VZ Piscium

A light curve for VZ Piscium plotted from TESS data[1]
Observation data
Epoch J2000      Equinox J2000
Constellation Pisces
Right ascension 23h 27m 48.388s[2]
Declination +04° 51′ 23.94″[2]
Apparent magnitude (V) 10.20 – 10.45[3]
Characteristics
Evolutionary stage Main sequence
Spectral type K2–5V, most likely K3[4]
B−V color index 1.15[5]
Variable type Contact-type W UMa[3]
Astrometry
Radial velocity (Rv)−4.3±1.8[6] km/s
Proper motion (μ) RA: +437.182 mas/yr[2]
Dec.: +177.857 mas/yr[2]
Parallax (π)18.3420 ± 0.0166 mas[2]
Distance177.8 ± 0.2 ly
(54.52 ± 0.05 pc)
Absolute magnitude (MV)6.51[5]
Orbit[7]
Period (P)0.26125921 d
Semi-major axis (a)1.897763 R☉
Inclination (i)56.3±0.2°
Details[7]
Primary
Mass0.742 M☉
Radius0.798 R☉
Temperature4,908±8 K
Secondary
Mass0.5998 M☉
Radius0.648 R☉
Temperature4,011±42 K
Other designations
VZ Psc, BD+04°5012, HIP 115819, SAO 109778, G 29-37, LTT 16900[8]
Database references
SIMBADdata

VZ Piscium is a binary star system in the equatorial constellation of Pisces. it is located at a distance of 178 light years from the Sun based on parallax measurements,[2] and has an apparent visual magnitude of about 10.3.[3][9] This is an eclipsing binary system that undergoes shallow eclipses; the brightness decreases to magnitude 10.45 during the primary eclipse, then to magnitude 10.43 with the secondary eclipse, although as a contact binary the brightness varies continuously with no period of constant maximum brightness.[3] The system is drifting closer with a radial velocity of approximately −4 km/s,[6] and has a net heliocentric velocity of 144.1 km/s.[9]

S. C. Wolff and associates examined the spectrum of this star in 1965 and found very weak H and K lines with an emission component. Some of the lines are doubled, which suggested this is a contact binary. It was confirmed as a W Ursae Majoris (W UMa) variable using photometric observations made by J. Moorhead.[10] O. J. Eggen in 1967 found a period of just 6.26 hours and a high tangential space velocity of at least 100 km/s.[11] Most of the variability of the system was found to be ellipsoidal and a small O'Connell effect was detected. The combined stellar class of the system matches a K-type main-sequence star with a type of about K3. A mass ratio close to one indicates the two stars have similar mass.[12]

Due to physical contact, most W UMa-type variables show eclipse minima of almost equal depth, but that is not the case for VZ Psc.[13] The H and K line emission for this system suggests surface magnetic activity, and thus star spots. These darker features may explain the varying light curve of the system.[13] A variation in the orbital period of the system has been observed over a time frame of 25 years, which may be explained by a magnetic activity cycle of the lower mass component.[14] There is a temperature difference of about 900 K between the two components, which remains unexplained as direct contact would tend to even out the temperature. Both stars are highly distorted by the gravity of the other star. The more massive star is a third larger in the direction of the companion than pole-to-pole, and the less massive star is even more distorted.[7]

