View source for Astronomy:U Sagittarii

{{Short description|Star in the constellation Sagittarius}}
{{Starbox begin}}
{{Starbox image
 | image = [[File:M025.jpg|335px]]
 | caption = U Sagittarii (center) is the brightest star in the open cluster Messier 25.<ref name=Luginbuhl_Skiff_1998/>
}}
{{Starbox observe
 | epoch       = [[Astronomy:J2000|J2000]]
 | constell    = [[Astronomy:Sagittarius (constellation)|Sagittarius]]
 | ra          = {{RA|18|31|53.332}}<ref name=GaiaEDR3/>
 | dec         = {{DEC|−19|07|30.26}}<ref name=GaiaEDR3/>
 | appmag_v    = {{val|6.28|to|7.15}}<ref name=Samus_et_al_2017/>
}}
{{Starbox character
 | type        = [[Astronomy:Supergiant|Supergiant]]
 | class       = G1Ib<ref name=Houk_Smith-Moore_1988/>
 | b-v         = +1.06<ref name=Sandage_1960/>
 | u-b         = +0.85<ref name=Sandage_1960/>
 | variable    = δ Cep<ref name=Samus_et_al_2017/>
}}
{{Starbox astrometry
 | radial_v    = 2.2{{±|0.3}}<ref name=Breger_1967/>
 | prop_mo_ra  = −1.795
 | prop_mo_dec = −6.127
 | pm_footnote = <ref name=GaiaEDR3/>
 | parallax    = 1.5693
 | p_error     = 0.0224
 | parallax_footnote = <ref name=GaiaEDR3/>
 | absmag_v    = {{val|−3.86|to|−3.10}}<ref name=Sandage_1960/>
}}
{{Starbox detail
 | source      = 
 | mass        = {{val|6.54|to|6.64}}<ref name=Fadeyev_2018/>
 | radius      = {{val|55.5|to|56.3}}<ref name=Fadeyev_2018/>
 | temperature = 5,802<ref name=Prugniel_et_al_2011/>
 | luminosity  = {{val|4370|to|4650|fmt=commas}}<ref name=Fadeyev_2018/>
 | gravity     = 0.99<ref name=Prugniel_et_al_2011/>
 | metal_fe    = 0.17<ref name=Prugniel_et_al_2011/>
 | rotational_velocity = 15.4<ref name=johnsson2020/>
 | rotation    = 
 | age_myr     = 91<ref name=skowron2019/>
}}
{{Starbox catalog
 | names = {{odlist | V=U Sgr | BD=−19°5047 | GC=25287 | HD=170764 | HIP=90836 | HR=6947 | SAO=161571 | WDS=J18319-1908A }}<ref name=SIMBAD/>
}}
{{Starbox reference
 | Simbad=U+Sgr
}}
{{Starbox end}}

'''U Sagittarii''' is a [[Astronomy:Variable star|variable star]] in the southern [[Astronomy:Constellation|constellation]] of [[Astronomy:Sagittarius (constellation)|Sagittarius]], abbreviated U Sgr. It is a [[Astronomy:Classical Cepheid variable|classical Cepheid variable]] that ranges in brightness from an [[Astronomy:Apparent visual magnitude|apparent visual magnitude]] of 6.28 down to 7.15, with a [[Astronomy:Stellar pulsation|pulsation]] period of 6.745226&nbsp;days.<ref name=Samus_et_al_2017/> At its brightest, this star is dimly visible to the naked eye. The distance to this star is approximately 2,080&nbsp;[[Light year|light year]]s based on [[Astronomy:Stellar parallax|parallax]] measurements,<ref name=GaiaEDR3/> and it is drifting further away with a [[Astronomy:Radial velocity|radial velocity]] of 2&nbsp;km/s.<ref name=Breger_1967/>

[[File:USgrLightCurve.png|thumb|left|A [[Astronomy:Light curve|light curve]] for U Sagittarii, plotted from ASAS data<ref name=ASASServer/>]]
The variability of this star was announced by J. Schmidt in 1866, who found a preliminary period of 6.74784&nbsp;days.<ref name=Schmidt_1868/> It was later determined to be a variable of the Cepheid type.<ref name=Shapley_1918/> In 1925, P. Doig assumed that the star is a member of the [[Astronomy:Open cluster|open cluster]] [[Astronomy:Messier 25|Messier 25]] (M25), but actual evidence of its membership would not be available until 1932 when P. Hayford made radial velocity measurements of the cluster.<ref name=Wallerstein_1957/> Membership in this cluster is now reasonably established,<ref name=Chen_2015/> and as such this Cepheid serves as one of the anchors for the [[Astronomy:Cosmic distance ladder|cosmic distance scale]] since the distance to the cluster can be determined independently from the star.<ref name=Majaess_et_al_2013/>

