U Sagittarii
Star in the constellation Sagittarius
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 31m 53.332s[2] |
| Declination | −19° 07′ 30.26″[2] |
| Apparent magnitude (V) | 6.28 to 7.15[3] |
| Characteristics | |
| Evolutionary stage | Supergiant |
| Spectral type | G1Ib[4] |
| U−B color index | +0.85[5] |
| B−V color index | +1.06[5] |
| Variable type | δ Cep[3] |
| Astrometry | |
| Radial velocity (Rv) | 2.2±0.3[6] km/s |
| Proper motion (μ) | RA: −1.795 mas/yr[2] Dec.: −6.127 mas/yr[2] |
| Parallax (π) | 1.5693 ± 0.0224 mas[2] |
| Distance | 2,080 ± 30 ly (637 ± 9 pc) |
| Absolute magnitude (MV) | −3.86 to −3.10[5] |
| Details | |
| Mass | 6.54 to 6.64[7] M☉ |
| Radius | 55.5 to 56.3[7] R☉ |
| Luminosity | 4,370 to 4,650[7] L☉ |
| Surface gravity (log g) | 0.99[8] cgs |
| Temperature | 5,802[8] K |
| Metallicity [Fe/H] | 0.17[8] dex |
| Rotational velocity (v sin i) | 15.4[9] km/s |
| Age | 91[10] Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
U Sagittarii is a variable star in the southern constellation of Sagittarius, abbreviated U Sgr. It is a classical Cepheid variable that ranges in brightness from an apparent visual magnitude of 6.28 down to 7.15, with a pulsation period of 6.745226 days.[3] At its brightest, this star is dimly visible to the naked eye. The distance to this star is approximately 2,080 light years based on parallax measurements,[2] and it is drifting further away with a radial velocity of 2 km/s.[6]
The variability of this star was announced by J. Schmidt in 1866, who found a preliminary period of 6.74784 days.[13] It was later determined to be a variable of the Cepheid type.[14] In 1925, P. Doig assumed that the star is a member of the open cluster Messier 25 (M25), but actual evidence of its membership would not be available until 1932 when P. Hayford made radial velocity measurements of the cluster.[15] Membership in this cluster is now reasonably established,[16] and as such this Cepheid serves as one of the anchors for the cosmic distance scale since the distance to the cluster can be determined independently from the star.[17]
This is an evolved G-type supergiant star with a typical stellar classification of G1Ib.[4] It appears to be making its third traversal of the instability strip with its period changing at the rate of +0.073±0.010 s·yr−1. Elemental abundances are similar to those in the Sun.[17] It has an estimated 6.6 times the mass of the Sun and 56 times the Sun's radius. The star is radiating over 4,000[7] times the Sun's luminosity from its photosphere at an effective temperature of 5,802 K.[8]
References
- ^ Luginbuhl, Christian B.; Skiff, Brian A. (1998), Observing Handbook and Catalogue of Deep-Sky Objects, Cambridge University Press, p. 213, ISBN 9780521625562.
- ^ a b c d e Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
- ^ a b c Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
- ^ a b Houk, N.; Smith-Moore, M. (1988), Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars, vol. 4, Bibcode:1988mcts.book.....H.
- ^ a b c Sandage, Allan (May 1960), "Cepheids in Galactic Clusters.VI. U SGR in M25", Astrophysical Journal, 131: 610, Bibcode:1960ApJ...131..610S, doi:10.1086/146873.
- ^ a b Breger, M. (1967), "Velocity, radius and light variations of the cepheid U Sgr", Monthly Notices of the Royal Astronomical Society, 136: 61, Bibcode:1967MNRAS.136...61B, doi:10.1093/mnras/136.1.61.
- ^ a b c d Fadeyev, Yu. A. (August 2018), Shustov, B. M.; Wiebe, D. S. (eds.), "Secular period change in the cepheid U Sgr and the theory of stellar evolution", Stars and Satellites, Proceedings of the Memorial Conference Devoted to A.G. Masevich 100th Anniversary, held in Moscow, Russia, in Oct 15-16, 2018, INASAN Science Proceedings (in Russian), Moscow: Yanus-K, pp. 152–156, Bibcode:2018sas..conf..152F, doi:10.26087/INASAN.2018.2.2.024.
- ^ a b c d Prugniel, Ph.; et al. (July 2011), "The atmospheric parameters and spectral interpolator for the MILES stars", Astronomy & Astrophysics, 531: A165, arXiv:1104.4952, Bibcode:2011A&A...531A.165P, doi:10.1051/0004-6361/201116769, S2CID 54940439, A165.
