U Sagittae

U Sagittae is an eclipsing binary star system in the northern constellation of Sagitta. It has been actively studied since its discovery in 1901.[9] The maximum apparent visual magnitude of this system is 6.50,[3] which is near the lower limit of visibility to the naked eye. The system is located at a distance of approximately 868 light years from the Sun based on parallax measurements,[2] but is drifting closer with a radial velocity of −17 km/s.[7] It is positioned about 2° from the middle of the Collinder 399 asterism, but lies much further away than the purported member stars.[12]

U Sagittae

A light curve for U Sagittae, plotted from TESS data[1]
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Sagitta
Right ascension 19h 18m 48.4083s[2]
Declination +19° 36′ 37.72″[2]
Apparent magnitude (V) 6.50[3]
Characteristics
Spectral type B7.5 IV/V + G2 III/IV[4]
B7.5 V + G4 III–IV[5]
B−V color index −0.006±0.006[3]
Variable type β Per[6]
Astrometry
Radial velocity (Rv)−17.1±0.9[7] km/s
Proper motion (μ) RA: +0.146 mas/yr[2]
Dec.: +1.076 mas/yr[2]
Parallax (π)3.7591 ± 0.0284 mas[2]
Distance868 ± 7 ly
(266 ± 2 pc)
Absolute magnitude (MV)−0.36[3]
Orbit[8]
Period (P)3.3806184 d
Semi-major axis (a)≥ 0.0217 AU (3.24 Gm)
Eccentricity (e)0.030±0.008
Argument of periastron (ω)
(secondary)		194.4±14.1°
Semi-amplitude (K1)
(primary)		69.69±0.59 km/s
Details[5]
Primary
Mass4.629±0.061 M☉
Radius3.9193±0.029 R☉
Surface gravity (log g)3.9[9] cgs
Temperature13,300 K
Rotational velocity (v sin i)100[10] km/s
Secondary
Mass1.731±0.204 M☉
Radius5.4772±0.027 R☉
Luminosity2.655±0.062 L☉
Surface gravity (log g)3.27[9] cgs
Temperature5,500[10] K
Other designations
AG 432, U Sge, BD+19° 3975, GC 26639, HD 181182, HIP 94910, HR 7326, SAO 104711, WDS J19188+1937[11]
Database references
SIMBADdata

The variable nature of this system was discovered by German astronomer Friedrich Schwab in 1901.[13] He determined it to be an Algol variable with a brightness that decreased by 2.1 magnitudes during an eclipse.[14] A single-lined spectroscopic orbit was published in 1916 by Mary Fowler using spectrograms taken from the Allegheny Observatory.[14] With a larger set of observations, D. H. McNamara published a revised orbit in 1951.[8] In 1959, hydrogen lines from the system were found to show a systematically different radial velocity compared to other lines from the two stars.[15]

This is a spectroscopic binary system in a near circular orbit with a period of 3.38 days.[8] It is a semidetached binary and the brightest fully eclipsing Algol variable.[16] During the primary eclipse the brightness of the system drops to magnitude 9.28, while the secondary eclipse lowers the magnitude to 6.71.[6] Observations of the system minima over a period of more than 80 years do not indicate a significant change in the orbital period.[17] The orbital plane is inclined at an angle of 89° to the line of sight from the Earth, so it is being viewed from edge-on.[10] The system contains circumstellar gas with a temperature of ~104 K that is streaming between the stars.[10] This forms an intermittent accretion disk around the primary.[9]

The primary component is a B-type main-sequence star with a stellar classification of B7.5V. It has 4.6 times the mass and 3.9 times the radius of the Sun. The star is rotating with a projected rotational velocity of 100 km/s.[10] It is radiating 48 times the luminosity of the Sun from its photosphere at an effective temperature of 13,300 K. The gas stream from the secondary is causing an increase in ultraviolet emission from this star[5] from an impact hot spot.[10]

The secondary has a class of G4 III–IV,[5] indicating it is the more evolved member of the pair. It was originally the primary component of the system before expanding and transferring much of its mass to the present day primary.[18][19] The secondary has filled its Roche lobe and is shedding mass at an estimated rate of 6.15×10−7 M☉·yr−1.[4] It has 1.7 times the mass of the Sun and 5.5 times the Sun's radius. This star is rotating slightly faster than synchronous with the orbit, showing a projected rotational velocity of 73 km/s.[18] It is radiating 2.7 times the luminosity of the Sun from its photosphere at an effective temperature of 5,500 K.[10]

