Omicron Draconis

Omicron Draconis
	Location of ο Dra (circled)
Observation data; Epoch J2000 Equinox J2000
Constellation	Draco
Right ascension	18h 51m 12.09530s
Declination	+59° 23′ 18.0627″
Apparent magnitude (V)	4.65
Characteristics
Spectral type	G9III
U−B color index	+1.19
Variable type	RS CVn + eclipsing
Astrometry
Radial velocity (Rv)	−19.52 km/s
Proper motion (μ)	RA: 77.47 mas/yr ; Dec.: 25.37 mas/yr
Parallax (π)	9.54 ± 0.21 mas
Distance	106.8 pc
Absolute magnitude (MV)	−0.344
Orbit
Period (P)	138.444 ± 0.003 days
Semi-major axis (a)	0.00651 ± 0.00003″
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
Mass	1.35 M☉
Radius	25.1 R☉
Luminosity	220 L☉
Surface gravity (log g)	1.769 cgs
Temperature	4400 K
Metallicity [Fe/H]	−0.5 dex
Rotation	79
Rotational velocity (v sin i)	20.0 km/s
Age	3.0 Gyr
ο Dra B
Mass	0.99 M☉
Radius	1.0 R☉
Luminosity	1.3 L☉
Surface gravity (log g)	4.43 cgs
Temperature	6,000 K
Other designations
	Omicron Draconis, 47 Draconis, HR 7125, HD 175306, HIP 92512, BD+59°1925
Database references
SIMBAD	data

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. Its path in the night sky is circumpolar for latitudes greater than 31^o north, meaning the star never rises or sets when viewed in the night sky.

A visual band light curve for Omicron Draconis, adapted from Roettenbacher *et al.* (2015)^[4]

This is a single-lined spectroscopic binary system,^[7] but the secondary has been detected using interferometry. It is an RS Canum Venaticorum variable system with eclipses. The total amplitude of variation is only a few hundredths of a magnitude.^[8]^[4] 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.

Identities as pole star

Omicron Draconis can be considered the north pole star of Mercury, as it is the closest star to Mercury's north celestial pole.^[9] In addition to that, this star is currently the Moon's north pole star, which occurs once every 18.6 years.^[10] The pole star status changes periodically, because of the precession of the Moon's rotational axis.

References

^ ^a ^b ^c ^d ^e Van Leeuwen, F. (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.
^ ^a ^b Hoffleit, Dorrit; Jaschek, Carlos (1991). "The Bright star catalogue". New Haven. Bibcode:1991bsc..book.....H.
^ ^a ^b 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.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p 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. S2CID 119228345.
^ Karataș, Yüksel; Bilir, Selçuk; Eker, Zeki; Demircan, Osman; Liebert, James; Hawley, Suzanne L.; Fraser, Oliver J.; Covey, Kevin R.; Lowrance, Patrick; Kirkpatrick, J. Davy; Burgasser, Adam J. (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): 1069–1092. arXiv:astro-ph/0404219. Bibcode:2004MNRAS.349.1069K. doi:10.1111/j.1365-2966.2004.07588.x. S2CID 15290475.
^ ^a ^b 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.
^ ^a ^b 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, S2CID 12361870
^ "omi Dra". The International Variable Star Index. AAVSO. Retrieved 15 July 2022.
^ Sharrah, Paul C. (1975). "Pole Stars of Other Planets" (pdf). Arkansas Academy of Sciences Proceedings. XXIX: 62–63.
^ Patrick Moore (1983), The Guinness Book of Astronomy Facts & Feats, p. 29, In 1968 the north pole star of the Moon was Omega Draconis; by 1977 it was 36 Draconis. The south pole star is Delta Doradus.