{{Short description|Triple star system in the constellation Hydra}} {{Starbox begin}} {{Starbox image | image = {{Location mark |image=Hydra constellation map.svg|alt=|float=center|width=300 |label=|position=right |mark=Red circle.svg|mark_width=10|mark_link=27 Hydrae |x=792|y=232 }} | caption = Location of 27 Hydrae (circled in red) }} {{Starbox observe | epoch = J2000 | constell = [[Hydra (constellation)|Hydra]] | ra = {{RA|09|20|29.01857}}<ref name=vanLeeuwen2007/> | dec = {{DEC|−09|33|20.5054}}<ref name=vanLeeuwen2007/> | appmag_v = 4.818<ref name=Luck2015/> {{nowrap|(4.91 + 7.03 + 10.99)}}<ref name=WDSC2014/> }} {{Starbox character | type = [[red clump]]<ref name=Alves2000/> | class = {{nowrap|K0III<ref name=Houk1999/> + F4V + K2V}}<ref name=Eggleton2008/> | b-v = | u-b = | variable = }} {{Starbox astrometry | radial_v = {{Val|+25.60|0.13}}<ref name=Massarotti2008/> | prop_mo_ra = −12.48<ref name=vanLeeuwen2007/> | prop_mo_dec = −27.37<ref name=vanLeeuwen2007/> | parallax = 14.66 | p_error = 0.31 | parallax_footnote = <ref name=vanLeeuwen2007/> | absmag_v = }} {{Starbox detail | source = | component1 = A | mass = 2.17<ref name=Luck2015/> | radius = 11<ref name=Massarotti2008/> | luminosity = 57.5<ref name=Luck2015/> | temperature = {{Val|4965|26|fmt=commas}}<ref name=Luck2015/> | metal_fe = −0.07<ref name=Massarotti2008/> | gravity = 2.9<ref name=Massarotti2008/> | rotational_velocity = 3.3<ref name=Massarotti2008/> | rotation = | age_gyr = 1.91<ref name=Luck2015/> }} {{Starbox detail|no_heading=y | component1 = B | temperature = 6,664<ref name=dr2b/> | radius = 1.82<ref name=dr2b/> | luminosity = 5.885<ref name=dr2b/> | component2 = C | temperature2 = 4,685<ref name=dr2c/> | radius2 = 0.72<ref name=dr2c/> | luminosity2 = 0.227<ref name=dr2c/> }} {{Starbox catalog | names = {{odlist | CCDM=J09204-0934 | WDS=J09204-0934 }}<ref name=SIMBAD/> | component1 = A | names1 = {{odlist | F=27 Hya | BD=−08°2643 | HD=80586 | HIP=45811 | HR=3709 | SAO=136768 }} | component2 = B | names2 = {{odlist | BD=−09°2801 | HD=80550 | HIP=45802 | SAO=136767 }} | component3 = C | names3 = {{odlist | TYC=5463-1518-1 }} }} {{Starbox reference | Simbad=27+Hya | Simbad2=HD+80550|sn2=B | Simbad3=TYC+5463-1518-1|sn3=C }} {{Starbox end}}
'''27 Hydrae''' is a [[triple star system]]<ref name=Eggleton2008/> in the [[celestial equator|equatorial]] [[constellation]] of [[Hydra (constellation)|Hydra]],<ref name=SIMBAD/> located 222 [[light year]]s away from the Sun.<ref name=vanLeeuwen2007/> It is visible to the naked eye as a faint, orange-hued star with a combined [[apparent visual magnitude]] of 4.82.<ref name=Luck2015/> The system is moving further from the Earth with a heliocentric [[radial velocity]] of +25.6 km/s.<ref name=Massarotti2008/>
The magnitude 4.91<ref name=Eggleton2008/> primary, component A, is an aging [[giant star]] with a [[stellar classification]] of K0 III.<ref name=Houk1999/> It is a [[red clump]] giant,<ref name=Alves2000/> which indicates it is on the [[horizontal branch]] and is generating energy through [[helium fusion]] at its [[stellar core|core]]. The star is 1.9<ref name=Luck2015/> billion years old with 2.17<ref name=Luck2015/> times the [[mass of the Sun]]. It has swelled to 11<ref name=Massarotti2008/> times the [[Sun's radius]] and is radiating 57.5<ref name=Luck2015/> times the [[Sun's luminosity]] from its enlarged [[photosphere]] at an [[effective temperature]] of 4,965 K.<ref name=Luck2015/> The star is suspected to host a [[planemo|low-mass]] companion.<ref name=Toyota2009/>
The stellar companions to this star, designated components B and C, lie at an [[angular separation]] of {{Val|229.10|ul=arcsecond}} from the primary, and form a binary pair with a separation of 9.20″ as of 2015.<ref name=WDSC2014/> The brighter member of the pair, component B, is a seventh magnitude [[F-type main-sequence star]] with a class of F4 V, while its companion is an eleventh magnitude [[K-type main-sequence star]] with a class of K2 V.<ref name=Eggleton2008/>
==Substellar companion candidate== The [[Okayama Planet Search Program|Okayama Planet Search]] team published a paper in late 2008 reporting investigations into radial velocity variations observed for a set of evolved stars, showing hints of a [[substellar]] companion orbiting the primary member of the wide [[binary system]] 27 Hydrae (ADS 7311).<ref name=Toyota2009/> A later study revised the [[minimum mass]] of this candidate companion to 28 [[Jupiter mass]]es, indicating that if it exists, it is a [[brown dwarf]] rather than a planet.<ref name=Katoh2018/>
