U Sagittae

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U Sagittae
USgeLightCurve.png
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]
Distance 868 ± 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
Mass 4.629±0.061  M☉
Radius 3.9193±0.029  R☉
Surface gravity (log g)3.9 [9]   cgs
Temperature 13,300  K
Rotational velocity (v sin i)100 [10]  km/s
Secondary
Mass 1.731±0.204  M☉
Radius 5.4772±0.027  R☉
Luminosity2.655±0.062  L☉
Surface gravity (log g)3.27 [9]   cgs
Temperature 5,500 [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
SIMBAD data

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]

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]

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References

  1. ↑ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.
  2. 1 2 3 4 5 6 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. 1 2 3 4 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. 1 2 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. 1 2 3 4 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. 1 2 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. 1 2 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. 1 2 3 McNamara, D. H. (November 1951), "The Eclipsing Binary U Sagittae", Astrophysical Journal, 114: 513, Bibcode:1951ApJ...114..513M, doi:10.1086/145495.
  9. 1 2 3 4 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. 1 2 3 4 5 6 7 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. 1 2 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. 1 2 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.

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