{{Short description|Multiple star system}} {{Starbox begin | name=ε Lupi }} {{Starbox image | image= {{Location mark |image=Lupus constellation map.svg|alt=|float=center|width=240 |label=|position=right |mark=Red circle.svg|mark_width=10|mark_link=ε Lupi |x=468|y=818 }} |caption=Location of ε Lupi (circled) }} {{Starbox observe | epoch = [[J2000.0]] | ra = {{RA|15|22|40.86826}}<ref name=aaa474_2_653/> | dec = {{DEC|-44|41|22.6146}}<ref name=aaa474_2_653/> | appmag_v = 3.41<ref name=apjs15_459/> | constell = [[Lupus (constellation)|Lupus]] }} {{Starbox character | class = B2&nbsp;IV-V<ref name=aaa440_1_249/> | b-v = −0.195<ref name=apjs15_459/> | u-b = −0.778<ref name=apjs15_459/> | variable = }} {{Starbox astrometry | radial_v = +7.9<ref name=rgcrv/> | prop_mo_ra = −22.86<ref name=aaa474_2_653/> | prop_mo_dec = −18.87<ref name=aaa474_2_653/> | parallax = 6.37 | p_error = 0.70 | parallax_footnote = <ref name=aaa474_2_653/> | absmag_v = −2.55<ref name=Anderson2012/> }} {{Starbox orbit |reference=<ref name=Pablo2019/> |primary = Aa |name = Ab |period_unitless=4.559646 days |axis_unitless = {{val|ul=solar radius|31.5|2.5|2.3}} |periastron=2,452,790.33<ref name=aaa440_1_249/> |eccentricity= {{Val|0.2806|0.0059|0.0047}} |k1=53.8<ref name=aaa440_1_249/> |k2=64.7<ref name=aaa440_1_249/> |periarg_primary = {{Val|335.7|4.8|4.5}} |inclination= {{Val|18.8|1.6|1.4}} }} {{Starbox detail | source = <ref name=Pablo2019/> | component1=&epsilon; Lup Aa | mass = {{val|11.0|2.9|2.2}} | radius = {{Val|4.64|0.37|0.48}} | luminosity_bolometric = {{val|3407|658|567|fmt=commas}} | temperature = 20,500 | gravity = {{nowrap|3.89 ± 0.17}}<ref name=aaa440_1_249/> | metal_fe = | rotational_velocity = 133<ref name=aaa440_1_249/> | age = | component2=&epsilon; Lup Ab | mass2 = {{val|9.2|2.4|1.9}} | radius2 = {{Val|4.83|0.42|0.46}} | luminosity2 = {{Val|2197|489|399|fmt=commas}} | temperature2 = 18,000 }} {{Starbox catalog | names = &epsilon; Lup, [[Cape Photographic Durchmusterung|CPD]]−44°7342, [[Henry Draper Catalogue|HD]]&nbsp;136504, [[Hipparcos|HIP]]&nbsp;75264, [[Bright Star Catalogue|HR]]&nbsp;5708, [[Star catalogue#SAO|SAO]]&nbsp;225712<ref name=SIMBAD/> }} {{Starbox reference |Simbad=eps+Lup }} {{Starbox end}}

'''Epsilon Lupi''', [[Latinisation of names|Latinized]] from '''ε Lup''', is a multiple [[star system]] in the southern [[constellation]] of [[Lupus (constellation)|Lupus]]. At an [[apparent visual magnitude]] of 3.41, Epsilon Lupi can be readily viewed from the southern hemisphere with [[Bortle Dark-Sky Scale|sufficiently dark skies]]. It is the [[List of stars in Lupus|fifth-brightest star]] or star system in the constellation.<ref name=apjs15_459/> [[Parallax]] measurements give a distance to this system of roughly {{Convert|510|ly|pc|abbr=off|lk=on}}.<ref name=aaa474_2_653/>

This system is what astronomers term a double-lined [[spectroscopic binary]]. When the [[spectrum]] is examined, the [[absorption line]] features of both stars can be viewed. As a result of the [[Doppler effect]], these lines shift back and forth in frequency as the two stars orbit around each other. This allows some of their [[orbital elements]] to be deduced, even though the individual stars have not been resolved with a telescope. The pair share a close, elliptical orbit with a [[orbital period|period]] of 4.55970&nbsp;days. The [[orbital eccentricity]] is 0.277,<ref name=aaa440_1_249/> which means that at the separation at closest approach, or [[periapsis]], is only 57% of the distance at their greatest separation, or [[apoapsis]].<ref name=ratio/> There is a third, more distant companion at an [[angular separation]] of around 1&nbsp;[[arcsecond]] that may be orbiting the pair with a period of about 64 years.<ref name=aaa440_1_249/>

