Delta Aurigae
Location of δ Aurigae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Auriga
Right ascension 05h 59m 31.61842s[1]
Declination +54° 17′ 05.0567″[1]
Apparent magnitude (V) 3.715[2]
Characteristics
Spectral type K0 IIIb[3]
U−B color index +0.837[2]
B−V color index +1.017[2]
R−I color index 0.5
Astrometry
Radial velocity (Rv)+9.75±0.44[4] km/s
Proper motion (μ) RA: +85.814[1] mas/yr
Dec.: −142.928[1] mas/yr
Parallax (π)23.0557 ± 0.4512 mas[1]
Distance141 ± 3 ly
(43.4 ± 0.8 pc)
Absolute magnitude (MV)0.56[5]
Orbit[6]
Period (P)1,283.4±0.7 d
Semi-major axis (a)≥ 39.1 ± 0.8 Gm (0.2614 ± 0.0053 AU)
Eccentricity (e)0.231±0.017
Periastron epoch (T)52,980±16 MJD
Argument of periastron (ω)
(secondary)		200±5°
Semi-amplitude (K1)
(primary)		2.28±0.04 km/s
Details
Mass1.63[7] M☉
Radius11[8] R☉
Luminosity62[8] L☉
Surface gravity (log g)2.7[8] cgs
Temperature4,786[8] K
Metallicity [Fe/H]−0.15[8] dex
Rotational velocity (v sin i)3.9[8] km/s
Age3.26[7] Gyr
Other designations
δ Aur, 33 Aurigae, BD+54 970, FK5 225, HD 40035, HIP 28358, HR 2077, SAO 25502[9]
Database references
SIMBADdata

Delta Aurigae, Latinized from δ Aurigae, is the Bayer designation for an astrometric binary[10] star in the northern constellation of Auriga. It is visible to the naked eye with an apparent visual magnitude of 3.715.[2] Based upon its annual parallax shift of 23.06 mas,[1] it is some 141 light-years (43 parsecs) distant from the Earth, give or take a three light-year margin of error. It is drifting further away with a radial velocity of +10 km/s.[4] This star is the namesake for the Delta Aurigids, a meteor shower that occurs between October 6–15.[11] The radiant point for this shower passes several degrees to the south of the star.[12]

The variable radial velocity of this system was not recognized until 1999, more than a century following the first measurement in 1897. Delta Aurigae is a single-lined spectroscopic binary: periodic Doppler shifts in the star's spectrum indicate orbital motion. The pair have an orbital period of 1,283.4 days (3.514 years) and an eccentricity of 0.231. Based on the small amplitude of the radial velocity variation, the companion is most likely a small K- or early M-type main-sequence star with around half the mass of the Sun.[6]

The visible component of this system is an evolved giant star with a stellar classification of K0 IIIb.[3] It is a red clump star, indicating that it is generating energy through helium fusion at its core.[13] The star is 3.26[7] billion years old and is spinning with a projected rotational velocity of 4 km/s.[8] It has 1.63[7] times the mass of the Sun and has expanded to 11[8] times the Sun's radius. The star is radiating 62 times the Sun's luminosity[8] from the star's photosphere at an effective temperature of 4,786 K.[8] This heat gives the star the orange-hued glow of a K-type star.[14]

Name

In Indian astronomy, it is known by the name Prajapati /prəˈdʒɑːpəti/, from the Sanskrit प्रजापति prajāpati "the Lord of Created Beings".[15][16]

In Chinese, 八穀 (Bā Gǔ), meaning Eight Kinds of Crops, refers to an asterism consisting of δ Aurigae, ξ Aurigae, 26 Camelopardalis, 14 Camelopardalis, 7 Camelopardalis, 9 Aurigae, 11 Camelopardalis and 31 Camelopardalis.[17] Consequently, the Chinese name for δ Aurigae itself is 八穀一 (Bā Gǔ yī, English: the First Star of Eight Kinds of Crops), refers to the rice.

References

  1. 1 2 3 4 5 6 Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. 1 2 3 4 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. 1 2 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. 1 2 Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209.
  5. ↑ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
  6. 1 2 Griffin, R. F. (April 2009), "Spectroscopic binary orbits from photoelectric radial velocities. Paper 205: HD 9519, delta Aurigae, HR 4427, and HR 7795", The Observatory, 129: 54–79, Bibcode:2009Obs...129...54G.
  7. 1 2 3 4 Luck, R. Earle (September 2015), "Abundances in the Local Region. I. G and K Giants", The Astronomical Journal, 150 (3): 23, arXiv:1507.01466, Bibcode:2015AJ....150...88L, doi:10.1088/0004-6256/150/3/88, S2CID 118505114, 88.
  8. 1 2 3 4 5 6 7 8 9 10 Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209, S2CID 121883397.
  9. ↑ "del Aur". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-08-18.
  10. ↑ Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
  11. ↑ Reynolds, Mike D. (2010), Falling Stars: A Guide to Meteors and Meteorites, Haunted Series (2nd ed.), Stackpole Books, p. 42, ISBN 978-0811736169
  12. ↑ Lunsford, Robert (2008), Meteors and How to Observe Them, Astronomers' Observing Guides, Springer, p. 86, ISBN 978-0387094601
  13. ↑ Alves, David R. (August 2000), "K-Band Calibration of the Red Clump Luminosity", The Astrophysical Journal, 539 (2): 732–741, arXiv:astro-ph/0003329, Bibcode:2000ApJ...539..732A, doi:10.1086/309278, S2CID 16673121.
  14. ↑ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-18, retrieved 2012-01-16
  15. ↑ "Auriga", by Richard Hinckley Allen in Star Names: Their Lore and Meaning
  16. ↑ Monier-Williams Sanskrit dictionary: pra-cchana—pra-jalpa
  17. ↑ (in Chinese) 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.
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