Astronomy:U Sagittarii
| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| 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[2] mas/yr Dec.: −6.127[2] mas/yr |
| Parallax (π) | 1.5693 ± 0.0224[2] mas |
| 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, https://books.google.com/books?id=MwCyjQpGU7UC&pg=PA213.
- ↑ 2.0 2.1 2.2 2.3 2.4 Brown, A. G. A. (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics 649: A1. doi:10.1051/0004-6361/202039657. Bibcode: 2021A&A...649A...1G. Gaia EDR3 record for this source at VizieR.
- ↑ 3.0 3.1 3.2 Samus, N. N. et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1 61 (1): 80–88, doi:10.1134/S1063772917010085, Bibcode: 2017ARep...61...80S.
- ↑ 4.0 4.1 Houk, N.; Smith-Moore, M. (1988), Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars, 4, Bibcode: 1988mcts.book.....H.
- ↑ 5.0 5.1 5.2 Sandage, Allan (May 1960), "Cepheids in Galactic Clusters.VI. U SGR in M25", Astrophysical Journal 131: 610, doi:10.1086/146873, Bibcode: 1960ApJ...131..610S.
- ↑ 6.0 6.1 Breger, M. (1967), "Velocity, radius and light variations of the cepheid U Sgr", Monthly Notices of the Royal Astronomical Society 136: 61, doi:10.1093/mnras/136.1.61, Bibcode: 1967MNRAS.136...61B.
- ↑ 7.0 7.1 7.2 7.3 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" (in ru), 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 (Moscow: Yanus-K): pp. 152–156, doi:10.26087/INASAN.2018.2.2.024, Bibcode: 2018sas..conf..152F.
- ↑ 8.0 8.1 8.2 8.3 Prugniel, Ph. et al. (July 2011), "The atmospheric parameters and spectral interpolator for the MILES stars", Astronomy & Astrophysics 531: A165, doi:10.1051/0004-6361/201116769, A165, Bibcode: 2011A&A...531A.165P.
- ↑ 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, doi:10.3847/1538-3881/aba592, Bibcode: 2020AJ....160..120J.
- ↑ Skowron, Dorota M. et al. (2019), "A three-dimensional map of the Milky Way using classical Cepheid variable stars", Science 365 (6452): 478–482, doi:10.1126/science.aau3181, PMID 31371611, Bibcode: 2019Sci...365..478S.
- ↑ "U Sgr". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=U+Sgr.
- ↑ "ASAS All Star Catalogue". The All Sky Automated Survey. http://www.astrouw.edu.pl/asas/?page=aasc.
- ↑ Schmidt, Johann Friedrich Julius (March 1868), "Über die Lichtphasen von A, γ und U Sagittarii in den Jahren 1866 und 1867" (in de), Astronomische Nachrichten 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, doi:10.1086/142435, Bibcode: 1918ApJ....48..279S.
- ↑ 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, doi:10.1086/127041, Bibcode: 1957PASP...69..172W.
- ↑ 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, doi:10.1093/mnras/stu2165, Bibcode: 2015MNRAS.446.1268C.
- ↑ 17.0 17.1 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, doi:10.1051/0004-6361/201322670, A22, Bibcode: 2013A&A...560A..22M.
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, doi:10.1134/S1063773714030025, Bibcode: 2014AstL...40..193B.
- 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, doi:10.1093/mnras/237.1.163, Bibcode: 1989MNRAS.237..163S.
- Burnham, Robert (1978), Burnham's Celestial Handbook, An Observer's Guide to the Universe Beyond the Solar System, 3, Dover Publications, ISBN 9780486236735, https://books.google.com/books?id=tBQoCSRdLAAC&pg=PA1606.
- Jacobsen, T. S. (February 1970), "A High-Dispersion Velocity Curve of U Sagittarii", Astrophysical Journal 159: 569, doi:10.1086/150331, Bibcode: 1970ApJ...159..569J.
- Wampler, J. et al. (May 1961), "Cepheids in Galactic Clusters. VIII. a Reinvestigation of U SGR in M25 (= IC 4725).", Astrophysical Journal 133: 895, doi:10.1086/147092, Bibcode: 1961ApJ...133..895W.
- Mitchell, Richard I. et al. (May 1961), "U, B, V, Observations of U SGR", Astrophysical Journal 133: 1083, doi:10.1086/147114, Bibcode: 1961ApJ...133.1083M.
- 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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