# Phi Draconis

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Star in the constellation Draco

φ Draconis Location of φ Draconis (circled) Observation data Epoch J2000 Equinox J2000 Constellation Draco Right ascension 18h 20m 45.43224s[1] Declination +71° 20′ 16.1499″[1] Apparent magnitude (V) 4.22[2] Characteristics Spectral type B8VpSi[3] + A4V + B9V[4] U−B color index −0.38[5] B−V color index −0.10[5] Variable type α2 CVn[2] Astrometry Radial velocity (Rv) −16.44[6] km/s Proper motion (μ) RA: −5.03[1] mas/yr Dec.: +37.86[1] mas/yr Parallax (π) 10.77±0.38 mas[1] Distance 300 ± 10 ly (93 ± 3 pc) Absolute magnitude (MV) −0.74 (−0.48/+0.94)[4] Orbit[4] Primary A Name B Period (P) 307.8 yr Semi-major axis (a) 0.965" (89.60 au) Eccentricity (e) 0.752 Inclination (i) 95.6° Orbit[6] Primary Aa Name Ab Period (P) 127.914 d Eccentricity (e) 0.6725 Inclination (i) 48° Semi-amplitude (K1) (primary) 33.87 km/s Details Aa Mass 3.3[4] M☉ Radius 2.7±0.2[7] R☉ Luminosity 107[7] L☉ Surface gravity (log g) 4.21±0.08[7] cgs Temperature 11,429[7] K Rotation 1.7165[6] Rotational velocity (v sin i) 81.5[6] km/s Age 245[4] Myr Ab Mass 1.36[8] M☉ B Mass 2.25[8] M☉ Age 330[4] Myr Other designations φ Dra, 43 Dra, BD+71°889, CCDM J18208+7120AB, GC 25114, HD 170000, HIP 89908, HR 6920, SAO 9084 Database references SIMBAD data

**Phi Draconis** (φ Dra / φ Draconis) is a fourth-magnitude [variable star](/source/Variable_star) in the [constellation](/source/Constellation) [Draco](/source/Draco_(constellation)). It has the [Flamsteed designation](/source/Flamsteed_designation) **43 Draconis**. It is also a [triple star](/source/Triple_star) system where the brightest component is a [chemically peculiar](/source/Chemically_peculiar_star) [Ap star](/source/Ap_star).

A [light curve](/source/Light_curve) for Phi Draconis, plotted from *[TESS](/source/Transiting_Exoplanet_Survey_Satellite)* data[9]

The brightness of φ Draconis varies by about 0.04 of a [magnitude](/source/Magnitude_(astronomy)) every 1.7 days. This is due to very strong magnetic fields at the surface of the star, and it is classified as an [α2 Canum Venaticorum](/source/Alpha2_Canum_Venaticorum_variable) variable.[2]

φ Draconis is a multiple [star system](/source/Star_system) containing three stars. The inner pair form a single-lined [spectroscopic binary](/source/Spectroscopic_binary) in an eccentric 128-day orbit. The outermost star orbits the inner pair every 308 years. The outer pair can be resolved visually and have a [semi-major axis](/source/Semi-major_axis) of 0.752[″](/source/Second_of_arc). A fourth component, C, is also listed in multiple star catalogues, but is only a chance alignment with the triple system.[4]

Phi Draconis Aa is a [main-sequence](/source/Main-sequence) Ap star with a spectral class of B8. The main abundance excess is silicon, although iron and chromium and also notably elevated.[10]

In [Chinese astronomy](/source/Chinese_astronomy), φ Draconis is called 柱史 ([Pinyin](/source/Pinyin): Zhùshǐ), meaning *Official of Royal Archives*, because this star is marking itself and stand alone in *Official of Royal Archives* [asterism](/source/Asterism_(astronomy)), [Purple Forbidden enclosure](/source/Purple_Forbidden_enclosure) (see: [Chinese constellations](/source/Chinese_constellations)).[11]

