# BY Draconis

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Star in the constellation Draco

BY Draconis Visual band light curves for BY Draconis from six different years, adapted from Pettersen et al. (1992)[1] Observation data Epoch J2000 Equinox ICRS Constellation Draco AB Right ascension 18h 33m 55.7728s[citation needed] Declination +51° 43′ 08.905″[citation needed] Apparent magnitude (V) 8.07[citation needed] Characteristics Spectral type K4Ve + K7.5Ve + M5[2] U−B color index +0.99[3] B−V color index +1.19[3] Variable type BY Dra + UV Cet[4] Astrometry AB Radial velocity (Rv) −25.484±0.046[5] km/s Proper motion (μ) RA: 185.759[citation needed] mas/yr Dec.: −325.590[citation needed] mas/yr Parallax (π) 60.59±0.28 mas[citation needed] Distance 53.8 ± 0.2 ly (16.50 ± 0.08 pc) Absolute magnitude (MV) 7.48 / 8.63[6] Orbit[5] Primary BY Dra A Name BY Dra B Period (P) 5.9751139 ± 0.0000046 d Semi-major axis (a) 4.4472 ± 0.0091 mas Eccentricity (e) 0.30014 ± 0.00062 Inclination (i) 154.41± 0.29° Longitude of the node (Ω) 152.3 ± 0.1° Periastron epoch (T) JD 2453999.2144 ± 0.0021 Argument of periastron (ω) (secondary) 230.33 ± 0.17° Semi-amplitude (K1) (primary) 28.394 ± 0.060 km/s Semi-amplitude (K2) (secondary) 32.284 ± 0.061 km/s Details[5] BY Dra A Mass 0.792 ± 0.026 M☉ BY Dra B Mass 0.697 ± 0.023 M☉ Other designations BY Dra, GJ 719, BD+51 2402, HD 234677, LTT 15477, SAO 31048, HIP 91009[2] Database references SIMBAD BY Dra AB BY Dra C ARICNS data

**BY Draconis** is a [multiple star system](/source/Multiple_star_system) in the [constellation](/source/Constellation) [Draco](/source/Draco_(constellation)), consisting of at least three components. Components A and B are [main sequence](/source/Main_sequence) stars,[5] and form a close [binary star](/source/Binary_star) system with a short [orbital period](/source/Orbital_period) of only 5.98 days. Their individual [spectroscopic](/source/Spectroscopy) classifications are dK5e and dK7e.[1] They form the prototype of a class of [variable stars](/source/Variable_star) known as [BY Draconis variables](/source/BY_Draconis_variable).[6]

The third component (C) is, by comparison, widely separated from the A-B pair by an [angular distance](/source/Angular_distance) of 17 [arcseconds](/source/Arcsecond), which corresponds to 260 [AU](/source/Astronomical_Unit) at the estimated distance of this star system—where an AU is the average distance from the [Earth](/source/Earth) to the Sun. Component C is an [M5 class](/source/Spectral_classification) [red dwarf](/source/Red_dwarf) star. There may be a fourth component to the system, orbiting with a ≤1000‑day period, responsible for the eccentricity of the 5.98-day orbit, but this has not been visually confirmed.[5]

The variability of BY Draconis is caused by activity in the stellar [photosphere](/source/Photosphere) called [starspots](/source/Starspot), which are comparable to [sunspots](/source/Sunspot) on the [Sun](/source/Sun), in combination with [rapid rotation](/source/Stellar_rotation) that changes the viewing angle of the activity relative to the observer. This variation has an average periodicity of 3.8285 days, but the brightness also changes over the course of several years—depending on the level of surface activity. Most observers believe that the primary star (A) is responsible for the variability as the secondary produces only a third of the total luminosity from the system. However, the spots may occur on both stars. Unlike the Sun, these spots may occur in the polar regions of the stars.[1]

## References

1. ^ [***a***](#cite_ref-aaass96_1-0) [***b***](#cite_ref-aaass96_1-1) [***c***](#cite_ref-aaass96_1-2) Pettersen, B. R.; Olah, K.; Sandmann, W. H. (1992). "Longterm behaviour of starspots. II - A decade of new starspot photometry of BY Draconis and EV Lacertae". *Astronomy and Astrophysics Supplement Series*. **96** (3): 497–504. [Bibcode](/source/Bibcode_(identifier)):[1992A&AS...96..497P](https://ui.adsabs.harvard.edu/abs/1992A&AS...96..497P).

