{{Short description|Variable Star in Constellation Sextans }} {{Starbox begin | name = [[Flamsteed designation|23 Sextantis]] }} {{Starbox image | image = {{Location mark | image = Sextans constellation map.svg | float = center | width = 260 | position = right | mark = Red circle.svg | mark_width = 10 | mark_link = 23 Sextantis | x = 410 | y = 427 }} | caption = Location of 23 Sex on the map (circled in red) }} {{Starbox observe | epoch = [[J2000.0]] ([[International Celestial Reference System|ICRS]]) | constell = [[Sextans]]<ref name=xhip>{{cite XHIP|50684}}</ref> | ra = {{RA|10|21|02.01}}<ref name=dr3/> | dec = {{DEC|+02|17|23.0}}<ref name=dr3/> | appmag_v = 6.64–6.68<ref name=AAVSO/> }} {{Starbox character | type = [[subgiant]] / [[main sequence star]] | class = B2IV/V<ref name=SIMBAD/> | b-v = −0.094<ref name=HIP/> | variable = [[Beta Cephei variable|β Cep]] + [[Slowly pulsating B star|SPB]] candidate<ref name=AAVSO/> }} {{Starbox astrometry | radial_v = 5{{±|4.4}}<ref name=SIMBAD/> | parallax = 1.1613 | p_error = 0.0659 | parallax_footnote = <ref name=dr3>{{cite Gaia DR3|3856568374801242752}}</ref> | prop_mo_ra = −8.900 | prop_mo_dec = −0.447 | pm_footnote = <ref name=dr3/> | absmag_v = −2.6<ref name=sand2020>{{cite journal |last1=Melnik |first1=A. M. |last2=Dambis |first2=A. K. |title=Distance scale for high-luminosity stars in OB associations and in field with Gaia DR2. Spurious systematic motions |journal=Astrophysics and Space Science |date=2020 |volume=365 |issue=7 |page=112 |doi=10.1007/s10509-020-03827-0 |arxiv=2006.14649 |bibcode=2020Ap&SS.365..112M }}</ref> }} {{Starbox detail | mass = 7.3<ref name=quintana2025/> | temperature = 17,947<ref name=quintana2025>{{cite journal |last1=Quintana |first1=Alexis L. |last2=Wright |first2=Nicholas J. |last3=Martínez García |first3=Juan |title=A census of OB stars within 1 KPC and the star formation and core collapse supernova rates of the Milky Way |journal=Monthly Notices of the Royal Astronomical Society |date=2025 |volume=538 |issue=3 |page=1367 |doi=10.1093/mnras/staf083 |doi-access=free |arxiv=2503.08286 |bibcode=2025MNRAS.538.1367Q }}</ref> | luminosity = 3,990<ref name=quintana2025/> | radius = 10.0<ref name=yu2023>{{cite journal |last1=Yu |first1=Jie |last2=Khanna |first2=Shourya |last3=Themessl |first3=Nathalie |last4=Hekker |first4=Saskia |last5=Dréau |first5=Guillaume |last6=Gizon |first6=Laurent |last7=Bi |first7=Shaolan |title=Revised Extinctions and Radii for 1.5 Million Stars Observed by APOGEE, GALAH, and RAVE |journal=The Astrophysical Journal Supplement Series |date=2023 |volume=264 |issue=2 |page=41 |doi=10.3847/1538-4365/acabc8 |doi-access=free |arxiv=2206.00046 |bibcode=2023ApJS..264...41Y }}</ref> | gravity = 4.03<ref name=yu2023/> | rotational_velocity = 96.0<ref name=abdurrouf2022>{{cite journal |author1=Abdurro'uf |last2=Accetta |first2=Katherine |last3=Aerts |first3=Conny |last4=Silva Aguirre |first4=Víctor |last5=Ahumada |first5=Romina |last6=Ajgaonkar |first6=Nikhil |last7=Filiz Ak |first7=N. |last8=Alam |first8=Shadab |last9=Allende Prieto |first9=Carlos |last10=Almeida |first10=Andrés |last11=Anders |first11=Friedrich |last12=Anderson |first12=Scott F. |last13=Andrews |first13=Brett H. |last14=Anguiano |first14=Borja |last15=Aquino-Ortíz |first15=Erik |last16=Aragón-Salamanca |first16=Alfonso |last17=Argudo-Fernández |first17=Maria |last18=Ata |first18=Metin |last19=Aubert |first19=Marie |last20=Avila-Reese |first20=Vladimir |last21=Badenes |first21=Carles |last22=Barbá |first22=Rodolfo H. |last23=Barger |first23=Kat |last24=Barrera-Ballesteros |first24=Jorge K. |last25=Beaton |first25=Rachael