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Star in the constellation Libra From Wikipedia, the free encyclopedia
HN Librae, also known as Gliese 555, is a small star with one or more orbiting exoplanets in the constellation Libra. With an apparent visual magnitude of 11.32,[3] it can only be viewed through a telescope. The system is located at a distance of 20.4 light years based on parallax measurements, but is drifting closer to the Sun with a radial velocity of −1.4 km/s.[2] It does not appear to belong to any known stellar moving group or association.[4]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Libra |
| Right ascension | 14h 34m 16.81166s[2] |
| Declination | −12° 31′ 10.4145″[2] |
| Apparent magnitude (V) | 11.32[3] |
| Characteristics | |
| Spectral type | M4.0V[4] |
| B−V color index | 1.633±0.052[3] |
| Variable type | BY Dra |
| Astrometry | |
| Radial velocity (Rv) | −1.36±0.20[2] km/s |
| Proper motion (μ) | RA: −355.138 mas/yr[2] Dec.: 593.040 mas/yr[2] |
| Parallax (π) | 159.9225 ± 0.0546 mas[2] |
| Distance | 20.395 ± 0.007 ly (6.253 ± 0.002 pc) |
| Absolute magnitude (MV) | 12.41[3] |
| Details[4] | |
| Mass | 0.291±0.013 M☉ |
| Radius | 0.299±0.009 R☉ |
| Luminosity (bolometric) | 0.010106±0.000069 L☉ |
| Surface gravity (log g) | 4.76±0.13 cgs |
| Temperature | 3347±50 K |
| Metallicity [Fe/H] | −0.18±0.15 dex |
| Rotation | 96±2 d |
| Rotational velocity (v sin i) | <2.0 km/s |
| Age | 0.8–8.0 Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
  HN Librae Location of HN Librae in the constellation Libra | |
This is an M-type main-sequence star, a red dwarf, with a stellar classification of M4.0V. The chromosphere of this star is weakly active, causing starspots that vary the stellar luminosity as it rotates.[4] It has 29% of the mass of the Sun and 30% of the Sun's girth. On average, the star is radiating just 1% of the luminosity of the Sun from its photosphere at an effective temperature of 3,347 K. The star is spinning slowly with a rotation period of around 96 days.[4]
In 2019, one planet candidate detected by radial velocity was reported in a preprint (never accepted for publication as of 2024), among 118 planets around M dwarf stars. This would have a minimum mass about 30 times that of Earth and orbit with a period of about 450 days.[6]
However, later radial velocity observations by the CARMENES survey published in 2023 did not confirm a planet at this period, but instead found a different planet.[7] This is a super-Earth or mini-Neptune (the discovery paper uses the term "sub-Neptune") with a minimum mass of 5.5 Earths and a period of 36 days, placing it within the habitable zone. A second planet candidate was also found, with a minimum mass of 9.7 Earths and a period of 113 days, but this signal could not be confirmed as having a planetary origin due to its similarity to the rotation period of the star.[4]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | ≥5.46±0.75 M🜨 | 0.1417±0.0023 | 36.116+0.027 −0.029 |
0.079+0.090 −0.055 |
— | — |
| c (unconfirmed) | ≥9.7±1.9 M🜨 | 0.3040+0.0048 −0.0051 |
113.46+0.19 −0.20 |
— | — | — |
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