View source for HR 858

{{Short description|Star in the constellation Fornax}}
{{Starbox begin}}
{{Starbox image
| image = [[File:HR858-tess-exoplanets.png|260px]]
| caption = Position of HR 858 in Fornax
| credit =
}}
{{Starbox observe
| constell    = [[Fornax]]
| epoch       = J2000.00
| ra          = {{RA|02|51|56.246}}<ref name=GaiaDR3/>
| dec         = {{DEC|-30|48|52.26}}<ref name=GaiaDR3/>
| appmag_v    = 6.382<ref name=tycho2/>
}}
{{Starbox character
| class       = [[Main sequence]]
| type        = F6V<ref name=nstars/> + M<ref name=tess/>
| b-v         = +0.484<ref name=xhip/>
| u-b         =
| variable    =
}}
{{Starbox astrometry
| radial_v    = {{val|+9.77|0.12}}<ref name=GaiaDR3/>
| prop_mo_ra  = {{val|123.435|(25)}}
| prop_mo_dec = {{val|105.996|(37)}}
| pm_footnote = <ref name=GaiaDR3/>
| parallax    = 31.5418
| p_error     = 0.0352
| parallax_footnote = <ref name=GaiaDR3/>
| absmag_v    = +3.82<ref name=xhip/>
}}
{{Starbox detail
| source      = <ref name="Bonfanti2024"/>
| component1  = A
| mass        = {{val|1.204|0.052}}
| radius      = {{val|1.258|0.019}}
| luminosity  = {{val|2.31|0.12}}
| gravity     = {{val|4.30|0.06}}
| temperature = {{val|6354|70|fmt=commas}}
| metal_fe    = {{val|0.025|0.050}}
| rotation    = {{val|6.7|1.3|ul=d}}
| rotational_velocity = {{val|7.5|0.2}}
| age_gyr     = {{val|2.0|0.6}}
| component2  = B
| radius2     = {{Val|0.17|0.04}}<ref name=tess/>
| temperature2 = {{Val|2800|300|fmt=commas}}<ref name=tess/>
}}
{{Starbox catalogue
| names = {{odlist | CD=-31°1148 | GC=3443 | HD=17926 | HIP=13363 | HR=858 | SAO=193951 | TIC=178155732 | TOI=396}}<ref name=SIMBAD/>
}}
{{Starbox reference
| Simbad = HR+858
}}
{{Starbox end
}}
'''HR 858''' (also known as '''HD 17926''' or '''TOI-396''') is a [[star]] with a [[planetary system]] located 103&nbsp;[[light-year]]s from the [[Sun]] in the southern [[constellation]] of [[Fornax]]. It has a yellow-white hue and is visible to the naked eye, but it is a challenge to see with an [[apparent visual magnitude]] of 6.4.<ref name=tycho2/> The star is drifting further away with a [[radial velocity]] of 10&nbsp;km/s.<ref name=GaiaDR3/> It has an [[absolute magnitude]] of +3.82.<ref name=xhip/>
This object is a slightly-[[stellar evolution|evolved]] [[F-type main-sequence star]] with a [[stellar classification]] of F6V,<ref name=nstars/> which indicates it is generating energy through [[stellar core|core]] [[hydrogen fusion]]. It is roughly two<ref name=Pace2013/>&nbsp;billion years old and is spinning with a [[projected rotational velocity]] of 8.3&nbsp;km/s. The star has 1.1 times the [[mass of the Sun]] and 1.3 times the [[Sun's radius]]. It is radiating 2.3 times the [[luminosity of the Sun]] from its [[photosphere]] at an [[effective temperature]] of 6,201&nbsp;K.<ref name=tess/>
A faint co-moving stellar companion, designated component B, at an angular separation of {{Val|8.4|ul=arcsecond}}. This corresponds to a projected separation of {{Val|270|ul=AU}}. It is a [[red dwarf]] star.<ref name=tess/>
==Planetary system==
