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{{Starbox begin 
| name = Rho Geminorum ABC
}}
{{Starbox image
| image = [[File:RhoGem2MASS.png|250px]]
| caption = A [[2MASS]] image of Rho Geminorum A. The image is extended upwards to include the wide companion, Rho Geminorum C. The star to the mid-right is HD 58830, a background G-giant.
}}
{{Starbox detail|no_heading=y
}}
{{Starbox image
| image =
     <div style="position: relative">[[File:Gemini IAU.svg|250px|alt=Diagram showing star positions and boundaries of the constellation of Gemini and its surroundings]]
     <div style="position: absolute; left: 83px; top: 50px">[[File:Cercle rouge 100%.svg|9px]]</div>
     </div>
| caption = A [[star chart]] of the constellation of Gemini showing the position of Rho Geminorum (circled).
}}
{{Starbox observe 3s
| epoch = J2000.0
| constell = [[Gemini (constellation)|Gemini]]
| component1 = Rho Geminorum A
| ra1 = {{RA|07|29|06.719}} ± 2.72<ref name="van Leeuwen2007"/>
| dec1 = {{DEC|+31|47|04.38}} ± 2.72<ref name="van Leeuwen2007"/>
| appmag_v1 = 4.2473 ± 0.003<ref name="van Leeuwen2007"/>
| component2 = Rho Geminorum B
| ra2 = 07 29 06.0
| dec2 = +31 46 56
| appmag_v2 = 12.5
| component3 = Rho Geminorum C
| ra3 = {{RA|07|29|01.769}} ± 11.24<ref name="van Leeuwen2007"/>
| dec3 = {{DEC|+31|59|37.84}} ± 6.41<ref name="van Leeuwen2007"/>
| appmag_v3 = 7.8621 ± 0.0017
}} 
{{Starbox character
| component = Rho Geminorum A
| class = F0V
| b-v = 0.320 ± 0.012<ref name="van Leeuwen2007"/>
}}
{{Starbox character|no_heading=y
| component = Rho Geminorum B
| class = M5
| b-v = 
}}
{{Starbox character|no_heading=y
| component = Rho Geminorum C
| class = K2V
| b-v = 0.923 ± 0.018<ref name="van Leeuwen2007"/>
| variable = [[BY Draconis variable|BY Dra]]
}}
{{Starbox astrometry 
| component1 = Rho Geminorum A
| radial_v = -4.4 ± 0.9
| prop_mo_ra = 159.09 ± 0.31<ref name="van Leeuwen2007"/>
| prop_mo_dec = 193.29 ± 0.18<ref name="van Leeuwen2007"/>
| parallax = 55.41
| p_error = 0.24
| parallax_footnote = <ref name="van Leeuwen2007"/>
| absmag_v = 2.9639<ref name="AbsMag"/>
}}
{{Starbox astrometry|no_heading=y
| component1 = Rho Geminorum B
| radial_v = 
| prop_mo_ra = 
| prop_mo_dec = 
| parallax = 
| p_error = 
| parallax_footnote = 
| absmag_v = 11.217<ref name="AbsMag"/>
}}
{{Starbox astrometry|no_heading=y
| component1 = Rho Geminorum C
| radial_v = -1.1 ± 5
| prop_mo_ra = 157.85 ± 1.28<ref name="van Leeuwen2007"/>
| prop_mo_dec = 175.95 ± 0.73<ref name="van Leeuwen2007"/>
| parallax = 56.63
| p_error = 0.93
| parallax_footnote = <ref name="van Leeuwen2007"/>
| absmag_v = 6.5787<ref name="AbsMag"/>
}}
{{Starbox detail
| component1 = Rho Geminorum A
| mass = 1.355 ± 0.013<ref name="Boyajian2012"/>
| metal_fe = -0.25 ± 0.04<ref name="Wu2011"/>
| radius = 1.655 ± 0.028<ref name="Boyajian2012"/>
| luminosity = 5.542 ± 0.089<ref name="Boyajian2012"/>
| temperature = 6899 ± 63<ref name="Boyajian2012"/>
| gravity = 4.11 ± 0.03<ref name="Wu2011"/>
| rotational_velocity = 59.0 ± 3.0<ref name="AmmlerVonEiff2012"/>
| age_gyr = 2.1 ± 0.2<ref name="Boyajian2012"/>
}}
{{Starbox detail|no_heading=y
| component1 = Rho Geminorum C
| mass = 0.77<ref name="Shaya2011"/>
| metal_fe = -0.06 ± 0.08<ref name="Wu2011"/>
| radius = 
| luminosity = 
| temperature = 4948 ± 41<ref name="Wu2011"/>
| gravity = 4.71 ± 0.08
| rotational_velocity = 
| age_gyr = 
}}
{{Starbox catalog 
| names = 
| component1 = Rho Geminorum A
| names1 = 62 Geminorum, HD 58946, HIP 36366, Gliese 274 A, HR 2852
| component2 = Rho Geminorum B
| names2 = Gliese 274 B
| component3 = Rho Geminorum C
| names3 = HIP 36357, Gliese 273.1, V376 Geminorum
}}
{{Starbox reference
| component = Rho Geminorum A
| Simbad = rho+Gem
}}
{{Starbox reference|no_heading=y
| component = Rho Geminorum B
| Simbad = GJ+274+B
}}
{{Starbox reference|no_heading=y
| component = Rho Geminorum C
| Simbad = HIP+36357
}}
{{Starbox end}}

