7 Sagittarii

7 Sagittarii
Location of 7 Sagittarius (circled)
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]
Distance1,100 ± 100 ly
(330 ± 30 pc)
Absolute magnitude (MV)−2.21[2]
Details
Radius18[6] R☉
Luminosity658.07[2] L☉
Surface gravity (log g)3.54±0.20[5] cgs
Temperature6,800±200[5] K
Metallicity [Fe/H]0.0[5] dex
Rotational velocity (v sin i)35[7] km/s
Other designations
7 Sgr, CD−24° 13793, HD 164584, HIP 88380, HR 6724, SAO 186163[8]
Database references
SIMBADdata
7 Sagittarii is the brightest star in the region of the Lagoon Nebula, towards the right edge.

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]

  1. ^ a b c d e f Cite error: The named reference vanLeeuwen2007 was invoked but never defined (see the help page).
  2. ^ a b c d e Cite error: The named reference Anderson2012 was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference Gray1989 was invoked but never defined (see the help page).
  4. ^ a b c d Cite error: The named reference aaa498_3_961 was invoked but never defined (see the help page).
  5. ^ a b c d e f g Cite error: The named reference Khalack2015 was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference Fracassini2001 was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference Rutten1988 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference Damiani2017 was invoked but never defined (see the help page).
  10. ^ a b Cite error: The named reference Sowell1987 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference houk1978 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Hauck1973 was invoked but never defined (see the help page).