HN Librae

{{Short description|Star in the constellation Libra}} {{Sky|14|34|16.81183|-|12|31|10.3965|20.395}} {{Starbox begin}} {{Starbox image | image = [[Image:HNLibLightCurve.png|300px]] | caption = A [[Photometric_system#Photometric_letters|visual band]] [[light curve]] for HN Librae, adapted from Weis (1994)<ref name="Weis"/> }} {{Starbox observe | epoch = [[J2000.0]] | constell = [[Libra (constellation)|Libra]] | ra = {{RA|14|34|16.81166}}<ref name="GaiaDR3"/> | dec = {{DEC|−12|31|10.4145}}<ref name="GaiaDR3"/> | appmag_v = 11.32<ref name=Anderson_Francis_2012/> }} {{Starbox character | class = M4.0V<ref name="González-Álvarez2023"/> | b-v = 1.633{{±|0.052}}<ref name=Anderson_Francis_2012/> | u-b = | variable = [[BY Draconis variable|BY Dra]]<ref name=gcvs/> }} {{Starbox astrometry | radial_v = {{val|-1.36|0.20}}<ref name="GaiaDR3"/> | prop_mo_ra = {{val|-355.138}} | prop_mo_dec = {{val|593.040}} | pm_footnote = <ref name="GaiaDR3"/> | parallax = 159.9225 | p_error = 0.0546 | parallax_footnote = <ref name="GaiaDR3"/> | absmag_v = 12.41<ref name=Anderson_Francis_2012/> }} {{Starbox detail | source = <ref name="González-Álvarez2023"/> | mass = {{val|0.291|0.013}} | radius = {{val|0.299|0.009}} | luminosity_bolometric = {{val|0.010106|0.000069}} | gravity = {{val|4.76|0.13}} | temperature = {{val|3347|50}} | metal_fe = {{val|−0.18|0.15}} | rotation = {{val|96|2|ul=d}} | rotational_velocity = <2.0 | age_gyr = 0.8–8.0 }} {{Starbox catalog | names={{Odlist | V=HN Lib | BD=-11 3759 | GJ=555 | Wolf=1481 | Ci 20=870 | LHS=2945 | LFT=1120 | LPM=532 | LTT=5759 | NLTT=37751 | PM=14316-1219 | PLX=3296 | HIP=71253 | TYC=5572-804-1 | GSC=05572-00804 | 2MASS=J14341683-1231106 }}<ref name="SIMBAD"/> }} {{Starbox reference | Simbad=Gliese+555 | NSTED=GJ-555 }} {{Starbox image | image={{Location map|100x100|AlternativeMap=Libra_constellation_map.svg | alt=HN Librae is located in the constellation Libra | caption=Location of HN Librae in the constellation [[Libra (constellation)|Libra]]|border=infobox|mark=Red_pog.png|width=300 | label=HN Librae | lat=65.2 | long=78.7 }}|caption= }} {{Starbox end}}

'''HN Librae''', also known as '''Gliese 555''', is a [[red dwarf]] with at least one orbiting [[exoplanet]] in the constellation [[Libra (constellation)|Libra]]. With an [[apparent visual magnitude]] of 11.32,<ref name=Anderson_Francis_2012/> it can only be viewed through a telescope. The system is located at a distance of 20.4 [[light year]]s (6.25 [[Parsec|parsecs]]) based on [[stellar parallax|parallax measurements]], but is drifting closer to the Sun with a [[radial velocity]] of −1.4 km/s.<ref name="GaiaDR3"/> It does not appear to belong to any known stellar [[moving group]] or association.<ref name="González-Álvarez2023"/>

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 [[magnetic activity|active]], causing [[starspots]] that vary the stellar luminosity as it rotates.<ref name="González-Álvarez2023"/> 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.<ref name="González-Álvarez2023"/>

==Planetary system== In 2019, one planet candidate detected by [[Doppler spectroscopy|radial velocity]] was reported in a [[preprint]] (never accepted for publication as of 2024), among 118 planets around [[Red dwarf|M dwarf stars]]. This would have a [[minimum mass]] about 30 times that of Earth and orbit with a period of about 450 days.<ref name="Tuomi2019"/>

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.<ref name="Ribas2023"/> 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.<ref name="González-Álvarez2023"/>

