Gamma Draconis

Gamma Draconis
Draco_constellation_map.png: Torsten Bronger derivative work: Kxx (talk) · CC BY-SA 3.0 · source
Name	Gamma Draconis
Other names	Eltanin, 17 Draconis, HR 5603, HD 164058
Constellation	Draco
Epoch	J2000
Apparent magnitude	2.23
Spectral type	K5III
Distance pc	21.4
Radial velocity km s	-13.0
Mass solar	1.7
Radius solar	48
Luminosity solar	400

Gamma Draconis is a bright K-type giant star in the northern circumpolar constellation Draco, historically prominent in navigation and astronomy. It has been cataloged and studied by observatories, astronomers, and space missions across centuries, appearing in star catalogs, astrometric surveys, and cultural records. Its properties and motion have made it a subject in stellar evolution, astrometry, and exoplanet searches.

Nomenclature and Designations

The traditional name Eltanin appears in medieval and classical sources and is preserved in catalogs compiled by Johann Bayer, John Flamsteed, and later by the Henry Draper Catalogue. Modern designations include instrumental and survey identifiers such as 17 Draconis (Flamsteed), HR 5603 (Bright Star Catalogue), and HD 164058 (Henry Draper). The star is listed in astrometric missions and catalogs maintained by institutions like the Hipparcos, Gaia (spacecraft), and the SIMBAD database, and appears in compilations by the Bayer designation system and the Bright Star Catalogue editors.

Stellar Properties

Spectral classification places the star as a K5III giant, a stage detailed in reviews by researchers at institutions such as the European Southern Observatory, Harvard College Observatory, and the Mount Wilson Observatory. Fundamental parameters—effective temperature, radius, and luminosity—are determined through methods used in the Stefan–Boltzmann law analyses cited by teams at the Keck Observatory and Lowell Observatory. Mass and evolutionary state are inferred from comparisons with stellar models developed by groups at the Geneva Observatory and the Padova and Trieste Astronomical Observatory collaborators, and fitting performed with isochrones from the Yonsei–Yale and PARSEC model sets. Measurements of metallicity and chemical composition reference spectroscopic analyses employed at Royal Greenwich Observatory-era spectrographs and modern instruments at European Space Agency member facilities. Angular diameter determinations using optical interferometers at facilities like the CHARA Array and the Infrared Optical Telescope Array inform radius estimates, while bolometric luminosity ties into calibrations used by the International Astronomical Union committees on stellar parameters.

Planetary and Companion Searches

Searches for substellar companions and planets around bright giants have been pursued by teams affiliated with the California Planet Survey, European Southern Observatory programs, and long-term radial-velocity projects at the Lick Observatory. Techniques borrowed from exoplanet detections reported by the Kepler (spacecraft) and TESS missions, including transit photometry and Doppler spectroscopy, have been adapted to evolved stars studied at the Anglo-Australian Observatory and McDonald Observatory. Results are discussed in context with discoveries by groups led by figures such as Geoffrey Marcy, Michel Mayor, and Didier Queloz, and compared with the population outcomes summarized by the NASA Exoplanet Archive and consortium reviews published by the Max Planck Institute for Astronomy. Null detections and limits on companion mass and orbital parameters are incorporated into statistical analyses used by the Exoplanet Archive and surveys coordinated by the European Research Council.

Motion and Distance

Parallax and proper motion have been measured by space missions and observatories including Hipparcos and Gaia (spacecraft), with distance estimates refined by the European Space Agency data releases and cross-checked against ground-based astrometry from the US Naval Observatory. Radial velocity monitoring links to programs at the Gemini Observatory and the Subaru Telescope, while kinematic context is compared with stellar population studies from the Sloan Digital Sky Survey and galactic dynamics work by researchers at the Max Planck Institute for Astrophysics. These datasets place the star within local thin-disk population assessments discussed in literature from University of Cambridge and Princeton University groups.

Cultural and Historical Significance

Eltanin features in maritime navigation lore cited in compilations by the Royal Navy and historical atlases produced by the British Admiralty, and appears in star charts from institutions such as the Uranometria atlas tradition and the Carte du Ciel projects. Its depiction in literature and art includes references in works associated with figures like Homeric-era commentators and medieval Arabian astronomers whose catalogs influenced Tycho Brahe and Johannes Hevelius. Modern cultural mentions extend to science outreach by institutions like the Smithsonian Institution and planetarium programs at the Hayden Planetarium and Adler Planetarium, and it figures in naming used by organizations such as the International Astronomical Union for traditional star names.

Category:K-type giants Category:Draco (constellation)