Sigma Draconis
Encyclopedia
Sigma Draconis is a 4.7 magnitude star
located at a distance of 18.8 light-year
s in the constellation Draco
. Its traditional name is Alsafi.
for this star, was established in 1603 as part of the Uranometria
, a star catalogue produced by German celestial cartographer Johann Bayer
. The proper name Alsafi was derived from Arabic Athāfi, erroneously transcribed from the Arabic plurarl Athāfiyy, by which the nomads designated the tripods of their open-air kitchens. It was the name of an association of this star, τ Dra and υ Dra. According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Athāfi or Alsafi were the title for three stars: σ Dra as Alsafi, τ Dra as Athāfi I and υ Dra as Athāfi II.
In Chinese
, , meaning Celestial Kitchen
, refers to an asterism consisting of σ Draconis, δ Draconis
, ε Draconis
, ρ Draconis, 64 Draconis and π Draconis. Consequently, σ Draconis itself is known as
dwarf of spectral type G9 (formely was classified as K0). The radius has been directly measured using interferometery with the CHARA Array
, which yields a result of 77.8% of the Sun's radius. It has 87% of the Sun's mass
, but the luminosity of this star is only 43% that of the Sun. The projected rotation rate
(v sin i) is relatively low at 1.5 km/s. It is considered a slightly metal-poor
star, meaning that it has a lower proportion of isotopes with masses more than helium
when compared to the Sun.
The temperature, luminosity and surface activity appear to vary slightly in a manner very similar to the sunspot cycle, although the full length of the cycle has not yet been determined. The total variability is among the lowest of all stars that have been measured by the Hipparcos
spacecraft.
The components of Sigma Draconis's space velocity
are U=+36, V=+40 and W=-10 km/s. This gives the star an unusually large orbital eccentricity
about the Milky Way
galaxy of 0.30 (compared to 0.06 for the Sun.) The mean galactocentric distance for the orbit is 10.3 kiloparsecs (about 34,000 light-year
s).
As of 2007, no Jupiter-size or larger companion had been detected about the star and there was no indication of excess infrared
radiation that would be evidence of circumstellar matter (such as a debris disk
).
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
located at a distance of 18.8 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s in the constellation Draco
Draco (constellation)
Draco is a constellation in the far northern sky. Its name is Latin for dragon. Draco is circumpolar for many observers in the northern hemisphere...
. Its traditional name is Alsafi.
Name
Sigma Draconis, the Bayer designationBayer designation
A Bayer designation is a stellar designation in which a specific star is identified by a Greek letter, followed by the genitive form of its parent constellation's Latin name...
for this star, was established in 1603 as part of the Uranometria
Uranometria
Uranometria is the short title of a star atlas produced by Johann Bayer.It was published in Augsburg, Germany, in 1603 by Christophorus Mangus under the full title Uranometria : omnium asterismorum continens schemata, nova methodo delineata, aereis laminis expressa. This translates to...
, a star catalogue produced by German celestial cartographer Johann Bayer
Johann Bayer
Johann Bayer was a German lawyer and uranographer . He was born in Rain, Bavaria, in 1572. He began his study of philosophy in Ingolstadt in 1592, and moved later to Augsburg to begin work as a lawyer. He grew interested in astronomy during his time in Augsburg...
. The proper name Alsafi was derived from Arabic Athāfi, erroneously transcribed from the Arabic plurarl Athāfiyy, by which the nomads designated the tripods of their open-air kitchens. It was the name of an association of this star, τ Dra and υ Dra. According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Athāfi or Alsafi were the title for three stars: σ Dra as Alsafi, τ Dra as Athāfi I and υ Dra as Athāfi II.
In Chinese
Chinese language
The Chinese language is a language or language family consisting of varieties which are mutually intelligible to varying degrees. Originally the indigenous languages spoken by the Han Chinese in China, it forms one of the branches of Sino-Tibetan family of languages...
, , meaning Celestial Kitchen
Purple Forbidden enclosure
The Purple Forbidden enclosure is one of the San Yuan or Three enclosures. Stars and constellations of this group lie near the north celestial pole and visible all year from temperate latitudes in the Northern Hemisphere.-Asterisms:The asterisms are :...
, refers to an asterism consisting of σ Draconis, δ Draconis
Delta Draconis
Delta Draconis is a yellow star in the constellation Draco. It has the traditional names Aldib, Altais and Nodus Secundus....
, ε Draconis
Epsilon Draconis
Epsilon Draconis is a fourth-magnitude star in the constellation Draco. It has the traditional name Tyl. This star along with Delta Draconis , Pi Draconis and Rho Draconis forms an asterism known as Al Tāis, meaning "the Goat".In Chinese astronomy, , meaning the Celestial Kitchen, refers to an...
, ρ Draconis, 64 Draconis and π Draconis. Consequently, σ Draconis itself is known as
Properties
The star is a main sequenceMain sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
dwarf of spectral type G9 (formely was classified as K0). The radius has been directly measured using interferometery with the CHARA Array
CHARA array
The CHARA Array is an optical astronomical interferometer operated by The Center for High Angular Resolution Astronomy of the Georgia State University . CHARA is the World's highest angular resolution telescope at near-infrared wavelengths...
, which yields a result of 77.8% of the Sun's radius. It has 87% of the Sun's mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
, but the luminosity of this star is only 43% that of the Sun. The projected rotation rate
Stellar rotation
Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface....
(v sin i) is relatively low at 1.5 km/s. It is considered a slightly metal-poor
Metallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...
star, meaning that it has a lower proportion of isotopes with masses more than helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
when compared to the Sun.
The temperature, luminosity and surface activity appear to vary slightly in a manner very similar to the sunspot cycle, although the full length of the cycle has not yet been determined. The total variability is among the lowest of all stars that have been measured by the Hipparcos
Hipparcos
Hipparcos was a scientific mission of the European Space Agency , launched in 1989 and operated between 1989 and 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky...
spacecraft.
The components of Sigma Draconis's space velocity
Stellar kinematics
Stellar kinematics is the study of the movement of stars without needing to understand how they acquired their motion. This differs from stellar dynamics, which takes into account gravitational effects...
are U=+36, V=+40 and W=-10 km/s. This gives the star an unusually large orbital eccentricity
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
about the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
galaxy of 0.30 (compared to 0.06 for the Sun.) The mean galactocentric distance for the orbit is 10.3 kiloparsecs (about 34,000 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s).
As of 2007, no Jupiter-size or larger companion had been detected about the star and there was no indication of excess infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
radiation that would be evidence of circumstellar matter (such as a debris disk
Debris disk
A debris disk is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris disks have been found around both evolved and young stars, as well as at least one debris disk in orbit around a...
).
See also
- Sigma Draconis in fiction