Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Sagittarius |
Right ascension | 18h 02m 51.09872s [1] |
Declination | −24° 16′ 56.8825″ [1] |
Apparent magnitude (V) | 5.37 [2] |
Characteristics | |
Spectral type | F2 II/III [3] |
U−B color index | 0.25 [4] |
B−V color index | 0.51 [4] |
Astrometry | |
Radial velocity (Rv) | −11.2±1.0 [5] km/s |
Proper motion (μ) |
RA: +1.22
[1]
mas/
yr Dec.: −17.52 [1] mas/ yr |
Parallax (π) | 3.02 ± 0.28 mas [1] |
Distance | 1,100 ± 100
ly (330 ± 30 pc) |
Absolute magnitude (MV) | −2.21 [2] |
Details | |
Radius | 18 [6] R☉ |
Luminosity | 658.07 [2] L☉ |
Surface gravity (log g) | 3.54±0.20 [5] cgs |
Temperature | 6,800±200 [5] K |
Metallicity [Fe/H] | 0.0 [5] dex |
Rotational velocity (v sin i) | 35 [7] km/s |
Other designations | |
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), [9] although multiple sources have considered it a foreground star. [10] It is a dim star but visible to the naked eye with an apparent visual magnitude of 5.37. [2] The distance to this star can be determined from the annual parallax shift of 3.02±0.28 mas, [1] 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. [5]
Gray and Garrison (1989) listed a stellar classification of F2 II/III [3] 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. [11] 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. [10]
It is a suspected chemically peculiar star. [4] [5] 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. [12] This peculiarity is now considered doubtful. [4]
7 Sagittarii has an estimated 18 [6] times the Sun's radius and is radiating 658 [2] times the Sun's luminosity from its photosphere at an effective temperature of around 6,800 K. [5]
Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Sagittarius |
Right ascension | 18h 02m 51.09872s [1] |
Declination | −24° 16′ 56.8825″ [1] |
Apparent magnitude (V) | 5.37 [2] |
Characteristics | |
Spectral type | F2 II/III [3] |
U−B color index | 0.25 [4] |
B−V color index | 0.51 [4] |
Astrometry | |
Radial velocity (Rv) | −11.2±1.0 [5] km/s |
Proper motion (μ) |
RA: +1.22
[1]
mas/
yr Dec.: −17.52 [1] mas/ yr |
Parallax (π) | 3.02 ± 0.28 mas [1] |
Distance | 1,100 ± 100
ly (330 ± 30 pc) |
Absolute magnitude (MV) | −2.21 [2] |
Details | |
Radius | 18 [6] R☉ |
Luminosity | 658.07 [2] L☉ |
Surface gravity (log g) | 3.54±0.20 [5] cgs |
Temperature | 6,800±200 [5] K |
Metallicity [Fe/H] | 0.0 [5] dex |
Rotational velocity (v sin i) | 35 [7] km/s |
Other designations | |
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), [9] although multiple sources have considered it a foreground star. [10] It is a dim star but visible to the naked eye with an apparent visual magnitude of 5.37. [2] The distance to this star can be determined from the annual parallax shift of 3.02±0.28 mas, [1] 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. [5]
Gray and Garrison (1989) listed a stellar classification of F2 II/III [3] 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. [11] 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. [10]
It is a suspected chemically peculiar star. [4] [5] 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. [12] This peculiarity is now considered doubtful. [4]
7 Sagittarii has an estimated 18 [6] times the Sun's radius and is radiating 658 [2] times the Sun's luminosity from its photosphere at an effective temperature of around 6,800 K. [5]