View source for Lambda Tauri

{{short description|Triple star system in the constellation Taurus}}
{{Starbox begin
 | name = λ Tauri
}}
{{Starbox image
 | image=
{{Location mark
|image=Taurus constellation map.svg|alt=|float=center|width=260
|label=|position=right
|mark=Red circle.svg|mark_width=10|mark_link=λ Tau
|x=738|y=650
}}
|caption=Location of λ Tauri (circled)
}}
{{Starbox observe
 | epoch    = [[J2000.0]]
 | ra       = {{RA|04|00|40.81572}}<ref name=aaa474_2_653/>
 | dec      = {{DEC|+12|29|25.2259}}<ref name=aaa474_2_653/>
 | appmag_v = +3.37 (- 3.54) - 3.91<ref name=gcvs/>
 | constell = [[Taurus (constellation)|Taurus]]
}}
{{Starbox character
 | class    = {{nowrap|B3 V + A4 IV}}<ref name=an331_4_349/>
 | b-v      = −0.12<ref name=aaass34_1/>
 | u-b      = −0.62<ref name=aaass34_1/>
 | variable = [[Algol variable|Algol]]<ref name=gcvs/>
}}
{{Starbox astrometry
 | radial_v = +17.8<ref name=rgcrv/>
 | prop_mo_ra  = −8.02<ref name=aaa474_2_653/>
 | prop_mo_dec = −14.42<ref name=aaa474_2_653/>
 | parallax = 6.74
 | p_error  = 0.17
 | parallax_footnote = <ref name=aaa474_2_653/>
 | absmag_v = −2.45<ref name=Anderson2012/>
}}
{{Starbox orbit
| reference = <ref name=apj1_263_289/>
| primary = λ Tau A
| name = λ Tau B
| period_unitless = 3.9529552&nbsp;days
| axis_unitless = {{Solar radius|21.91}}<ref name=aj121_5_2723/>
| eccentricity = {{val|0.025|0.015}}
| inclination = {{val|76|1|2}}<ref name=aaa611_a69/>
| node = {{val|15|2}} or {{val|195|2}}<ref name=aaa611_a69/>
| periastron = {{val|2,444,667.3|2.1|u=HJD|fmt=commas}}
| periarg = <!--Argument of periastron (in degrees), secondary -->
| periarg_primary = <!--Argument of periastron (in degrees), primary -->
| k1 = {{val|56.9|0.6}}
| k2 = {{val|215.6|0.7}}
}}
{{Starbox detail
 | component1 = λ Tau A
 | mass     = 7.18<ref name=mnras406_2_1071/>
 | radius   = 6.40<ref name=mnras406_2_1071/>
 | metal_fe = 
 | gravity  = 3.38<ref name=aaa202_1_101/>
 | age_myr  = {{val|33.2|3.9}}<ref name=mnras410_1_190/>
 | luminosity  = 5,801<ref name=an331_4_349/>
 | temperature = 18,700<ref name=an331_4_349/>
 | rotational_velocity = 85<ref name=aj121_5_2723/>
 | component2 = λ Tau B
 | mass2    = 1.89<ref name=mnras406_2_1071/>
 | radius2  = 5.30<ref name=mnras406_2_1071/>
 | luminosity2 = 128<ref name=an331_4_349/>
 | temperature2 = 8,405<ref name=an331_4_349/>
 | rotational_velocity2 = 76<ref name=aj121_5_2723/>
}}
{{Starbox catalog
 | names = 35&nbsp;Tauri, [[Star catalogue#BD/CD/CPD|BD]]+12&nbsp;539, FK5&nbsp;150, [[Henry Draper Catalogue|HD]]&nbsp;25204, [[Hipparcos catalogue|HIP]]&nbsp;18724, [[Star catalogue#BS, BSC, HR|HR]]&nbsp;1239, [[Star catalogue#SAO|SAO]]&nbsp;93719<ref name=SIMBAD/>
}}
{{Starbox reference
 | Simbad = lam+Tau
}}
{{Starbox end}}
'''Lambda Tauri''' (λ Tau, λ Tauri) is a [[triple star system]] in the [[constellation]] [[Taurus (constellation)|Taurus]]. In the ''Calendarium of Al Achsasi Al Mouakket'', this star was designated ''Sadr al Tauri'', which was translated into [[Latin]] as ''Pectus Tauri'', meaning "the bull chest".<ref name=mnras55_429/> In 1848, the light from this system was found to vary periodically and it was determined to be an [[eclipsing binary]] system—the third such discovered.<ref name=apj1_263_289/> The components of this system have a combined [[apparent visual magnitude]] of +3.37 at its brightest, making it one of the [[List of stars in Taurus|brighter members]] of the constellation. Based upon [[parallax]] measurements from the [[Hipparcos]] mission, the distance to this system is approximately {{Convert|480|ly|pc|abbr=off|lk=on}}.<ref name=aaa474_2_653/>

