View source for 91 Aquarii

{{short description|Triple star system in the constellation Aquarius}}
{{redirect|ψ¹ Aquarii|other stars with this Bayer designation|ψ Aquarii}}
{{Starbox begin
 | name = 91 Aquarii
}}
{{Starbox image
 | image=
{{Location mark
|image=Aquarius constellation map.svg|alt=|float=center|width=280
|label=|position=right
|mark=Red circle.svg|mark_width=8|mark_link=ψ<sup>1</sup> Aqr
|x=238|y=470
}}
|caption=Location of ψ<sup>1</sup> Aquarii (circled)
}}
{{Starbox observe
| epoch       = J2000.0
| constell    = [[Aquarius (constellation)|Aquarius]]
| ra          = {{RA|23|15|53.49482}}<ref name=aaa474_2_653/>
| dec         = {{DEC|–9|05|15.8546}}<ref name=aaa474_2_653/>
| appmag_v    = +4.248<ref name=mnras172_667/>
}}
{{Starbox character
| class       = K1&nbsp;III<ref name="Baines2018"/>
| r-i         = 0.56<ref name="Viz"/>
| v-r         = 
| b-v         = +1.104<ref name=mnras172_667/>
| u-b         = +1.035<ref name=mnras172_667/>
| variable    =
}}
{{Starbox astrometry
 | radial_v    = {{val|-25.49|0.74}}<ref name=aj135_1_209/>
 | prop_mo_ra  = +368.78<ref name=aaa474_2_653/>
 | prop_mo_dec = –17.16<ref name=aaa474_2_653/>
 | parallax    = 21.77
 | p_error     = 0.29
 | parallax_footnote = <ref name=aaa474_2_653/>
 | absmag_v    = 0.919<ref name=Liu2007/>
}}
{{Starbox detail
| mass = {{val|1.38|0.29}}<ref name="Baines2018"/>
| radius = {{val|10.96|0.21}}<ref name="Baines2018"/>
| luminosity = {{val|54.3|3.1}}<ref name="Baines2018"/>
| gravity = 2.6<ref name=aj135_1_209/>
| temperature = {{val|4730|68}}<ref name="Baines2018"/>
| metal_fe = –0.14<ref name=aj135_1_209/>
| rotational_velocity = 2.9<ref name=aj135_1_209/>
| age_gyr = {{val|2.98|1.63}}<ref name="Baines2018"/>
}}
{{Starbox catalog
| names = Psi<sup>1</sup>&nbsp;Aquarii, [[Star catalogue#ADS|ADS]]&nbsp;16633, [[Star catalogue#Gl, GJ, Wo|Gl]]&nbsp;893.2, [[Washington Double Star Catalog|WDS]]&nbsp;J23159-0905
| component2 = A
| names2 = [[Star catalogue#BD/CD/CPD|BD]]–09&nbsp;6156, [[FK5]]&nbsp;1608, [[Henry Draper Catalogue|HD]]&nbsp;219449, [[Hipparcos catalogue|HIP]]&nbsp;114855, [[Star catalogue#BS, BSC, HR|HR]]&nbsp;8841, [[Willem Jacob Luyten|LTT]]&nbsp;9437, [[Star catalogue#SAO|SAO]]&nbsp;146598
| component3 = BC
| names3 = [[Star catalogue#BD/CD/CPD|BD]]–09&nbsp;6155, [[Henry Draper Catalogue|HD]]&nbsp;219430, [[Willem Jacob Luyten|LTT]]&nbsp;9434, [[Star catalogue#SAO|SAO]]&nbsp;146596
}}
{{Starbox reference
| Simbad = HD+219449|sn=A
| Simbad2 = HD+219430|sn2=BC
}}
{{Starbox end}}
'''91 Aquarii''' is the [[Flamsteed designation]] for a [[triple star]]<ref name=mnras389_2_869/> system in the [[celestial equator|equatorial]] [[constellation]] of [[Aquarius (constellation)|Aquarius]]. It also bears the [[Bayer designation]] '''Psi<sup>1</sup> Aquarii''' ({{bayer-blank|ψ|1|Aqr}}, {{bayer-blank|ψ|1|Aquarii}}). It is visible to the naked eye with an [[apparent visual magnitude]] of +4.248.<ref name=mnras172_667/> [[Parallax]] measurements yield an estimated distance of around {{Convert|150|ly|pc|abbr=off|lk=on}} from Earth.<ref name=aaa474_2_653/> An [[extrasolar planet]] is known to orbit the main star.

==Stellar system==
91 Aquarii is a triple star system.<ref name=mnras389_2_869/> The primary component, 91 Aqr A, is a [[giant star]] with a [[stellar classification]] of K1&nbsp;III.<ref name="Baines2018"/> This is an [[stellar evolution|evolved star]] with 138% of the Sun's mass that has expanded to over 10 times the size of the Sun.<ref name="Baines2018"/> It is radiating 54<ref name="Baines2018"/> times the Sun's luminosity from its [[stellar atmosphere|outer envelope]] at an [[effective temperature]] of 4,730&nbsp;K.<ref name="Baines2018"/> This gives it the orange-hued glow of a [[K-type star]].<ref name=csiro/>

The primary shares a [[common proper motion]] with two others stars, 91 Aqr B and C, suggesting that they are physically connected.<ref name=aaa542_A92/> The latter pair form a binary system located at an [[angular separation]] of 52&nbsp;[[arcsecond]]s from the primary.<ref name=msom1962/> They are 10th magnitude stars separated by 0.3 arcseconds from each other.

