Phi Sagittarii
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 45m 39.38610s |
| Declination | −26° 59′ 26.7944″ |
| Apparent magnitude (V) | 3.17 |
| Characteristics | |
| Spectral type | B8.5 III |
| U−B color index | −0.36 |
| B−V color index | −0.11 |
| Astrometry | |
| Radial velocity (Rv) | +21.5 km/s |
| Proper motion (μ) | RA: +50.61 mas/yr Dec.: +1.22 mas/yr |
| Parallax (π) | 13.63±0.19 mas |
| Distance | 239 ± 3 ly (73 ± 1 pc) |
| Absolute magnitude (MV) | −1.16 |
| Details | |
| A | |
| Mass | 3.48 M☉ |
| Radius | 5.31 R☉ |
| Luminosity | 475 L☉ |
| Surface gravity (log g) | 3.73 cgs |
| Temperature | 10,620 K |
| Rotational velocity (v sin i) | 46 km/s |
| Age | 152 Myr |
| B | |
| Mass | 1.59 M☉ |
| Radius | 1.50 R☉ |
| Temperature | 7,630 K |
| Other designations | |
| Namalsadirah 1, Awal al Sadira, φ Sgr, Phi Sgr, 27 Sagittarii, CPD−27 5241, FK5 1487, GC 25661, HD 173300, HIP 92041, HR 7039, SAO 268859, PPM 297231 | |
| Database references | |
| SIMBAD | data |
Phi Sagittarii, Latinized from φ Sagittarii, is a binary star in the southern constellation of Sagittarius. With an apparent visual magnitude of 3.17, it is the ninth-brightest star in the constellation and is readily visible to the naked eye. Parallax measurements place it at a distance of roughly 239 light-years (73 parsecs) from the Earth. It is receding with a radial velocity of +21.5 km/s.
The stellar classification of this star has been rated at B8.5 III, with the luminosity class of III indicating it is a giant star evolved away from the main sequence after it has exhausted the hydrogen at its core. This energy is being radiated from the star's outer envelope at an effective temperature of 12487 K, which produces the blue-white hue typical of B-type stars.
This star has been catalogued as a spectroscopic binary and a companion was apparently detected through lunar occultation. However, the latter was pointed out as spurious. Interferometric observations taken in 2017 finally revealed that Phi Sgr is indeed a binary. The companion is a main sequence star around 60% more massive than the Sun, with an orbital period of roughly a year and an orbital separation of 1.31 AU.