SY Equulei

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SY Equulei

A light curve for SY Equulei, plotted from Hipparcos data[1]
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
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 mas/yr[2]
Dec.: −9.049 mas/yr[2]
Parallax (π)0.3869±0.0558 mas[2]
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, AG+09°2978, 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

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