Delta1 Tauri
{{short description|Binary star in the constellation Taurus}}
{{DISPLAYTITLE:Delta1 Tauri}}
{{other stars by Bayer designation|Delta Tauri{{!}}δ Tauri}}
{{Starbox begin
| name = δ1 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 δ1 Tauri (circled)
}}
{{Starbox observe
| epoch = J2000.0
| constell = Taurus
| dec = {{DEC|+17|32|33.0487}}
| appmag_v = +3.772 {{nowrap|(3.90 + 9.50)}}
}}
{{Starbox character
| type = red clump
| class = {{nowrap|G9.5 III CN0.5}}
| variable =
}}
{{Starbox astrometry
| radial_v =
| parallax = 20.96
| p_error = 0.58
}}
{{Starbox orbit
| period_unitless = 529.8 d
| eccentricity = 0.42
| periastron = 2434356.5 JD
| periarg = 335
| k1 = 3.0
}}
{{Starbox detail
| source =
| component1 = δ1 Tau Aa
| component2 = δ1 Tau Ab
| mass2 = {{Val|1.28|0.1}}
}}
{{Starbox catalog
| names = {{odlist | name=Hyadum II | B=δ1 Tau | F=61 Tauri | BD=+17°712 | FK5=162 | HD=27697 | HIP=20455 | HR=1373 | SAO=93897 }}
}}
{{Starbox reference
| Simbad = del01+Tau
}}
{{Starbox end}}
Delta1 Tauri (δ1 Tauri, abbreviated Delta1 Tau, δ1 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, 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. It is considered a member of the Hyades cluster.
The two constituents are designated δ1 Tauri A and B. A is itself a binary star with components designated δ1 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){{cite web | url=https://www.iau.org/public/themes/naming_stars/ | title=Naming Stars |publisher=IAU.org |access-date=16 December 2017}} and Ab.
Nomenclature
δ1 Tauri (Latinised to Delta1 Tauri) is the system's Bayer designation. The designations of the two constituents as Delta1 Tauri A and B, and those of A's components - Delta1 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).{{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. }}
The system bore the traditional name Hyadum II, which is Latin for "Second of the Hyades". In 2016, the IAU organized a Working Group on Star Names (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}} to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.{{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}} It approved the name Secunda Hyadum for the component Delta1 Tauri Aa on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.
In Chinese, {{lang|zh|畢宿}} ({{lang|zh-Latn|Bì Xiù}}), meaning Net, refers to an asterism consisting of δ1 Tauri, Epsilon Tauri, Delta³ Tauri, Gamma Tauri, Alpha Tauri (Aldebaran), 71 Tauri and Lambda Tauri.{{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}}. Consequently, the Chinese name for Delta1 Tauri itself is {{lang|zh|畢宿三}} ({{lang|zh-Latn|Bì Xiù sān}}), "the Third Star of Net".{{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.
Properties
Delta1 Tauri A is a single-lined spectroscopic binary with an orbital period of 529.8 days and an eccentricity of 0.42. 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}}. 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.
Delta1 Tauri B is a magnitude 13.21 visual companion separated by 111.8 arcseconds from A. It is most likely not physically related to the main star.
References
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}}
{{Stars of Taurus|state=collapsed}}
{{Authority control}}
{{DEFAULTSORT:Delta1 Tauri}}
Category:Spectroscopic binaries
Category:Hyades (star cluster)
Category:Taurus (constellation)