References

  1. ^ MAST: Barbara A. Mikulski Archive for Space Telescopes, Space Telescope Science Institute, retrieved 8 December 2021.
  2. ^ a b c d e 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. ^ a b c d Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
  4. ^ Hrivnak, Bruce J.; Milone, E. F. (February 1989), "The Unusual, High-Mass Ratio Contact Binary VZ Piscium", Astronomical Journal, 97: 532, Bibcode:1989AJ.....97..532H, doi:10.1086/115002.
  5. ^ a b Mateo, Nicole M.; Rucinski, Slavek M. (2017), "Absolute-magnitude Calibration for W UMa-type Systems Based on Gaia Data", The Astronomical Journal, 154 (3): 125, arXiv:1708.01097, Bibcode:2017AJ....154..125M, doi:10.3847/1538-3881/aa8453, S2CID 119099680.
  6. ^ a b Bilir, S.; Karataş, Y.; Demircan, O.; Eker, Z. (2005), "Kinematics of W Ursae Majoris type binaries and evidence of the two types of formation", Monthly Notices of the Royal Astronomical Society, 357 (2): 497–517, arXiv:astro-ph/0411291, Bibcode:2005MNRAS.357..497B, doi:10.1111/j.1365-2966.2005.08609.x, S2CID 16274339.
  7. ^ a b c Yue, Qiang; et al. (July 2019), "Orbital parameters and period variation studies of the short-period eclipsing binaries FG Sct, VZ Lib and VZ Psc", Research in Astronomy and Astrophysics, 19 (7): 097, Bibcode:2019RAA....19...97Y, doi:10.1088/1674-4527/19/7/97, S2CID 199127733, 097.
  8. ^ "VZ Psc", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2022-07-10.
  9. ^ a b 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, S2CID 119257644.
  10. ^ Wolff, Sidney Carne; et al. (October 1965), "Low-Dispersion Spectroscopic Observations of Proper Motion Stars with Ultraviolet Excesses", Publications of the Astronomical Society of the Pacific, 77 (458): 370, Bibcode:1965PASP...77..370W, doi:10.1086/128234, S2CID 120281332.
  11. ^ Eggen, O. J. (November 1967), "A High-Velocity Contact Binary", Astrophysical Journal, 150: L111, Bibcode:1967ApJ...150L.111E, doi:10.1086/180103.
  12. ^ Milone, E. F.; et al. (June 1985), "Preliminary analyses of VZ PSC photometry", Bulletin of the American Astronomical Society, 17: 754, Bibcode:1985BAAS...17..754M.
  13. ^ a b Maceroni, C.; et al. (August 1990), "A spotted component in the very close late-type binary system VZ Piscium", Astronomy and Astrophysics, 234: 177, Bibcode:1990A&A...234..177M.
  14. ^ Qian, S. B.; et al. (December 2004), "Possible connection between period change and magnetic activity of the very short-period binary VZ Piscium", Astronomische Nachrichten, 325 (9): 714–717, Bibcode:2004AN....325..714Q, doi:10.1002/asna.200410251.

Further reading

  • Hrivnak, Bruce J.; et al. (December 1995), "A Study of the Chromospherically Active, Short-Period Binary VZ Piscium", Astrophysical Journal, 455: 300, Bibcode:1995ApJ...455..300H, doi:10.1086/176578.
  • Barone, F.; et al. (September 1989), "UU-Cancri and VZ-Piscium, Contact Systems Before the Common Envelope Phase?", Astrophysics and Space Science, 159 (1): 67–83, Bibcode:1989Ap&SS.159...67B, doi:10.1007/BF00640488, S2CID 119748358.
  • Samec, Ronald G. (July 1989), "B and V Light Curves of the Very Short Period Binary VZ Piscium", Publications of the Astronomical Society of the Pacific, 101: 661, Bibcode:1989PASP..101..661S, doi:10.1086/132483, S2CID 121209441.
  • Samec, R. G.; Bookmyer, B. B. (February 1987), "Photoelectric Light Curves of VZ Piscium", Information Bulletin on Variable Stars, 2990: 1, Bibcode:1987IBVS.2990....1S.
  • Hrivnak, B. J.; Milone, E. F. (March 1985), "A Spectroscopic Study of VZ Psc", Bulletin of the American Astronomical Society, 17: 584, Bibcode:1985BAAS...17..584H.
  • Poretti, E. (February 1985), "A New Photoelectric Time of Minimum for VZ Psc", Information Bulletin on Variable Stars, 2671: 1, Bibcode:1985IBVS.2671....1P.
  • Davidge, T. J.; Milone, E. F. (December 1984), "B and V Photometry of VZ Psc", Information Bulletin on Variable Stars, 2639: 1, Bibcode:1984IBVS.2639....1D.
  • Poretti, E. (March 1984), "Photoelectric Observations of the EW-Variable VZ Psc", Information Bulletin on Variable Stars, 2487: 1, Bibcode:1984IBVS.2487....1P.
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