## References

1. ^ [***a***](#cite_ref-LEEUWEN_1-0) [***b***](#cite_ref-LEEUWEN_1-1) [***c***](#cite_ref-LEEUWEN_1-2) [***d***](#cite_ref-LEEUWEN_1-3) [***e***](#cite_ref-LEEUWEN_1-4) van Leeuwen, F. (November 2007). ["Hipparcos, the New Reduction"](http://vizier.u-strasbg.fr/viz-bin/VizieR-S?HIP%2089908) ([VizieR](/source/VizieR)). *Astronomy and Astrophysics*. **474** (2): 653–664. [arXiv](/source/ArXiv_(identifier)):[0708.1752](https://arxiv.org/abs/0708.1752). [Bibcode](/source/Bibcode_(identifier)):[2007A&A...474..653V](https://ui.adsabs.harvard.edu/abs/2007A&A...474..653V). [doi](/source/Doi_(identifier)):[10.1051/0004-6361:20078357](https://doi.org/10.1051%2F0004-6361%3A20078357). [S2CID](/source/S2CID_(identifier)) [18759600](https://api.semanticscholar.org/CorpusID:18759600). Retrieved 2010-11-22.

1. ^ [***a***](#cite_ref-gcvs_2-0) [***b***](#cite_ref-gcvs_2-1) [***c***](#cite_ref-gcvs_2-2) Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". *VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S*. **1**. [Bibcode](/source/Bibcode_(identifier)):[2009yCat....102025S](https://ui.adsabs.harvard.edu/abs/2009yCat....102025S).

1. **[^](#cite_ref-mk_3-0)** Gray, R. O.; Corbally, C. J. (2014). ["An Expert Computer Program for Classifying Stars on the MK Spectral Classification System"](https://doi.org/10.1088%2F0004-6256%2F147%2F4%2F80). *The Astronomical Journal*. **147** (4): 80. [Bibcode](/source/Bibcode_(identifier)):[2014AJ....147...80G](https://ui.adsabs.harvard.edu/abs/2014AJ....147...80G). [doi](/source/Doi_(identifier)):[10.1088/0004-6256/147/4/80](https://doi.org/10.1088%2F0004-6256%2F147%2F4%2F80). [S2CID](/source/S2CID_(identifier)) [28584130](https://api.semanticscholar.org/CorpusID:28584130).

1. ^ [***a***](#cite_ref-liska_4-0) [***b***](#cite_ref-liska_4-1) [***c***](#cite_ref-liska_4-2) [***d***](#cite_ref-liska_4-3) [***e***](#cite_ref-liska_4-4) [***f***](#cite_ref-liska_4-5) [***g***](#cite_ref-liska_4-6) Liška, J. (2016). ["Analysis of the multiple system with chemically peculiar component φ Draconis"](https://doi.org/10.1093%2Fmnras%2Fstw1355). *Monthly Notices of the Royal Astronomical Society*. **461** (1): 939–947. [arXiv](/source/ArXiv_(identifier)):[1606.01333](https://arxiv.org/abs/1606.01333). [Bibcode](/source/Bibcode_(identifier)):[2016MNRAS.461..939L](https://ui.adsabs.harvard.edu/abs/2016MNRAS.461..939L). [doi](/source/Doi_(identifier)):[10.1093/mnras/stw1355](https://doi.org/10.1093%2Fmnras%2Fstw1355).

1. ^ [***a***](#cite_ref-MERMILLIOD_5-0) [***b***](#cite_ref-MERMILLIOD_5-1) Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". *Catalogue of Eggen's UBV Data*: 0. [Bibcode](/source/Bibcode_(identifier)):[1986EgUBV........0M](https://ui.adsabs.harvard.edu/abs/1986EgUBV........0M).

