.8+2.5 −2.8 [5]   Gyr
Other designations
BD+18°683, HD 285968, HIP 21932, Ross 33, 2MASS J04425581+1857285
Database references
SIMBAD	data
Exoplanet Archive	data

Gliese 176 is a small star with an orbiting exoplanet in the constellation of Taurus. With an apparent visual magnitude of 9.95, ^[2] it is too faint to be visible to the naked eye. It is located at a distance of 30.9  light years based on parallax measurements, ^[1] and is drifting further away with a heliocentric radial velocity of 26.4 km/s. ^[3]

This is an M-type main-sequence star, sometimes called a red dwarf, with a stellar classification of M2V. ^[3] It has 49% of the Sun's mass and 47% of the radius of the Sun. The star is radiating just 3.5% of the luminosity of the Sun from its photosphere at an effective temperature of 3,632 K. It is estimated to be around nine billion years old, ^[5] and is spinning slowly with a rotation period of 40 days. The star is orbited by a Super-Earth.

Planetary system

A planetary companion to Gliese 176 was announced in 2008. ^[7] Radial velocity observations with the Hobby-Eberly Telescope (HET) showed a 10.24-day periodicity, which was interpreted as being caused by a planet. With a semi-amplitude of 11.6 m/s, its minimum mass equated to 24.5 Earth masses, or approximately 1.4 Neptune masses.

Observations with the HARPS spectrograph could not confirm the 10.24-day variation. ^[3] Instead, two other periodicities were detected at 8.78 and 40.0 days, with amplitudes below the HET observational errors. The 40-day variation coincides with the rotational period of the star and is therefore caused by activity, but the shorter-period variation is not explained by activity and is therefore caused by a planet. Its semi-amplitude of 4.1 m/s corresponds to a minimum mass of 8.4 Earth masses, making the planet a Super-Earth.

In an independent study, observations with Keck-HIRES also failed to confirm the 10.24-day signal. ^[8] An 8.77-day periodicity - corresponding to the planet announced by the HARPS team - was detected to intermediate significance, though it was not deemed significant enough to claim a planetary cause with their data alone.

The Gliese 176 planetary system ^[9]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	≥9.06+1.54 −0.70  M🜨	0.066±0.001	8.776+0.001 −0.002	0.148+0.249 −0.036	—	—

See also

• List of extrasolar planets
• Gliese 674

References

1. 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.
2. Koen, C.; Kilkenny, D.; van Wyk, F.; Marang, F. (2010). "UBV(RI)_C JHK observations of Hipparcos-selected nearby stars". Monthly Notices of the Royal Astronomical Society . 403 (4): 1949–1968. Bibcode:2010MNRAS.403.1949K. doi: 10.1111/j.1365-2966.2009.16182.x .
3. Forveille, Thierry; Bonfils, Xavier; Delfosse, Xavier; Gillon, Michaël; Udry, Stéphane; Bouchy, François; Lovis, Christophe; Mayor, Michel; Pepe, Francesco; Perrier, Christian; Queloz, Didier; Santos, Nuno C.; Bertaux, Jean-Loup (2009). "The HARPS search for southern extra-solar planets. XIV. Gl 176b, a super-Earth rather than a Neptune, and at a different period". Astronomy and Astrophysics. 493 (2): 645–650. arXiv: 0809.0750 . Bibcode:2009A&A...493..645F. doi:10.1051/0004-6361:200810557. S2CID   115697713. Archived from the original on 2021-02-27. Retrieved 2018-03-16.
4. 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 2013-09-11.
5. Brown, Alexander; et al. (May 2023). "Coronal X-Ray Emission from Nearby, Low-mass, Exoplanet Host Stars Observed by the MUSCLES and Mega-MUSCLES HST Treasury Survey Projects". The Astronomical Journal. 165 (5): 195. arXiv: 2303.12929 . Bibcode:2023AJ....165..195B. doi: 10.3847/1538-3881/acc38a . 195.
6. Pineda, J. Sebastian; et al. (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.
7. Endl, Michael; et al. (2008). "An m sin i = 24 M_🜨 Planetary Companion to the Nearby M Dwarf GJ 176". The Astrophysical Journal. 673 (2): 1165–1168. arXiv: 0709.0944 . Bibcode:2008ApJ...673.1165E. doi:10.1086/524703. S2CID   118332426.
8. Butler, R. Paul; et al. (2009). "Nondetection of the Neptune-Mass Planet Reported Around GJ 176". The Astrophysical Journal. 691 (2): 1738–1743. Bibcode:2009ApJ...691.1738B. doi: 10.1088/0004-637X/691/2/1738 .
9. Trifonov, Trifon; Kürster, Martin; Zechmeister, Mathias; Tal-Or, Lev; Caballero, José A.; Quirrenbach, Andreas; Amado, Pedro J.; Ribas, Ignasi; Reiners, Ansgar; et al. (2018). "The CARMENES search for exoplanets around M dwarfs. First visual-channel radial-velocity measurements and orbital parameter updates of seven M-dwarf planetary systems". Astronomy and Astrophysics. 609. A117. arXiv: 1710.01595 . Bibcode:2018A&A...609A.117T. doi:10.1051/0004-6361/201731442. S2CID   119340839.