- ^ Jönsson, Henrik; et al. (2020), "APOGEE Data and Spectral Analysis from SDSS Data Release 16: Seven Years of Observations Including First Results from APOGEE-South", The Astronomical Journal, 160 (3): 120, arXiv:2007.05537, Bibcode:2020AJ....160..120J, doi:10.3847/1538-3881/aba592, S2CID 220496397.
- ^ Skowron, Dorota M.; et al. (2019), "A three-dimensional map of the Milky Way using classical Cepheid variable stars", Science, 365 (6452): 478–482, arXiv:1806.10653, Bibcode:2019Sci...365..478S, doi:10.1126/science.aau3181, PMID 31371611, S2CID 199064609.
- ^ "U Sgr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2022-12-03.
- ^ "ASAS All Star Catalogue". The All Sky Automated Survey. Retrieved 5 December 2022.
- ^ Schmidt, Johann Friedrich Julius (March 1868), "Über die Lichtphasen von A, γ und U Sagittarii in den Jahren 1866 und 1867", Astronomische Nachrichten (in German), 71: 139, Bibcode:1868AN.....71..139S.
- ^ Shapley, H. (December 1918), "Studies based on the colors and magnitudes in stellar clusters. VIII. The luminosities and distances of 139 Cepheid variables", Astrophysical Journal, 48: 279–294, Bibcode:1918ApJ....48..279S, doi:10.1086/142435.
- ^ Wallerstein, George (April 1957), "The Absolute Magnitude of U Sagittarii and Its Membership in M 25", Publications of the Astronomical Society of the Pacific, 69 (407): 172, Bibcode:1957PASP...69..172W, doi:10.1086/127041, S2CID 121527741.
- ^ Chen, Xiaodian; et al. (January 2015), "A search for open cluster Cepheids in the Galactic plane", Monthly Notices of the Royal Astronomical Society, 446 (2): 1268–1282, arXiv:1410.4489, Bibcode:2015MNRAS.446.1268C, doi:10.1093/mnras/stu2165.
- ^ a b Majaess, D.; et al. (December 2013), "Anchors for the cosmic distance scale: the Cepheids U Sagittarii, CF Cassiopeiae, and CEab Cassiopeiae", Astronomy & Astrophysics, 560: A22, arXiv:1311.0865, Bibcode:2013A&A...560A..22M, doi:10.1051/0004-6361/201322670, S2CID 55934597, A22.
Further reading
- Berdnikov, L. N.; Majaess, D. (April 2014), "Search for evolutionary changes in the periods of Cepheids: U Sgr", Astronomy Letters, 40 (4): 193–200, Bibcode:2014AstL...40..193B, doi:10.1134/S1063773714030025, S2CID 255203281.
- Simon, Norman R. (March 1989), "Application of the Baade-Wesselink inversion technique to SW Dra, X Ari and U Sgr", Monthly Notices of the Royal Astronomical Society, 237: 163–185, Bibcode:1989MNRAS.237..163S, doi:10.1093/mnras/237.1.163.
- Burnham, Robert (1978), Burnham's Celestial Handbook, An Observer's Guide to the Universe Beyond the Solar System, vol. 3, Dover Publications, ISBN 9780486236735.
- Jacobsen, T. S. (February 1970), "A High-Dispersion Velocity Curve of U Sagittarii", Astrophysical Journal, 159: 569, Bibcode:1970ApJ...159..569J, doi:10.1086/150331.
- Wampler, J.; et al. (May 1961), "Cepheids in Galactic Clusters. VIII. a Reinvestigation of U SGR in M25 (= IC 4725).", Astrophysical Journal, 133: 895, Bibcode:1961ApJ...133..895W, doi:10.1086/147092.
- Mitchell, Richard I.; et al. (May 1961), "U, B, V, Observations of U SGR", Astrophysical Journal, 133: 1083, Bibcode:1961ApJ...133.1083M, doi:10.1086/147114.
- Voûte, J.; ten Bruggencate, P. (1927), "U Sagittarii", Annals of the Bosscha Observatory Lembang (Java) Indonesia, 2: B28–B33, Bibcode:1927AnBos...2B..28V.
- Yendell, Paul S. (1895), "On variable stars of short period. IV--The Sagittarius Group", Popular Astronomy, 2: 362–366, Bibcode:1895PA......2..362Y.
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