1. ^ [***a***](#cite_ref-SIMBAD_2-0) [***b***](#cite_ref-SIMBAD_2-1) ["V* BY Dra"](http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=V%2A+BY+Dra). *[SIMBAD](/source/SIMBAD)*. [Centre de données astronomiques de Strasbourg](/source/Centre_de_donn%C3%A9es_astronomiques_de_Strasbourg). Retrieved 2008-04-18.

1. ^ [***a***](#cite_ref-rob176_3-0) [***b***](#cite_ref-rob176_3-1) Epps, E. A. (1972). "UBV photoelectric observations. I. Stars within 25 parasecs of the Sun. II. Stars in quasar, galaxy fields. III. Stars in Kapteyn selected areas. IV. Miscellaneous stars". *[Royal Observatory Bulletin](https://en.wikipedia.org/w/index.php?title=Royal_Observatory_Bulletin&action=edit&redlink=1)*. **176**: 77–115. [Bibcode](/source/Bibcode_(identifier)):[1972RGOB..176..127E](https://ui.adsabs.harvard.edu/abs/1972RGOB..176..127E).

1. **[^](#cite_ref-gcvs_4-0)** Samus', N. N; Kazarovets, E. V; Durlevich, O. V; Kireeva, N. N; Pastukhova, E. N (2017). "General catalogue of variable stars: Version GCVS 5.1". *Astronomy Reports*. **61** (1): 80. [Bibcode](/source/Bibcode_(identifier)):[2017ARep...61...80S](https://ui.adsabs.harvard.edu/abs/2017ARep...61...80S). [doi](/source/Doi_(identifier)):[10.1134/S1063772917010085](https://doi.org/10.1134%2FS1063772917010085). [S2CID](/source/S2CID_(identifier)) [125853869](https://api.semanticscholar.org/CorpusID:125853869).

1. ^ [***a***](#cite_ref-mnras419_5-0) [***b***](#cite_ref-mnras419_5-1) [***c***](#cite_ref-mnras419_5-2) [***d***](#cite_ref-mnras419_5-3) [***e***](#cite_ref-mnras419_5-4) Hełminiak, K.G. (2012). ["New high-precision orbital and physical parameters of the double-lined low-mass spectroscopic binary BY Draconis"](https://doi.org/10.1111%2Fj.1365-2966.2011.19785.x). *[Monthly Notices of the Royal Astronomical Society](/source/Monthly_Notices_of_the_Royal_Astronomical_Society)*. **419** (2): 1285–1293. [arXiv](/source/ArXiv_(identifier)):[1109.5059](https://arxiv.org/abs/1109.5059). [Bibcode](/source/Bibcode_(identifier)):[2012MNRAS.419.1285H](https://ui.adsabs.harvard.edu/abs/2012MNRAS.419.1285H). [doi](/source/Doi_(identifier)):[10.1111/j.1365-2966.2011.19785.x](https://doi.org/10.1111%2Fj.1365-2966.2011.19785.x). [S2CID](/source/S2CID_(identifier)) [19002972](https://api.semanticscholar.org/CorpusID:19002972).

1. ^ [***a***](#cite_ref-apj547_6-0) [***b***](#cite_ref-apj547_6-1) Boden, A. F.; Lane, B. F. (2001). "A Preliminary Visual Orbit of BY Draconis". *[The Astrophysical Journal](/source/The_Astrophysical_Journal)*. **547** (2): 1071–1076. [arXiv](/source/ArXiv_(identifier)):[astro-ph/0001138](https://arxiv.org/abs/astro-ph/0001138). [Bibcode](/source/Bibcode_(identifier)):[2001ApJ...547.1071B](https://ui.adsabs.harvard.edu/abs/2001ApJ...547.1071B). [doi](/source/Doi_(identifier)):[10.1086/318394](https://doi.org/10.1086%2F318394). [S2CID](/source/S2CID_(identifier)) [10704476](https://api.semanticscholar.org/CorpusID:10704476).

## External links

- ["BY Draconis star"](http://www.daviddarling.info/encyclopedia/B/BY_Draconis_star.html). The Internet Encyclopedia of Science. [Archived](https://web.archive.org/web/20080304192144/http://www.daviddarling.info/encyclopedia/B/BY_Draconis_star.html) from the original on 4 March 2008. Retrieved 2008-04-18.

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 [BY Draconis](https://en.wikipedia.org/wiki/BY_Draconis) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/BY_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.