'''Rho Geminorum''' ('''ρ Gem''') is a star system that lies approximately 59 [[light-year]]s away in the constellation of Gemini, about 5 arcminutes east of [[Castor (star)|Castor]]. The system consists of a primary bright enough to be seen with the naked eye, a faint secondary which has rarely been observed even professionally, and a distant, somewhat bright tertiary which requires telescopic equipment for observation.

==Components==
[[File:RhoGem.png|thumb|left|A diagram Rho Geminorum and the four companions listed in the WDS (Click to enlarge).]]
[[File:RhoGemHR.png|thumb|left|The positions of the three stars in the Rho Geminorum system on the [[Hertzsprung-Russell diagram]] (Click to enlarge). As Rho Geminorum B does not have a known B-V or temperature, a line through its absolute magnitude is drawn instead.]]
Rho Geminorum A is a bright star with a spectral type F0V, meaning that it is a [[main sequence]] that is over a thousand degrees kelvin hotter, one-third more massive, two-thirds larger and five-and-a-half times more luminous than the Sun. With an apparent magnitude of 4.25, it is approximately the seventeenth-brightest star in the constellation of Gemini. Though there are some sources indicating that the star is a spectroscopic binary, including the [[Washington Double Star Catalog]] (WDS) and the [[Gliese Catalogue of Nearby Stars]], no orbit has been provided.

The WDS lists four companions to Rho Geminorum. Of these, surprisingly little is known about the closest companion, the magnitude 12.5 Rho Geminorum B. The most recent measurement lists a separation of 3.4 arcseconds, corresponding to a separation perpendicular to the line of sight of approximately 85 AU. The spectral type listed in SIMBAD is M5, though this is without a source; Plotting the star's absolute magnitude on the [[Hertzsprung-Russell diagram]] (see left) indicates a B-V of 1.53, a value closer to that of an M3V star.<ref name="Teff"/><br/>Peculiarly, the five observations recorded in the WDS date between 1910 and 1935 and none have been made since; even in literature, more recent attempts to resolve Rho Geminorum B have been unsuccessful.<ref name="Hartkopf2009"/> The measurements listed in the WDS seem to be inconsistent with the star being in the background, so the reasons for the failure to observe Rho Geminorum B is unclear.

The next-closest companion, the magnitude 11.59 WDS 07291+3147 C, had a much larger separation of 211.6 arcseconds in 1886. However, this separation increased by 10 arcseconds by 2001, indicating that it is a background star that is unrelated to Rho Geminorum. Correcting for Rho Geminorum A's proper motion, this star's proper motion is RA = -19 mas/yr and Dec = -55 mas/yr. This is a modestly large value, consistent with a distance of a few hundred light-years.<br/> WDS 07291+3147 C is itself listed as having a companion, the magnitude 13.20 WDS 07291+3147 D. Relative to WDS 07291+3147 C its separation has remained at about 100 arcseconds between 1909 and 2001, indicating similar proper motion. While this would indicate that the two stars are bound, at a large distance this separation would indicate a separation of at least several thousand AU and their mutual separation has not been entirely consistent (the position angle has increased from 267 to 270°, and the separation has decreased from 104.1 to 102.3 arcseconds). It is therefore possible that the two background stars are bound, but it is not certain.

The final companion in the WDS, the magnitude 7.86 WDS 07291+3147 E (Rho Geminorum C), has a larger still separation of 756 arcseconds, translating to a separation perpendicular to the line of sight of about 18600 AU. The position of this star relative to the primary has remained consistent over decades, indicating that it has a common proper motion and is therefore a wide tertiary component. The wide separation has also facilitated for observations without contamination from Rho Geminorum A, and as of such Rho Geminorum C has its own Gliese catalogue number (273.1) and HIPPARCOS catalogue number (36357). The HIPPARCOS parallax is consistent with that of the primary to 1σ, leading to a probability that they are bound of approximately 100%.<ref name="Shaya2011"/> The star is also known to be a [[BY Draconis variable]] with a period of 11.63 days, caused by varying brightness as starspots move across the stellar surface across its rotation period. While the derived age for Rho Geminorum A of 2.1 Gigayears is not excessively young, Rho Geminorum C is still very active: It has an S'<sub>HK</sub> of about 0.5,<ref name="Isaacson2010"/> a value similar to that of the near-analogous [[Epsilon Eridani]] whose Log R'<sub>HK</sub> is -4.45. This is much higher than a "quiet" value of <-4.8, making Rho Geminorum C bizarrely active for a modestly old star.

