S Sagittae

S Sagittae, also known by the Flamsteed designation of 10 Sagittae, a Classical Cepheid variable in the constellation Sagitta that varies from magnitude 5.24 to 6.04 in 8.382 days.[2] Its variable star designation of "S" indicates that it was the second star discovered to be variable in the constellation. Irish amateur astronomer John Ellard Gore was the first to observe its variability in 1885, and Ralph Hamilton Curtiss discovered its changing radial velocity in 1903–04.[10] Harlow Shapley observed in 1916 that the spectrum of it and other Cepheids varied with its brightness, recording it as spectral type F0 leading to maximum, F4 at maximum, and G3 just before minimum brightness.[11]

S Sagittae
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Sagitta
Right ascension  19h 56m 01.26s[1]
Declination +16° 38′ 05.3″[1]
Apparent magnitude (V) 5.24 – 6.04[2]
Characteristics
Evolutionary stage Supergiant
Spectral type F6Ib-G5Ib[3]
U−B color index +0.6-+0.9[2]
B−V color index +0.7-+1.0[2]
Variable type Classical Cepheid[2]
Astrometry
Radial velocity (Rv)−9.91[4] km/s
Proper motion (μ) RA: +1.763 ± 0.122[5] mas/yr
Dec.: −9.91 ± 0.01[5] mas/yr
Parallax (π)0.6426 ± 0.0932[5] mas
Distanceapprox. 5,100 ly
(approx. 1,600 pc)
Absolute magnitude (MV)–3.8[6]
Details
Mass7[7] M☉
Radius58.5[8] R☉
Luminosity5,200[9] L☉
Temperature5,400[6] K
Other designations
10 Sge, BD+16° 4067, HD 188727, HIP 98085, HR 7609, SAO 105436
Database references
SIMBADdata

S Sagittae is a yellow-white supergiant that varies between spectral types F6Ib and G5Ib. It is around six or seven times as massive and five thousand times as luminous as the Sun and is located around 2,000 light-years away from Earth.[2] Its radius is 58.5 times that of the Sun.[8] The radius, temperature, luminosity, and colour are all variable as the star pulsates during its eight-day period. The period is slowly increasing.[2]

S Sagittae has been reported as a double or triple system with a hotter main sequence star companion in a 676-day orbit. The companion, and its own possible fainter companion, are only detectable from radial velocity changes in the spectral lines of the Cepheid primary and an ultraviolet excess. Analysis of the spectrum indicates a star of spectral type A7V to F0V, and 1.5 to 1.7 times as massive as the Sun. However, as the mass of the companion is greater than 2.8 solar masses, this strongly suggests this companion is itself a binary star.[7]

References
  1. Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. Kiss, L. L. (1998). "A photometric and spectroscopic study of the brightest northern Cepheids – I. Observations". Monthly Notices of the Royal Astronomical Society. 297 (3): 825. Bibcode:1998MNRAS.297..825K. doi:10.1046/j.1365-8711.1998.01559.x.
  3. Payne-Gaposchkin, Cecilia (1984). "Der Seufzer des Fusionsofens – Die Cepheiden". Sterne und Sternhaufen (in German). p. 96. doi:10.1007/978-3-322-86266-2_8. ISBN 978-3-528-08486-8.
  4. Pourbaix, D.; Tokovinin, A. A.; Batten, A. H.; Fekel, F. C.; Hartkopf, W. I.; Levato, H.; Morrell, N. I.; Torres, G.; Udry, S. (2004). "SB9: The ninth catalogue of spectroscopic binary orbits". Astronomy and Astrophysics. 424 (2): 727. arXiv:astro-ph/0406573. Bibcode:2004A&A...424..727P. doi:10.1051/0004-6361:20041213.
  5. 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.
  6. Kovtyukh, V. V.; Chekhonadskikh, F. A.; Luck, R. E.; Soubiran, C.; Yasinskaya, M. P.; Belik, S. I. (2010). "Accurate luminosities for F-G supergiants from Fe ii / Fe i line depth ratios". Monthly Notices of the Royal Astronomical Society. 408 (3): 1568. Bibcode:2010MNRAS.408.1568K. doi:10.1111/j.1365-2966.2010.17217.x.
  7. Evans, Nancy R.; Welch, Douglas L.; Slovak, Mark H.; Barnes, Thomas G.; Moffett, Thomas J. (1993). "The orbit and companion of the Cepheid S SGE – A probable triple system". Astronomical Journal. 106: 1599. arXiv:astro-ph/9706292. Bibcode:1993AJ....106.1599E. doi:10.1086/116750.
  8. Moskalik, P.; Gorynya, N. A. (2005). "Mean Angular Diameters and Angular Diameter Amplitudes of Bright Cepheids". Acta Astronomica. 55: 247. arXiv:astro-ph/0507076. Bibcode:2005AcA....55..247M.
  9. McDonald, I.; Zijlstra, A. A.; Boyer, M. L. (2012). "Fundamental parameters and infrared excesses of Hipparcos stars". Monthly Notices of the Royal Astronomical Society. 427: 343. arXiv:1208.2037. Bibcode:2012MNRAS.427..343M. doi:10.1111/j.1365-2966.2012.21873.x.
  10. Aldrich, John A. (1932). "A study of S Sagittae". Publications of the Observatory of the University of Michigan. 4 (5): 75–92. Bibcode:1932POMic...4...75A.
  11. Shapley, Harlow (1916). "The variations in spectral type of twenty Cepheid variables". The Astrophysical Journal. 44 (`): 273–91. Bibcode:1916ApJ....44..273S. doi:10.1086/142295.
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