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]
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 | |
Database references | |
SIMBAD | data |
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.
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.
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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