Astronomy:SY Equulei

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Short description: High galactic latitude β Cephei variable
SY Equulei
SYEquLightCurve.png
A light curve for SY Equulei, plotted from Hipparcos data[1]
Observation data
Epoch J2000.0   Equinox (celestial coordinates)
Constellation Equuleus
Right ascension  21h 23m 28.8086s[2]
Declination +09° 55′ 54.9204″[2]
Apparent magnitude (V) 8.52 - 8.58[3]
Characteristics
Spectral type B0.5 IIIn[4]
U−B color index −1.00[5]
B−V color index −0.20[5]
Variable type β Cephei[6]
Astrometry
Radial velocity (Rv)48±5.5[7] km/s
Proper motion (μ) RA: −0.185[2] mas/yr
Dec.: −9.049[2] mas/yr
Parallax (π)0.3869 ± 0.0558[2] mas
Distanceapprox. 8,000 ly
(approx. 2,600 pc)
Absolute bolometric
magnitude (Mbol)		−6.04[8]
Details
Mass14[9] M☉
Radius10.44[10] R☉
Luminosity2,490[11] L☉
Surface gravity (log g)3.8±0.2[12] cgs
Temperature28,184+1,328−1,268[12] K
Metallicity [Fe/H]0.00[13] dex
Rotational velocity (v sin i)180[14] km/s
Age~7.5[12] Myr
Other designations
SY Equueli, BD+09°4793, HD 203664, HIP 105614, SAO 126757[15]
Database references
SIMBADdata

SY Equulei, also known as HD 203664, is a single variable star located in the equatorial constellation Equuleus. It has an average apparent magnitude of about 8.5, varying by a few hundredths of a magnitude, making it readily visible in binoculars and small telescopes, but not to the naked eye. The star is relatively far away at a distance of 8,000 light years[2] and is receding with a heliocentric radial velocity of 48 km/s.[7] At that distance, SY Equulei is dimmed by 0.19 magnitudes due to interstellar dust.[16]

Throughout the late 20th century, HD 203664 was known to have a dust cloud surrounding it. Subsequent observations from Kenneth R. Sembach (1995) reveal it to contain high abundances of calcium as well as traces of magnesium, aluminum, and silicon.[17] The cloud probably came from outside the galactic plane and is moving towards the star at a rate of 70 km/s.[17] The star has a high galactic latitude, indicating its location in the galactic halo. HD 203664 was most likely ejected from its birthplace to its current distance.[9] However, its status as a Beta Cephei variable wasn't discovered until a survey of 2000 using Hipparcos data.[8] It was then given the designation SY Equulei.[18]

SY Equulei has a stellar classification of B0.5 IIIn,[4] indicating an evolved B-type star with nebulous (broad) absorption lines due to rapid rotation. Unlike most stars of its type, it spins rapidly with a projected rotational velocity of 180 km/s,[14] which is 40% of its break-up velocity.[12] It has 14 times the mass of the Sun[9] and a radius of 10.4 radius.[10] It radiates at 2,490 times the luminosity of the Sun[11] from its photosphere at an effective temperature of 28,184 K,[12] giving a whitish blue hue.

SY Equueli is a variable star with an amplitude of 0.07 magnitudes[6] and an average period of 3.98 hours.[19] In later observations, SY Equulei was found to have multiple periods.[12]

