{{short description|Binary star in the constellation Taurus}} {{DISPLAYTITLE:Delta<sup>1</sup> Tauri}} {{other stars by Bayer designation|Delta Tauri{{!}}δ Tauri}} {{Starbox begin | name = δ<sup>1</sup> Tauri }} {{Starbox image | image = {{Location mark | image=Taurus IAU.svg | alt= | float=center | width=250 | label= | position=right | mark=Red circle.svg | mark_width=10 | mark_link=δ² Tau | x=595 | y=408 }} | caption=Location of δ<sup>1</sup> Tauri (circled) }} {{Starbox observe | epoch = J2000.0 | equinox = J2000.0 (ICRS) | constell = Taurus | ra = {{RA|04|22|56.09253}}<ref name=vanLeeuwen2007/> | dec = {{DEC|+17|32|33.0487}}<ref name=vanLeeuwen2007/> | appmag_v = +3.772<ref name=Jennens1975/> {{nowrap|(3.90 + 9.50)}}<ref name=WDSC2014/> }} {{Starbox character | type = red clump<ref name=schroder2020/> | class = {{nowrap|G9.5 III CN0.5}}<ref name=perkins1989/> | b-v = +0.919<ref name=Jennens1975/> | u-b = +0.801<ref name=Jennens1975/> | variable = }} {{Starbox astrometry | radial_v = | prop_mo_ra = +106.56<ref name=vanLeeuwen2007/> | prop_mo_dec = −29.18<ref name=vanLeeuwen2007/> | parallax = 20.96 | p_error = 0.58 | parallax_footnote = <ref name=vanLeeuwen2007/> | absmag_v = +0.41<ref name=Cardini2005/> }} {{Starbox orbit | reference = <ref name=Pourbaix2004/> | period_unitless = 529.8 d | eccentricity = 0.42 | periastron = 2434356.5 JD | periarg = 335 | k1 = 3.0 }} {{Starbox detail | source = | component1 = δ<sup>1</sup> Tau Aa | mass = 2.75<ref name=schroder2020/> | radius = 14.9<ref name=schroder2020/> | luminosity = 107<ref name=schroder2020/> | temperature = 4,819<ref name=schroder2020/> | gravity = 2.72<ref name=rp2024/> | metal_fe = +0.11<ref name=rp2024/> | rotational_velocity = 2.31<ref name=jofre2015/> | rotation = 148.2 d<ref name=schroder2020/> | age_myr = 588<ref name=schroder2020/> | component2 = δ<sup>1</sup> Tau Ab | mass2 = {{Val|1.28|0.1}} }} {{Starbox catalog | names = {{odlist | name=Hyadum II | B=δ<sup>1</sup> Tau | F=61 Tauri | BD=+17°712 | FK5=162 | HD=27697 | HIP=20455 | HR=1373 | SAO=93897 }}<ref name=SIMBAD/> }} {{Starbox reference | Simbad = del01+Tau }} {{Starbox end}} '''Delta<sup>1</sup> Tauri''' ('''δ<sup>1</sup> Tauri''', abbreviated '''Delta<sup>1</sup> Tau''', '''δ<sup>1</sup> Tau''') is a double star in the zodiac constellation of Taurus. Based upon an annual parallax shift of 20.96 mas as seen from Earth,<ref name=vanLeeuwen2007/> it is located roughly 156 light-years distant from the Sun. The system is faintly visible to the naked eye with a combined apparent visual magnitude of +3.772.<ref name=Jennens1975/> It is considered a member of the Hyades cluster.<ref name=schroder2020/>
The two constituents are designated δ<sup>1</sup> Tauri A and B. A is itself a binary star with components designated δ<sup>1</sup> Tauri Aa (officially named '''Secunda Hyadum''' {{IPAc-en|s|I|'|k|V|n|d|@|_|'|h|ai|@|d|@|m}}, the traditional name for the entire system)<ref name="IAU-LSN">{{cite web | url=https://www.iau.org/public/themes/naming_stars/ | title=Naming Stars | publisher=IAU.org | access-date=16 December 2017 | archive-date=10 March 2025 | archive-url=https://web.archive.org/web/20250310063743/https://www.iau.org/public/themes/naming_stars/ | url-status=dead }}</ref> and Ab.
