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SY Equulei

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High galactic latitude β Cephei variable
SY Equulei

A light curve for SY Equulei, plotted from Hipparcos data
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Equuleus
Right ascension 21 23 28.8086
Declination +09° 55′ 54.9204″
Apparent magnitude (V) 8.52 - 8.58
Characteristics
Spectral type B0.5 IIIn
U−B color index −1.00
B−V color index −0.20
Variable type β Cephei
Astrometry
Radial velocity (Rv)48±5.5 km/s
Proper motion (μ) RA: −0.185 mas/yr
Dec.: −9.049 mas/yr
Parallax (π)0.3869 ± 0.0558 mas
Distanceapprox. 8,000 ly
(approx. 2,600 pc)
Absolute bolometric
magnitude (Mbol)		−6.04
Details
Mass14 M☉
Radius10.44 R☉
Luminosity2,490 L☉
Surface gravity (log g)3.8±0.2 cgs
Temperature28,184
−1,268 K
Metallicity 0.00 dex
Rotational velocity (v sin i)180 km/s
Age~7.5 Myr
Other designations
SY Equueli, AG+09°2978, BD+09°4793, HD 203664, HIP 105614, SAO 126757
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 and is receding with a heliocentric radial velocity of 48 km/s. At that distance, SY Equulei is dimmed by 0.19 magnitudes due to interstellar dust.

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. The cloud probably came from outside the galactic plane and is moving towards the star at a rate of 70 km/s. 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. However, its status as a Beta Cephei variable wasn't discovered until a survey of 2000 using Hipparcos data. It was then given the designation SY Equulei.

SY Equulei has a stellar classification of B0.5 IIIn, 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, which is 40% of its break-up velocity. It has 14 times the mass of the Sun and a radius of 10.4 radius. It radiates at 2,490 times the luminosity of the Sun from its photosphere at an effective temperature of 28,184 K, giving a whitish blue hue.

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

References

  1. "Light Curve". Hipparcos ESA. ESA. Retrieved 17 February 2022.
  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. "SY Equ". International Variable Star Index. AAVSO. Retrieved 2022-07-31.
  4. ^ 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. Bibcode:1971ApJS...23..257W. doi:10.1086/190239. eISSN 1538-4365. ISSN 0067-0049.
  5. ^ Guetter, H. H. (October 1974). "UBV photometry of 180 early-type stars". Publications of the Astronomical Society of the Pacific. 86: 795. Bibcode:1974PASP...86..795G. doi:10.1086/129675. eISSN 1538-3873. ISSN 0004-6280.
  6. ^ 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. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. eISSN 1562-6881. ISSN 1063-7729. S2CID 125853869.
  7. ^ 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. arXiv:0705.0878. Bibcode:2007AN....328..889K. doi:10.1002/asna.200710776. ISSN 0004-6337.
  8. ^ Aerts, C. (September 2000). "Follow-up photometry of six new beta Cephei stars discovered from the HIPPARCOS mission". Astronomy and Astrophysics. 361: 245–257. Bibcode:2000A&A...361..245A. ISSN 0004-6361.
  9. ^ 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. Bibcode:1982MNRAS.200..673K. doi:10.1093/mnras/200.3.673. eISSN 1365-2966. ISSN 0035-8711.
  10. ^ Kervella, Pierre; Arenou, Frédéric; Thévenin, Frédéric (2022). "Stellar and substellar companions from Gaia EDR3". Astronomy & Astrophysics. 657: A7. arXiv:2109.10912. Bibcode:2022A&A...657A...7K. doi:10.1051/0004-6361/202142146. eISSN 1432-0746. ISSN 0004-6361.
  11. ^ 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. arXiv:1208.2037. Bibcode:2012MNRAS.427..343M. doi:10.1111/j.1365-2966.2012.21873.x. ISSN 0035-8711.
  12. ^ 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. arXiv:astro-ph/0511306. Bibcode:2006A&A...449..305A. doi:10.1051/0004-6361:20054142. eISSN 1432-0746. ISSN 0004-6361.
  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. arXiv:2111.01860. Bibcode:2022A&A...658A..91A. doi:10.1051/0004-6361/202142369. eISSN 1432-0746. ISSN 0004-6361.
  14. ^ 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. Bibcode:1965PDAO...12..401W. ISSN 0078-6950.
  15. "SY Equulei". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved July 29, 2022.
  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. Bibcode:1980BICDS..19...61N. ISSN 1169-8837.
  17. ^ Sembach, Kenneth R. (May 1995). "Properties of the +70 kilometers per second cloud toward HD 203664". The Astrophysical Journal. 445: 314. Bibcode:1995ApJ...445..314S. doi:10.1086/175695. eISSN 1538-4357. ISSN 0004-637X.
  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. Bibcode:1999IBVS.4659....1K. ISSN 0374-0676.
  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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