Theta Geminorum

	Theta Geminorum (θ)
Observationsdata; Epok: J2000.0
Stjärnbild	Tvillingarna
Rektascension	06t 52m 47,33887s
Deklination	33° 57′ 40,5175″
Skenbar magnitud ()	3,59
Stjärntyp
Spektraltyp	A2 IV
U–B	0,13
B–V	0,10
Astrometri
Radialhastighet ()	21 km/s
Egenrörelse (µ)	RA: -1,66 mas/år; Dek.: -47,31 mas/år
Parallax ()	17,25 ± 0,19 mas
Avstånd	189 ± 2 lå (58,0 ± 0,6 pc)
Detaljer
Massa	1,80 M☉
Radie	5,1 R☉
Luminositet	93 L☉
Temperatur	8 502 ± 289 K
Vinkelhastighet	133 km/s
Ålder	252 miljoner år
Andra beteckningar
	θ Gem, 34 Geminorum, BD+34°1481, FK5 261, HD 50019, HIP 33018, HR 2540, SAO 59570.

Theta Geminorum (θ Gem, θ Geminorum) är en^[10] stjärna i norra delen av stjärnbilden Tvillingarna. Den är synlig med blotta ögat med en magnitud på 3,59.^[2] Baserat på en årlig parallaxförskjutning på 17,25 mas,^[1] befinner sig stjärnan på ca 189 ljusårs avstånd från solen.

Egenskaper[redigera | redigera wikitext]

Theta Geminorum är en framväxande underjätte av A-typ med spektraltyp A2 IV.^[3] Den har massa som är 1,80^[5] gånger solens och en strålning som är 93^[7] gånger solens. Den uppmätta diametervinkeln är 0,82 ± 0,03 mas.^[11] Utifrån uppskattat avstånd till stjärnan, ger detta en fysisk storlek på ca 5,1 gånger solens radie.^[6] Stjärnan är cirka 252 miljoner år gammal och har en projicerad rotationshastighet på 133 km/s^[8]. Denna rotationshastighet ger stjärnan en tillplattad form, med en ekvatorial utvidgning som är 11% större än polarradien.^[12]

Washington Visual Double Star Catalog listar fem synliga följeslagare till θ Geminorum inom 100". Närmast och ljusast av dessa var år 2010 θ Geminorum E (magnitud 8,6) med en separationsvinkel på 2,4" längs lägesvinkeln 295°.^[13]

Källor[redigera | redigera wikitext]

Den här artikeln är helt eller delvis baserad på material från engelskspråkiga Wikipedia, tidigare version.

Referenser[redigera | redigera wikitext]

^ [a b c d e f] van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
^ [a b c d] Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV data, SIMBAD, Bibcode:1986EgUBV........0M.
^ [a b] Abt, Helmut A.; Morrell, Nidia I. (1995), "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars", Astrophysical Journal Supplement, 99: 135, Bibcode:1995ApJS...99..135A, doi:10.1086/192182.
^ Evans, D. S. (June 20–24, 1966), "The Revision of the General Catalogue of Radial Velocities", in Batten, Alan Henry; Heard, John Frederick, Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, University of Toronto: International Astronomical Union, Bibcode:1967IAUS...30...57E.
^ [a b c d] David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154Freely accessible, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146.
^ [a b] Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. Radien (R_*) ges av:
${\begin{aligned}2\cdot R_{*}&={\frac {(58.0\cdot 0.82\cdot 10^{-3})\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\approx 10.2\cdot R_{\bigodot }\end{aligned}}$
^ [a b] McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, arXiv:1208.2037Freely accessible, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x.
^ [a b] Royer, F.; et al. (October 2012), "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i", Astronomy and Astrophysics, 393: 897−911, arXiv:astro-ph/0205255Freely accessible, Bibcode:2002A&A...393..897R, doi:10.1051/0004-6361:20020943.
^ "tet Gem -- Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2016-12-02.
^ Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878Freely accessible, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
^ Richichi, A.; et al. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431 (2): 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039.
^ van Belle, Gerard T., Gerard T. (March 2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20 (1): 51, arXiv:1204.2572Freely accessible, Bibcode:2012A&ARv..20...51V, doi:10.1007/s00159-012-0051-2.
^ Mason, B. D.; et al. (2014), The Washington Visual Double Star Catalog, Bibcode:2001AJ....122.3466M, doi:10.1086/323920.

[A-1] [a b c d e f] van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.

[B-2] [a b c d] Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV data, SIMBAD, Bibcode:1986EgUBV........0M.

[C-3] [a b] Abt, Helmut A.; Morrell, Nidia I. (1995), "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars", Astrophysical Journal Supplement, 99: 135, Bibcode:1995ApJS...99..135A, doi:10.1086/192182.

[4] Evans, D. S. (June 20–24, 1966), "The Revision of the General Catalogue of Radial Velocities", in Batten, Alan Henry; Heard, John Frederick, Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, University of Toronto: International Astronomical Union, Bibcode:1967IAUS...30...57E.

[D-5] [a b c d] David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154Freely accessible, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146.

[E-6] [a b] Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. Radien (R_*) ges av:
${\begin{aligned}2\cdot R_{*}&={\frac {(58.0\cdot 0.82\cdot 10^{-3})\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\approx 10.2\cdot R_{\bigodot }\end{aligned}}$

[F-7] [a b] McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, arXiv:1208.2037Freely accessible, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x.

[G-8] [a b] Royer, F.; et al. (October 2012), "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i", Astronomy and Astrophysics, 393: 897−911, arXiv:astro-ph/0205255Freely accessible, Bibcode:2002A&A...393..897R, doi:10.1051/0004-6361:20020943.

[9] "tet Gem -- Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2016-12-02.

[10] Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878Freely accessible, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.

[11] Richichi, A.; et al. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431 (2): 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039.

[12] van Belle, Gerard T., Gerard T. (March 2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20 (1): 51, arXiv:1204.2572Freely accessible, Bibcode:2012A&ARv..20...51V, doi:10.1007/s00159-012-0051-2.

[13] Mason, B. D.; et al. (2014), The Washington Visual Double Star Catalog, Bibcode:2001AJ....122.3466M, doi:10.1086/323920.

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