The Rho Geminorum system is an interesting look into a system architecture similar to the [[40 Eridani]] system while the most massive component is on the main sequence, before becoming a white dwarf.

==References==
{{reflist|refs=

<ref name="van Leeuwen2007">{{cite journal | url=http://www.aanda.org/index.php?option=com_article&access=bibcode&Itemid=129&bibcode=2007A%2526A...474..653VFUL | title=Validation of the new Hipparcos reduction | last1=van Leeuwen | first1=F. | journal=Astronomy and Astrophysics | volume=474 | issue=2 | pages=653–664 | year=2007 | arxiv=0708.1752 | bibcode=2007A&A...474..653V | doi=10.1051/0004-6361:20078357 }}</ref>

<ref name="AbsMag">The relevant calculation for absolute magnitude is <math> M = m - 5 ((\log_{10}{D_L}) - 1)\!\,</math>, where <math>m\!\,</math> is the apparent magnitude and <math>D_L\!\,</math> is the distance in light-years. The distance was assumed to be 58.9 light-years, derived from the parallax of Rho Geminorum A.</ref>

<ref name="Boyajian2012">{{cite journal | title=Stellar Diameters and Temperatures. I. Main-sequence A, F, and G Stars | last1=Boyajian | first1=Tabetha S. | coauthors = ''et al.'' | year=2012 | arxiv=1112.3316 | bibcode=2012ApJ...746..101B | doi=10.1088/0004-637X/746/1/101 }}</ref>

<ref name="Wu2011">{{cite journal | title=Coudé-feed stellar spectral library - atmospheric parameters | last1=Wu | first1=Yue | coauthors = ''et al.'' | year=2011 | arxiv=1009.1491 | bibcode=2011A&A...525A..71W | doi=10.1051/0004-6361/201015014 }}</ref>

<ref name="AmmlerVonEiff2012">{{cite journal | title=New measurements of rotation and differential rotation in A-F stars: are there two populations of differentially rotating stars? | last1=Ammler-von Eiff | first1=M. | coauthors = ''et al.'' | year=2012 | arxiv=1204.2459 | bibcode=2012A&A...542A.116A | doi=10.1051/0004-6361/201118724 }}</ref>

<ref name="Shaya2011">{{citation | last1=Shaya | first1=Ed J. | last2=Olling | first2=Rob P. | title=Very Wide Binaries and Other Comoving Stellar Companions: A Bayesian Analysis of the Hipparcos Catalogue | journal=The Astrophysical Journal Supplement | volume=192 | issue=1 | page=2 |date=January 2011 | doi=10.1088/0067-0049/192/1/2 | bibcode=2011ApJS..192....2S |arxiv = 1007.0425 }}</ref>

<ref name="Teff">[http://www.pas.rochester.edu/~emamajek/EEM_dwarf_UBVIJHK_colors_Teff.dat A Modern Mean Stellar Color and Effective Temperatures (Teff)  # Sequence for O9V-Y0V Dwarf Stars], E. Mamajek, 2011, website</ref>

<ref name="Hartkopf2009">{{cite journal | title=Speckle Interferometry at Mount Wilson Observatory: Observations Obtained in 2006-2007 and 35 New Orbits | last1=Hartkopf | first1=William I. | coauthors = ''et al.'' | year=2009 | bibcode=2009AJ....138..813H | doi=10.1088/0004-6256/138/3/813 }}</ref>

<ref name="Isaacson2010">{{cite journal | title=Chromospheric Activity and Jitter Measurements for 2630 Stars on the California Planet Search | last1=Isaacson | first1=Howard | coauthors = ''et al.'' | year=2010 | arxiv=1009.2301 | bibcode=2010ApJ...725..875I | doi=10.1088/0004-637X/725/1/875 }}</ref>

}}

{{Nearest star systems|12}}
{{Stars of Gemini}}

[[Category:Gemini (constellation)]]
[[Category:Bayer objects|Geminorum, Rho]]
[[Category:Henry Draper Catalogue objects|058946]]
[[Category:Hipparcos objects|36366]]
[[Category:Gliese and GJ objects|0274]]
[[Category:HR objects|2852]]
[[Category:F-type main-sequence stars]]
[[Category:K-type main-sequence stars]]
[[Category:M-type main-sequence stars]]
[[Category:Multiple star systems]]