The pair that share the close orbit, Epsilon Lupi Aa and Epsilon Lupi Ab, have estimated masses of 13.24 and 11.46 times the [[solar mass|mass of the Sun]], respectively. The more distant component, Epsilon Lupi B, has a mass of about 7.64 times the Sun. The combined [[stellar classification]] of the system is B2&nbsp;IV-V, while the individual components may have spectral classes of B3&nbsp;IV, B3&nbsp;V, and A5&nbsp;V, in order of decreasing mass. The inner A-a pair appear to have their rate of spin synchronized with their orbit, so that the same face of each star always faces its partner. The secondary, Epsilon Lupi a, shows regular variation in luminosity of the type that occurs with [[Beta Cephei variable]]s, at a periodicity of 10.36 cycles per day.<ref name=aaa440_1_249/>

This star system is a probable member of the [[Scorpius–Centaurus association]], a [[moving group]] of stars that originated together and share a similar trajectory through space.<ref name=apjs15_459/>

==References== {{reflist|30em|refs=

<ref name=aaa474_2_653>{{citation | first=F. | last=van Leeuwen |date=November 2007 | title=Validation of the new Hipparcos reduction | journal=Astronomy and Astrophysics | volume=474 | issue=2 | pages=653–664 | bibcode=2007A&A...474..653V | doi=10.1051/0004-6361:20078357 |arxiv = 0708.1752 | s2cid=18759600 }}</ref>

<ref name=Anderson2012>{{citation | title=XHIP: An extended hipparcos compilation | last1=Anderson | first1=E. | last2=Francis | first2=Ch. | journal=Astronomy Letters | volume=38 | issue=5 | pages=331 | year=2012 | bibcode=2012AstL...38..331A | doi=10.1134/S1063773712050015 | arxiv=1108.4971 | s2cid=119257644 | postscript=. }}</ref>

<ref name=rgcrv>{{cite conference | last1=Evans | first1=D. S. | date=June 20–24, 1966 | editor1-last=Batten | editor1-first=Alan Henry | editor2-last=Heard | editor2-first=John Frederick | contribution=The Revision of the General Catalogue of Radial Velocities | title=Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30 | journal=Determination of Radial Velocities and Their Applications | volume=30 | pages=57 | location=University of Toronto | publisher=[[International Astronomical Union]] | bibcode=1967IAUS...30...57E }}</ref>

<ref name=Pablo2019>{{Cite journal |last1=Pablo |first1=H. |last2=Shultz |first2=M. |last3=Fuller |first3=J. |last4=Wade |first4=G. A. |last5=Paunzen |first5=E. |last6=Mathis |first6=S. |last7=Le Bouquin |first7=J. -B. |last8=Pigulski |first8=A. |last9=Handler |first9=G. |last10=Alecian |first10=E. |last11=Kuschnig |first11=R. |last12=Moffat |first12=A. F. J. |last13=Neiner |first13=C. |last14=Popowicz |first14=A. |last15=Rucinski |first15=S. |date=2019-09-01 |title=ɛ Lupi: measuring the heartbeat of a doubly magnetic massive binary with BRITE Constellation |journal=Monthly Notices of the Royal Astronomical Society |volume=488 |issue=1 |pages=64–77 |doi=10.1093/mnras/stz1661 |doi-access=free |arxiv=1906.09251 |bibcode=2019MNRAS.488...64P |issn=0035-8711}}</ref>

<ref name=apjs15_459>{{citation | last1=Gutierrez-Moreno | first1=Adelina | last2=Moreno | first2=Hugo | title=A photometric investigation of the Scorpio-Centaurus association | journal=Astrophysical Journal Supplement | volume=15 | page=459 |date=June 1968 | bibcode=1968ApJS...15..459G | doi=10.1086/190168 | doi-access=free }}</ref>

<ref name=aaa440_1_249>{{citation | display-authors=1 | last1=Uytterhoeven | first1=K. | last2=Harmanec | first2=P. | last3=Telting | first4=J. H. | last5=Aerts | first5=C. | title=The orbit of the close spectroscopic binary epsilon Lup and the intrinsic variability of its early B-type components | journal=Astronomy and Astrophysics | volume=440 | issue=1 | pages=249–260 |date=September 2005 | doi=10.1051/0004-6361:20053009 | bibcode=2005A&A...440..249U |arxiv = astro-ph/0507376 | last4=Aerts | s2cid=16644667 }}</ref>

<ref name=SIMBAD>{{citation | title=gam Sgr -- Variable Star | work=SIMBAD | publisher=[[Centre de Données astronomiques de Strasbourg]] | url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Epsilon+Lupi | access-date=2012-01-08 }}</ref>

<ref name=ratio>The ratio of the periapsis (r<sub>p</sub>) to the apoapsis (r<sub>a</sub>) is given by: :<math>{{r_p}\over{r_a}}={{1-e}\over{1+e}}={{0.723}\over{1.277}}=0.566</math> where ''e'' is the ellipticity.</ref>

}}

{{Stars of Lupus}}

[[Category:Bayer objects|Lupi, Epsilon]] [[Category:Lupus (constellation)]] [[Category:B-type main-sequence stars]] [[Category:Hipparcos objects|075264]] [[Category:Bright Star Catalogue objects|5708]] [[Category:Henry Draper Catalogue objects|136504]] [[Category:Durchmusterung objects]] [[Category:Spectroscopic binaries]]