References

  1. ↑ "Light Curve". ESA. https://www.cosmos.esa.int/web/hipparcos/java-tools/light-curve. 
  2. ↑ 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. ↑ "SY Equ". AAVSO. https://www.aavso.org/vsx/index.php?view=detail.top&oid=13977. 
  4. ↑ 4.0 4.1 Walborn, Nolan R. (August 1971). "Some Spectroscopic Characteristics of the OB Stars: an Investigation of the Space Distribution of Certain OB Stars and the Reference Frame of the Classification". The Astrophysical Journal Supplement Series 23: 257. doi:10.1086/190239. ISSN 0067-0049. Bibcode: 1971ApJS...23..257W. 
  5. ↑ 5.0 5.1 Guetter, H. H. (October 1974). "UBV photometry of 180 early-type stars". Publications of the Astronomical Society of the Pacific 86: 795. doi:10.1086/129675. ISSN 0004-6280. Bibcode: 1974PASP...86..795G. 
  6. ↑ 6.0 6.1 Samus’, N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (January 2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports 61 (1): 80–88. doi:10.1134/S1063772917010085. ISSN 1063-7729. Bibcode: 2017ARep...61...80S. 
  7. ↑ 7.0 7.1 Kharchenko, N.V.; Scholz, R.-D.; Piskunov, A.E.; Röser, S.; Schilbach, E. (November 2007). "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ~55000 stars and mean radial velocities of 516 Galactic open clusters and associations". Astronomische Nachrichten 328 (9): 889–896. doi:10.1002/asna.200710776. ISSN 0004-6337. Bibcode: 2007AN....328..889K. 
  8. ↑ 8.0 8.1 Aerts, C. (September 2000). "Follow-up photometry of six new beta Cephei stars discovered from the HIPPARCOS mission". Astronomy and Astrophysics 361: 245–257. ISSN 0004-6361. Bibcode: 2000A&A...361..245A. 
  9. ↑ 9.0 9.1 9.2 Keenan, F. P.; Dufton, P. L.; McKeith, C. D. (1 October 1982). "Atmospheric parameters and chemical compositions of eighteen halo OB stars". Monthly Notices of the Royal Astronomical Society 200 (3): 673–685. doi:10.1093/mnras/200.3.673. ISSN 0035-8711. Bibcode: 1982MNRAS.200..673K. 
  10. ↑ 10.0 10.1 Kervella, Pierre; Arenou, Frédéric; Thévenin, Frédéric (2022). "Stellar and substellar companions from Gaia EDR3". Astronomy & Astrophysics 657: A7. doi:10.1051/0004-6361/202142146. ISSN 0004-6361. Bibcode: 2022A&A...657A...7K. 
  11. ↑ 11.0 11.1 McDonald, I.; Zijlstra, A. A.; Boyer, M. L. (21 November 2012). "Fundamental parameters and infrared excesses of Hipparcos stars: Parameters and IR excesses from Hipparcos". Monthly Notices of the Royal Astronomical Society 427 (1): 343–357. doi:10.1111/j.1365-2966.2012.21873.x. ISSN 0035-8711. Bibcode: 2012MNRAS.427..343M. 
  12. ↑ 12.0 12.1 12.2 12.3 12.4 12.5 Aerts, C.; De Cat, P.; De Ridder, J.; Van Winckel, H.; Raskin, G.; Davignon, G.; Uytterhoeven, K. (16 March 2006). "Multiperiodicity in the large-amplitude rapidly-rotating β Cephei star HD 203664". Astronomy & Astrophysics 449 (1): 305–311. doi:10.1051/0004-6361:20054142. ISSN 0004-6361. Bibcode: 2006A&A...449..305A. 
  13. ↑ Anders, F. et al. (February 2022). "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia EDR3 stars brighter than G = 18.5". Astronomy & Astrophysics 658: A91. doi:10.1051/0004-6361/202142369. ISSN 0004-6361. Bibcode: 2022A&A...658A..91A. 
  14. ↑ 14.0 14.1 Walker, G. A. H.; Hodge, S. M. (1965). "Equivalent widths and halfwidths of the λ4388 and λ4471 He I lines, rotational velocities and λ4430 central depths for 450O to B5 stars.". Publications of the Dominion Astrophysical Observatory Victoria 12: 401. ISSN 0078-6950. Bibcode: 1965PDAO...12..401W. 
  15. ↑ "SY Equulei". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=SY+Equulei. 
  16. ↑ Neckel, T.; Klare, G.; Sarcander, M. (July 1980). "Catalogue of Extinction Data of 12547 O-Stars to F-Stars Galactic Clusters and Delta-Cephei Stars". Bulletin d'Information du Centre de Donnees Stellaires 19: 61. ISSN 1169-8837. Bibcode: 1980BICDS..19...61N. 
  17. ↑ 17.0 17.1 Sembach, Kenneth R. (May 1995). "Properties of the +70 kilometers per second cloud toward HD 203664". The Astrophysical Journal 445: 314. doi:10.1086/175695. ISSN 0004-637X. Bibcode: 1995ApJ...445..314S. 
  18. ↑ Kazarovets, E. V.; Samus, N. N.; Durlevich, O. V.; Frolov, M. S.; Antipin, S. V.; Kireeva, N. N.; Pastukhova, E. N. (January 1999). "The 74th Special Name-list of Variable Stars". Information Bulletin on Variable Stars 4659: 1. ISSN 0374-0676. Bibcode: 1999IBVS.4659....1K. 
  19. ↑ Watson, C. L.; Henden, A. A.; Price, A. (May 2006). "The International Variable Star Index (VSX)". Society for Astronomical Sciences Annual Symposium 25: 47. Bibcode: 2006SASS...25...47W. 



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