{| class=wikitable style="text-align: center;"
! Component
! [[Apparent magnitude]] (V)
! [[Spectral type]]
|-
| A || 4.22 || K0&nbsp;III
|-
| B || 9.62 || K3&nbsp;V
|-
| C || 10.10 ||
|}

Because it lies near the same line of sight, the binary star system CCDM J23159-0905DE was listed to belong to the 91 Aquarii system according to the CCDM catalogue.<ref>{{cite web | url=http://vizier.u-strasbg.fr/viz-bin/VizieR-S?CCDM%20J23159-0905A | title=VizieR }}</ref> However, it is listed as physically unconnected in the WDS catalogue<ref>{{Cite web|url=http://ad.usno.navy.mil/wds/Webtextfiles/wdsnewframe4.html|title=|date=January 31, 2009|archive-url=https://web.archive.org/web/20090131051103/http://ad.usno.navy.mil/wds/Webtextfiles/wdsnewframe4.html |archive-date=2009-01-31 }}</ref> and the pair have a different proper motion than 91 Aquarii.<ref name=aaa542_A92/> CCDM J23159-0905DE has two components, the 13th magnitude CCDM J23159-0905D 80.4 arcseconds from 91 Aquarii, and the 14th magnitude CCDM J23159-0905E 19.7 arcseconds from 91 Aquarii.

==Planetary system==
In 2003, the discovery of an [[extrasolar planet]] orbiting 91 Aquarii A was announced,<ref name="Mitchell2003"/> but its confirmation was not formally published until 2013.<ref name="Mitchell2013"/>

{{OrbitboxPlanet begin
| table_ref = <ref name="Mitchell2013"/>
}}
{{OrbitboxPlanet
| exoplanet = [[91 Aquarii b|b]]
| mass = >3.2
| semimajor = 0.70
| period = {{val|181.4|0.1}}
| eccentricity = {{val|0.027|0.026}}
}}
{{Orbitbox end}}

==See also==
* [[Aldebaran]]
* [[Iota Draconis]]
* [[Pollux (star)]]

==References==
{{Reflist|refs=

<ref name="Mitchell2003">{{citation |postscript=. |first=D. S. |last=Mitchell |author2= S. Frink |author3= A. Quirrenbach |author4= D. A. Fischer |author5= G. W. Marcy |author6= R. P. Butler |title=Four Substellar Companions Found Around K Giant Stars |journal=Bulletin of the American Astronomical Society, 35#5; AAS 203rd Meeting; Session 17 Extra Solar Planets |date=2004-01-05 |volume=203 |pages=17.03 |bibcode=2003AAS...203.1703M }}</ref>

<ref name=aaa474_2_653>{{citation | first=F. | last=van Leeuwen |date=November 2007 | title=Validation of the new Hipparcos reduction | journal=Astronomy and Astrophysics | volume=474 | issue=2 | pages=653–664 | bibcode=2007A&A...474..653V | doi=10.1051/0004-6361:20078357 | postscript=. |arxiv = 0708.1752 | s2cid=18759600 }}</ref>

<ref name=Liu2007>{{citation | postscript=.
 | display-authors=1 | last1=Liu | first1=Y. J.
 | last2=Zhao | first2=G. | last3=Shi | first3=J. R.
 | last4=Pietrzyński | first4=G. | last5=Gieren | first5=W.
 | title=The abundances of nearby red clump giants
 | journal=Monthly Notices of the Royal Astronomical Society
 | volume=382 | issue=2 | pages=553–66 | date=2007
 | bibcode=2007MNRAS.382..553L | doi=10.1111/j.1365-2966.2007.11852.x | doi-access=free }}</ref>

<ref name=aj135_1_209>{{citation | display-authors=1 | last1=Massarotti | first1=Alessandro | last2=Latham | first2=David W. | last3=Stefanik | first3=Robert P. | last4=Fogel | first4=Jeffrey | title=Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity | journal=The Astronomical Journal | volume=135 | issue=1 | pages=209–231 |date=January 2008 | doi=10.1088/0004-6256/135/1/209 | bibcode=2008AJ....135..209M | postscript=. | doi-access=free }}</ref>

<ref name=msom1962>{{citation | last=Buscombe | first=W. | title=Spectral classification of Southern fundamental stars | journal=Mount Stromlo Observatory Mimeogram | volume=4 | date=1962 | page=1 | bibcode=1962MtSOM...4....1B | postscript=. }}</ref>

<ref name=mnras172_667>{{citation | last1=Jennens | first1=P. A. | last2=Helfer | first2=H. L. | title=A new photometric metal abundance and luminosity calibration for field G and K giants. | journal=[[Monthly Notices of the Royal Astronomical Society]] | volume=172 | pages=667–679 |date=September 1975 | issue=3 | bibcode=1975MNRAS.172..667J | postscript=. | doi=10.1093/mnras/172.3.667| doi-access=free }}</ref>

