Gliese 176
Star in the constellation Taurus
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Gliese 176 is a small star with an orbiting exoplanet in the constellation of Taurus. With an apparent visual magnitude of 9.95,[3] it is too faint to be visible to the naked eye but is the nearest star in the constellation, with a distance of 30.9 light years based on parallax measurements,[2] and is drifting further away with a heliocentric radial velocity of 26.4 km/s.[4]
| Observation data Epoch J2000.0 Equinox ICRS | |
|---|---|
| Constellation | Taurus[1] |
| Right ascension | 04h 42m 55.7750s[2] |
| Declination | +18° 57′ 29.396″[2] |
| Apparent magnitude (V) | 9.95[3] |
| Characteristics | |
| Spectral type | M2V[4] |
| B−V color index | 1.523±0.025[5] |
| Variable type | None[6] |
| Astrometry | |
| Radial velocity (Rv) | 26.4105±0.0004[4] km/s |
| Proper motion (μ) | RA: +656.647[2] mas/yr Dec.: −1116.594[2] mas/yr |
| Parallax (π) | 105.4275±0.0210 mas[2] |
| Distance | 30.937 ± 0.006 ly (9.485 ± 0.002 pc) |
| Absolute magnitude (MV) | 10.10±0.06[4] |
| Details | |
| Mass | 0.485±0.012[7] M☉ |
| Radius | 0.474±0.015[7] R☉ |
| Luminosity | 0.03516±0.00032[7] L☉ |
| Temperature | 3,632+58 −56[7] K |
| Metallicity [Fe/H] | −0.1±0.2[4] dex |
| Rotation | 40.00±0.11[4] days |
| Rotational velocity (v sin i) | ≤0.8[4] km/s |
| Age | 8.8+2.5 −2.8[6] Gyr |
| Other designations | |
| BD+18°683, HD 285968, HIP 21932, Ross 33, 2MASS J04425581+1857285 | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
This is an M-type main-sequence star, sometimes called a red dwarf, with a stellar classification of M2V.[4] 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,[6] 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.[8] 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.[4] 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.[9] 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.
| 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 |
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