References
  1. "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.
  2. 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.
  3. 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, S2CID 119257644.
  4. Manzoori, Davood (February 2008), "Further confirmations of mass transfer in Algol type binary U Sagittae", Astrophysics and Space Science, 313 (4): 339–344, Bibcode:2008Ap&SS.313..339M, doi:10.1007/s10509-007-9683-5, S2CID 121915490.
  5. Manzoori, Davood; et al. (April 2006), "Photometric Study of Eclipsing Binary U Sagittae", Astrophysics and Space Science, 302 (1–4): 145–151, Bibcode:2006Ap&SS.302..145M, doi:10.1007/s10509-005-9015-6, S2CID 119993759.
  6. 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.
  7. Wilson, Ralph Elmer (1953), "General catalogue of stellar radial velocities", Carnegie Institute Washington D.C. Publication, Washington: Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W.
  8. McNamara, D. H. (November 1951), "The Eclipsing Binary U Sagittae", Astrophysical Journal, 114: 513, Bibcode:1951ApJ...114..513M, doi:10.1086/145495.
  9. Albright, Geary E.; Richards, Mercedes T. (March 1995), "The Transient Accretion Disk in the Algol-Type Binary U Sagittae", Astrophysical Journal, 441: 806, Bibcode:1995ApJ...441..806A, doi:10.1086/175404.
  10. Kempner, Joshua C.; Richards, Mercedes T. (February 1999), "Analysis of the Si IV Ultraviolet Spectra of U Sagittae", The Astrophysical Journal, 512 (1): 345–350, Bibcode:1999ApJ...512..345K, doi:10.1086/306774, S2CID 122699856.
  11. "U Sge", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2022-02-02.
  12. Hall, Douglas S.; Vanlandingham, Franklin G. (June 1970), "On the Membership of U Sagittae in Collinder 399", Publications of the Astronomical Society of the Pacific, 82 (487): 749, Bibcode:1970PASP...82..749H, doi:10.1086/128955, S2CID 121016630.
  13. Pickering, E. C.; et al. (April 1902), "Early observations of algol stars", Astrophysical Journal, 15: 229–233, Bibcode:1902ApJ....15..229P, doi:10.1086/140912.
  14. Fowler, Mary (1916), "The orbit of U Sagittae", Publications of the Allegheny Observatory of the University of Pittsburgh, 3 (2): 11–15, Bibcode:1916PAllO...3...11F.
  15. McNamara, D. H. (June 1959), "The Hydrogen Lines in the Spectrum of U Sagittae", Publications of the Astronomical Society of the Pacific, 71 (420): 241, Bibcode:1959PASP...71..241M, doi:10.1086/127375, S2CID 120804728.
  16. Manzoori, D.; Gozaliasl, G. (April 2007), "A Period Study of the Eclipsing Binary U Sagittae", The Astronomical Journal, 133 (4): 1302–1306, Bibcode:2007AJ....133.1302M, doi:10.1086/511064, S2CID 122183151.
  17. Kreiner, J. M.; Ziolkowski, J. (April 2007), "Period changes and evolutionary status of 18 Algol-type systems", The Astronomical Journal, 133 (4): 1302–1306, Bibcode:2007AJ....133.1302M, doi:10.1086/511064, S2CID 122183151
  18. Sarna, M. J.; De Greve, J. -P. (January 1994), "Evolutionary status of U Sagittae", Astronomy and Astrophysics, 281: 433–443, Bibcode:1994A&A...281..433S.
  19. Dobias, J. J.; Plavec, M. J. (December 1984), "The eclipsing binary U Sagittae: evidence for CNO processing and mass exchange in the past", Goddard Space Flight Center Future of Ultraviolet Astronomy Based on Six Years of IUE Res, vol. 2349, pp. 412–415, Bibcode:1984NASCP2349..412D.

