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. The star is orbited by a Super-Earth.
Epoch J2000.0 Equinox J2000.0
|Right ascension||04h 42m 55.7749s|
|Declination||+18° 57′ 29.399″|
|Apparent magnitude (V)||9.95|
|B−V color index||1.523 ± 0.025|
|Variable type||BY Dra|
|Radial velocity (Rv)||26.4105 ± 0.0004 km/s|
|Proper motion (μ)|| RA: 656.744±0.166 mas/yr |
Dec.: −1116.790±0.104 mas/yr
|Parallax (π)||105.4275 ± 0.0210 mas|
|Distance||30.937 ± 0.006 ly |
(9.485 ± 0.002 pc)
|Absolute magnitude (MV)||10.10 ± 0.06|
|Mass||0.50 ± 0.03 M☉|
|Metallicity [Fe/H]||–0.1 ± 0.2 dex|
|Rotation||40.00 ± 0.11 days|
|Rotational velocity (v sin i)||≤0.8 km/s|
A planetary companion to Gliese 176 was announced in 2008. 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. 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. 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.
(in order from star)