Epsilon Sagittarii

From Infogalactic: the planetary knowledge core
Jump to: navigation, search
Epsilon Sagittarii

Epsilon Sagittarii (circled) in the constellation Sagittarius.
Observation data
Epoch J2000      Equinox J2000
Constellation Sagittarius
Right ascension 18h 24m 10.31840s[1]
Declination –34° 23′ 04.6193″[1]
Apparent magnitude (V) +1.85[2]
Characteristics
Spectral type B9.5 III[3]
U−B color index +0.13[2]
B−V color index –0.03[2]
Astrometry
Radial velocity (Rv) –15[4] km/s
Proper motion (μ) RA: –39.42[1] mas/yr
Dec.: –124.20[1] mas/yr
Parallax (π) 22.76 ± 0.24[1] mas
Distance 143 ± 2 ly
(43.9 ± 0.5 pc)
Absolute magnitude (MV) –1.41[5]
Details
ε Sgr A
Mass 3.515 ± 0.138[5] M☉
Radius 6.8[6] R☉
Luminosity 363[5] L☉
Surface gravity (log g) 4.50[7] cgs
Temperature 9,960[8] K
Rotational velocity (v sin i) 236[9] km/s
Age 232[5] Myr
ε Sgr B
Mass 0.95[5] M☉
Luminosity 0.89[5] L☉
Temperature 5,807[5] K
Other designations
Kaus Australis, ε Sagittarii, ε Sgr, Epsilon Sgr, 20 Sagittarii, CCDM J18242-3423A, FK5 689, GC 25100, HD 169022, HIP 90185, HR 6879, IDS 18175-3427 A, PPM 297655, SAO 210091, WDS J18242-3423A.[10]

Epsilon Sagittarii (Epsilon Sgr, ε Sagittarii, ε Sgr) is a binary star system in the southern zodiac constellation Sagittarius. Its traditional name is Kaus Australis. The apparent visual magnitude of +1.85[2] makes it the brightest star in the constellation. Based upon parallax measurements, the distance to this star is around 143 light-years (44 parsecs).

Properties

The primary component of this binary star system has a stellar classification of B9.5 III,[3] with the luminosity class of III suggesting this is an evolved giant star that has exhausted the supply of hydrogen at its core. The interferometry-measured angular diameter of this star, after correcting for limb darkening, is 1.44 ± 0.06 mas,[11] which, at its estimated distance, equates to a physical radius of about 6.8 times the radius of the Sun.[6] This is a close match to the empirically-determined value of 6.9 solar radii.[12] It has about 3.5 times the mass of the Sun and is radiating around 363 times the Sun's luminosity from its outer atmosphere at an effective temperature of 9,960 K.[5] At this heat, the star glows with a blue-white hue.[13]

This star is spinning rapidly with a projected rotational velocity of 236 km s−1.[9] It has a magnetic field with a strength in the range 10.5–130.5 G[14] and it is an X-ray source with a luminosity of about 1030 erg s−1.[5] The system displays an excess emission of infrared radiation, which suggests the presence of a circumstellar disk of dust. Based upon the temperature of this disk, it is orbiting at a mean separation of 155 AU from the primary.[15]

As of 2001, the secondary companion is located at an angular separation of 2.392 arcseconds from the primary along a position angle of 142.3°. At the distance of this system, this angle is equivalent to a physical separation of about 106 AU, which places it inside the debris disk. It is a main sequence star with about 95% of the mass of the Sun. The system has a higher optical linear polarisation than expected for its distance from the Sun; this has been attributed to light scattered off the disk from the secondary.[16] Prior to its 1993 identification using an adaptive optics coronagraph, this companion may have been responsible for the spectral anomalies that were attributed to the primary star.[17] There is a candidate stellar companion at an angular separation of 32.3 arcseconds.[5]

Name and etymology

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ 2.0 2.1 2.2 2.3 Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ 3.0 3.1 Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ 6.0 6.1 Lua error in package.lua at line 80: module 'strict' not found.. The radius (R*) is given by:
    \begin{align} 2\cdot R_* & = \frac{(10^{-3}\cdot 43.9\cdot 1.44)\ \text{AU}}{0.0046491\ \text{AU}/R_{\bigodot}} \\ & \approx 13.6\cdot R_{\bigodot} \end{align}
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ 9.0 9.1 Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  12. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  13. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  14. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  15. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  16. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  17. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  18. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  19. ↑ skywatchers Archived May 17, 2007 at the Wayback Machine
  20. ↑ 20.0 20.1 Lua error in package.lua at line 80: module 'strict' not found.
  21. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  22. ↑ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日
  23. ↑ Lua error in package.lua at line 80: module 'strict' not found.

External links

Retrieved from "https://infogalactic.com/w/index.php?title=Epsilon_Sagittarii&oldid=3679019"