== System ==
[[File:LambdaTauLightCurve.png|thumb|left|A [[light curve]] for Lambda Tauri, plotted from ''[[Transiting Exoplanet Survey Satellite|TESS]]'' data<ref name=MAST/>]]
The inner pair of this triple star system, Lambda Tauri AB, orbit around each other with a [[orbital period|period]] of 3.95&nbsp;days and a low [[orbital eccentricity|eccentricity]] of about 0.025.<ref name=apj1_263_289/> Their [[Orbital plane (astronomy)|orbital plane]] is inclined by around 76° to the line of sight from the Earth,<ref name=mnras406_2_1071/> so it is being viewed from nearly edge on and the two stars form an [[Algol]]-like [[eclipsing binary]] system. The combined brightness of the pair varies from magnitude +3.37 to +3.91 as first one star and then the other pass in front of its companion. The primary member, λ Tau A, undergoes a decrease of {{val|0.435|0.050}} in magnitude during an eclipse, while the secondary component, λ Tau B, decreases by 0.09–0.10 in magnitude.<ref name=aaa42_2_229/> The mean physical separation between these two stars is estimated at 21.91 times the radius of the Sun, or {{val|0.1|ul=Astronomical Units}}.<ref name=aj121_5_2723/>

The primary component has a [[stellar classification]] of B3&nbsp;V, making this a massive [[B-type main sequence star]]. It has over seven times the [[mass of the Sun]]<ref name=aaa42_2_229/> and 6.4 times the [[Sun's radius]].<ref name=aj121_5_2723/> This star is the brightest member of the system, radiating about 5,801<ref name=an331_4_349/> times the [[luminosity of the Sun]] from its outer envelope at an [[effective temperature]] of {{val|18,700|ul=K|fmt=commas}}, which gives it a blue-white hue common to the B-type stars.<ref name=csiro/> Lambda Tauri A is rotating rapidly with a [[projected rotational velocity]] of {{val|85|u=km/s}}.<ref name=aj121_5_2723/> It, along with [[Delta Librae|δ Librae]], were the first stars on which rotational line broadening was observed, by [[Frank Schlesinger]] in 1909.<ref name=mnras71_719/>

The third component, λ Tau C, is orbiting the inner pair over a 33.025 day period with an [[orbital eccentricity|eccentricity]] of roughly 0.15. The orbital plane of this component is nearly coplanar with the orbit of Lambda Tauri AB, differing by no more than 7°. It has about half the mass of the Sun.<ref name=aaa42_2_229/> The orbit of this star causes perturbation effects on the orbit of the AB pair, resulting in periodic changes in their orbital eccentricity and other [[orbital elements]].<ref name=apj1_263_289/>

== Physical characteristics ==

The spectrum of Lambda Tauri A shows an under abundance of carbon relative to the norm for this category of star. A possible explanation for this is a loss of mass by the star some time in the past. An inner region of the star became depleted by the conversion of carbon into nitrogen during the nuclear fusion process, and this region was later exposed when the outer envelope of the star was lost. Alternatively, the star may have undergone a period of convective mixing, bringing the carbon-depleted material to the surface. However, the cause of such a fully convective behavior in a [[main sequence]] star of this mass is unclear.<ref name=aaa202_1_101/>