== Nomenclature ==
''δ<sup>1</sup> Tauri'' (Latinised to ''Delta<sup>1</sup> Tauri'') is the system's Bayer designation. The designations of the two constituents as ''Delta<sup>1</sup> Tauri A'' and ''B'', and those of ''A's'' components - ''Delta<sup>1</sup> Tauri Aa'' and ''Ab'' - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).<ref name="planetnaming">{{cite arXiv |title=On the naming convention used for multiple star systems and extrasolar planets |date=2010 |eprint=1012.0707 |class=astro-ph.SR |last1= Hessman |first1=F. V. |last2= Dhillon |first2=V. S. |last3= Winget |first3=D. E. |last4= Schreiber |first4=M. R. |last5= Horne |first5=K. |last6= Marsh |first6=T. R. |last7= Guenther |first7=E. |last8= Schwope |first8=A. |last9= Heber |first9=U. }}</ref>
The system bore the traditional name ''Hyadum II'', which is Latin for "Second of the Hyades".<ref name=Kaler/> In 2016, the IAU organized a Working Group on Star Names (WGSN)<ref name="WGSN">{{cite web | url=https://www.iau.org/science/scientific_bodies/working_groups/280/ | title=IAU Working Group on Star Names (WGSN) | access-date=22 May 2016 | archive-date=30 March 2019 | archive-url=https://web.archive.org/web/20190330194042/https://www.iau.org/science/scientific_bodies/working_groups/280/ | url-status=dead }}</ref> to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.<ref name="TriRpt18">{{cite web | url=https://www.iau.org/static/science/scientific_bodies/working_groups/280/wg-starnames-triennial-report-2015-2018.pdf | page=5 | title=WG Triennial Report (2015-2018) - Star Names | access-date=2018-07-14 | archive-date=2022-10-09 | archive-url=https://ghostarchive.org/archive/20221009/https://www.iau.org/static/science/scientific_bodies/working_groups/280/wg-starnames-triennial-report-2015-2018.pdf | url-status=dead }}</ref> It approved the name ''Secunda Hyadum'' for the component Delta<sup>1</sup> Tauri Aa on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.<ref name="IAU-LSN"/>
In Chinese, {{lang|zh|畢宿}} ({{lang|zh-Latn|Bì Xiù}}), meaning ''Net'', refers to an asterism consisting of δ<sup>1</sup> Tauri, Epsilon Tauri, Delta³ Tauri, Gamma Tauri, Alpha Tauri (Aldebaran), 71 Tauri and Lambda Tauri.<ref>{{in lang|zh}} ''中國星座神話'', written by 陳久金. Published by 台灣書房出版有限公司, 2005, {{ISBN|978-986-7332-25-7}}.</ref> Consequently, the Chinese name for Delta<sup>1</sup> Tauri itself is {{lang|zh|畢宿三}} ({{lang|zh-Latn|Bì Xiù sān}}), "the Third Star of Net".<ref>{{in lang|zh}} [http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_ala_alz.htm 香港太空館 - 研究資源 - 亮星中英對照表] {{webarchive|url=https://web.archive.org/web/20081025110153/http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_ala_alz.htm |date=2008-10-25 }}, Hong Kong Space Museum. Accessed on line November 23, 2010.</ref>
== Properties ==
Delta<sup>1</sup> Tauri A is a single-lined spectroscopic binary with an orbital period of 529.8 days and an eccentricity of 0.42.<ref name=Pourbaix2004/> The visible member, component Aa, is an evolved G- or K-type giant star with a stellar classification of {{nowrap|G9.5 III CN0.5}}.<ref name=perkins1989/> The 'CN0.5' suffix indicates a mild overabundance of cyanogen in the outer atmosphere. It is chromospherically active and shows a radial velocity variation of {{Val|9.3|0.2|u=m/s}} with a period of {{Val|165|3|u=d}}. The primary, component Aa, has 2.75 times the mass of the Sun, while the secondary, component Ab, has 1.3 times the Sun's mass. The primary star, at an age of 588 million years, is just evolving away from the horizontal branch toward the asymptotic giant branch after exhausting its core helium.<ref name=schroder2020/>
Delta<sup>1</sup> Tauri B is a magnitude 13.21 visual companion separated by 111.8 arcseconds from A.<ref name=WDSC2014/> It is most likely not physically related to the main star.<ref name=Eggleton2008/>
