Sigma Draconis

Sigma Draconis (σ Draconis, abbreviated Sig Dra, σ Dra), also named Alsafi /ælˈseɪfi/,[10] is a 4.7-magnitude star located at a distance of 18.8 light-years from the Sun in the constellation of Draco.

Sigma Draconis
Observation data
Epoch J2000      Equinox J2000
Constellation Draco
Right ascension 19h 32m 21.59026s[1]
Declination +69° 39′ 40.2354″[1]
Apparent magnitude (V) 4.674[2]
Characteristics
Spectral type K0 V[3]
U−B color index +0.386[2]
B−V color index +0.791[2]
Variable type None[4]
Astrometry
Radial velocity (Rv)26.7[5] km/s
Proper motion (μ) RA: 598.07[1] mas/yr
Dec.: −1738.40[1] mas/yr
Parallax (π)173.77 ± 0.18[1] mas
Distance18.77 ± 0.02 ly
(5.755 ± 0.006 pc)
Absolute magnitude (MV)5.89[6]
Details
Mass0.85+0.01
−0.03[7] M☉
Radius0.776±0.008[8] R☉
Luminosity0.410±0.006[8] L☉
Surface gravity (log g)4.59±0.02[7] cgs
Temperature5,255±31[8] K
Metallicity [Fe/H]−0.20±0.04[7] dex
Rotational velocity (v sin i)1.4[9] km/s
Age3.00±0.60[7] Gyr
Other designations
Alsafi, σ Draconis, 61 Draconis, BD+69°1053, GCTP 4607.00, GJ 764, HD 185144, HIP 96100, HR 7462, LHS 477.[5]
Database references
SIMBADdata
ARICNSdata

Name

σ Draconis (Latinised to Sigma Draconis) is the star's Bayer designation, established in 1603 as part of the Uranometria, a star catalogue produced by German celestial cartographer Johann Bayer.

It bore the traditional name Alsafi, derived from the Arabic Athāfi, itself erroneously transcribed from the Arabic plural Athāfiyy, by which the nomads designated the tripods of their open-air kitchens. It was the name of an association of this star, Tau Draconis and Upsilon Draconis.[11] According to a 1971 NASA memorandum, Athāfi or Alsafi were the title for three stars: Sigma Draconis as Alsafi, Tau Draconis as Athāfi I and Upsilon Draconis as Athāfi II.[12] In 2016, the IAU organized a Working Group on Star Names (WGSN)[13] to catalog and standardize proper names for stars. The WGSN approved the name Alsafi for Sigma Draconis on 30 June 2017 and it is now so included in the List of IAU-approved Star Names.[10]

In Chinese, 天廚 (Tiān Chú), meaning Celestial Kitchen, refers to an asterism consisting of Sigma Draconis, Delta Draconis, Epsilon Draconis, Rho Draconis, 64 Draconis (see 64 Draconis (Portuguese)) and Pi Draconis.[14] Consequently, the Chinese name for Sigma Draconis itself is 天廚二 (Tiān Chú èr, English: the Second Star of Celestial Kitchen.)[15]

Properties

Sigma Draconis is a main sequence dwarf which has long served as a K0 V spectral standard star.[16][17][3] Its classification as K0 V defines one of the anchor points of the Morgan–Keenan system that have remained unchanged since the original 1943 MKK Atlas.[18] However, some modern spectroscopy gives it as designation of G9 V.[19][20]

The radius of Sigma Draconis has been directly measured using interferometry with the CHARA array, which yields a result of 77.6% of the Sun's radius.[8] It has 85% of the Sun's mass, but the luminosity of this star is only 41% that of the Sun.[7][8] The projected rotation rate (v sin i) is relatively low at 1.4 km/s.[9] It is considered a slightly metal-poor star, meaning that it has a lower proportion of elements with masses greater than helium when compared to the Sun.[21]

The temperature, luminosity and surface activity appear to vary slightly in a manner very similar to the sunspot cycle, although the full length of the cycle has not yet been determined (as of 1992).[22] The total variability is among the lowest of all stars that have been measured by the Hipparcos spacecraft.[21]

