# HN Librae

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Star in the constellation Libra

HN Librae A visual band light curve for HN Librae, adapted from Weis (1994)[1] 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[5] 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 HN Lib, BD−11 3759, GJ 555, HIP 71253, Ci 20 870, LFT 1120, LHS 2945, LPM 532, LTT 5759, NLTT 37751, PLX 3296, PM 14316-1219, Wolf 1481, TYC 5572-804-1, GSC 05572-00804, 2MASS J14341683-1231106[6] Database references SIMBAD data Exoplanet Archive data HN Librae Location of HN Librae in the constellation Libra

**HN Librae**, also known as **Gliese 555**, is a [red dwarf](/source/Red_dwarf) with at least one orbiting [exoplanet](/source/Exoplanet) in the constellation [Libra](/source/Libra_(constellation)). With an [apparent visual magnitude](/source/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](/source/Light_year) (6.25 [parsecs](/source/Parsec)) based on [parallax measurements](/source/Stellar_parallax), but is drifting closer to the Sun with a [radial velocity](/source/Radial_velocity) of −1.4 km/s.[2] It does not appear to belong to any known stellar [moving group](/source/Moving_group) or association.[4]

This is an [M-type main-sequence star](/source/M-type_main-sequence_star), a red dwarf, with a [stellar classification](/source/Stellar_classification) of M4.0V. The [chromosphere](/source/Chromosphere) of this star is weakly [active](/source/Magnetic_activity), causing [starspots](/source/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](/source/Photosphere) at an [effective temperature](/source/Effective_temperature) of 3,347 K. The star is spinning slowly with a [rotation period](/source/Rotation_period) of around 96 days.[4]

## Planetary system

In 2019, one planet candidate detected by [radial velocity](/source/Doppler_spectroscopy) was reported in a [preprint](/source/Preprint) (never accepted for publication as of 2024), among 118 planets around [M dwarf stars](/source/Red_dwarf). This would have a [minimum mass](/source/Minimum_mass) about 30 times that of Earth and orbit with a period of about 450 days.[7]

However, later radial velocity observations by the [CARMENES survey](/source/CARMENES_survey) published in 2023 did not confirm a planet at this period, but instead found a different planet.[8] This is a [super-Earth](/source/Super-Earth) or [mini-Neptune](/source/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](/source/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]

The HN Librae planetary system[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 — — —

## References

1. **[^](#cite_ref-Weis_1-0)** Weis, Edward W. (March 1994). ["Long Term Variability in Dwarf M Stars"](https://ui.adsabs.harvard.edu/abs/1994AJ....107.1135W). *The Astronomical Journal*. **107**: 1135–1140. [Bibcode](/source/Bibcode_(identifier)):[1994AJ....107.1135W](https://ui.adsabs.harvard.edu/abs/1994AJ....107.1135W). [doi](/source/Doi_(identifier)):[10.1086/116925](https://doi.org/10.1086%2F116925). [Archived](https://web.archive.org/web/20220301120151/https://ui.adsabs.harvard.edu/abs/1994AJ....107.1135W) from the original on 1 March 2022. Retrieved 20 January 2022.

1. ^ [***a***](#cite_ref-GaiaDR3_2-0) [***b***](#cite_ref-GaiaDR3_2-1) [***c***](#cite_ref-GaiaDR3_2-2) [***d***](#cite_ref-GaiaDR3_2-3) [***e***](#cite_ref-GaiaDR3_2-4) [***f***](#cite_ref-GaiaDR3_2-5) Vallenari, A.; et al. (Gaia collaboration) (2023). ["*Gaia* Data Release 3. Summary of the content and survey properties"](https://doi.org/10.1051%2F0004-6361%2F202243940). *Astronomy and Astrophysics*. **674**: A1. [arXiv](/source/ArXiv_(identifier)):[2208.00211](https://arxiv.org/abs/2208.00211). [Bibcode](/source/Bibcode_(identifier)):[2023A&A...674A...1G](https://ui.adsabs.harvard.edu/abs/2023A&A...674A...1G). [doi](/source/Doi_(identifier)):[10.1051/0004-6361/202243940](https://doi.org/10.1051%2F0004-6361%2F202243940). [S2CID](/source/S2CID_(identifier)) [244398875](https://api.semanticscholar.org/CorpusID:244398875). [Gaia DR3 record for this source](https://vizier.cds.unistra.fr/viz-bin/VizieR-4?-source=+I%2F355&-from=nav&-nav=cat%3AI%2F355%26tab%3A%7BI%2F355%2Fgaiadr3%7D%26key%3Asource%3D1355%2Fgaiadr3%26HTTPPRM%3A%26-out.add%3D.%26Source%3D%3D%3D6324325225803432320%26-go+%25%23Sesame%23%25%26) at [VizieR](/source/VizieR).