This is an [[Astronomy:Stellar evolution|evolved]] G-type [[Astronomy:Supergiant star|supergiant star]] with a typical [[Astronomy:Stellar classification|stellar classification]] of G1Ib.<ref name=Houk_Smith-Moore_1988/> It appears to be making its third traversal of the [[Astronomy:Instability strip|instability strip]] with its period changing at the rate of {{val|+0.073|0.010|u=s·yr<sup>−1</sup>}}. Elemental abundances are similar to those in the Sun.<ref name=Majaess_et_al_2013/> It has an estimated 6.6 times the mass of the Sun and 56 times the Sun's radius. The star is radiating over 4,000<ref name=Fadeyev_2018/> times the Sun's luminosity from its [[Astronomy:Photosphere|photosphere]] at an [[Astronomy:Effective temperature|effective temperature]] of 5,802&nbsp;K.<ref name=Prugniel_et_al_2011/>

==References==
{{reflist|refs=

<ref name=SIMBAD>{{cite simbad | title=U Sgr | access-date=2022-12-03 }}</ref>

<ref name=GaiaEDR3>{{Cite Gaia EDR3|4092905375639902464}}</ref>

<ref name=johnsson2020>{{citation |postscript=.
 | title=APOGEE Data and Spectral Analysis from SDSS Data Release 16: Seven Years of Observations Including First Results from APOGEE-South
 | last1=Jönsson | first1=Henrik | last2=Holtzman | first2=Jon A.
 | last3=Allende Prieto | first3=Carlos | last4=Cunha | first4=Katia
 | last5=García-Hernández | first5=D. A. | last6=Hasselquist | first6=Sten
 | last7=Masseron | first7=Thomas | last8=Osorio | first8=Yeisson
 | last9=Shetrone | first9=Matthew | last10=Smith | first10=Verne
 | last11=Stringfellow | first11=Guy S. | last12=Bizyaev | first12=Dmitry
 | last13=Edvardsson | first13=Bengt | last14=Majewski | first14=Steven R.
 | last15=Mészáros | first15=Szabolcs | last16=Souto | first16=Diogo
 | last17=Zamora | first17=Olga | last18=Beaton | first18=Rachael L.
 | last19=Bovy | first19=Jo | last20=Donor | first20=John
 | last21=Pinsonneault | first21=Marc H. | last22=Poovelil | first22=Vijith Jacob
 | last23=Sobeck |first23=Jennifer | display-authors=1
 | journal=The Astronomical Journal
 | year=2020 | volume=160 | issue=3 | page=120
 | doi=10.3847/1538-3881/aba592 | arxiv=2007.05537
 | bibcode=2020AJ....160..120J | s2cid=220496397 | doi-access=free
 }}</ref>

<ref name=skowron2019>{{citation |postscript=.
 | title=A three-dimensional map of the Milky Way using classical Cepheid variable stars
 | last1=Skowron | first1=Dorota M. | last2=Skowron | first2=Jan
 | last3=Mróz | first3=Przemek | last4=Udalski | first4=Andrzej
 | last5=Pietrukowicz | first5=Paweł | last6=Soszyński | first6=Igor
 | last7=Szymański | first7=Michał K. | last8=Poleski | first8=Radosław
 | last9=Kozłowski | first9=Szymon | last10=Ulaczyk | first10=Krzysztof
 | last11=Rybicki | first11=Krzysztof | last12=Iwanek | first12=Patryk
 | display-authors=1 | journal=Science
 | year=2019 | volume=365 | issue=6452 | pages=478–482
 | doi=10.1126/science.aau3181 | pmid=31371611
 | bibcode=2019Sci...365..478S | arxiv=1806.10653
 | s2cid=199064609 }}</ref>

<ref name=ASASServer>{{cite web
 | title=ASAS All Star Catalogue | url=http://www.astrouw.edu.pl/asas/?page=aasc
 | publisher=The All Sky Automated Survey | access-date=5 December 2022}}</ref>

<ref name=Samus_et_al_2017>{{citation
 | display-authors=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.
 | title=General Catalogue of Variable Stars
 | version=5.1 | journal=[[Astronomy:Astronomy Reports|Astronomy Reports]]
 | year=2017 | volume=61 | issue=1 | pages=80–88
 | bibcode=2017ARep...61...80S | doi=10.1134/S1063772917010085
 | s2cid=125853869 | postscript=. }}</ref>

