Gliese 555

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
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]
Distance20.395 ± 0.007 ly
(6.253 ± 0.002 pc)
Absolute magnitude (MV)12.41[3]
Details[4]
Mass0.291±0.013 M☉
Radius0.299±0.009 R☉
Luminosity (bolometric)0.010106±0.000069 L☉
Surface gravity (log g)4.76±0.13 cgs
Temperature3347±50 K
Metallicity [Fe/H]−0.18±0.15 dex
Rotation96±2 d
Rotational velocity (v sin i)<2.0 km/s
Age0.8–8.0 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[5]
Database references
SIMBADdata
Gliese 555 is located in the constellation Libra
Gliese 555 is located in the constellation Libra
Gliese 555
Location of Gliese 555 in the constellation Libra

Gliese 555 is a small star with one or more orbiting exoplanets in the constellation Libra. It has the variable star designation HN Librae, abbreviated HM Lib. 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]

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]

Planetary system

In 2019, one planet candidate detected by radial velocity was reported in a preprint, 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]

The Gliese 555 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. ↑ Weis, Edward W. (March 1994). "Long Term Variability in Dwarf M Stars". The Astronomical Journal. 107: 1135–1140. Bibcode:1994AJ....107.1135W. doi:10.1086/116925. Retrieved 20 January 2022.
  2. 1 2 3 4 5 6 7 Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  3. 1 2 3 4 Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
  4. 1 2 3 4 5 6 7 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. 675: A141. arXiv:2305.19677. Bibcode:2023A&A...675A.141G. doi:10.1051/0004-6361/202346276.
  5. ↑ "BD-11 3759". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2023-12-09.
  6. ↑ Barnes, J. R.; et al. (2019-06-11). "Frequency of planets orbiting M dwarfs in the Solar neighbourhood". arXiv:1906.04644 [astro-ph.EP].
  7. ↑ 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. 670: A139. arXiv:2302.10528. Bibcode:2023A&A...670A.139R. doi:10.1051/0004-6361/202244879.
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