Omicron Draconis

Omicron Draconis (Latinised as ο Draconis, abbreviated to ο Dra) is a giant star in the constellation Draco located 322.93 light years from the Earth. It has a radius of 30 solar radii, and a luminosity of 269 suns. Its path in the night sky is circumpolar above the ecliptic, meaning the star never rises or sets when viewed in the night sky from certain positions in the northern hemisphere.

Omicron Draconis
Location of ο Dra (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Draco
Right ascension  18h 51m 12.09530s[1]
Declination +59° 23′ 18.0627″[1]
Apparent magnitude (V) 4.65[2]
Characteristics
Spectral type G9III[3]
U−B color index +1.19[2]
Variable type RS CVn
Astrometry
Radial velocity (Rv)−19.52[4] km/s
Proper motion (μ) RA: 77.47[1] mas/yr
Dec.: 25.37[1] mas/yr
Parallax (π)9.54 ± 0.21[1] mas
Distance106.8[5] pc
Absolute magnitude (MV)−0.344[6]
Orbit[5]
Primaryο Dra A
Companionο Dra B
Period (P)138.444 ± 0.003 days
Semi-major axis (a)6.51 ± 0.03″
Eccentricity (e)0.158 ± 0.003
Inclination (i)89.6 ± 0.3°
Longitude of the node (Ω)22.9 ± 0.2°
Periastron epoch (T)2454983.0 ± 0.2
Argument of periastron (ω)
(secondary)		293.0 ± 0.6°
Semi-amplitude (K1)
(primary)		23.42 ± 0.05 km/s
Semi-amplitude (K2)
(secondary)		32.0 ± 0.4 km/s
Details
ο Dra A
Mass1.35[5] M☉
Radius25.1[5] R☉
Luminosity220[5] L☉
Surface gravity (log g)1.769[5] cgs
Temperature4400[7] K
Metallicity [Fe/H]−0.5[3] dex
Rotation79[5]
Rotational velocity (v sin i)20.0[6] km/s
Age3.0[5] Gyr
ο Dra B
Mass0.99[5] M☉
Radius1.0[5] R☉
Luminosity1.3[5] L☉
Surface gravity (log g)4.43[5] cgs
Temperature6,000[5] K
Other designations
Omicron Draconis, 47 Draconis, HR 7125, HD 175306, HIP 92512, BD+59°1925
Database references
SIMBADdata

Omicron Draconis can be considered the north pole star of Mercury, as it is the closest star to Mercury's north celestial pole.[8]

This is a single-lined spectroscopic binary system,[7] but the secondary has been detected using interferometry. It is a RS Canum Venaticorum variable system with eclipses. The total amplitude of variation is only about a thousandth of a magnitude.[5] The secondary star is similar to the sun, presumably a main sequence star, while the primary is a giant star 25 times larger than the sun and two hundred times more luminous.

References
  1. Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. Hoffleit, Dorrit; Jaschek, Carlos (1991). "The Bright star catalogue". New Haven. Bibcode:1991bsc..book.....H.
  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. Karataş, Y.; Bilir, S.; Eker, Z.; Demircan, O. (2004). "Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution". Monthly Notices of the Royal Astronomical Society. 349 (3): 1069. arXiv:astro-ph/0404219. Bibcode:2004MNRAS.349.1069K. doi:10.1111/j.1365-2966.2004.07588.x.
  5. Roettenbacher, Rachael M.; Monnier, John D.; Fekel, Francis C.; Henry, Gregory W.; Korhonen, Heidi; Latham, David W.; Muterspaugh, Matthew W.; Williamson, Michael H.; Baron, Fabien; Ten Brummelaar, Theo A.; Che, Xiao; Harmon, Robert O.; Schaefer, Gail H.; Scott, Nicholas J.; Sturmann, Judit; Sturmann, Laszlo; Turner, Nils H. (2015). "Detecting the Companions and Ellipsoidal Variations of RS CVn Primaries. II. O Draconis, a Candidate for Recent Low-mass Companion Ingestion". The Astrophysical Journal. 809 (2): 159. arXiv:1507.03601. Bibcode:2015ApJ...809..159R. doi:10.1088/0004-637X/809/2/159.
  6. Böhm-Vitense, Erika; et al. (December 2000), "Ultraviolet Emission Lines in BA and Non-BA Giants", The Astrophysical Journal, 545 (2): 992–999, Bibcode:2000ApJ...545..992B, doi:10.1086/317850.
  7. Pourbaix, D.; Boffin, H. M. J. (February 2003), "Reprocessing the Hipparcos Intermediate Astrometric Data of spectroscopic binaries. II. Systems with a giant component", Astronomy and Astrophysics, 398 (3): 1163–1177, arXiv:astro-ph/0211483, Bibcode:2003A&A...398.1163P, doi:10.1051/0004-6361:20021736
  8. Sharrah, Paul C. (1975). "Pole Stars of Other Planets" (pdf). Arkansas Academy of Sciences Proceedings. XXIX: 62–63.
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