{{Short description|Triple star system in the constellation Hercules}} {{about-distinguish2|u Herculis|υ (upsilon) Herculis|U Herculis}} {{Starbox begin}} {{Starbox image | image= {{Location mark |image=Hercules constellation map.svg|alt=|float=center|width=240 |label=|position=right |mark=Red circle.svg|mark_width=10|mark_link=68 Her |x=570|y=484 }} |caption=Location of 68 Herculis (circled) }} {{Starbox observe | epoch = J2000 | constell = Hercules | ra = {{RA|17|17|19.56781}}<ref name=GaiaDR3/> | dec = {{DEC|+33|06|00.3684}}<ref name=GaiaDR3/> | appmag_v = 4.80<ref name=Anderson2012/> }} {{Starbox character | type = | class = {{nowrap|B2 V + B8-9}}<ref name=Hilditch2005/> | b-v = {{Val|−0.166|0.011}}<ref name=Anderson2012/> | u-b = | variable = Algol/semi-detached<ref name=Samus2017/> }} {{Starbox astrometry | radial_v = {{Val|−17.1|2.8}}<ref name=Anderson2012/> | prop_mo_ra = −4.298<ref name=GaiaDR3/> | prop_mo_dec = −5.621<ref name=GaiaDR3/> | parallax = 3.4346 | p_error = 0.1164 | parallax_footnote = <ref name=GaiaDR3/> | absmag_v = {{Val|−2.66|0.30}} {{nowrap|(−2.35 + −1.15)}}<ref name=Hilditch2005/> }} {{Starbox orbit | reference = <ref name=Kolbas2014/> | primary = 68 Her Aa | name = 68 Her Ab | period_unitless = 2.05102685 days | axis_unitless = {{Val|14.95|0.17|ul=solar radius}} | eccentricity = 0.0<ref name=Saad2011/> (fixed) | inclination = {{Val|78.9|0.4}} | periastron = {{Val|50344.99|0.009|fmt=commas}}<ref name=Saad2011/> | periarg = 0.0<ref name=Saad2011/> (fixed) | k1 = {{Val|101|1}}<ref name=Saad2011/> | k2 = {{Val|252|1.8}}<ref name=Saad2011/> }} {{Starbox detail | source = <ref name=Kolbas2014/> | component1 = 68 Her Aa | mass = {{Val|7.88|0.26}} | radius = {{Val|4.93|0.15}} | temperature = {{Val|21600|220|fmt=commas}} | luminosity = {{Val|4786|343|319|fmt=commas}} | gravity = {{Val|3.948|0.024}} | metal_fe = | rotational_velocity = {{Val|145|5}}<ref name=Saad2011/> | age_myr = | component2 = 68 Her Ab | mass2 = {{Val|2.79|0.12}} | radius2 = {{Val|4.26|0.06}} | temperature2 = {{Val|12600|550|fmt=commas}} | luminosity2 = {{Val|426.5|86.4|71.7}} | gravity2 = {{Val|3.625|0.013}} | rotational_velocity2 = {{Val|105|5}}<ref name=Saad2011/> }} {{Starbox catalog | names={{odlist | B=u Her | F=68 Her | BD=+33°2864 | HD=156633 | HIP=84573 | HR=6431 | SAO=65913 | WDS=J17173+3306A }}<ref name=SIMBAD/> }} {{Starbox reference | Simbad=68+Her }} {{Starbox end}}
'''68 Herculis''' is a triple star<ref name=Eggleton2008/> system located around 950 light-years away from the Sun in the northern constellation of Hercules. In the astronomical community it is often referred to by its Bayer designation of '''u Herculis''',<ref name=Hilditch2005/> while ''68 Herculis'' is the Flamsteed designation. The system is visible to the naked eye as a faint, blue-white-hued point of light with a peak apparent visual magnitude of 4.80.<ref name=Anderson2012/> It is approaching the Earth with a heliocentric radial velocity of −17 km/s.<ref name=Anderson2012/>
As early as the 1840s, Johann Friedrich Julius Schmidt believed 68 Herculis was a variable star, initially thinking it might be a long period or irregular variable. By 1869 he had concluded that its brightness varies with a regular period, but his period estimates were far longer than the true value.<ref name="Schmidt1869"/> In 1908 the star was put on an observing program at Harvard College Observatory, and professor Oliver Wendell determined that the star is an eclipsing binary with a period of 2.05 days.<ref name="Schlesinger1912"/>