Sigma Draconis has a high proper motion, advancing across the celestial sphere at a rate of 1.835 arc seconds per year.[23] The star made its perihelion passage about 46,725 years ago, when it came within 16.55 ly (5.075 pc).[24] The components of Sigma Draconis's space velocity are U=+36, V=+40 and W=-10 km/s. This gives the star an unusually large orbital eccentricity about the Milky Way galaxy of 0.30 (compared to 0.06 for the Sun.) The mean galactocentric distance for the orbit is 10.3 kiloparsecs (about 34,000 light-years).[21]

As of 2013, no Jupiter-size or larger companion had been detected about the star and there was no indication of excess infrared radiation that would be evidence of circumstellar matter (such as a debris disk).[9][25]

Between 2004 and 2013, extensive radial velocity measurements were gathered on Sigma Draconis using the High Resolution Echelle Spectrometer on the Keck Observatory. The Keck/HIRES data indicated a possible period of about 300 days and a likely alias period of 2800 days. Adding data taken with the Automated Planet Finder at the Lick Observatory strengthened and narrowed the 300-day period while reducing the significance of the 2800-day period. The combined analysis suggests there may be a Uranus-mass planet on a 308-day orbit, though the authors do not yet consider the discovery to be publishable as they have not yet attempted to rule out other non-planetary explanations for the velocity variations.[26]

The unconfirmed Sigma Draconis planetary system[26]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
(unconfirmed) ≳12 M⊕ ≈0.814[note 1] 308 ~0 (assumed) — —

See also

Notes
  1. Kepler's Third Law, assuming a circular orbit gives . The mass of the star (ignoring the comparatively insignificant mass of the planet as the star Sigma Draconis has approximately 25,000 times more mass than the unconfirmed planet) and period of planet's orbit are known from the paper,[26] so the semimajor axis can be calculated using .[27]