Further reading
  • Simon, Vojtech (November 1997), "On the relation of changes of the period and brightness in the close binaries SW Cygni and U Sagittae", Astronomy and Astrophysics, 327: 1087–1093, Bibcode:1997A&A...327.1087S.
  • McCluskey, George E., Jr.; et al. (September 1991), "IUE Investigation of Mass Flow in the Interacting Binary U Sagittae", Astrophysical Journal, 378: 281, Bibcode:1991ApJ...378..281M, doi:10.1086/170427.{{citation}}: CS1 maint: multiple names: authors list (link)
  • Olson, Edward C. (October 1987), "Photometric Solutions and the Rate of Mass Transfer in U Sagittae", Astronomical Journal, 94: 1043, Bibcode:1987AJ.....94.1043O, doi:10.1086/114538.
  • van Hamme, W.; Wilson, R. E. (November 1986), "The asynchronously rotating Algol binaries U Sagittae and RY Persei", Astronomical Journal, 92: 1168–1177, Bibcode:1986AJ.....92.1168V, doi:10.1086/114249.
  • Dobias, J. J.; Plavec, M. J. (February 1985), "IUE and optical spectral scans of U Sagittae : an analysis and comparison with U Cephei", Publications of the Astronomical Society of the Pacific, 97: 138–150, Bibcode:1985PASP...97..138D, doi:10.1086/131509, S2CID 121759158.
  • McCluskey, G. E., Jr.; Kondo, Y. (December 1984), "Ultraviolet spectroscopy of the interacting binary U Sagittae", In its Future of Ultraviolet Astronomy Based on Six Years of IUE Res, vol. 2349, pp. 382–386, Bibcode:1984NASCP2349..382M.{{citation}}: CS1 maint: multiple names: authors list (link)
  • Olson, E. C. (February 1982), "Radius variations in the classical algol binary U Sge", Publications of the Astronomical Society of the Pacific, 94: 70–75, Bibcode:1982PASP...94...70O, doi:10.1086/130943, S2CID 120141610.
  • Tomkin, J. (July 1979), "Secondaries of eclipsing binaries. II. U Sagittae", Astrophysical Journal, 231: 495–501, Bibcode:1979ApJ...231..495T, doi:10.1086/157211.
  • Tsouroplis, A. G. (April 1977), "Determination of the Elements of Eclipsing Variables RW Tauri and U Sagittae by an Analysis of the Light Changes in the Frequency Domain", Astrophysics and Space Science, 47 (2): 361–373, Bibcode:1977Ap&SS..47..361T, doi:10.1007/BF00642844, S2CID 119572340.
  • Rhombs, Craig G.; Fix, John D. (November 1976), "Spectrophotometry of the Algol-Type Binaries U Cephei, U Sagittae, and SX Cassiopeiae", Astrophysical Journal, 209: 821–828, Bibcode:1976ApJ...209..821R, doi:10.1086/154780.
  • McNamara, D. H.; Feltz, K. A., Jr. (October 1976), "A photometric study of the eclipsing binary U Sagittae", Publications of the Astronomical Society of the Pacific, 88: 688–698, Bibcode:1976PASP...88..688M, doi:10.1086/130012.{{citation}}: CS1 maint: multiple names: authors list (link)
  • Naftilan, S. A. (June 1976), "The secondary of U Sagittae", Astrophysical Journal, 206: 785–789, Bibcode:1976ApJ...206..785N, doi:10.1086/154439.
  • McNamara, D. H.; Feltz, K. A. (July 1975), "Minima of the Eclipsing Variable U Sagittae", Information Bulletin on Variable Stars, 1022 (1): 1, Bibcode:1975IBVS.1022....1M.
  • Plavec, M. (1967), "A formula for the rotation factor, with application to U SGE", Bulletin of the Astronomical Institute of Czechoslovakia, 18: 93, Bibcode:1967BAICz..18...93P.
  • McNamara, D. H. (February 1951), "The Spectrum of U Sagittae at Minimum Light", Publications of the Astronomical Society of the Pacific, 63 (370): 38, Bibcode:1951PASP...63...38M, doi:10.1086/126313, S2CID 122607419.
  • Irwin, John B. (February 1947), "A photoelectric study of U Sagittae", Astronomical Journal, 52: 125, Bibcode:1947AJ.....52..125I, doi:10.1086/105963.
  • Jacchia, Luigi (June 1941), "The Period of U Sagittae", Harvard College Observatory Bulletin, 915: 33–37, Bibcode:1941BHarO.915...33J.
  • Joy, A. H. (June 1930), "A spectrographic study of U Sagittae", Astrophysical Journal, 71: 336–350, Bibcode:1930ApJ....71..336J, doi:10.1086/143254.
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