VW Cephei

VW Cephei (VW Cep) is an eclipsing contact binary of W Ursae Majoris-type located roughly at 90.6 light years from the Sun, whose two component stars share a common outer layer. Because the two components share their outer layers, as the components of W Ursae Majoris do, they have the same stellar classification, and are classified as yellow G-type main sequence dwarfs. The components take 0.2783 days (roughly 6.7 hours) to revolve around a common barycentre. Orbital period variations suggest the presence of one more additional perturbing objects of likely low-mass stellar nature.

Not to be confused with VV Cephei or W Cephei.
VW Cephei
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cepheus
Right ascension 20h 37m 21.5449s
Declination +75° 36′ 01.456″
Apparent magnitude (V) 7.38
Characteristics
Spectral type G5V/G8V/?K3V/?M5V
Astrometry
Distance90.95 ly
(27.9[1] pc)
Details
Mass1.21/0.22/0.75/0.19? M☉
Radius0.9/0.55/0.77/0.23? R☉
Luminosity0.66/0.17/0.26/0.0038? L☉
Temperature≈5500/5000/≈4700/≈3000 K
Orbit
Period (P)0.0007625 yr
Semi-major axis (a)0.0083AUs″
Eccentricity (e)0 (fixed)
Other designations
VW Cep, LHS 3565, SAO 9828, LTT 16039, BD+75 752, GJ 9703, HD 197433, HIP 101750.
Database references
SIMBADdata

Unseen companion(s)

Orbital period variations suggest the presence of one more perturbing unseen object around the eclipsing binary.[1] Several publications have tried to set constrains to putative orbital period and minimum mass for unseen component. The most recent article[1] proposes an orbital period of 29.8 years for a stellar object with roughly three fourths the Sun's mass and high orbital eccentricity (e=0.66). Inclination is assumed being 33.6 degrees.s Nevertheless, hints of an additional body in the system still subsist and the authors infer a period of 77.46 years and eccentricity of 0.54 for unseen fourth component. Minimum mass is unclear, tentatively assumed being as small as 0.19 solar masses, as inferred by Pribulla et al. in 2000.[2] In any case orbital solutions are still blurry and further calculations are needed to provide a more robust model.

With the release of Gaia DR2, the presence of any stellar companions was ruled out.[note 1]

The VW Cephei planetary system
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b (unconfirmed) 750 (0.75 M☉) MJ 4.33 ≈10877 0.77 — —
c (unconfirmed) ≤190 (0.19 M☉)? MJ 18.2? ≈28273 0.543 — —

Notes
  1. The recorded excess noise for the stars is 0.398 ± 0.008 mas, which corresponds to an angular size of 0.0106 ± 0.0002 AU at the stars' distance. This rules out any bodies capable of perturbing the stars by more than 0.0106 AU from their current velocities over the 2-year observation period. The stars, for comparison, orbit each other 0.0083 AU apart.

References
  1. Zasche & Wolf, M. (2007). "Combining astrometry with the light-time effect: The case of VW Cep, zeta Phe and HT Vir". Astronomische Nachrichten. 328 (9): 928–938. arXiv:0711.3980. Bibcode:2007AN....328..928Z. doi:10.1002/asna.200710828. S2CID 14956926.
  2. Pribulla; Chochol, D.; Tremko, J.; Parimucha, S.; Vanko, M.; Kreiner, J. M. (2007). "Period study of the contact system VW Cep". Contributions of the Astronomical Observatory Skalnate Pleso. 30 (2): 117–139. arXiv:0711.3980. Bibcode:2000CoSka..30..117P. doi:10.1002/asna.200710828. S2CID 14956926.


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