References
  1. van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600
  2. Oja, T. (August 1986), "UBV photometry of stars whose positions are accurately known. III", Astronomy and Astrophysics Supplement Series, 65 (2): 405–409, Bibcode:1986A&AS...65..405O
  3. Keenan, Philip C.; McNeil, Raymond C. (1989). "The Perkins catalog of revised MK types for the cooler stars". Astrophysical Journal Supplement Series. 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373.
  4. Radick, Richard R.; et al. (September 1998), "Patterns of Variation among Sun-like Stars", The Astrophysical Journal Supplement Series, 118 (1): 239–258, Bibcode:1998ApJS..118..239R, doi:10.1086/313135.
  5. "Query Result: NSV 12176 -- Variable Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2007-06-15
  6. Kim, Bokyoung; et al. (February 2016), "Spectroscopic Survey of G and K Dwarfs in the Hipparcos Catalog. I. Comparison between the Hipparcos and Photometric Parallaxes", The Astrophysical Journal Supplement Series, 222 (2): 29, arXiv:1601.01459, Bibcode:2016ApJS..222...19K, doi:10.3847/0067-0049/222/2/19, S2CID 15793261, 19.
  7. Ramírez, I.; et al. (September 2012), "Lithium Abundances in nearby FGK Dwarf and Subgiant Stars: Internal Destruction, Galactic Chemical Evolution, and Exoplanets", The Astrophysical Journal, 756 (1): 46, arXiv:1207.0499, Bibcode:2012ApJ...756...46R, doi:10.1088/0004-637X/756/1/46, S2CID 119199829.
  8. Boyajian, Tabetha S.; et al. (February 2012), "Stellar Diameters and Temperatures. I. Main-sequence A, F, and G Stars", The Astrophysical Journal, 746 (1): 101, arXiv:1112.3316, Bibcode:2012ApJ...746..101B, doi:10.1088/0004-637X/746/1/101, S2CID 18993744. See Table 10.
  9. Absil, O.; et al. (July 2013), "A near-infrared interferometric survey of debris-disc stars. III. First statistics based on 42 stars observed with CHARA/FLUOR", Astronomy and Astrophysics, 555: A104, arXiv:1307.2488, Bibcode:2013A&A...555A.104A, doi:10.1051/0004-6361/201321673, S2CID 16945896
  10. "Naming Stars". IAU.org. Retrieved 16 December 2017.
  11. Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York, NY: Dover Publications Inc, p. 210, ISBN 0-486-21079-0, retrieved 2010-12-12
  12. Rhoads, Jack W. (November 15, 1971), Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars (PDF), Jet Propulsion Laboratory, California Institute of Technology
  13. "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  14. 陳久金 [Chen Jiujin] (2005). 中國星座神話 [Chinese Constellation Mythology] (in Chinese). 台灣書房出版有限公司 [Taiwan Shufang Publishing Co., Ltd.] ISBN 978-986-7332-25-7.
  15. "香港太空館 - 研究資源 - 亮星中英對照表" [Hong Kong Space Museum - Research Resources - Bright Star Chinese-English Table] (in Chinese). Hong Kong Space Museum. Archived from the original on 2008-10-25. Retrieved November 23, 2010.
  16. Johnson, H. L.; Morgan, W. W. (1953). "Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas". Astrophysical Journal. 117: 313. Bibcode:1953ApJ...117..313J. doi:10.1086/145697.
  17. Morgan, W. W.; Keenan, P. C. (1973). "Spectral Classification". Annual Review of Astronomy and Astrophysics. 11: 29–50. Bibcode:1973ARA&A..11...29M. doi:10.1146/annurev.aa.11.090173.000333.
  18. Robert F. Garrison. "MK ANCHOR POINTS". Retrieved 2017-04-30.
  19. Gray, R. O.; et al. (2003). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 parsecs: The Northern Sample I". The Astronomical Journal. 126 (4): 2048–2059. arXiv:astro-ph/0308182v1. Bibcode:2003AJ....126.2048G. doi:10.1086/378365. S2CID 119417105.
  20. Henry, Todd J. (October 1, 2006), The One Hundred Nearest Star Systems, Research Consortium on Nearby Stars, retrieved 2011-10-14
  21. Porto de Mello, Gustavo; del Peloso, Eduardo F.; Ghezzi, Luan (2006), "Astrobiologically Interesting Stars Within 10 Parsecs of the Sun", Astrobiology, 6 (2): 308–331, arXiv:astro-ph/0511180, Bibcode:2006AsBio...6..308P, doi:10.1089/ast.2006.6.308, PMID 16689649, S2CID 119459291
  22. Gray, David F.; et al. (1992), "The activity cycle of Sigma Draconis", Astrophysical Journal, 400 (2): 681–691, Bibcode:1992ApJ...400..681G, doi:10.1086/172030
  23. Lépine, Sébastien; Shara, Michael M. (March 2005), "A Catalog of Northern Stars with Annual Proper Motions Larger than 0.15" (LSPM-NORTH Catalog)", The Astronomical Journal, 129 (3): 1483–1522, arXiv:astro-ph/0412070, Bibcode:2005AJ....129.1483L, doi:10.1086/427854, S2CID 2603568.
  24. Bailer-Jones, C. A. L. (March 2015), "Close encounters of the stellar kind", Astronomy & Astrophysics, 575: 13, arXiv:1412.3648, Bibcode:2015A&A...575A..35B, doi:10.1051/0004-6361/201425221, S2CID 59039482, A35.
  25. Holmes, E. K.; et al. (2003), "A Survey of Nearby Main-Sequence Stars for Submillimeter Emission", The Astronomical Journal, 125 (6): 3334–3343, Bibcode:2003AJ....125.3334H, doi:10.1086/375202
  26. Vogt, Steven S.; et al. (February 2014), "APF - The Lick Observatory Automated Planet Finder", Publications of the Astronomical Society of the Pacific, 126 (938): 359–379, arXiv:1402.6684, Bibcode:2014PASP..126..359V, doi:10.1086/676120, S2CID 12067979
  27. Agnew, Matthew T.; et al. (2019). "Predicting multiple planet stability and habitable zone companions in the TESS era". Monthly Notices of the Royal Astronomical Society. 485 (4): 4703–4725. arXiv:1901.11297. Bibcode:2019MNRAS.485.4703A. doi:10.1093/mnras/stz345. S2CID 119028049. — A random example of Kepler's 3rd law equation rearranged to change the subject to the orbital radius, and it being used in that rearranged state thereafter. See in the paper section 3.1, under the title "Numerical approach".
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