View source for Astronomy:Tau Geminorum

{{short description|Star in the constellation Gemini}}
{{Starbox begin}}
{{Starbox image
 | image =
   {{Location mark
     | image=Gemini IAU.svg
     | float=center | width=240 | position=right
     | mark=Red circle.svg | mark_width=10 | mark_link=τ Gem
     | x%=41.6 | y%=26.4
   }}
 | caption = Location of τ Geminorum (circled)
}}
{{Starbox observe
 | epoch       = [[Astronomy:J2000.0|J2000.0]]
 | ra          = {{RA|07|11|08.37042}}<ref name=aaa474_2_653/>
 | dec         = {{DEC|+30|14|42.5831}}<ref name=aaa474_2_653/>
 | appmag_v    = +4.42<ref name=clpl4_99/>
 | constell    = [[Astronomy:Gemini (constellation)|Gemini]]
}}
{{Starbox character
 | class       = K2&nbsp;III<ref name=Mitchell_et_al_2013/>
 | b-v         = +1.261<ref name=Mitchell_et_al_2013/>
 | u-b         = +1.41<ref name=clpl4_99/>
 | variable    =
}}
{{Starbox astrometry
 | radial_v    = {{val|+22.02|0.07}}<ref name=Mitchell_et_al_2013/>
 | prop_mo_ra  = -31.21<ref name=aaa474_2_653/>
 | prop_mo_dec = -48.92<ref name=aaa474_2_653/>
 | parallax    = 10.16
 | p_error     = 0.25
 | parallax_footnote = <ref name=aaa474_2_653/>
 | absmag_v    = {{val|−0.56|0.05}}<ref name=Mitchell_et_al_2013/>
}}
{{Starbox detail
 | source      = <ref name=Mitchell_et_al_2013/>
 | mass        = {{val|2.3|0.3}}
 | radius      = {{val|26.8|0.7}}
 | luminosity  = 224<ref name=aj133_6_2464/>
 | temperature = {{val|4388|25|fmt=commas}}
 | metal_fe    = {{val|0.14|0.10}}
 | gravity     = {{val|1.96|0.08}}
 | age_gyr     = {{val|1.22|0.76}}
 | rotational_velocity = 5.8<ref name=aj135_1_209/>
}}
{{Starbox catalog
}}
{{Starbox reference
|Simbad=tau+Gem
}}
{{Starbox end}}

'''Tau Geminorum''', [[Social:Latinisation of names|Latinized]] from τ Geminorum, is a [[Astronomy:Star|star]] in the northern [[Astronomy:Zodiac|zodiac]] [[Astronomy:Constellation|constellation]] of [[Astronomy:Gemini (constellation)|Gemini]]. It has the [[Astronomy:Apparent visual magnitude|apparent visual magnitude]] of +4.42,<ref name=clpl4_99/> making it visible to the naked eye under suitably good seeing conditions. This star is close enough to the Earth that its distance can be measured using the [[Astronomy:Parallax|parallax]] technique, which yields a value of roughly {{Convert|321|ly|pc|abbr=off|lk=on}}.<ref name=aaa474_2_653/>

