7 Sagittarii
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 02m 51.09872s |
| Declination | −24° 16′ 56.8825″ |
| Apparent magnitude (V) | 5.37 |
| Characteristics | |
| Spectral type | F2 II/III |
| U−B color index | 0.25 |
| B−V color index | 0.51 |
| Astrometry | |
| Radial velocity (Rv) | −11.2±1.0 km/s |
| Proper motion (μ) | RA: +1.22 mas/yr Dec.: −17.52 mas/yr |
| Parallax (π) | 3.02±0.28 mas |
| Distance | 1,100 ± 100 ly (330 ± 30 pc) |
| Absolute magnitude (MV) | −2.21 |
| Details | |
| Radius | 18 R☉ |
| Luminosity | 658.07 L☉ |
| Surface gravity (log g) | 3.54±0.20 cgs |
| Temperature | 6,800±200 K |
| Metallicity [Fe/H] | 0.0 dex |
| Rotational velocity (v sin i) | 35 km/s |
| Other designations | |
| 7 Sgr, CD−24° 13793, HD 164584, HIP 88380, HR 6724, SAO 186163 | |
| Database references | |
| SIMBAD | data |
7 Sagittarii is a massive star in the southern zodiac constellation of Sagittarius which is located in the Lagoon Nebula (NGC 6530), although multiple sources have considered it a foreground star. It is a dim star but visible to the naked eye with an apparent visual magnitude of 5.37. The distance to this star can be determined from the annual parallax shift of 3.02±0.28 mas, yielding a value of roughly 1,100 light years. It is moving closer to the Sun with a heliocentric radial velocity of −11 km/s.
Gray and Garrison (1989) listed a stellar classification of F2 II/III for this star, suggesting it is a K-type star with a spectrum showing mixed traits of a giant/bright giant. Houk and Smith-Moore (1978) had a similar classification of F2/3 II/III. This may indicate it is not a member of NGC 6530, since it should not have evolved to this class from the O-type stars that still populate this cluster, and hasn't had time to evolve from a less massive cluster star.
It is a suspected chemically peculiar star. The spectral class from the calcium K line has been given as A8 while the class determined from other metallic lines was F4, making it an Am star. This peculiarity is now considered doubtful.
7 Sagittarii has an estimated 18 times the Sun's radius and is radiating 658 times the Sun's luminosity from its photosphere at an effective temperature of around 6,800 K.