{{OrbitboxPlanet begin | table_ref = <ref name="González-Álvarez2023"/> }} {{OrbitboxPlanet | exoplanet = b | mass_earth = {{val|5.46|0.75|p=≥}} | period = {{val|36.116|0.027|0.029}} | semimajor = {{val|0.1417|0.0023}} | eccentricity = {{val|0.079|0.090|0.055}} }} {{OrbitboxPlanet hypothetical | exoplanet = c | mass_earth = {{val|9.7|1.9|p=≥}} | period = {{val|113.46|0.19|0.20}} | semimajor = {{val|0.3040|0.0048|0.0051}} | eccentricity = }} {{Orbitbox end}}

==References== <references> <ref name="GaiaDR3">{{Cite Gaia DR3|6324325225803432320}}</ref>

<ref name="SIMBAD">{{cite simbad | title=BD-11 3759 | access-date=2023-12-09}}</ref>

<ref name=gcvs>{{cite journal |bibcode=2017ARep...61...80S |title=General catalogue of variable stars: Version GCVS 5.1 |last1=Samus' |first1=N. N. |last2=Kazarovets |first2=E. V. |last3=Durlevich |first3=O. V. |last4=Kireeva |first4=N. N. |last5=Pastukhova |first5=E. N. |journal=Astronomy Reports |date=2017 |volume=61 |issue=1 |page=80 |doi=10.1134/S1063772917010085 }}</ref>

<ref name="Weis">{{cite journal |last1=Weis |first1=Edward W. |title=Long Term Variability in Dwarf M Stars |journal=The Astronomical Journal |date=March 1994 |volume=107 |pages=1135–1140 |doi=10.1086/116925 |bibcode=1994AJ....107.1135W |url=https://ui.adsabs.harvard.edu/abs/1994AJ....107.1135W |access-date=20 January 2022 |archive-date=1 March 2022 |archive-url=https://web.archive.org/web/20220301120151/https://ui.adsabs.harvard.edu/abs/1994AJ....107.1135W |url-status=live }}</ref>

<ref name="Tuomi2019">{{Cite arXiv|last1=Barnes|first1=J. R.|last2=Kiraga|first2=M.|last3=Diaz|first3=M.|last4=Berdiñas|first4=Z.|last5=Jenkins|first5=J. S.|last6=Keiser|first6=S.|last7=Thompson|first7=I.|last8=Crane|first8=J. D.|last9=Shectman|first9=S. A. | display-authors=1 |date=2019-06-11|title=Frequency of planets orbiting M dwarfs in the Solar neighbourhood|class=astro-ph.EP|eprint=1906.04644|language=en}}</ref>

<ref name="Ribas2023">{{cite journal |last1=Ribas |first1=I. |last2=Reiners |first2=A. |display-authors=etal |date=February 2023 |title=The CARMENES search for exoplanets around M dwarfs. Guaranteed time observations Data Release 1 (2016-2020) |journal=[[Astronomy & Astrophysics]] |volume=670 |issue= |pages=A139 |doi=10.1051/0004-6361/202244879 |arxiv=2302.10528 |bibcode=2023A&A...670A.139R}}</ref>

<ref name="González-Álvarez2023">{{cite journal |last1=González-Álvarez |first1=E. |last2=Kemmer |first2=J. |display-authors=etal |date=July 2023 |title=The CARMENES search for exoplanets around M dwarfs. A sub-Neptunian mass planet in the habitable zone of HN Lib |journal=[[Astronomy & Astrophysics]] |volume=675 |issue= |pages=A141 |doi=10.1051/0004-6361/202346276 |arxiv=2305.19677 |bibcode=2023A&A...675A.141G}}</ref>

<ref name=Anderson_Francis_2012>{{cite journal | last1=Anderson | first1=E. | last2=Francis | first2=Ch. | title=XHIP: An extended hipparcos compilation | journal=Astronomy Letters | volume=38 | issue=5 | pages=331 | year=2012 | bibcode=2012AstL...38..331A | arxiv=1108.4971 | doi=10.1134/S1063773712050015 | s2cid=119257644 }}</ref> </references>

[[Category:M-type main-sequence stars]] [[Category:Planetary systems with one confirmed planet]]  [[Category:Libra (constellation)]] [[Category:Durchmusterung objects|BD-11 3759]] [[Category:Gliese and GJ objects|0555]] [[Category:Hipparcos objects|071253]] [[Category:Wolf objects|1481]] [[Category:Objects with variable star designations|Librae, HN]] [[Category:BY Draconis variables]]