1. ^ [***a***](#cite_ref-kochukhov2022_6-0) [***b***](#cite_ref-kochukhov2022_6-1) [***c***](#cite_ref-kochukhov2022_6-2) [***d***](#cite_ref-kochukhov2022_6-3) Kochukhov, O.; Papakonstantinou, N.; Neiner, C. (2022). ["Magnetic field topology, chemical spot distributions, and photometric variability of the Ap star φ Draconis"](https://doi.org/10.1093%2Fmnras%2Fstac066). *Monthly Notices of the Royal Astronomical Society*. **510** (4): 5821. [arXiv](/source/ArXiv_(identifier)):[2201.02554](https://arxiv.org/abs/2201.02554). [Bibcode](/source/Bibcode_(identifier)):[2022MNRAS.510.5821K](https://ui.adsabs.harvard.edu/abs/2022MNRAS.510.5821K). [doi](/source/Doi_(identifier)):[10.1093/mnras/stac066](https://doi.org/10.1093%2Fmnras%2Fstac066).

1. ^ [***a***](#cite_ref-aaa334_181_7-0) [***b***](#cite_ref-aaa334_181_7-1) [***c***](#cite_ref-aaa334_181_7-2) [***d***](#cite_ref-aaa334_181_7-3) North, P. (June 1998). "Do SI stars undergo any rotational braking?". *Astronomy and Astrophysics*. **334**: 181–187. [arXiv](/source/ArXiv_(identifier)):[astro-ph/9802286](https://arxiv.org/abs/astro-ph/9802286). [Bibcode](/source/Bibcode_(identifier)):[1998A&A...334..181N](https://ui.adsabs.harvard.edu/abs/1998A&A...334..181N).

1. ^ [***a***](#cite_ref-msc_8-0) [***b***](#cite_ref-msc_8-1) Tokovinin, Andrei (2018-03-01). ["The Updated Multiple Star Catalog"](https://doi.org/10.3847%2F1538-4365%2Faaa1a5). *[The Astrophysical Journal Supplement Series](/source/The_Astrophysical_Journal_Supplement_Series)*. **235** (1): 6. [arXiv](/source/ArXiv_(identifier)):[1712.04750](https://arxiv.org/abs/1712.04750). [Bibcode](/source/Bibcode_(identifier)):[2018ApJS..235....6T](https://ui.adsabs.harvard.edu/abs/2018ApJS..235....6T). [doi](/source/Doi_(identifier)):[10.3847/1538-4365/aaa1a5](https://doi.org/10.3847%2F1538-4365%2Faaa1a5). [ISSN](/source/ISSN_(identifier)) [0067-0049](https://search.worldcat.org/issn/0067-0049). [S2CID](/source/S2CID_(identifier)) [119047709](https://api.semanticscholar.org/CorpusID:119047709).

1. **[^](#cite_ref-MAST_9-0)** ["MAST: Barbara A. Mikulski Archive for Space Telescopes"](https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html). Space Telescope Science Institute. Retrieved 8 December 2021.

1. **[^](#cite_ref-prvak_10-0)** Prvák, M.; Liška, J.; Krtička, J.; Mikulášek, Z.; Lüftinger, T. (2015). ["Modelling of variability of the chemically peculiar star ϕ Draconis"](https://doi.org/10.1051%2F0004-6361%2F201526647). *Astronomy and Astrophysics*. **584**: A17. [arXiv](/source/ArXiv_(identifier)):[1510.01192](https://arxiv.org/abs/1510.01192). [Bibcode](/source/Bibcode_(identifier)):[2015A&A...584A..17P](https://ui.adsabs.harvard.edu/abs/2015A&A...584A..17P). [doi](/source/Doi_(identifier)):[10.1051/0004-6361/201526647](https://doi.org/10.1051%2F0004-6361%2F201526647).

