4 Sagittarii

4 Sagittarii is a suspected astrometric binary[8] star system in the zodiac constellation of Sagittarius, located approximately 390 light years away based on parallax.[1] It is visible to the naked eye as a faint, blue-white hued star with an apparent visual magnitude of 4.74,[2] The system is moving closer to the Earth with a heliocentric radial velocity of −18 km/s.[5]

4 Sagittarii
Location of 4 Sagittarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Sagittarius
Right ascension  17h 59m 47.55132s[1]
Declination −23° 48′ 58.0269″[1]
Apparent magnitude (V) 4.74[2]
Characteristics
Spectral type B9V[3]
U−B color index −0.03[4]
B−V color index -0.05[4]
Astrometry
Radial velocity (Rv)−18.00[5] km/s
Proper motion (μ) RA: +3.673[1] mas/yr
Dec.: −50.327[1] mas/yr
Parallax (π)8.3677 ± 0.4521[1] mas
Distance390 ± 20 ly
(120 ± 6 pc)
Absolute magnitude (MV)−0.77[2]
Details
Mass3.23[6] M☉
Luminosity240[6] L☉
Temperature9,661[6] K
Rotational velocity (v sin i)149[6] km/s
Other designations
4 Sgr, CD−23°13731, FK5 3430, GC 24483, HD 163955, HIP 88116, HR 6700, SAO 186061, GSC 06841-01403[7]
Database references
SIMBADdata

The visible component is a B-type main-sequence star with a stellar classification of B9 V.[3] It has a high rate of spin, displaying a projected rotational velocity of 149 km/s.[6] This is giving it an oblate shape with an equatorial bulge that is an estimated 14% larger than the polar radius.[9] 4 Sagittarii has 3.23 times the mass of the Sun and is radiating 240 times the Sun's luminosity from its photosphere at an effective temperature of 9,661 K.[6]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. Vizier catalog entry
  3. Hoffleit, D.; Warren, W. H. (1995). "VizieR Online Data Catalog: Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)". VizieR On-line Data Catalog: V/50. Originally Published in: 1964BS....C......0H. 5050. Bibcode:1995yCat.5050....0H.
  4. Mallama, A. (2014). "Sloan Magnitudes for the Brightest Stars". The Journal of the American Association of Variable Star Observers. 42: 443. Bibcode:2014JAVSO..42..443M.Vizier catalog entry
  5. Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065.
  6. Zorec, J.; Royer, F. (2012). "Rotational velocities of A-type stars". Astronomy & Astrophysics. 537: A120. arXiv:1201.2052. Bibcode:2012A&A...537A.120Z. doi:10.1051/0004-6361/201117691. Vizier catalog entry
  7. "4 Sgr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-03-23.
  8. Eggleton, P. P.; Tokovinin, A. A. (2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x.
  9. van Belle, Gerard T. (March 2012). "Interferometric observations of rapidly rotating stars". The Astronomy and Astrophysics Review. 20 (1): 51. arXiv:1204.2572. Bibcode:2012A&ARv..20...51V. doi:10.1007/s00159-012-0051-2.
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