L. |last26=Beers |first26=Timothy C. |last27=Belfiore |first27=Francesco |last28=Bender |first28=Chad F. |last29=Bernardi |first29=Mariangela |last30=Bershady |first30=Matthew A. |display-authors=1 |title=The Seventeenth Data Release of the Sloan Digital Sky Surveys: Complete Release of MaNGA, MaStar, and APOGEE-2 Data |journal=The Astrophysical Journal Supplement Series |date=2022 |volume=259 |issue=2 |page=35 |doi=10.3847/1538-4365/ac4414 |doi-access=free |arxiv=2112.02026 |bibcode=2022ApJS..259...35A }}</ref> | age_myr = 33<ref name=tetzlaff2012>{{cite journal |last1=Tetzlaff |first1=N. |last2=Neuhäuser |first2=R. |last3=Hohle |first3=M. M. |title=A catalogue of young runaway Hipparcos stars within 3 KPC from the Sun |journal=Monthly Notices of the Royal Astronomical Society |date=2011 |volume=410 |issue=1 |page=190 |doi=10.1111/j.1365-2966.2010.17434.x |doi-access=free |arxiv=1007.4883 |bibcode=2011MNRAS.410..190T }}</ref> }} {{Starbox catalog | names = {{odlist | F = 23 Sex | V = RS Sextantis | HD = 89688 | HIP = 50684 | HR = 4064 | SAO = 118248 }}<ref name=SIMBAD/> }} {{Starbox reference | Simbad = 23+Sex }} {{Starbox end}}
'''23 Sextantis''' (also known as '''RS Sextantis'''), is a [[B-type star]] located in the equatorial constellation [[Sextans]]. The star has been identified as a pulsating variable candidate showing characteristics associated with both [[Beta Cephei variable]] and [[53 Persei variable]] stars.<ref name="AAVSO">{{cite web|title=RS Sex|url=https://www.aavso.org/vsx/index.php?view=detail.top&oid=34984|website=International Variable Star Index|publisher=American Association of Variable Star Observers|access-date=15 March 2026}}</ref><ref name="SIMBAD">{{cite web|title=V* 23 Sex – Pulsating variable star|url=http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=23+Sex|publisher=Centre de Données astronomiques de Strasbourg|access-date=15 March 2026}}</ref> It lies in the faint equatorial constellation Sextans.<ref name="AAVSO"/>
==Early observations==
Early spectroscopic and photometric observations of the star were reported by [[Jorge Sahade|Sahade]], [[Otto Struve|Struve]] and A. D. Williams in 1956 after the star had been designated the variable star RS Sextantis in the seventh supplement of the [[General Catalogue of Variable Stars]]<ref name="Sahade1956">{{cite journal|last1=Sahade|first1=J.|last2=Struve|first2=O.|last3=Williams|first3=A. D.|title=Spectroscopic and Photometric Observations of 23 Sextantis|journal=Publications of the Astronomical Society of the Pacific|year=1956|volume=68|issue=402|pages=266|doi=10.1086/126931|bibcode=1956PASP...68..266S}}</ref>
The authors described the star as having a spectral type of B3 and an [[absolute magnitude]] of about −2.0, and noted that earlier photoelectric observations suggested it might belong to the [[β Canis Majoris]] ([[β Cephei]]) class with a period of roughly four hours.<ref name="Sahade1956"/>
Spectroscopic observations were obtained at [[Mount Wilson Observatory]], while photometric measurements were carried out at [[Lick Observatory]]. The study also reported mean radial velocities of about +5 to +6 km/s from earlier catalogues, although the available photometric data at the time were considered insufficient to establish the star’s variability firmly.<ref name="Sahade1956"/>
== Stellar characteristics ==
23 Sextantis is spectroscopically classified as a B-type star.<ref name="SIMBAD"/> Photometric measurements indicate a small variation in brightness between visual magnitudes 6.64 and 6.68.<ref name="AAVSO"/> The star has a B−V [[color index]] of −0.094.<ref name="HIP">{{cite web|title=Hipparcos, the New Reduction|url=http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-source=I/311/hip2&HIP=50684|author=van Leeuwen, F.|year=2007|publisher=VizieR catalogue service|access-date=15 March 2026}}</ref>