==References== <references> <ref name=rp2024>{{citation |postscript=. |bibcode=2024A&A...692A.189R |title=In pursuit of precise Ca II H&K chromospheric surface fluxes: A gravity and temperature dependence |last1=Rosas-Portilla |first1=F. |last2=Jack |first2=D. |last3=Schröder |first3=K. -P. |journal=Astronomy and Astrophysics |date=2024 |volume=692 |doi=10.1051/0004-6361/202450691 |doi-access=free }}</ref>
<ref name=schroder2020>{{citation |postscript=. |bibcode=2020MNRAS.492.1110S |title=Magnetic activity and evolution of the four Hyades K giants |last1=Schröder |first1=K. -P. |last2=Mittag |first2=M. |last3=Jack |first3=D. |last4=Rodríguez Jiménez |first4=A. |last5=Schmitt |first5=J. H. M. M. |journal=Monthly Notices of the Royal Astronomical Society |date=2020 |volume=492 |issue=1 |page=1110 |doi=10.1093/mnras/stz3476 |doi-access=free |arxiv=1912.03638 }}</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=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. | journal=The Astronomical Journal | postscript=. | title=The Washington Visual Double Star Catalog | pages=3466–3471 | volume=122 | year=2014 | issue=6 | bibcode=2001AJ....122.3466M | doi=10.1086/323920 | doi-access=free }}</ref>
<ref name=Pourbaix2004>{{citation | display-authors=1 | last1=Pourbaix | first1=D. | last2=Tokovinin | first2=A. A. | last3=Batten | first3=A. H. | last4=Fekel | first4=F. C. | last5=Hartkopf | first5=W. I. | last6=Levato | first6=H. | last7=Morrell | first7=N. I. | last8=Torres | first8=G. | last9=Udry | first9=S. | title=SB9: The Ninth Catalogue of Spectroscopic Binary Orbits | journal=Astronomy & Astrophysics | postscript=. | year=2004 | volume=424 | issue=2 | pages=727–732 | bibcode=2004A&A...424..727P | doi=10.1051/0004-6361:20041213 | arxiv=astro-ph/0406573| s2cid=119387088 }}</ref>
<ref name=perkins1989>{{citation | last1=Keenan | first1=Philip C. | last2=McNeil | first2=Raymond C. | title=The Perkins catalog of revised MK types for the cooler stars | journal=Astrophysical Journal Supplement Series | volume=71 | pages=245 | year=1989 | postscript=. | bibcode=1989ApJS...71..245K | doi=10.1086/191373 }}</ref>
<ref name=jofre2015>{{citation | last1=Jofré | first1=E. | last2=Petrucci | first2=R. | last3=Saffe | first3=C. | last4=Saker | first4=L. | last5=Artur de la Villarmois | first5=E. | last6=Chavero | first6=C. | last7=Gómez | first7=M. | last8=Mauas | first8=P. J. D. | title=Stellar parameters and chemical abundances of 223 evolved stars with and without planets | journal=Astronomy & Astrophysics | display-authors=1 | volume=574 | pages=A50 | year=2015 | arxiv=1410.6422 | bibcode=2015A&A...574A..50J | doi=10.1051/0004-6361/201424474 | s2cid=53666931 | postscript=. }}</ref>
<ref name=Jennens1975>{{citation | postscript=. | last1=Jennens | first1=P. A. | last2=Helfer | first2=H. L. | title=A new photometric metal abundance and luminosity calibration for field G and K giants | journal=Monthly Notices of the Royal Astronomical Society | volume=172 | pages=667–679 | date=September 1975 | issue=3 | bibcode=1975MNRAS.172..667J | doi=10.1093/mnras/172.3.667 | doi-access=free }}</ref>
<ref name=Kaler>{{citation | title=Hyadum II | work=STARS | publisher=University of Illinois | first=James B. | last=Kaler | url=http://stars.astro.illinois.edu/sow/hyadum2.html | access-date=2017-08-09 | postscript=. }}</ref>
<ref name=Eggleton2008>{{citation | 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 | postscript=. }}</ref>
<ref name=Cardini2005>{{citation | title=Mg II chromospheric radiative loss rates in cool active and quiet stars | last1=Cardini | first1=D. | postscript=. | journal=Astronomy and Astrophysics | volume=430 | pages=303–311 | date=January 2005 | issue=1 | doi=10.1051/0004-6361:20041440 | bibcode=2005A&A...430..303C |arxiv = astro-ph/0409683 | s2cid=12136256 }}</ref>
<ref name=SIMBAD>{{cite simbad | mode=cs2 | title=del01 Tau | accessdate=2017-08-08 | postscript=. }}</ref> </references>
{{Stars of Taurus|state=collapsed}}
{{Authority control}}
Category:G-type giants Category:Spectroscopic binaries Category:Hyades (star cluster) Tauri, Delta Category:Taurus (constellation) Secunda Hyadum Category:Durchmusterung objects Tauri, 061 027697 020455 1373 Category:Horizontal-branch stars