Beta1 Sagittarii
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 19h 22m 38.29770s |
| Declination | −44° 27′ 32.2458″ |
| Apparent magnitude (V) | +4.01 |
| Characteristics | |
| Spectral type | B9 V + A5 V |
| U−B color index | −0.39 |
| B−V color index | −0.10 |
| Astrometry | |
| Radial velocity (Rv) | −10.7±2.7 km/s |
| Proper motion (μ) | RA: +13.67 mas/yr Dec.: −19.03 mas/yr |
| Parallax (π) | 10.40±1.14 mas |
| Distance | approx. 310 ly (approx. 100 pc) |
| Absolute magnitude (MV) | −1.32 |
| Details | |
| β1 Sgr A | |
| Mass | 3.67±0.14 M☉ |
| Radius | 2.73 R☉ |
| Luminosity | 324 L☉ |
| Surface gravity (log g) | 3.83 cgs |
| Temperature | 11,960 K |
| Metallicity [Fe/H] | −0.35 dex |
| Rotational velocity (v sin i) | 85±13 km/s |
| Age | 224 Myr |
| β1 Sgr B | |
| Radius | 1.89 R☉ |
| Rotational velocity (v sin i) | 140±21 km/s |
| Other designations | |
| Arkab Prior, β1 Sgr, CD−44°13277, FK5 1502, HD 181454, HIP 95241, HR 7337, SAO 229646, WDS J19226-4428A | |
| Database references | |
| SIMBAD | data |
Beta1 Sagittarii, Latinized from β1 Sagittarii, is a binary star system in the zodiac constellation of Sagittarius, next to the southern constellation border with Telescopium. The brighter primary is named Arkab Prior /ˈɑːrkæb ˈpraɪər/, the traditional name of the system. It is visible to the naked eye with a combined apparent visual magnitude of +4.01. Based upon an annual parallax shift of 10.40 mas as seen from Earth, it is located roughly 310 light-years from the Sun. At Beta1 Sagittarii's distance, the visual magnitude is diminished by an extinction factor of 0.17 due to interstellar dust.
The pair of stars that constitute this system have an angular separation of 28.3 arc seconds, with an estimated physical separation of about 3,290 AU. The primary, Beta1 Sagittarii A, is a B-type main sequence star with a stellar classification of B9 V. It is about 95% of the way through its lifespan on the main sequence. The star has around 3.7 times the mass of the Sun and 2.7 times the Sun's radius. It is an estimated 224 million years old and is spinning with a projected rotational velocity of 85 km/s. The star is radiating 324 times the luminosity of the Sun from its photosphere at an effective temperature of 11,960 K.
The companion, Beta1 Sagittarii B, is a magnitude 7.4 A-type main sequence star with a class of A5 V. It has 1.89 times the radius of the Sun and may be spinning faster than the primary with a projected rotational velocity of 140 km/s.