Gliese 176

Gliese 176 is a red dwarf in the constellation of Taurus. Based upon parallax measurements from the Hipparcos mission, it is located approximately 30 light-years away.[1] The star is orbited by a Super-Earth.

Gliese 176
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Taurus
Right ascension  04h 42m 55.7749s[1]
Declination +18° 57′ 29.399″[1]
Apparent magnitude (V) 9.95
Characteristics
Spectral type M2V[2]
B−V color index 1.523 ± 0.025[3]
Variable type BY Dra
Astrometry
Radial velocity (Rv)26.4105 ± 0.0004[2] km/s
Proper motion (μ) RA: 656.744±0.166[1] mas/yr
Dec.: −1116.790±0.104[1] mas/yr
Parallax (π)106.32 ± 0.60[1] mas
Distance30.7 ± 0.2 ly
(9.41 ± 0.05 pc)
Absolute magnitude (MV)10.10 ± 0.06[2]
Details
Mass0.50 ± 0.03[4] M☉
Radius0.4525±0.0221[5] R☉
Luminosity0.0337±0.0018[5] L☉
Temperature3679±77[5] K
Metallicity [Fe/H]–0.1 ± 0.2[2] dex
Rotation40.00 ± 0.11[2] days
Rotational velocity (v sin i)≤0.8[2] km/s
Age0.56 Gyr
Other designations
BD+18° 683, HD 285968, HIP 21932, Ross 33
Database references
SIMBADdata
Extrasolar Planets
Encyclopaedia		data

Planetary system

A planetary companion to Gliese 176 was announced in 2008.[6] 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.[2] 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.[7] 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[8]
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		 — —
gollark: Well, isn't comparatively bad.
gollark: Just because something *isn't bad now* doesn't mean it can't be bad *later*.
gollark: I was talking about <@665664987578236961>'s "the flu is worse" thing.
gollark: That... no.
gollark: It'll be *worse* if it *spreads more*.

See also

References
  1. Brown, A. G. A.; et al. (2016). "Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties". Astronomy and Astrophysics. 595. A2. arXiv:1609.04172. Bibcode:2016A&A...595A...2G. doi:10.1051/0004-6361/201629512.Gaia Data Release 1 catalog entry
  2. Forveille, T.; et al. (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.
  3. 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.
  4. Neves, V.; et al. (March 2013). "Metallicity of M dwarfs. III. Planet-metallicity and planet-stellar mass correlations of the HARPS GTO M dwarf sample". Astronomy and Astrophysics. 551: A36. arXiv:1212.3372. Bibcode:2013A&A...551A..36N. doi:10.1051/0004-6361/201220574.
  5. von Braun, Kaspar; et al. (2014). "Stellar diameters and temperatures - V. 11 newly characterized exoplanet host stars". Monthly Notices of the Royal Astronomical Society. 438 (3): 2413–2425. arXiv:1312.1792. Bibcode:2014MNRAS.438.2413V. doi:10.1093/mnras/stt2360.
  6. 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.
  7. 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.
  8. Trifonov, T.; 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.

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