S Antliae

S Antliae is a W Ursae Majoris-type eclipsing binary star in Antlia.

S Antliae
Observation data
Epoch J2000      Equinox J2000
Constellation Antlia
Right ascension  09h 32m 18.386s[1]
Declination −28° 37′ 39.97″[1]
Apparent magnitude (V) 6.27 to 6.83[2]
Characteristics
Spectral type A9V
B−V color index 0.33
Variable type Eclipsing binary W UMa type
Astrometry
Parallax (π)12.5121 ± 0.0491[3] mas
Distance261 ± 1 ly
(79.9 ± 0.3 pc)
Absolute magnitude (MV)1.963[4]
Details
Mass1.82 M☉
Radius2.23 R☉
Luminosity17 L☉
Temperature7900 K
Other designations
CD-28° 7373, HD 82610, SAO 177619, HIP 46810, HR 3798.
Database references
SIMBADdata

Characteristics

S Antilia is classed as an A-type W Ursae Majoris variable, since the primary is hotter than the secondary and the drop in magnitude is caused by the latter passing in front of the former. S Antilia varies in apparent magnitude from 6.27 to 6.83 over a period of 15.6 hours.[2] The system shines with a combined spectrum of A9V.

The system's orbital period is 6.48 days.[5] The eccentricity of the orbit is 0.66.[6] The stars' centres are an average of 3.31 times the sun's radius apart, which places their surfaces just 0.36 times the sun's radius apart. Thus, the two stars will eventually merge to form a single fast-spinning star.[7]

Calculating the properties of the component stars from the orbital period indicates that the primary star has a mass 1.94 times and a diameter 2.026 times that of the Sun, and the secondary has a mass 0.76 times and a diameter 1.322 times that of the Sun.[7] The primary has a surface temperature of 7800 K, while the secondary is a little cooler at 7340 K. The two stars have similar luminosity and spectral type as they have a common envelope and share stellar material.[8] The system is thought to be around 5-6 billion years old.

Based upon an annual parallax shift of 11.84 milliarc seconds as measured by the Hipparcos satellite,[1] this system is 270 light-years (84 parsecs) from Earth. Analysing and recalibrating yields a parallax of 13.30 and hence a distance of 250 light-years (76 parsecs).[4]

History

The star's variability was first recorded in 1888 by H.M. Paul,[9]. At the time, it had the shortest known period of any variable star. It was initially thought to be an Algol-type eclipsing binary, but this was discounted by E.C. Pickering on account of it lacking a shallow minimum in its maximum and the width of its minimum period. Alfred H. Joy noted the similarity of its light curve to W Ursae Majoris in 1926, concluding the system was indeed an eclipsing binary with two stars of spectral type A8.[10]

gollark: Except it can't, because we also have thick walls or something.
gollark: Generally not very good, yes.
gollark: Well, I have 34/8 (Mbps) VDSL, and powerline adapters which reduce it to about 300kbps upstairs on the wired connection.
gollark: My cheap network switch seems to generate some high-frequency audio noise I can BARELY hear and it's annoying.
gollark: Hmm. It seems to not like that.

References
  1. van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.Vizier catalog entry
  2. Watson, Christopher (4 January 2010). "S Antliae". AAVSO Website. American Association of Variable Star Observers. Retrieved 22 May 2014.
  3. 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.
  4. Eker, Z.; Bilir, S.; Yaz, E.; Demircan, O.; Helvaci, M. (2009). "New absolute magnitude calibrations for W Ursa Majoris type binaries". Astronomische Nachrichten. 330 (1): 68–77. arXiv:0807.4989. Bibcode:2009AN....330...68E. doi:10.1002/asna.200811041.
  5. http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1922PAAS....4S.266J&db_key=AST&page_ind=1&plate_select=NO&data_type=GIF&type=SCREEN_GIF&classic=YES
  6. http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1922PAAS....4S.266J&db_key=AST&page_ind=1&plate_select=NO&data_type=GIF&type=SCREEN_GIF&classic=YES
  7. Gazeas, K.; Stȩpień, K. (2008). "Angular momentum and mass evolution of contact binaries". Monthly Notices of the Royal Astronomical Society. 390 (4): 1577–86. arXiv:0803.0212. Bibcode:2008MNRAS.390.1577G. doi:10.1111/j.1365-2966.2008.13844.x.
  8. Csizmadia, Sz.; Klagyivik, P. (2004). "On the properties of contact binary stars". Astronomy and Astrophysics. 426: 1001–05. arXiv:astro-ph/0408049. Bibcode:2004A&A...426.1001C. doi:10.1051/0004-6361:20040430.
  9. Paul, H. M. (1891). "Observations of 3407 S Antliae". Astronomical Journal. 10 (234): 139–142. Bibcode:1891AJ.....10..139P. doi:10.1086/101491.
  10. Joy, Alfred H. (1926). "Provisional elements and dimensions of S Antliae considered as an eclipsing binary". Astrophysical Journal. 64: 287–94. Bibcode:1926ApJ....64..287J. doi:10.1086/143015.
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