1. ^ [***a***](#cite_ref-Anderson_Francis_2012_3-0) [***b***](#cite_ref-Anderson_Francis_2012_3-1) [***c***](#cite_ref-Anderson_Francis_2012_3-2) [***d***](#cite_ref-Anderson_Francis_2012_3-3) Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". *Astronomy Letters*. **38** (5): 331. [arXiv](/source/ArXiv_(identifier)):[1108.4971](https://arxiv.org/abs/1108.4971). [Bibcode](/source/Bibcode_(identifier)):[2012AstL...38..331A](https://ui.adsabs.harvard.edu/abs/2012AstL...38..331A). [doi](/source/Doi_(identifier)):[10.1134/S1063773712050015](https://doi.org/10.1134%2FS1063773712050015). [S2CID](/source/S2CID_(identifier)) [119257644](https://api.semanticscholar.org/CorpusID:119257644).

1. ^ [***a***](#cite_ref-González-Álvarez2023_4-0) [***b***](#cite_ref-González-Álvarez2023_4-1) [***c***](#cite_ref-González-Álvarez2023_4-2) [***d***](#cite_ref-González-Álvarez2023_4-3) [***e***](#cite_ref-González-Álvarez2023_4-4) [***f***](#cite_ref-González-Álvarez2023_4-5) [***g***](#cite_ref-González-Álvarez2023_4-6) González-Álvarez, E.; Kemmer, J.; et al. (July 2023). "The CARMENES search for exoplanets around M dwarfs. A sub-Neptunian mass planet in the habitable zone of HN Lib". *[Astronomy & Astrophysics](/source/Astronomy_%26_Astrophysics)*. **675**: A141. [arXiv](/source/ArXiv_(identifier)):[2305.19677](https://arxiv.org/abs/2305.19677). [Bibcode](/source/Bibcode_(identifier)):[2023A&A...675A.141G](https://ui.adsabs.harvard.edu/abs/2023A&A...675A.141G). [doi](/source/Doi_(identifier)):[10.1051/0004-6361/202346276](https://doi.org/10.1051%2F0004-6361%2F202346276).

1. **[^](#cite_ref-gcvs_5-0)** Samus', N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (2017). "General catalogue of variable stars: Version GCVS 5.1". *Astronomy Reports*. **61** (1): 80. [Bibcode](/source/Bibcode_(identifier)):[2017ARep...61...80S](https://ui.adsabs.harvard.edu/abs/2017ARep...61...80S). [doi](/source/Doi_(identifier)):[10.1134/S1063772917010085](https://doi.org/10.1134%2FS1063772917010085).

1. **[^](#cite_ref-SIMBAD_6-0)** ["BD-11 3759"](http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=BD-11+3759). *[SIMBAD](/source/SIMBAD)*. [Centre de données astronomiques de Strasbourg](/source/Centre_de_donn%C3%A9es_astronomiques_de_Strasbourg). Retrieved 2023-12-09.

1. **[^](#cite_ref-Tuomi2019_7-0)** Barnes, J. R.; et al. (2019-06-11). "Frequency of planets orbiting M dwarfs in the Solar neighbourhood". [arXiv](/source/ArXiv_(identifier)):[1906.04644](https://arxiv.org/abs/1906.04644) [[astro-ph.EP](https://arxiv.org/archive/astro-ph.EP)].

1. **[^](#cite_ref-Ribas2023_8-0)** Ribas, I.; Reiners, A.; et al. (February 2023). "The CARMENES search for exoplanets around M dwarfs. Guaranteed time observations Data Release 1 (2016-2020)". *[Astronomy & Astrophysics](/source/Astronomy_%26_Astrophysics)*. **670**: A139. [arXiv](/source/ArXiv_(identifier)):[2302.10528](https://arxiv.org/abs/2302.10528). [Bibcode](/source/Bibcode_(identifier)):[2023A&A...670A.139R](https://ui.adsabs.harvard.edu/abs/2023A&A...670A.139R). [doi](/source/Doi_(identifier)):[10.1051/0004-6361/202244879](https://doi.org/10.1051%2F0004-6361%2F202244879).

v t e Constellation of Libra List of stars in Libra Libra in Chinese astronomy Stars Bayer α1 α2 (Zubenelgenubi) β (Zubeneschamali) γ (Zubenelhakrabi) δ ε ζ1 ζ2 ζ3 ζ4 η θ ι1 ι2 κ λ μ ν ξ1 ξ2 ο σ (Brachium) τ υ Flamsteed 2 3 4 5 10 11 12 16 17 18 22 23 26 28 30 36 37 41 42 47 48 49 50 Variable HN HO KU KX HR 5504 5455 HD 133131 134439 134440 135485 137010 139139 140283 141569 141937 Other 2M1510 2MASS 1507−1627 CWISEP J1446−2317 HE 1523−0901 WASP-57 WISE 1534−1043 WISE 1541−2250 Exoplanets 23 Librae b c Gliese 581b c e HD 137010 b (unconfirmed) K2-315b WASP-189b Star clusters NGC 5897 Galaxies NGC 5597 5605 5716 5728 5792 5793 5861 5885 5890 5898 5915 5917 Other AP Librae IC 1059 IRAS 14348−1447 PKS 1510−089 PKS 1519−273 QSO B1524−136 RXC J1504.1−0248 BCG Category

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Adapted from the Wikipedia article [HN Librae](https://en.wikipedia.org/wiki/HN_Librae) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/HN_Librae?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.