<ref name=Houk_Smith-Moore_1988>{{citation
 | title=Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars
 | last1=Houk | first1=N. | last2=Smith-Moore | first2=M.
 | volume=4 | year=1988 | postscript=.
 | bibcode=1988mcts.book.....H }}</ref>

<ref name=Breger_1967>{{citation
 | title=Velocity, radius and light variations of the cepheid U Sgr
 | last=Breger | first=M. | postscript=.
 | journal=Monthly Notices of the Royal Astronomical Society
 | volume=136 | page=61 | date=1967
 | doi=10.1093/mnras/136.1.61 | bibcode=1967MNRAS.136...61B | doi-access=free }}</ref>

<ref name=Chen_2015>{{citation
 | title=A search for open cluster Cepheids in the Galactic plane
 | display-authors=1 | last1=Chen | first1=Xiaodian
 | last2=de Grijs | first2=Richard | last3=Deng | first3=Licai
 | journal=Monthly Notices of the Royal Astronomical Society
 | volume=446 | issue=2 | pages=1268–1282 | postscript=.
 | date=January 2015 | doi=10.1093/mnras/stu2165 
 | arxiv=1410.4489 | bibcode=2015MNRAS.446.1268C }}</ref>

<ref name=Luginbuhl_Skiff_1998>{{citation
 | title=Observing Handbook and Catalogue of Deep-Sky Objects
 | first1=Christian B. | last1=Luginbuhl | first2=Brian A. | last2=Skiff
 | year=1998 | page=213 | isbn=9780521625562
 | publisher=Cambridge University Press | postscript=.
 | url=https://books.google.com/books?id=MwCyjQpGU7UC&pg=PA213 }}</ref>

<ref name=Schmidt_1868>{{citation
 | title=Über die Lichtphasen von A, γ und U Sagittarii in den Jahren 1866 und 1867
 | last=Schmidt | first=Johann Friedrich Julius
 | journal=Astronomische Nachrichten | postscript=.
 | volume=71 | page=139 | language=de
 | date=March 1868 | bibcode=1868AN.....71..139S }}</ref>

<ref name=Wallerstein_1957>{{citation | postscript=.
 | title=The Absolute Magnitude of U Sagittarii and Its Membership in M 25
 | last=Wallerstein | first=George
 | journal=Publications of the Astronomical Society of the Pacific
 | volume=69 | issue=407 | page=172 | date=April 1957
 | doi=10.1086/127041 | bibcode=1957PASP...69..172W | s2cid=121527741
 | doi-access=free}}</ref>

<ref name=Majaess_et_al_2013>{{citation | postscript=.
 | title=Anchors for the cosmic distance scale: the Cepheids U Sagittarii, CF Cassiopeiae, and CEab Cassiopeiae
 | last1=Majaess | first1=D. | last2=Carraro | first2=G.
 | last3=Moni Bidin | first3=C. | last4=Bonatto | first4=C.
 | last5=Berdnikov | first5=L. | last6=Balam | first6=D.
 | last7=Moyano | first7=M. | last8=Gallo | first8=L.
 | last9=Turner | first9=D. | last10=Lane | first10=D.
 | last11=Gieren | first11=W. | last12=Borissova | first12=J.
 | last13=Kovtyukh | first13=V. | last14=Beletsky | first14=Y.
 | display-authors=1 | journal=Astronomy & Astrophysics
 | volume=560 | id=A22 | date=December 2013
 | pages=A22
 | doi=10.1051/0004-6361/201322670 | arxiv=1311.0865
 | bibcode=2013A&A...560A..22M | s2cid=55934597
 }}</ref>

<ref name=Shapley_1918>{{citation | postscript=.
 | title=Studies based on the colors and magnitudes in stellar clusters. VIII. The luminosities and distances of 139 Cepheid variables
 | last=Shapley | first=H.
 | journal=Astrophysical Journal
 | volume=48 | pages=279–294 | date=December 1918
 | doi=10.1086/142435 | bibcode=1918ApJ....48..279S }}</ref>

<ref name=Fadeyev_2018>{{citation | postscript=.
 | title=Secular period change in the cepheid U Sgr and the theory of stellar evolution
 | last=Fadeyev | first=Yu. A.
 | work=Stars and Satellites, Proceedings of the Memorial Conference Devoted to A.G. Masevich 100th Anniversary, held in Moscow, Russia, in Oct 15-16, 2018
 | series=INASAN Science Proceedings
 | editor1-first=B. M. | editor1-last=Shustov
 | editor2-first=D. S. | editor2-last=Wiebe
 | publication-place=Moscow | language=ru
 | publisher=Yanus-K | pages=152–156 | date=August 2018
 | doi=10.26087/INASAN.2018.2.2.024 | bibcode=2018sas..conf..152F }}</ref>

