Epsilon Sagittarii
 Location of ε CygSgr (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 24m 10.31840s |
| Declination | –34° 23′ 04.6193″ |
| Apparent magnitude (V) | +1.85 |
| Characteristics | |
| Spectral type | B9.5 III |
| U−B color index | +0.13 |
| B−V color index | –0.03 |
| Astrometry | |
| Radial velocity (Rv) | –15 km/s |
| Proper motion (μ) |
RA: –39.42 mas/yr Dec.: –124.20 mas/yr |
| Parallax (π) | 22.76 ± 0.24mas |
| Distance | 143 ± 2 ly (43.9 ± 0.5 pc) |
| Absolute magnitude (MV) | –1.41 |
| Details | |
| ε Sgr A | |
| Mass | 3.515 ± 0.138 M☉ |
| Radius | 6.8 R☉ |
| Luminosity | 363 L☉ |
| Surface gravity (log g) | 4.50 cgs |
| Temperature | 9,960 K |
| Rotational velocity (v sin i) | 236 km/s |
| Age | 232 Myr |
| ε Sgr B | |
| Mass | 0.95 M☉ |
| Luminosity | 0.89 L☉ |
| Temperature | 5,807 K |
| Other designations | |
| Database references | |
| SIMBAD | data |
Epsilon Sagittarii (ε Sagittarii, abbreviated Epsilon Sgr, ε Sgr), also named Kaus Australis, is a binary star system in the southern zodiac constellation of Sagittarius. The apparent visual magnitude of +1.85 makes it the brightest star in the constellation. Based upon parallax measurements, this star is around 143 light-years (44 parsecs) from the Sun.
The primary component of this binary star system has a stellar classification of B9.5 III, 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, which, at its estimated distance, equates to a physical radius of about 6.8 times the radius of the Sun. This is a close match to the empirically-determined value of 6.9 solar radii. 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. At this heat, the star glows with a blue-white hue.
This star is spinning rapidly with a projected rotational velocity of 236 km s−1. It has a magnetic field with a strength in the range 10.5–130.5 G and it is an X-ray source with a luminosity of about 1030 erg s−1. 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.
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