The secondary companion has a stellar classification of A4&nbsp;IV,<ref name=an331_4_349/> suggesting that it is a [[subgiant star]] that has nearly exhausted the supply of hydrogen at its core and is in the process of [[stellar evolution|evolving]] into a [[giant star]]. It has nearly 1.9 times the mass of the Sun, 5.3 times the Sun's radius,<ref name=aj121_5_2723/> and is radiating 128 times the Sun's luminosity at an effective temperature of {{val|8,405|u=K|fmt=commas}}.<ref name=an331_4_349/> As with the primary, this star is spinning rapidly with a projected rotational velocity of {{val|76|u=km/s}}.<ref name=aj121_5_2723/> The side of the secondary facing the more massive star is being heated by an additional {{val|1,440|u=K|fmt=commas}}, which produces a rotational effect that causes the strength of the secondary's [[spectral line]]s to vary over the course of its orbit.<ref name=apj1_263_289/>

A conundrum with this system is the large radius of the secondary star. In [[stellar evolution]]ary terms, the more massive primary should be the first to reach the subgiant stage. Hence the enlarged radius of the secondary must be caused by a means other than the star's age. This suggests that the pair Lambda Tauri AB form a [[semidetached binary]] with the secondary filling its [[Roche lobe]], giving it a distorted shape.<ref name=apj1_263_289/>

==References==
{{Reflist|30em|refs=

<ref name=aaa474_2_653>{{citation | last1=van Leeuwen | first1=F. | title=Validation of the new Hipparcos reduction | journal=Astronomy and Astrophysics | volume=474 | issue=2 |date=November 2007 | pages=653–664 | doi=10.1051/0004-6361:20078357 | bibcode=2007A&A...474..653V | 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 | page=331 | year=2012
 | bibcode=2012AstL...38..331A | doi=10.1134/S1063773712050015
 | arxiv=1108.4971 | s2cid=119257644 | postscript=. }}</ref>

<ref name=rgcrv>{{citation | last=Evans | first=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 | volume=30 | page=57 | title=Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30 | location=University of Toronto | publisher=[[International Astronomical Union]] | bibcode=1967IAUS...30...57E }}<!--| access-date=2009-09-10 --></ref>

<ref name=MAST>{{cite web |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=8 December 2021}}</ref>

<ref name=aaass34_1>{{cite journal | last1=Nicolet | first1=B. | title=Catalogue of homogeneous data in the UBV photoelectric photometric system | journal=Astronomy and Astrophysics Supplement Series | volume=34 | pages=1–49 |date=October 1978 | bibcode=1978A&AS...34....1N }}</ref>

<ref name=aaa42_2_229>{{citation | last1=Soderhjelm | first1=S. | title=The three-body problem and eclipsing binaries – Application to algol and lambda Tauri | journal=Astronomy and Astrophysics | volume=42 | issue=2 | pages=229–236 |date=August 1975 | bibcode=1975A&A....42..229S }}</ref>

<ref name=an331_4_349>{{citation | last1=Hohle | first1=M. M. | last2=Neuhäuser | first2=R. | last3=Schutz | first3=B. F. | title=Masses and luminosities of O- and B-type stars and red supergiants | journal=Astronomische Nachrichten | volume=331 | issue=4 | pages=349–360 |date=April 2010 | doi=10.1002/asna.200911355 | bibcode=2010AN....331..349H |arxiv = 1003.2335 | s2cid=111387483 }}</ref>

<ref name=SIMBAD>{{citation | title=HD 25204 -- Eclipsing binary of Algol type | work=SIMBAD Astronomical Database | url=http://simbad.u-strasbg.fr/sim-id.pl?protocol=html&Ident=lambda+tauri | access-date=2007-01-26 }}</ref>

<ref name=mnras55_429>{{citation | last1=Knobel | first1=E. B. | title=Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of | journal=[[Monthly Notices of the Royal Astronomical Society]] | volume=55 | pages=429–438 |date=June 1895 | issue=8 | bibcode=1895MNRAS..55..429K | doi=10.1093/mnras/55.8.429| doi-access=free }}</ref>

<ref name=mnras71_719>{{citation | first1=Frank | last1=Schlesinger | title=Rotation of Stars about their Axes | journal=Monthly Notices of the Royal Astronomical Society | volume=71 | issue=9 | page=719 | bibcode=1911MNRAS..71..719S | doi = 10.1093/mnras/71.9.719 | year=1911 | doi-access=free }}</ref>