1. **[^](#cite_ref-11)** (in Chinese) [AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 10 日](http://aeea.nmns.edu.tw/2006/0606/ap060610.html) [Archived](https://web.archive.org/web/20110521234349/http://aeea.nmns.edu.tw/2006/0606/ap060610.html) 2011-05-21 at the [Wayback Machine](/source/Wayback_Machine)

## External links

- Jim Kaler's Stars, University of Illinois: [PHI DRA (Phi Draconis)](http://stars.astro.illinois.edu/sow/phidra.html)

- An Atlas of the Universe: [Multiple Star Orbits](http://www.atlasoftheuniverse.com/orbits.html)

v t e Constellation of Draco List of stars in Draco Draco in Chinese astronomy Stars Bayer α (Thuban) β (Rastaban) γ (Eltanin) δ (Altais) ε (Tyl) ζ (Aldhibah) η (Athebyne) θ ι (Edasich) κ λ (Giausar) μ (Alrakis) ν (Kuma) ξ (Grumium) ο π ρ σ (Alsafi) τ υ φ χ ψ1 (Dziban) ψ2 ω Flamsteed 4 6 7 (Tianyi) 8 (Taiyi) 10 (i) 15 (A) 18 (g) 19 (h) 26 36 39 (b) 42 (Fafnir) 45 (d) 50 59 64 (e) 68 Variable TW YY AG BY CL CM CX DO EK HP V581 HR 3751 4126 4934 5811 6237 6518 6618 (Alruba) 6817 7137 7783 HD 109246 (Funi) 101364 128717 147379 156279 158259 176693 191939 Other 2MASS 1237+6526 2MASS J17554042+6551277 G 240-72 GD 356 Gliese 420 Gliese 625 Gliese 687 GRW +70 8247 Kepler-4 Kepler-10 Kepler-12 Kepler-90 Kepler-296 KOI-256 LP 71-82 Qatar-1 SDSS J1240+6710 Struve 2398 TOI-1136 WD 1856+534 WISE 1647+5632 WISE 1841+7000 Exoplanets HD 139357 b HD 167042 b ι Dra b (Hypatia) Kepler-4b Kepler-10b c Kepler-12b Kepler-90e f g h i Kepler-296b c d e f TOI-1452 b TrES-2b Star clusters LAMOST 1 Nebulae Cat's Eye Nebula NGC 6742 Galaxies NGC 3147 3197 3735 4121 4125 4221 4236 4319 4331 4332 4363 4441 4513 4545 4589 5678 5777 5866 5866B 5879 5905 5907 5949 5963 5965 5982 5985 6090 6248 6285 6286 6338 6340 6365 6373 6394 6412 6503 6505 6566 6621 6622 6670 6676 6786 6789 Other 1ES 1927+654 1ES 1959+650 3C 249.1 3C 305 3C 319 3C 343 3C 343.1 3C 351 3C 356 3C 371 3C 380 3C 390.3 3C 401 4C +72.26 4C 73.08 8C 1241+735 Abell 2218 BCG Bean galaxy Beaver galaxy BZQ J1727+5510 Draco Dwarf Draco II GB 1508+5714 Goldfish galaxy H1821+643 HFLS3 IERS B1946+708 IRAS F17179+5444 IRAS 18580+6527 J120011.1+680924.8 KKR 25 Markarian 817 Markarian 876 Original TRG PGC 39058 Porphyrion QSO B1823+568 RGZ J172749.5+534647 S5 1803+784 S5 2007+777 SDSS J1715+6008 Tadpole Galaxy UGC 9391 UGC 9405 UGC 11241 UGC 11411 WISEA J145223.62+611707.5 WN B1851+5707 Galaxy clusters Abell 2218 CL1358+62 Draco Supercluster NGC 5866 Group Astronomical events SN 2003jb SN 2005B SN 2016aps Swift J1644+57 Category

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Adapted from the Wikipedia article [Phi Draconis](https://en.wikipedia.org/wiki/Phi_Draconis) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Phi_Draconis?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.