{{OrbitboxPlanet begin | name = 27 Hydrae A }} {{OrbitboxPlanet hypothetical | exoplanet = | mass = ≥28 | period = 3,400 | semimajor = ≈5.9 | eccentricity = }} {{Orbitbox end}}
==References== <references> <ref name=SIMBAD>{{cite simbad | title=27 Hya | access-date=May 3, 2019 }}</ref>
<ref name=dr2b>{{cite DR2|5742848123496954112}}</ref>
<ref name=dr2c>{{cite DR2|5742848123496954496}}</ref>
<ref name=vanLeeuwen2007>{{citation | 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=. }}</ref>
<ref name=Toyota2009>{{cite journal | last1=Toyota | first1=Eri | last2=Itoh | first2=Yoichi | last3=Ishiguma | first3=Shinichiro | last4=Urakawa | first4=Seitaro | last5=Murata | first5=Daisuke | last6=Oasa | first6=Yumiko | last7=Matsuyama | first7=Hiroko | last8=Funayama | first8=Hitoshi | last9=Sato | first9=Bun'ei | last10=Mukai | first10=Tadashi | title=Radial Velocity Search for Extrasolar Planets in Visual Binary Systems | journal=[[Publications of the Astronomical Society of Japan]] | volume=61| issue=1 | pages=19–28| year=2008 | bibcode=2009PASJ...61...19T | doi=10.1093/pasj/61.1.19 | display-authors=1 | doi-access=free | hdl=20.500.14094/90001422 | hdl-access=free }}</ref>
<ref name=Eggleton2008>{{cite journal | last1=Eggleton | first1=P. P. | last2=Tokovinin | first2=A. A. | title=A catalogue of multiplicity among bright stellar systems | journal=[[Monthly Notices of the Royal Astronomical Society]] | volume=389 | issue=2 | pages=869–879 | date=September 2008 | doi=10.1111/j.1365-2966.2008.13596.x | doi-access=free | bibcode=2008MNRAS.389..869E | arxiv=0806.2878 | s2cid=14878976 }}</ref>
<ref name=Houk1999>{{cite journal | last1=Houk | first1=N. | last2=Swift | first2=C. | title=Michigan catalogue of two-dimensional spectral types for the HD Stars | journal=Michigan Spectral Survey | volume=5 | year=1999 | bibcode=1999MSS...C05....0H }}</ref>
<ref name=Luck2015>{{cite journal | title=Abundances in the Local Region. I. G and K Giants | last1=Luck | first1=R. Earle | journal=Astronomical Journal | volume=150 | issue=3 | at=88 | year=2015 | arxiv=1507.01466 | bibcode=2015AJ....150...88L | doi=10.1088/0004-6256/150/3/88 | s2cid=118505114 }}</ref>
<ref name=Massarotti2008>{{cite journal | 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 | display-authors=1 | 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=Alves2000>{{citation | last1=Alves | first1=David R. | title=K-Band Calibration of the Red Clump Luminosity | journal=The Astrophysical Journal | volume=539 | issue=2 | pages=732–741 | date=August 2000 | doi=10.1086/309278 | bibcode=2000ApJ...539..732A | arxiv=astro-ph/0003329 | s2cid=16673121 }}</ref>
<ref name=WDSC2014>{{citation | display-authors=1 | last1=Mason | first1=B. D. | last2=Wycoff | first2=G. L. | last3=Hartkopf | first3=W. I. | last4=Douglass | first4=G. G. | last5=Worley | first5=C. E. | title=The Washington Visual Double Star Catalog | journal=The Astronomical Journal | year=2014 | volume=122 | issue=6 | page=3466 | bibcode=2001AJ....122.3466M | url=http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/wds | access-date=2015-07-22 | doi=10.1086/323920 | doi-access=free }}</ref>
<ref name=Katoh2018>{{Cite journal |last=Katoh |first=Noriyuki |last2=Itoh |first2=Yoichi |last3=Sato |first3=Bun’ei |date=August 1, 2018 |title=Search for companions in visual binary systems using precise radial-velocity measurements |url=https://academic.oup.com/pasj/article/doi/10.1093/pasj/psy054/5025942 |journal=Publications of the Astronomical Society of Japan |language=en |volume=70 |issue=4 |doi=10.1093/pasj/psy054 |issn=0004-6264|url-access=subscription }}</ref> </references>
{{Stars of Hydra}}
[[Category:K-type giants]] [[Category:F-type main-sequence stars]] [[Category:K-type main-sequence stars]] [[Category:Horizontal-branch stars]] [[Category:Triple star systems]] [[Category:Hypothetical planetary systems]] [[Category:Hydra (constellation)]] [[Category:Bayer objects|Hydrae, P]] [[Category:Durchmusterung objects|BD-08 2643]] [[Category:Flamsteed objects|Hydrae, 27]] [[Category:Henry Draper Catalogue objects|080586]] [[Category:Hipparcos objects|045811]] [[Category:Bright Star Catalogue objects|3709]]