Theta1 Sagittarii
Binary star system in the constellation Sagittarius
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Theta1 Sagittarii (θ1 Sagittarii) is a close binary star[10] system in the zodiac constellation of Sagittarius. It is visible to the naked eye with an apparent visual magnitude of 4.37.[2] Based upon an annual parallax shift of 6.29 mas as seen from Earth,[1] this star is located around 520 light years from the Sun. At that distance, the visual magnitude is diminished by an extinction factor of 0.24 due to interstellar dust.[11]
 | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 19h 59m 44.17834s[1] |
| Declination | −35° 16′ 34.7049″[1] |
| Apparent magnitude (V) | 4.37[2] |
| Characteristics | |
| Spectral type | B3 IVp[3] |
| U−B color index | −0.67[2] |
| B−V color index | −0.15[2] |
| Astrometry | |
| Proper motion (μ) | RA: +5.60[1] mas/yr Dec.: −25.81[1] mas/yr |
| Parallax (π) | 6.29±0.21 mas[1] |
| Distance | 520 ± 20 ly (159 ± 5 pc) |
| Absolute magnitude (MV) | −1.63[4] |
| Orbit[5] | |
| Period (P) | 2.1051 d |
| Eccentricity (e) | 0.00 |
| Periastron epoch (T) | 2411140.645 JD |
| Argument of periastron (ω) (secondary) | 0.00° |
| Semi-amplitude (K1) (primary) | 15.9 km/s |
| Details | |
| θ1 Sgr A | |
| Mass | 6.6±0.1[6] M☉ |
| Radius | 5.6[7] R☉ |
| Luminosity (bolometric) | 2,271[8] L☉ |
| Temperature | 17,900[8] K |
| Rotational velocity (v sin i) | 73[3] km/s |
| Age | 32.8±5.0[6] Myr |
| Other designations | |
| θ1 Sgr, CD−35°13831, HD 189103, HIP 98412, HR 7623, SAO 211716, WDS J19597-3517[9] | |
| Database references | |
| SIMBAD | data |
This is a single-lined spectroscopic binary with an orbital period of just 2.1 days in a circular orbit.[5] The visible member, component A, is a B-type peculiar subgiant star with a stellar classification of B3 IVp.[3] It is around 33[6] million years old and is spinning with a projected rotational velocity of 73 km/s.[3] The primary has 6.6[6] times the mass of the Sun and about 5.6[7] times the Sun's radius. It is radiating 2,271[8] times the solar luminosity from its photosphere at an effective temperature of 17,900 K.[8]