Pi Geminorum
{{short description|Star in the constellation Gemini}}
{{Starbox begin
| name = π Geminorum
}}
{{Starbox image
| image=
{{Location mark
|image=Gemini constellation map.svg|alt=|float=center|width=280
|label=|position=right
|mark=Red circle.svg|mark_width=10|mark_link=π Geminorum
|x=220|y=60
}}
|caption=Location of π Geminorum (circled)
}}
{{Starbox observe
| epoch = J2000.0
| constell = Gemini
| dec = {{DEC|+33|24|56.5034}}
}}
{{Starbox character
| type = AGB
| r-i =
}}
{{Starbox astrometry
| radial_v = {{Val|-13.36|0.34}}
| parallax = 4.93
| p_error = 0.32
}}
{{Starbox detail
| rotational_velocity =
| rotation =
| age_gyr =
}}
{{Starbox catalog
| names = π Gem, 80 Geminorum, BD+33°1585, FK5 296, HD 62898, HIP 38016, HR 3013, SAO 60340.
}}
{{Starbox reference
| Simbad = pi.+Gem
}}
{{Starbox end}}
π Geminorum (Latinised as Pi Geminorum, abbreviated to π Gem or pi Gem) is a star located in the constellation Gemini, to the north of Castor. With an apparent visual magnitude of 5.14, it is faintly visible to the naked eye on a dark night. Based upon an annual parallax shift of 4.93 mas, Pi Geminorum is located roughly 660 light years from the Sun. At that distance, the visual magnitude of the star is diminished by an interstellar absorption factor of 0.033 due to interstellar dust.
This is an evolved red giant star with a stellar classification of M1 IIIa. The measured angular diameter of this star is {{Val|2.58|0.20|u=mas}}. At the estimated distance of this star, this yields a physical size of about 56 times the radius of the Sun. It is radiating roughly a thousand times the luminosity of the Sun from its outer atmosphere at an effective temperature of 3,900 K.
Unexpected for a red giant, Pi Geminorum was found to be a X-ray source during the ROSAT all-sky survey. The most likely source for this emission is a magnitude 11.4 star located at an angular separation of 21 arcseconds along a position angle of 214°. This is a background star, not gravitationally bound to Pi Geminorum.
In a 1930 study, Pi Geminorum was suspected to vary in brightness by a few hundredths of a magnitude, but this has not been confirmed by modern measurements.
References
{{reflist|refs=
{{cite Gaia DR3|882055857328203904}}
| title=Validation of the new Hipparcos reduction
| last1=van Leeuwen | first1=F.
| journal=Astronomy and Astrophysics
| volume=474 | issue=2 | pages=653–664 | date=2007
| arxiv=0708.1752 | bibcode=2007A&A...474..653V
| doi=10.1051/0004-6361:20078357 | s2cid=18759600 | postscript=. }}
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| title=A catalogue of multiplicity among bright stellar systems
| journal=Monthly Notices of the Royal Astronomical Society
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| doi=10.1111/j.1365-2966.2008.13596.x | doi-access=free | bibcode=2008MNRAS.389..869E
| arxiv=0806.2878 | s2cid=14878976 | postscript=. }}
| title=On the X-ray emission from M-type giants
| last1=Hunsch | first1=Matthias | last2=Schmitt | first2=Jurgen H. M. M.
| last3=Schroder | first3=Klaus-Peter | last4=Zickgraf | first4=Franz-Josef
| journal=Astronomy and Astrophysics | display-authors=1
| volume=330 | pages=225–231 | date=February 1998
| bibcode=1998A&A...330..225H | postscript=. }}
| title=Comparing the Ca ii H and K Emission Lines in Red Giant Stars
| display-authors=1 | last1=Ryon | first1=Jenna
| last2=Shetrone | first2=Matthew D. | last3=Smith | first3=Graeme H.
| journal=Publications of the Astronomical Society of the Pacific
| volume=121 | issue=882 | pages=842–856 | date=August 2009
| doi=10.1086/605456 | bibcode=2009PASP..121..842R
| arxiv=0907.3346 | s2cid=17821279 | postscript=. }}
| title=Spectroscopic binaries among Hipparcos M giants. I. Data, orbits, and intrinsic variations
| last1=Famaey | first1=B. | last2=Pourbaix | first2=D. | last3=Frankowski | first3=A. | last4=Van Eck | first4=S. | last5=Mayor | first5=M. | last6=Udry | first6=S. | last7=Jorissen | first7=H. A.
| display-authors=1 | journal=Astronomy and Astrophysics
| volume=498 | issue=2 | pages=627–640 | year=2009
| arxiv=0901.0934 | bibcode=2009A&A...498..627F
| doi=10.1051/0004-6361/200810698 | s2cid=18739721 | postscript=. }}
| display-authors=1 | last1=Richichi | first1=A.
| last2=Percheron | first2=I. | last3=Khristoforova | first3=M.
| title=CHARM2: An updated Catalog of High Angular Resolution Measurements
| journal=Astronomy and Astrophysics
| volume=431 | issue=2 | pages=773–777 | date=February 2005
| doi=10.1051/0004-6361:20042039 | bibcode=2005A&A...431..773R
| postscript=. | doi-access=free }}
| first1=Kenneth R. | last1=Lang
| title=Astrophysical formulae | volume=1
| series=Astronomy and astrophysics library
| edition=3rd | publisher=Birkhäuser
| date=2006 | isbn=3-540-29692-1 | postscript=.
| url=https://books.google.com/books?id=OvTjLcQ4MCQC&pg=PA41
}}. The radius (R*) is given by:
:
& = \frac{(203\cdot 2.58\cdot 10^{-3})\ \text{AU}}{0.0046491\ \text{AU}/R_{\bigodot}} \\
& \approx 112.6\cdot R_{\bigodot}
\end{align}
| last1=Mermilliod | first1=J.-C.
| title=Compilation of Eggen's UBV data, transformed to UBV (unpublished)
| journal=Catalogue of Eggen's UBV Data
| year=1986 | publisher=SIMBAD
| bibcode=1986EgUBV........0M | postscript=. }}
| title= pi. Gem
| access-date=2016-12-07 | postscript=. }}
}}
{{Stars of Gemini|state=collapsed}}
{{DEFAULTSORT:Pi Geminorum}}
Category:Gemini (constellation)