In May 2019, HR 858 was announced to have at least 3 [[exoplanet]]s as observed by the [[transit method]] with the [[Transiting Exoplanet Survey Satellite]]. All three are orbiting close to the host star and are close in size, each about twice the radius of the Earth. Described as [[super-Earth]]s by their discovery paper,<ref name=tess/> measurements of their masses suggest that in terms of composition they may be better described as [[mini-Neptune|sub-Neptune]]s.<ref name="Bonfanti2024"/> Planets 'b' and 'c' may be in a 3:5 [[mean-motion resonance]].<ref name=tess/>
Further research measured the masses of the planets b and d using accurate [[Doppler spectroscopy|radial velocities]], giving masses of {{Earth mass|3.55 and 7.1}} as well as planetary densities of 2.44 and 4.9 [[g/cm3|g/cm<sup>3</sup>]]. The system displays significant [[transit timing variation]]s. The mass of planet c could not be measured using radial velocities, but it is constrained to be less than {{Earth mass|3.8}}, and a not very reliable value of {{earth mass|2.24}} was measured using TTVs.<ref name=Bonfanti2024/>
{{OrbitboxPlanet begin
| table_ref = <ref name="Bonfanti2024"/>{{efn|In the 2024 model of the system used here the orbits are assumed to be circular. The 2019 discovery paper finds upper limits on the planets' eccentricities of 0.30, 0.19, and 0.28, respectively.<ref name=tess/>}}
}}
{{OrbitboxPlanet
| exoplanet = b
| mass_earth = {{val|3.55|0.94|0.96}}
| period = {{val|3.585287|0.000009|0.000012}}
| semimajor = {{val|0.04888|0.00066}}
| eccentricity = 0
| inclination = {{val|85.98|0.26|0.25}}
| radius_earth = {{val|2.004|0.045|0.047}}
}}
{{OrbitboxPlanet
| exoplanet = c
| mass_earth = <3.8
| period = {{val|5.973865|0.000015|0.000016}}
| semimajor = {{val|0.06870|0.00092}}
| eccentricity = 0
| inclination = {{val|86.59|0.15|0.14}}
| radius_earth = {{val|1.979|0.054|0.051}}
}}
{{OrbitboxPlanet
| exoplanet = d
| mass_earth = {{val|7.1|1.6}}
| period = {{val|11.230511|0.000043|0.000045}}
| semimajor = {{val|0.1046|0.0014}}
| eccentricity = 0
| inclination = {{val|87.72|0.10|0.11}}
| radius_earth = {{val|2.001|0.063|0.064}}
}}
{{Orbitbox end}}
[[File:HR 858 System.jpg|thumb|Artist's impression of known planets in the HR 858 system and their size comparison with Earth]]
==Notes==
{{notelist}}
==References==
{{reflist|refs=
<ref name=SIMBAD>{{cite simbad | title=HR 858 | access-date=2019-12-04 }}</ref>
<ref name=GaiaDR3>{{Cite Gaia DR3|5064574724769475968}}</ref>
<ref name=tycho2>{{cite journal
| title=The Tycho-2 catalogue of the 2.5 million brightest stars
| display-authors=1 | last1=Høg | first1=E.
| last2=Fabricius | first2=C. | last3=Makarov | first3=V. V.
| last4=Urban | first4=S. | last5=Corbin | first5=T.
| last6=Wycoff | first6=G. | last7=Bastian | first7=U.
| last8=Schwekendiek | first8=P. | last9=Wicenec | first9=A.
| journal=Astronomy and Astrophysics
| volume=355 | pages=L27–L30 | date=March 2000
| bibcode=2000A&A...355L..27H | doi=10.1888/0333750888/2862}}</ref>
<ref name=tess>{{cite journal
| title=TESS Spots a Compact System of Super-Earths around the Naked-Eye Star HR 858
| journal=The Astrophysical Journal | volume=881 | issue=1 | pages=L19 | last1=Vanderburg | first1=Andrew | last2=Huang | first2=Chelsea X.
| last3=Rodriguez | first3=Joseph E. | last4=Becker | first4=Juliette C.
| last5=Ricker | first5=George R. | last6=Vanderspek | first6=Roland K.