<ref name=mnras389_2_869>{{citation | last1=Eggleton | first1=P. P. | last2=Tokovinin | first2=A. A. | title=A catalogue of multiplicity among bright stellar systems | journal=Monthly Notices of the Royal Astronomical Society | volume=389 | issue=2 | pages=869–879 |date=September 2008 | doi=10.1111/j.1365-2966.2008.13596.x | doi-access=free | bibcode=2008MNRAS.389..869E | postscript=. |arxiv = 0806.2878 | s2cid=14878976 }}</ref>

<ref name=aaa542_A92>{{citation | last1=Roell | first1=T. | last2=Neuhäuser | first2=R. | last3=Seifahrt | first3=A. | last4=Mugrauer | first4=M. | title=Extrasolar planets in stellar multiple systems | journal=Astronomy & Astrophysics | volume=542 | page=A92 |date=June 2012 | doi=10.1051/0004-6361/201118051 | bibcode=2012A&A...542A..92R |arxiv = 1204.4833 | s2cid=55755453 }}</ref>

<ref name=Viz>{{citation | title=VizieR Detailed Page for HR 8841 | url=http://webviz.u-strasbg.fr/viz-bin/VizieR-S?HR%208841 | access-date=2009-11-28 | postscript=. }}</ref>

<ref name=csiro>{{citation|title=The Colour of Stars |date=December 21, 2004 |work=Australia Telescope, Outreach and Education |publisher=[[Commonwealth Scientific and Industrial Research Organisation]] |url=http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html |access-date=2012-01-16 |postscript=. |url-status=dead |archive-url=https://web.archive.org/web/20120222183238/http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html |archive-date=February 22, 2012 }}</ref>

<ref name="Baines2018">{{citation |postscript=. | title=Fundamental Parameters of 87 Stars from the Navy Precision Optical Interferometer | last1=Baines | first1=Ellyn K. | last2=Armstrong | first2=J. Thomas | last3=Schmitt | first3=Henrique R. | last4=Zavala | first4=R. T. | last5=Benson | first5=James A. | last6=Hutter | first6=Donald J. | last7=Tycner | first7=Christopher | last8=Belle | first8=Gerard T. van | display-authors=1 | journal=The Astronomical Journal | volume=155 | at=30 | year=2018 | issue=1 | arxiv=1712.08109 | bibcode=2018AJ....155...30B | doi=10.3847/1538-3881/aa9d8b | s2cid=119427037 | doi-access=free }}</ref>

<ref name="Mitchell2013">{{citation  |postscript=. | title=Precise radial velocities of giant stars. V. A brown dwarf and a planet orbiting the K giant stars τ Geminorum and 91 Aquarii | last1=Mitchell | first1=David S. | last2=Reffert | first2=Sabine | last3=Trifonov | first3=Trifon | last4=Quirrenbach | first4=Andreas | last5=Fischer | first5=Debra A. | display-authors=1 | journal=Astronomy and Astrophysics | volume=555 | at=A87 | year=2013 | arxiv=1305.5107 | bibcode=2013A&A...555A..87M | doi=10.1051/0004-6361/201321714 | s2cid=32245543 }}</ref>

}}

==External links==
* {{cite simbad|title=GJ 893.2 A}}
* {{cite simbad|title=GJ 893.2 B}}
* {{cite simbad|title=* psi01 Aqr}}
* [https://web.archive.org/web/20110505014620/http://exoplanet.eu/star.php?st=91+Aqr '''Extrasolar Planets Encyclopaedia''': 91 Aqr]
* [https://web.archive.org/web/20071203095254/http://media4.obspm.fr/exoplanets/base/planete.php?etoile=HD+219449&planete=b Orbit simulation]
* [http://aladin.u-strasbg.fr/AladinPreview?-c=NLTT+56282&ident=NLTT+56282&submit=Aladin+previewer Image Psi Aquarii]
* [http://server6.sky-map.org/starview?object_type=1&object_id=835&locale=ZH sky-map.org/]
* [https://web.archive.org/web/20080701125126/http://planetquest.jpl.nasa.gov/atlas/atlas_search.cfm planetquest.jpl.nasa.gov]

{{Stars of Aquarius}}

{{Sky|23|15|53.5|-|09|05|16|148}}

{{DEFAULTSORT:91 Aquarii}}
[[Category:Aquarius (constellation)]]
[[Category:Bayer objects|Aquarii, Psi1]]
[[Category:Flamsteed objects|Aquarii, 091]]
[[Category:Henry Draper Catalogue objects|219449]]
[[Category:Bright Star Catalogue objects|8841]]
[[Category:Hipparcos objects|114855]]
[[Category:Planetary systems with one confirmed planet]]
[[Category:K-type giants|Psi1 Aquarii A]]
[[Category:Triple star systems|3]]
[[Category:Multi-star planetary systems|3]]
[[Category:Durchmusterung objects|BD-09 6156]]
[[Category:Gliese and GJ objects|0893.2]]