18 Vulpeculae

18 Vulpeculae is a binary star[4] system in the northern constellation of Vulpecula, located about 489 light years away from the Sun.[1] It is visible to the naked eye as a faint, white-hued star with a combined apparent visual magnitude of 5.51.[2] The system is moving closer to the Earth with a heliocentric radial velocity of −11.7 km/s.[3]

18 Vulpeculae
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Vulpecula
Right ascension  20h 10m 33.53707s[1]
Declination +26° 54′ 15.0033″[1]
Apparent magnitude (V) 5.51[2]
Characteristics
Spectral type A3III or A3V[3]
B−V color index 0.087±0.003[2]
Variable type δ Sct[4]
Astrometry
Radial velocity (Rv)−11.70±0.11[3] km/s
Proper motion (μ) RA: 18.785±0.164[1] mas/yr
Dec.: 12.694±0.172[1] mas/yr
Parallax (π)6.6678 ± 0.1098[1] mas
Distance489 ± 8 ly
(150 ± 2 pc)
Absolute magnitude (MV)−0.05[2]
Orbit[3]
Period (P)9.314077±0.000039 d
Eccentricity (e)0.0116±0.0019
Periastron epoch (T)2454875.09±0.25 HJD
Argument of periastron (ω)
(secondary)		319.4±0.97°
Semi-amplitude (K1)
(primary)		78.33±0.13 km/s
Semi-amplitude (K2)
(secondary)		82.80±0.29 km/s
Details[4]
18 Vul A
Mass2.4 M☉
Radius3.5±0.3 R☉
Surface gravity (log g)3.73±0.07 cgs
Temperature8300±300 K
18 Vul B
Mass2.2 M☉
Radius2.4±0.2 R☉
Other designations
BD+26 3815, HD 191747, HIP 99404, HR 7711, SAO 88295[5]
Database references
SIMBADdata

This is a double-lined spectroscopic binary system with an orbital period of 9.3 days and a small eccentricity of 0.0116.[3] It is a detached binary with a semimajor axis of 0.14742 ± 0.00047 AU. The system contains a Delta Scuti variable,[4] but the temperature places it to the blue (hotter) side of the δ Scuti instability strip. The combined stellar classification of this system remains unclear, with classes of A3 III, A1 IV, A3 V, and A2 IV being given. The ultraviolet spectrum matches an A3 dwarf star. It shows no spectral peculiarities.[3]

References
  1. 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.
  2. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015.
  3. Fekel, Francis C.; et al. (2013). "New Precision Orbits of Bright Double-lined Spectroscopic Binaries. VIII. HR 1528, HR 6993, 2 Sagittae, and 18 Vulpeculae". The Astronomical Journal. 146 (5). 129. Bibcode:2013AJ....146..129F. doi:10.1088/0004-6256/146/5/129. hdl:2152/34407.
  4. Liakos, Alexios; Niarchos, Panagiotis (2017). "Catalogue and properties of δ Scuti stars in binaries". Monthly Notices of the Royal Astronomical Society. 465 (1): 1181. arXiv:1611.00200. Bibcode:2017MNRAS.465.1181L. doi:10.1093/mnras/stw2756.
  5. "18 Vulpeculae". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-11-18.

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