[[Image:68HerLightCurve.png|thumb|left|A light curve for 68 Herculis, plotted from TESS data<ref name=MAST/>]] The inner pair of this system form a well-studied<ref name=Hilditch2005/> semidetached binary with the orbital plane oriented near the line of sight to the Earth, making it an Algol-type eclipsing binary. They have an orbital period of just over two days and a semimajor axis of 15 times the radius of the Sun, with the secondary component transferring mass to the hotter primary star.<ref name=Kolbas2014/> The main eclipse reduces the magnitude of the system to 5.37, while the second eclipse lowers the brightness to magnitude 4.93.<ref name=Samus2017/> Theoretical calculations suggest the donor star began with 7.2 times the mass of the Sun, the current primary at 3.6 solar masses, and their initial orbital period was around 1.35 days.<ref name=Kolbas2014/>
The primary, designated component Aa or sometimes just A, displays Beta Cephei-like pulsational behavior. It appears to be a B-type main-sequence star with a stellar classification of B2 V.<ref name=Hilditch2005/> The star has a high rate of spin, with a projected rotational velocity of 145 km/s.<ref name=Saad2011/> It has nearly eight times the mass of the Sun and five times the Sun's radius. The star is radiating 4,786 times the Sun's luminosity from its photosphere at an effective temperature of {{val|21600|ul=K|fmt=commas}}.<ref name=Kolbas2014/>
The secondary, component Ab or occasionally just B, has proven difficult to classify, but appears as a B-type star of type B8-9.<ref name=Hilditch2005/> It is close to triple the mass of the Sun with 4.3 times the Sun's radius. The star is spinning with a projected rotational velocity of 105 km/s. It is radiating 426.5 times the Sun's luminosity from its photosphere at an effective temperature of 12,600 K.<ref name=Kolbas2014/>
The third member of this system, component B, lies at an angular separation of {{Val|4.4|ul=arcsecond}} from the inner pair with a visual magnitude of 10.2.<ref name=Eggleton2008/> It shares a common proper motion and similar parallax to the eclipsing pair, and is modelled to be a main-sequence star somewhat more massive, hotter, and more luminous than the Sun.<ref name=dr3b/> Any orbit would require thousands of years.<ref name=msc/>
==References== <references> <ref name="Schlesinger1912">{{cite journal |last1=Schlesinger |first1=Frank |author-link1=Frank Schlesinger |last2=Baker |first2=Robert Horace |author-link2=Robert Horace Baker |date=1912 |title=The eclipsing variable u Herculis |url=https://articles.adsabs.harvard.edu/pdf/1912PAllO...2...51S |journal=Publications of the Allegheny Observatory of the University of Pittsburgh |volume=II |issue=9 |page=51 |bibcode=1912PAllO...2...51S |access-date=17 December 2024}}</ref>
<ref name="Schmidt1869">{{cite journal |last=Schmidt |first=Johann Friedrich Julius |author-link=Johann Friedrich Julius Schmidt |date=August 1869 |title=Beobachtungen über die Veränderlichkeit von u Herculis. Von Herrn Director J. F. Julius Schmidt |url=https://articles.adsabs.harvard.edu/pdf/1869AN.....74..229S |journal=Astronomische Nachrichten |volume=74 |issue=14 |page=229 |bibcode=1869AN.....74..229S |doi=10.1002/asna.18690741404 |access-date=17 December 2024}}</ref>