[[File:Tau Geminorum and brown dwarf.png|thumb|left|200px|Artist's illustration of the giant star Tau Geminorum (left) and its brown dwarf companion—the dark disk at right.{{Dubious|reason=A brown dwarf has a non-zero bond albedo so it should be showing an illuminated crescent|date=March 2012}}]]
It is an [[Astronomy:Stellar evolution|evolved]] [[Astronomy:Giant star|giant star]] of the spectral type K2&nbsp;III. It has double<ref name=aj133_6_2464/> the mass of the Sun and has expanded to 27<ref name=aj135_1_209/> times the Sun's radius. Tau Geminorum is radiating 224<ref name=aj135_1_209/> as much [[Physics:Electromagnetic radiation|radiation]] as the Sun from its expanded [[Astronomy:Stellar atmosphere|outer atmosphere]] at an [[Astronomy:Effective temperature|effective temperature]] of 4,528&nbsp;K,<ref name=aj133_6_2464/> giving it the characteristic orange-hued glow of a [[Astronomy:K-type star|K-type star]]. It appears to be rotating slowly with a projected rotational velocity of {{nowrap|5.8 km s<sup>−1</sup>}}.<ref name=aj135_1_209/>
== Planetary system ==
This star has a [[Astronomy:Brown dwarf|brown dwarf]] or [[Astronomy:Super-Jupiter|Super-Jupiter]] companion designated '''Tau Geminorum b''', whose [[Physics:Mass|mass]] is at least 20.6 [[Astronomy:Jupiter mass|Jupiter mass]]es.<ref name=Mitchell_et_al_2013/> It was discovered in 2004 by Mitchell and colleagues, who also discovered [[Astronomy:Nu Ophiuchi b|Nu Ophiuchi b]] at the same time.<ref name="four"/> This brown dwarf takes {{convert|305|days|years|abbr=off}} to [[Astronomy:Orbital period|revolve]] around Tau Gem. It may also have a stellar companion; a magnitude 11, [[Astronomy:K-type main-sequence star|K0 dwarf]] at a projected separation of about {{val|187|u=AU}}.<ref name=Mitchell_et_al_2013/>

{{OrbitboxPlanet begin
| table_ref=<ref name=Mitchell_et_al_2013/>
| period_unit=day
}}
{{OrbitboxPlanet
| exoplanet = b
| mass = ≥20.6
| period =  305.5 ± 0.1
| semimajor = 1.17
| eccentricity = 0.031 ± 0.009
}}
{{Orbitbox end}}

==References==
{{reflist|refs=

<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 |arxiv = 0708.1752 | s2cid=18759600 }}</ref>

<ref name=aj133_6_2464>{{citation | last1=Luck | first1=R. Earle | last2=Heiter | first2=Ulrike | title=Giants in the Local Region | journal=The Astronomical Journal | volume=133 | issue=6 | pages=2464–2486 |date=June 2007 | doi=10.1086/513194 | bibcode=2007AJ....133.2464L | 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 | s2cid=121883397 | doi-access=free }}</ref>

<ref name=clpl4_99>{{citation | display-authors=1 | last1=Johnson | first1=H. L. | last2=Iriarte | first2=B. | last3=Mitchell | first3=R. I. | last4=Wisniewskj | first4=W. Z. | title=UBVRIJKL photometry of the bright stars | journal=Communications of the Lunar and Planetary Laboratory | volume=4 | issue=99 | date=1966 | page=99 | bibcode=1966CoLPL...4...99J }}</ref>

<ref name="four">{{citation | display-authors=1 | last1=Mitchell | first1=D. S. | last2=Frink | first2=S. | last3=Quirrenbach | first3=A. | last4=Fischer | first4=D. A. | last5=Marcy | first5=G. W. | last6=Butler | first6=R. P. | title=Four Substellar Companions Found Around K Giant Stars | journal=Bulletin of the American Astronomical Society | volume=35 | page=1234 | date=2004  |bibcode=2003AAS...203.1703M}}</ref>

<ref name=Mitchell_et_al_2013>{{citation
 | 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 & Astrophysics
 | volume=555 | id=A87 | pages=10 | date=July 2013
 | doi=10.1051/0004-6361/201321714 | arxiv=1305.5107
 | bibcode=2013A&A...555A..87M | s2cid=32245543 | postscript=. }}</ref>

}}

{{Stars of Gemini}}

{{DEFAULTSORT:Tau Geminorum}}
<!-- Properties -->
[[Category:K-type giants]]
[[Category:Brown dwarfs]]
<!-- Other -->
[[Category:Gemini (constellation)]]
[[Category:Bayer objects|Geminorum, Tau]]
[[Category:Durchmusterung objects]]
[[Category:Flamsteed objects|Geminorum, 46]]
[[Category:Henry Draper Catalogue objects|054719]]
[[Category:Hipparcos objects|034693]]
[[Category:Bright Star Catalogue objects|2697]]

{{Sourceattribution|Tau Geminorum}}