Astrometric measurements from the ''[[Hipparcos]]'' mission give a parallax of 1.30 milliarcseconds.<ref name="HIP"/> The star also shows a small proper motion across the sky.<ref name="HIP"/>
== Variability ==
Observations have revealed small variations in brightness with an amplitude of only a few hundredths of a magnitude.<ref name="AAVSO"/> The measured photometric period of approximately 0.1353 days (about 3.25 hours) places the star among short-period pulsating variables.<ref name="AAVSO"/>
Because its observed properties overlap with those of both β Cephei variables and [[slowly pulsating B-type star]]s of the 53 Persei class, 23 Sextantis has been described as a possible candidate for either type of pulsating variable star.<ref name="AAVSO"/>
== Interstellar medium ==
Spectroscopic studies of the sightline toward 23 Sextantis indicate the presence of intervening interstellar material associated with a [[molecular cloud]].<ref name="Penprase1993">{{cite journal |last=Penprase |first=B. E. |title=Photometric and Spectroscopic Analysis of High Galactic Latitude Molecular Clouds. II. High-Resolution Spectroscopic Observations of Na I, Ca II, Ca I, CH, and CH+ |journal=The Astrophysical Journal Supplement Series |year=1993 |volume=88 |pages=433–458 |doi=10.1086/191829 |bibcode=1993ApJS...88..433P}}</ref> The [[stellar spectrum]] exhibits absorption features corresponding to neutral and ionised metals as well as simple molecules, demonstrating that both atomic and molecular gas are present along the line of sight.<ref name="Penprase1993"/>
Analysis of the Na I profile reveals several distinct velocity components, including a dominant feature near −1.6 km s−1 and additional components extending from approximately −20 to +20 km s−1, consistent with a multi-component interstellar structure.<ref name="Penprase1993"/>
The absorbing material is associated with a compact molecular cloud identified as DBB 354 at an estimated distance of about 1 [[kiloparsec|kpc]].<ref name="Penprase1993"/> The cloud appears to be both dense and small in scale, with a characteristic size of roughly 0.08 [[Parsec|pc]] and particle densities of several thousand per cubic centimetre.<ref name="Penprase1993"/>
Infrared observations link this cloud to an [[IRAS]] source, suggesting that it may represent a previously unrecognized high-latitude molecular cloud.<ref name="Penprase1993"/>
== Designations ==
The star appears in several major stellar catalogues. In the ''[[Henry Draper Catalogue]]'' it is listed as HD 89688, while the ''[[Hipparcos catalogue]]'' designation is HIP 50684.<ref name="HIP"/> Additional identifiers include HR 4064 in the [[Bright Star Catalogue]] and SAO 118248.<ref name="SIMBAD"/> Its [[Flamsteed designation]], 23 Sextantis, reflects its approximate ordering by right ascension within the constellation Sextans.<ref>{{cite web |title=23 Sextantis |url=https://theskylive.com/sky/stars/23-sextantis-star |website=TheSkyLive |access-date=2026-03-15}}</ref>
==References== {{reflist}}
{{Sextans}}
[[Category:Sextans]] [[Category:Flamsteed objects|Sextantis, 23]] [[Category:Objects with variable star designations|Sextantis, RS]] [[Category:Hipparcos objects|050684]] [[Category:Henry Draper Catalogue objects|089688]] [[Category:Bright Star Catalogue objects|4064]] [[Category:B-type main-sequence stars]] [[Category:Beta Cephei variables]] [[Category:Slowly pulsating B-type stars]]