7 Sagittarii
{{short description|Star in the constellation Sagittarius}}
{{Starbox begin
| name = 7 Sagittarii
}}
{{Starbox image
| image=
{{Location mark
|image=Sagittarius constellation map.svg|alt=|float=center|width=300
|label=|position=right
|mark=Red circle.svg|mark_width=12|mark_link=7 Sgr
|x=690|y=364
}}
| caption=Location of 7 Sagittarius (circled)
}}
{{Starbox observe
| epoch = J2000
| constell = Sagittarius
| dec = {{DEC|-24|16|56.8825}}
}}
{{Starbox character
| variable =
}}
{{Starbox astrometry
| radial_v = {{Val|−11.2|1.0}}
| parallax = 3.02
| p_error = 0.28
}}
{{Starbox detail
| source =
| mass =
| temperature = {{Val|6800|200|fmt=commas}}
| age_myr =
}}
{{Starbox catalog
| names = {{odlist | F=7 Sgr | CD=-24° 13793 | FK5= | HD=164584 | HIP=88380 | HR=6724 | SAO=186163 }}
}}
{{Starbox reference
| Simbad = 7+Sgr
}}
{{Starbox end}}
File:VST images the Lagoon Nebula.jpg, 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), 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 {{Val|3.02|0.28|ul=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.
References
{{reflist|refs=
{{cite simbad | title=7 Sgr | access-date=2018-03-14 }}
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See NGC 6530 on p. 257.
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| last1=Houk | first1=Nancy | last2=Smith-Moore | first2=M.
| title=Michigan catalogue of two-dimensional spectral types for the HD stars
| volume=4 | location=Ann Arbor | year=1978
| publisher=Dept. of Astronomy, University of Michigan
| bibcode=1988mcts.book.....H | postscript=. }}
| title=The Gaia-ESO Survey: dynamics of ionized and neutral gas in the Lagoon nebula (M 8)
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{{citation | display-authors=1
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| title=Magnetic structure in cool stars. XV. The evolution of rotation rates and chromospheric activity of giants
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| journal=Astronomy and Astrophysics
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| bibcode=1988A&A...191..227R | postscript=. }}
| last1=Renson | first1=P. | last2=Manfroid | first2=J.
| title=Catalogue of Ap, HgMn and Am stars
| journal=Astronomy and Astrophysics
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| doi=10.1051/0004-6361/200810788 | bibcode=2009A&A...498..961R | url=https://zenodo.org/record/890529 | doi-access=free }}
| title=Project VeSElkA: Analysis of Balmer Line Profiles of Slowly Rotating Chemically Peculiar Stars
| last1=Khalack | first1=V. | last2=LeBlanc | first2=F.
| journal=The Astronomical Journal
| volume=150 | issue=1 | id=2 | pages=10 | date=July 2015
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| arxiv=1505.08158 | s2cid=118283214 | postscript=. }}
| title=The early F-type stars: refined classification, confrontation with Stroemgren photometry, and the effects of rotation
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| volume=69 | page=301 | date=February 1989
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}}
{{Stars of Sagittarius}}
{{DEFAULTSORT:7 Sagittarii}}
Category:Sagittarius (constellation)