<ref name="msc">{{citation |last=Tokovinin |first=Andrei |title=The Updated Multiple Star Catalog |date=23 February 2018 |journal=The Astrophysical Journal Supplement Series |volume=235 |issue=1 |page=6 |postscript=. |arxiv=1712.04750 |bibcode=2018ApJS..235....6T |doi=10.3847/1538-4365/aaa1a5 |eissn=1538-4365 |doi-access=free}}</ref>
<ref name="dr3b">{{cite Gaia DR3|1334035606852913664}}</ref>
<ref name=MAST>{{citation |postscript=. |title=MAST: Barbara A. Mikulski Archive for Space Telescopes |url=https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html |publisher=Space Telescope Science Institute |access-date=4 January 2023}}</ref>
<ref name=SIMBAD>{{cite simbad |title=68 Her |access-date=2019-06-14 |mode=cs2 |postscript=.}}</ref>
<ref name=GaiaDR3>{{Cite Gaia DR3|1334035606852913536}}</ref>
<ref name="Samus2017">{{citation |last1=Samus |first1=N. N. |last2=Kazarovets |first2=E. V. |last3=Durlevich |first3=O. V. |last4=Kireeva |first4=N. N. |last5=Pastukhova |first5=E. N. |title=General Catalogue of Variable Stars |journal=Astronomy Reports |volume=61 |issue=1 |pages=80–88 |year=2017 |postscript=. |version=5.1 |bibcode=2017ARep...61...80S |doi=10.1134/S1063772917010085 |s2cid=125853869}}</ref>
<ref name="Kolbas2014">{{citation |last1=Kolbas |first1=V. |last2=Dervișoğlu |first2=A. |last3=Pavlovski |first3=K. |last4=Southworth |first4=J. |title=Tracing CNO exposed layers in the Algol-type binary system u Her |date=November 2014 |journal=Monthly Notices of the Royal Astronomical Society |volume=444 |issue=4 |pages=3118–3129 |postscript=. |arxiv=1408.2681 |bibcode=2014MNRAS.444.3118K |doi=10.1093/mnras/stu1652 |doi-access=free}}</ref>
<ref name=Saad2011>{{citation |title=A study of the B+B double-lined eclipsing binary u Her |last1=Saad |first1=Somaya |last2=Nouh |first2=Mohamed |journal=Bulletin of the Astromical Society of India |volume=39 | pages=277–287 |date=June 2011 |bibcode=2011BASI...39..277S |postscript=.}}</ref>
<ref name="Hilditch2005">{{citation |last=Hilditch |first=R. W. |title=Astrophysical parameters for the eclipsing binary u Herculis |date=April 2005 |journal=The Observatory |volume=125 |pages=72–81 |bibcode=2005Obs...125...72H}}</ref>
<ref name="Anderson2012">{{citation |last1=Anderson |first1=E. |last2=Francis |first2=Ch. |title=XHIP: An extended hipparcos compilation |journal=Astronomy Letters |volume=38 |issue=5 |pages=331 |year=2012 |postscript=. |arxiv=1108.4971 |bibcode=2012AstL...38..331A |doi=10.1134/S1063773712050015 |s2cid=119257644}}</ref>
<ref name="Eggleton2008">{{citation |last1=Eggleton |first1=P. P. |last2=Tokovinin |first2=A. A. |title=A catalogue of multiplicity among bright stellar systems |date=September 2008 |journal=Monthly Notices of the Royal Astronomical Society |volume=389 |issue=2 |pages=869–879 |postscript=. |arxiv=0806.2878 |bibcode=2008MNRAS.389..869E |doi=10.1111/j.1365-2966.2008.13596.x |s2cid=14878976 |doi-access=free}}</ref> </references>
==External links== *{{citation | first1=James B. | last1=Kaler | title=68 Herculis | date=July 20, 2012 | work=STARS | publisher=University of Illinois | url=http://stars.astro.illinois.edu/sow/68her.html | access-date=2019-06-15 | postscript=. }}
{{Stars of Hercules}}
Category:B-type main-sequence stars Category:Algol variables Category:Triple stars Category:Hercules (constellation) Herculis, u Category:Durchmusterung objects Herculis, 068 156633 084573 6431