| last7=Latham | first7=David W. | last8=Seager | first8=Sara
| last9=Winn | first9=Joshua N. | last10=Jenkins | first10=Jon M.
| last11=Addison | first11=Brett | last12=Bieryla | first12=Allyson
| last13=Briceño | first13=Cesar | last14=Bowler | first14=Brendan P.
| last15=Burke | first15=Christopher J. | last16=Burt | first16=Jennifer A.
| last17=Caldwell | first17=Douglas A. | last18=Clark | first18=Jake T.
| last19=Crossfield | first19=Ian | last20=Dittmann | first20=Jason A.
| last21=Dynes | first21=Scott | last22=Guerrero | first22=Natalia
| last23=Horner | first23=Jonathan | last24=Kane | first24=Stephen R.
| last25=Kielkopf | first25=John | last26=Kraus | first26=Adam L.
| last27=Law | first27=Nicolas | last28=Mann | first28=Andrew W.
| last29=Mengel | first29=Matthew W. | last30=Morton | first30=Timothy D.
| display-authors=1 | year=2019
| arxiv=1905.05193 | doi=10.3847/2041-8213/ab322d | bibcode=2019ApJ...881L..19V | s2cid=153311715 | doi-access=free }}</ref>
<ref name=nstars>{{cite journal | display-authors=1
| last1=Gray | first1=R. O. | last2=Corbally | first2=C. J.
| last3=Garrison | first3=R. F. | last4=McFadden | first4=M. T.
| last5=Bubar | first5=E. J. | last6=McGahee | first6=C. E.
| last7=O'Donoghue | first7=A. A. | last8=Knox | first8=E. R.
| title=Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample
| journal=[[The Astronomical Journal]]
| volume=132 | issue=1 | pages=161–170 | date=July 2006
| doi=10.1086/504637 | bibcode=2006AJ....132..161G
| arxiv=astro-ph/0603770 | s2cid=119476992 }}</ref>
<ref name=xhip>{{cite journal
| bibcode=2012AstL...38..331A
| doi=10.1134/S1063773712050015 | arxiv=1108.4971
| title=XHIP: An extended hipparcos compilation
| journal=Astronomy Letters
| volume=38 | issue=5 | pages=331 | year=2012
| last1=Anderson | first1=E. | last2=Francis | first2=Ch. | s2cid=119257644 }}</ref>
<ref name=Pace2013>{{cite journal
| last1=Pace | first1=G.
| title=Chromospheric activity as age indicator. An L-shaped chromospheric-activity versus age diagram
| journal=Astronomy & Astrophysics
| volume=551 | id=L8 | pages=4 | date=March 2013
| bibcode=2013A&A...551L...8P | arxiv=1301.5651
| doi=10.1051/0004-6361/201220364 | s2cid=56420519
}}</ref>
<ref name="Bonfanti2024">{{cite journal |last1=Bonfanti |first1=A. |last2=Amateis |first2=I. |last3=Gandolfi |first3=D. |last4=Borsato |first4=L. |last5=Egger |first5=J. A. |last6=Cubillos |first6=P. E. |last7=Armstrong |first7=D. |last8=Leão |first8=I. C. |last9=Fridlund |first9=M. |display-authors=2 |date=November 2024 |title=Radii, masses, and transit-timing variations of the three-planet system orbiting the naked-eye star TOI-396 |journal=[[Astronomy & Astrophysics]] |volume= |issue= |pages= |doi= |arxiv=2411.14911}}</ref>
}}
==External links==
* [https://in-the-sky.org/data/object.php?id=TYC7012-833-1 in-the-sky.org]
{{Fornax}}
{{DEFAULTSORT:HR 858}}
[[Category:F-type main-sequence stars]]
[[Category:Planetary systems with three confirmed planets]]
[[Category:Binary stars]]
[[Category:Fornax]]
[[Category:Durchmusterung objects|CD-31 1148]]
[[Category:Henry Draper Catalogue objects|017926]]
[[Category:Hipparcos objects|013363]]
[[Category:Bright Star Catalogue objects|0858]]
[[Category:M-type main-sequence stars]]
[[Category:TESS Objects of Interest|396]]