Sigma Draconis
From Wikipedia, the free encyclopedia
| Observation data Epoch J2000 |
|
|---|---|
| Constellation (pronunciation) |
Draco |
| Right ascension | 19h 32m 21.5908s[1] |
| Declination | +69° 39′ 40.232″[1] |
| Apparent magnitude (V) | 4.70[1] |
| Characteristics | |
| Spectral type | K0 V[1] |
| U-B color index | 0.38[2] |
| B-V color index | 0.79[2] |
| Variable type | None |
| Astrometry | |
| Radial velocity (Rv) | 26.7[1] km/s |
| Proper motion (μ) | RA: 598.26[1] mas/yr Dec.: -1738.71[1] mas/yr |
| Parallax (π) | 173.40 ± 0.46[1] mas |
| Distance | 18.81 ± 0.05 ly (5.77 ± 0.02 pc) |
| Absolute magnitude (MV) | 5.87 |
| Details | |
| Mass | 0.87[3] M☉ |
| Radius | 0.89 R☉ |
| Surface gravity (log g) | 4.60[3] |
| Luminosity | 0.39 L☉ |
| Temperature | 5,196[3] K |
| Metallicity | [Fe/H]=-0.23[3] |
| Rotation | 1.5 km/s[4] |
| Age | 3.3 × 109 years |
| Other designations | |
|
σ Draconis, 61 Draconis, HD 185144, HR 7462, BD+69°1053, GCTP 4607.00, GJ 764, LHS 477, and HIP 96100.[1]
|
|
Sigma Draconis (σ Dra / σ Draconis) is a star 18.8 light-years away from Earth. Its traditional name is Alsafi. It is in constellation Draco. Its visual magnitude is 4.68.
The traditional name "Alsafi" (also Athafi) supposedly derives from an Arabic word al-athafi "the cooking tripods". This refers to the tripods used by nomads for open-air cooking[5]
Contents |
[edit] Properties
The star is an orange main sequence dwarf of spectral type K0. The projected rotation rate of this star (vsini) is relatively low at 1.5 km/s. It is considered a slightly metal-poor star; meaning it has a lower proportion of isotopes with more mass than Helium when compared to the Sun.[6]
The temperature, luminosity and surface activity of this star appear to vary slightly in a manner very similar to the sunspot cycle, although the full length of this cycle has not yet been determined.[4] The total variability of this star is among the lowest of all stars that have been measured by the Hipparcos spacecraft.[6]
The components of this star'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 this orbit is 10.3 kiloparsecs (about 34,000 light-years).[6]
No Jupiter-size or larger companion has yet been detected about this star and there is no indication of excess infrared radiation that would be evidence of circumstellar matter (such as a debris disk).[7]
[edit] See also
[edit] References
- ^ a b c d e f g h i SIMBAD Query Result: NSV 12176 -- Variable Star. Centre de Données astronomiques de Strasbourg. Retrieved on 2007-06-15.
- ^ a b ARICNS 4C01582. Astronomisches Rechen-Institut, Heidelberg. Retrieved on 2007-06-15.
- ^ a b c d Hearnshaw, J. B. (1974). "Carbon and iron abundances for twenty F and G type stars.". Astronomy and Astrophysics 36: 191-199.
- ^ a b Gray, David F.; Baliunas, Sallie L.; Lockwood, G. W.; Skiff, Brian A. (1992). "The activity cycle of Sigma Draconis". Astrophysical Journal 400 (2): 681-691. doi:.
- ^ Allen, Richard Hinkley (1963). Star Names, Their Lore and Meaning. New York: Dover. ISBN 0-486-21079-0.
- ^ a b c Porto de Mello, Gustavo; del Peloso, Eduardo F.; Ghezzi, Luan (1999). "Astrobiologically Interesting Stars Within 10 Parsecs of the Sun". Astrobiology 6 (2): 308-331.
- ^ E. K. Holmes, H. M. Butner, S. B. Fajardo-Acosta, L. M. Rebull (2003). "A Survey of Nearby Main-Sequence Stars for Submillimeter Emission". The Astronomical Journal 125 (6): 3334-3343. doi:.
[edit] External links
- Sigma Draconis. SolStation. Retrieved on 2007-06-15.
