{{Short description|Star in the constellation Hydra}} {{about-distinguish|a Hydrae|33 Hydrae{{!}}A Hydrae|Alphard{{!}}α Hydrae}} {{Starbox begin}} {{Starbox observe | epoch = [[J2000.0]] | constell = [[Hydra (constellation)|Hydra]]<ref name=Anderson2012/> | ra = {{RA|08|40|01.47182}}<ref name=GaiaDR2/> | dec = {{DEC|−12|28|31.3433}}<ref name=GaiaDR2/> | appmag_v = 4.98<ref name=Anderson2012/> }} {{Starbox character | type = [[red giant branch]]<ref name=mcwilliam1990/> | class = K3 III<ref name=houk1978/> | b-v = {{Val|1.415|0.001}}<ref name=Anderson2012/> | variable = }} {{Starbox astrometry | radial_v = {{Val|−7.8|0.6}}<ref name=deBruijne2012/> | prop_mo_ra = −81.619<ref name=GaiaDR2/> | prop_mo_dec = −1.646<ref name=GaiaDR2/> | parallax = 8.7394 | p_error = 0.1769 | parallax_footnote = <ref name=GaiaDR2/> | absmag_v = −0.40<ref name=Anderson2012/> }} {{Starbox detail | source = | mass = | radius = {{Val|32.7|0.5|2.6}}<ref name=GaiaDR2/> | gravity = 1.91<ref name=McWilliam1990/> | luminosity = {{Val|267|6}}<ref name=GaiaDR2/> | temperature = {{Val|4080|173|30|fmt=commas}}<ref name=GaiaDR2/> | metal_fe = −0.21<ref name=McWilliam1990/> | rotational_velocity = | age_myr = }} {{Starbox catalog | names = {{odlist | B=a Hya | F=6 Hya | BD=-11°2420 | HD=73840 | HIP=42509 | HR=3431 | SAO=154515 }}<ref name=SIMBAD/> }} {{Starbox reference | Simbad = 6+Hya }} {{Starbox end}}
'''6 Hydrae''' is a single<ref name=Eggleton2008/> [[star]] in the [[celestial equator|equatorial]] [[constellation]] of [[Hydra (constellation)|Hydra]], located 373 [[light-year]]s away from the [[Sun]].<ref name=GaiaDR2/> It has the [[Bayer designation]] '''a Hydrae'''; ''6 Hydrae'' is the [[Flamsteed designation]]. This object is visible to the naked eye as a faint, orange-hued star with an [[apparent visual magnitude]] of 4.98.<ref name=Anderson2012/> It is moving closer to the Earth with a heliocentric [[radial velocity]] of −8 km/s.<ref name=deBruijne2012/> Eggen (1995) listed it as a [[proper motion]] candidate for membership in the [[IC 2391]] [[supercluster]].<ref name=Eggen1995/>
This is an aging [[giant star]] with a [[stellar classification]] of K3 III,<ref name=houk1978/> which indicates it has exhausted the [[hydrogen]] at its [[stellar core|core]] and [[stellar evolution|evolved]] away from the [[main sequence]]. As a consequence, it has expanded to 33<ref name=GaiaDR2/> times the [[radius of the Sun]]. The star is radiating 267<ref name=GaiaDR2/> times the [[luminosity of the Sun]] from its swollen [[photosphere]] at an [[effective temperature]] of {{val|4080|ul=K|fmt=commas}}.<ref name=GaiaDR2/>
==References== <references> <ref name=GaiaDR2>{{cite DR2|5747442879511136640}}</ref>
<ref name=SIMBAD>{{cite simbad | title=6 Hya | access-date=2019-04-23 }}</ref>
<ref name=mcwilliam1990>{{cite journal |last1=McWilliam |first1=Andrew |title=High-Resolution Spectroscopic Survey of 671 GK Giants. I. Stellar Atmosphere Parameters and Abundances |journal=The Astrophysical Journal Supplement Series |date=1990 |volume=74 |page=1075 |doi=10.1086/191527 |bibcode=1990ApJS...74.1075M }}</ref>
<ref name=Anderson2012>{{cite XHIP|42509}}</ref>
<ref name=McWilliam1990>{{citation | last=McWilliam | first=Andrew | postscript=. | title=High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances | journal=Astrophysical Journal Supplement Series | volume=74 | pages=1075–1128 | date=December 1990 | doi=10.1086/191527 | bibcode=1990ApJS...74.1075M | doi-access=free }}</ref>
<ref name=deBruijne2012>{{citation | last1=de Bruijne | first1=J. H. J. | last2=Eilers | first2=A.-C. | title=Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project | journal=Astronomy & Astrophysics | volume=546 | id=A61 | pages=14 | date=October 2012 | doi=10.1051/0004-6361/201219219 | bibcode=2012A&A...546A..61D | arxiv=1208.3048 | s2cid=59451347 | postscript=. }}</ref>
<ref name=Eggleton2008>{{citation | title=A catalogue of multiplicity among bright stellar systems | last1=Eggleton | first1=P. P. | last2=Tokovinin | first2=A. A. | journal=Monthly Notices of the Royal Astronomical Society | volume=389 | issue=2 | pages=869 | date=2008 | doi=10.1111/j.1365-2966.2008.13596.x | doi-access=free | arxiv=0806.2878 | bibcode=2008MNRAS.389..869E | s2cid=14878976 | postscript=. }}</ref>
<ref name=Eggen1995>{{citation | title=Reality Tests of Superclusters in the Young Disk Population | last1=Eggen | first1=Olin J. | journal=Astronomical Journal | postscript=. | volume=110 | page=2862 | date=December 1995 | doi=10.1086/117734 | bibcode=1995AJ....110.2862E }}</ref>
<ref name=houk1978>{{citation | last1=Houk | first1=Nancy | last2=Smith-Moore | first2=M. | title=Michigan catalogue of two-dimensional spectral types for the HD stars | volume=4 | publication-place=Ann Arbor | year=1978 | publisher=Dept. of Astronomy, University of Michigan | bibcode=1988mcts.book.....H | postscript=. }}</ref> </references>
{{Stars of Hydra}}
[[Category:K-type giants]] [[Category:Hydra (constellation)]] [[Category:Bayer objects|Hydrae, a]] [[Category:Durchmusterung objects]] [[Category:Flamsteed objects|Hydrae, 06]] [[Category:Henry Draper Catalogue objects|073840]] [[Category:Hipparcos objects|042509]] [[Category:Bright Star Catalogue objects|3431]]