Epoch J2000 Equinox J2000
|Right ascension||16h 14m 20.73853s|
|Declination||–03° 41′ 39.5612″|
|Apparent magnitude (V)||2.75|
|Spectral type||M0.5 III|
|U−B color index||+1.96|
|B−V color index||+1.59|
|Radial velocity (Rv)||–19.9 km/s|
|Proper motion (μ)||RA: –47.54 mas/yr
Dec.: –142.73 mas/yr
|Parallax (π)||19.06 ± 0.16 mas|
|Distance||171 ± 1 ly
(52.5 ± 0.4 pc)
|Absolute magnitude (MV)||–0.90|
|Surface gravity (log g)||1.4 cgs|
|Metallicity [Fe/H]||0.32 dex|
|Rotational velocity (v sin i)||7.0 km/s|
Delta Ophiuchi (δ Oph, δ Ophiuchi) is a star in the constellation Ophiuchus. It has the traditional name Yed Prior. The star Epsilon Ophiuchi, with which it forms a naked eye optical double, is Yed Posterior. The apparent visual magnitude is 2.75, making this a third-magnitude star and the fourth brightest in the constellation. Parallax measurements from the Hipparcos spacecraft yield a distance estimate of around 171 light-years (52 parsecs) from Earth.
Delta Ophiuchi is 170 light years from Earth, while Epsilon is 108; hence they are a mere optical double. This star has a stellar classification of M0.5 III, making this a red giant star that has undergone expansion of its outer envelope after exhausting the supply of hydrogen at its core. The measured angular diameter of this star, after correction for limb darkening, is 10.47 ± 0.12 mas. At the estimated distance of Delta Ophiuchi, this yields a physical size of about 59 times the radius of the Sun. In spite of its enlarged size, this star has only 1.5 times the mass of the Sun and hence a much lower density. The effective temperature of the outer atmosphere of Delta Ophiuchi is a relatively cool 3,679 K, which is what gives it the orange-red hue of an M-type star.
Yed Prior is listed as a suspected variable star that may change by 0.03 in visual magnitude. It has a low projected rotational velocity of 7.0 km s−1, which gives a minimum value for the azimuthal velocity along the star's equator. The abundance of elements other than hydrogen and helium, what astronomers term the star's metallicity, is more than double the abundance in the Sun's photosphere.
It was a member of the indigenous Arabic asterism al-Nasaq al-Yamānī, the "Southern Line" of al-Nasaqān the "Two Lines", along with α Ser (Unukalhai), δ Ser (Qin, Tsin), ε Ser (Ba, Pa), ε Oph (Yed Posterior), ζ Oph (Han) and γ Oph (Tsung Ching).
According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, al-Nasaq al-Yamānī or Nasak Yamani were the titles for two stars :δ Ser as Nasak Yamani I and ε Ser as Nasak Yamani II (exclude this star, α Ser, ε Oph, ζ Oph and γ Oph[clarification needed] ).
In Chinese, 天市右垣 (Tiān Shì Yòu Yuán), meaning Right Wall of Heavenly Market Enclosure, refers to an asterism which is represent eleven old states in China which is marking the right borderline of the enclosure, consisting of δ Ophiuchi, β Herculis, γ Herculis, κ Herculis, γ Serpentis, β Serpentis, α Serpentis, δ Serpentis, ε Serpentis, ε Ophiuchi and ζ Ophiuchi. Consequently, δ Ophiuchi itself is known as 天市右垣九 (Tiān Shì Yòu Yuán jiǔ, English: the Ninth Star of Right Wall of Heavenly Market Enclosure), representing the state of Liang (梁) (or Leang).
- 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
- Johnson, H. L. et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory 4 (99), Bibcode:1966CoLPL...4...99J
- Morgan, W. W.; Keenan, P. C. (1973), "Spectral Classification", Annual Review of Astronomy and Astrophysics 11: 29, Bibcode:1973ARA&A..11...29M, doi:10.1146/annurev.aa.11.090173.000333
- Percy, J. R.; Shepherd, C. W. (October 1992), "A Photometric Survey of Small-Amplitude Red Variables", Information Bulletin on Variable Stars 3792: 1, Bibcode:1992IBVS.3792....1P
- Wilson, Ralph Elmer (1953), General Catalogue of Stellar Radial Velocities, Washington: Carnegie Institution of Washington, Bibcode:1953QB901.W495.....
- Schmidt-Kaler, T.; Oestreicher, M. O. (October 1998), "The luminosity index for M stars and the distance to the LMC", Astronomische Nachrichten 319 (6): 375–386, Bibcode:1998AN....319..375S, doi:10.1002/asna.2123190606
- Tsuji, Takashi (May 2007), "Isotopic abundances of Carbon and Oxygen in Oxygen-rich giant stars", in Kupka, F.; Roxburgh, I.; Chan, K., Convection in Astrophysics, Proceedings of IAU Symposium #239 held 21-25 August, 2006 in Prague, Czech Republic, pp. 307–310, arXiv:astro-ph/0610180, Bibcode:2007IAUS..239..307T, doi:10.1017/S1743921307000622
- Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
- Oinas, V. (October 1977), "Neutral-ion anomaly in cool stars", Astronomy and Astrophysics 61 (1): 17–20, Bibcode:1977A&A....61...17O
- 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
- "del Oph -- Variable Star", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2010-07-06
- Richichi, A.; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics 431: 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039
- "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16
- Kunitzsch, P.; Smart, T. (2006), A Dictionary of Modern Star names: A Short Guide to 254 Star names and Their Derivations (Second Revised ed.), Cambridge, MA: Sky Publishing, p. 31, ISBN 1-931559-44-9
- Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York, NY: Dover Publications Inc, p. 243, ISBN 0-486-21079-0, retrieved 2010-12-12
- 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
- (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.
- (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
- (Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name, Hong Kong Space Museum. Accessed on line November 23, 2010.
- Kaler, James B., "Yed Prior", Stars (University of Illinois), retrieved 2012-02-07