<ref name=aaa202_1_101>{{citation | last1=Cugier | first1=H. | last2=Hardorp | first2=J. | title=Carbon abundance in Beta Persei and Lambda Tauri | journal=Astronomy and Astrophysics | volume=202 | issue=1–2 | pages=101–108 |date=August 1988 | bibcode=1988A&A...202..101C }}</ref>

<ref name=aj121_5_2723>{{citation | last1=Vesper | first1=David | last2=Honeycutt | first2=Kent | last3=Hunt | first3=Thomas | title=Survey of Hα Mass Transfer Structures in Classical Algol-Type Binaries | journal=The Astronomical Journal | volume=121 | issue=5 | pages=2723–2736 |date=May 2001 | doi=10.1086/320381 | bibcode=2001AJ....121.2723V | doi-access= }}</ref>

<ref name=mnras406_2_1071>{{citation | last1=Dervişoğlu | first1=A. | last2=Tout | first2=Christopher A. | last3=Ibanoğlu | first3=C. | title=Spin angular momentum evolution of the long-period Algols | journal=Monthly Notices of the Royal Astronomical Society | volume=406 | issue=2 | pages=1071–1083 |date=August 2010 | doi=10.1111/j.1365-2966.2010.16732.x | doi-access=free | bibcode=2010MNRAS.406.1071D |arxiv = 1003.4392 | s2cid=119198387 }}</ref>

<ref name=apj1_263_289>{{citation | last1=Fekel | first1=F. C. Jr. | last2=Tomkin | first2=J. | title=Secondaries of eclipsing binaries. IV - The triple system Lambda Tauri | journal=Astrophysical Journal, Part 1 | volume=263 | pages=289–301 |date=December 1982 | doi=10.1086/160503 | bibcode=1982ApJ...263..289F | hdl=2152/34674 | hdl-access=free }}</ref>

<ref name=aaa611_a69>{{citation |last1=Berdyugin |first1=A. |last2=Piirola |first2=V. |last3=Sakanoi |first3=T. |last4=Kagitani |first4=M. |last5=Yoneda |first5=M. |title=High-precision broad-band linear polarimetry of early-type binaries: II. Variable, phase-locked polarization in triple Algol-type system λ Tauri |journal=Astronomy & Astrophysics |date=March 2018 |volume=611 |doi=10.1051/0004-6361/201732163 |doi-access=free |bibcode=2018A&A...611A..69B |id=A69|url=https://www.utupub.fi/bitstream/10024/153303/1/aa32163-17.pdf }}</ref>

<ref name=csiro>{{citation|title=The Colour of Stars |date=December 21, 2004 |work=Australia Telescope, Outreach and Education |publisher=Commonwealth Scientific and Industrial Research Organisation |url=http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html |access-date=2012-01-16  |archive-url=https://web.archive.org/web/20120318151427/http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html |archive-date=March 18, 2012 }}</ref>

<ref name=mnras410_1_190>{{citation | last1=Tetzlaff | first1=N. | last2=Neuhäuser | first2=R. | last3=Hohle | first3=M. M. | title=A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun | journal=Monthly Notices of the Royal Astronomical Society | volume=410 | issue=1 | pages=190–200 |date=January 2011 | doi=10.1111/j.1365-2966.2010.17434.x | doi-access=free | bibcode=2011MNRAS.410..190T |arxiv = 1007.4883 | s2cid=118629873 }}</ref>

<ref name=gcvs>{{citation |bibcode=2017ARep...61...80S |title=General catalogue of variable stars: Version GCVS 5.1 |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. |journal=Astronomy Reports |year=2017 |volume=61 |issue=1 |page=80 |doi=10.1134/S1063772917010085 |s2cid=125853869 }}</ref>

}}

{{Stars of Taurus}}

{{DEFAULTSORT:Lambda Tauri}}
[[Category:Algol variables]]
[[Category:Bayer objects|Tauri, Lambda]]
[[Category:B-type main-sequence stars]]
[[Category:Taurus (constellation)]]
[[Category:Triple star systems]]
[[Category:A-type subgiants]]
[[Category:Flamsteed objects|Tauri, 035]]
[[Category:Hipparcos objects|018724]]
[[Category:Bright Star Catalogue objects|1239]]
[[Category:Henry Draper Catalogue objects|025204]]
[[Category:Durchmusterung objects]]