<ref name=Prugniel_et_al_2011>{{citation | postscript=.
 | title=The atmospheric parameters and spectral interpolator for the MILES stars
 | display-authors=1 | last1=Prugniel | first1=Ph.
 | last2=Vauglin | first2=I. | last3=Koleva | first3=M.
 | journal=Astronomy & Astrophysics
 | volume=531 | id=A165 | date=July 2011
 | pages=A165
 | doi=10.1051/0004-6361/201116769 | arxiv=1104.4952
 | bibcode=2011A&A...531A.165P | s2cid=54940439
 }}</ref>

<ref name=Sandage_1960>{{citation | postscript=.
 | title=Cepheids in Galactic Clusters.VI. U SGR in M25
 | last=Sandage | first=Allan
 | journal=Astrophysical Journal
 | volume=131 | page=610 | date=May 1960
 | doi=10.1086/146873 | bibcode=1960ApJ...131..610S }}</ref>

}}

==Further reading==
{{Div col|small=yes}}
*{{citation | postscript=.
 | title=Search for evolutionary changes in the periods of Cepheids: U Sgr
 | last1=Berdnikov | first1=L. N. | last2=Majaess | first2=D.
 | journal=Astronomy Letters
 | volume=40 | issue=4 | pages=193–200 | date=April 2014
 | doi=10.1134/S1063773714030025 | bibcode=2014AstL...40..193B | s2cid=255203281
 }}
*{{citation | postscript=.
 | title=Application of the Baade-Wesselink inversion technique to SW Dra, X Ari and U Sgr
 | last=Simon | first=Norman R.
 | journal=Monthly Notices of the Royal Astronomical Society
 | volume=237 | pages=163–185 | date=March 1989
 | doi=10.1093/mnras/237.1.163 | bibcode=1989MNRAS.237..163S | doi-access=free}}
*{{citation | postscript=.
 | title=Burnham's Celestial Handbook, An Observer's Guide to the Universe Beyond the Solar System
 | first=Robert | last=Burnham | year=1978
 | volume=3 | publisher=Dover Publications | isbn=9780486236735
 | url=https://books.google.com/books?id=tBQoCSRdLAAC&pg=PA1606 }}
*{{citation | postscript=.
 | title=A High-Dispersion Velocity Curve of U Sagittarii
 | last=Jacobsen | first=T. S.
 | journal=Astrophysical Journal
 | volume=159 | page=569 | date=February 1970
 | doi=10.1086/150331 | bibcode=1970ApJ...159..569J }}
*{{citation | postscript=.
 | title=Cepheids in Galactic Clusters. VIII. a Reinvestigation of U SGR in M25 (= IC 4725).
 | last1=Wampler | first1=J. | last2=Pesch | first2=Peter
 | last3=Hiltner | first3=W. A. | last4=Kraft | first4=Robert P.
 | display-authors=1 | journal=Astrophysical Journal
 | volume=133 | page=895 | date=May 1961
 | doi=10.1086/147092 | bibcode=1961ApJ...133..895W | doi-access=free }}
*{{citation | postscript=.
 | title=U, B, V, Observations of U SGR
 | display-authors=1 | last1=Mitchell | first1=Richard I.
 | last2=Johnson | first2=Harold L. | last3=Iriarte | first3=Braulio
 | journal=Astrophysical Journal
 | volume=133 | page=1083 | date=May 1961
 | doi=10.1086/147114 | bibcode=1961ApJ...133.1083M }}
*{{citation | postscript=.
 | title=U Sagittarii
 | last1=Voûte | first1=J. | last2=ten Bruggencate | first2=P.
 | journal=Annals of the Bosscha Observatory Lembang (Java) Indonesia
 | volume=2 | pages=B28–B33 | date=1927
 | bibcode=1927AnBos...2B..28V }}
*{{citation | postscript=.
 | title=On variable stars of short period. IV--The Sagittarius Group
 | last=Yendell | first=Paul S.
 | journal=Popular Astronomy
 | volume=2 | pages=362–366 | year=1895
 | bibcode=1895PA......2..362Y }}
{{Div col end}}


{{DEFAULTSORT:U Sagittarii}}
<!-- Properties -->
[[Category:Classical Cepheid variables]]
[[Category:G-type supergiants]]
<!-- Location/catalogues -->
[[Category:Sagittarius (constellation)]]
[[Category:Bright Star Catalogue objects|6947]]
[[Category:Durchmusterung objects]]
[[Category:Henry Draper Catalogue objects|170764]]
[[Category:Hipparcos objects|90836]]

{{Sourceattribution|U Sagittarii}}