HD 4778

HD 4778, also known as HR 234 and GO Andromedae, is a variable star in the constellation Andromeda. Its magnitude varies by 0.04 magnitudes from the median of 6.12 with a period of approximately 2.55 days.[9] The star is located 350 light years away, as determined from its annual parallax shift of 9.32 mas.[1]

HD 4778
Observation data
Epoch J2000      Equinox J2000
Constellation Andromeda
Right ascension  00h 50m 18.26563s[1]
Declination +45° 00′ 08.1439″[1]
Apparent magnitude (V) 6.13[2]
Characteristics
Spectral type A3VpSiSrCrEuKsn[3]
B−V color index 0.043±0.004[2]
Variable type α2 CVn[4]
Astrometry
Radial velocity (Rv)1.60[5] km/s
Proper motion (μ) RA: 65.353[1] mas/yr
Dec.: 4.133[1] mas/yr
Parallax (π)9.3224 ± 0.0916[1] mas
Distance350 ± 3 ly
(107 ± 1 pc)
Absolute magnitude (MV)1.18[6]
Details[6]
Mass2.24±0.09 M☉
Radius2.2±0.2 R☉
Luminosity32 L☉
Surface gravity (log g)4.12±0.09 cgs
Temperature9,375 K
Rotation2.5616 days
Rotational velocity (v sin i)33[3] km/s
Age77[7] Myr
Other designations
GO Andromedae, BD+44° 176, FK5 2055, HD 4778, HIP 3919, HR 234, SAO 36702[8]
Database references
SIMBADdata

This is an Ap star with a stellar classification of A3VpSiSrCrEuKsn,[3] showing chemical peculiarities in its spectrum from strontium, chromium, and europium.[10] It is an Alpha2 Canum Venaticorum variable[4] with a magnetic field that varies across the range +1,400 to −1,100 G.[11] This rotation-modulated variability allows direct determination of the rotation rate of 2.5616 days.[6]

HD 4778 has 2.24 times the mass of the Sun and 2.2 times the Sun's radius. The star is radiating 32 times the Sun's luminosity from its photosphere at an effective temperature of 9,375 K.[6] It is about 77[7] million years old.

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.
  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. Abt, Helmut A.; Morrell, Nidia I. (1995). "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars". Astrophysical Journal Supplement. 99: 135. Bibcode:1995ApJS...99..135A. doi:10.1086/192182.
  4. Samus, N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (2017). "General Catalogue of Variable Stars". Astronomy Reports. GCVS 5.1. 61 (1): 80–88. Bibcode:2017ARep...61...80S.
  5. Kharchenko, N. V.; et al. (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. arXiv:0705.0878. Bibcode:2007AN....328..889K. doi:10.1002/asna.200710776.
  6. North, P. (June 1998), "Do SI stars undergo any rotational braking?", Astronomy and Astrophysics, 334: 181–187, arXiv:astro-ph/9802286, Bibcode:1998A&A...334..181N
  7. David, Trevor J.; Hillenbrand, Lynne A. (2015). "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets". The Astrophysical Journal. 804 (2): 146. arXiv:1501.03154. Bibcode:2015ApJ...804..146D. doi:10.1088/0004-637X/804/2/146.
  8. "HD 3167". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved October 6, 2018.
  9. VSX (4 January 2010). "GO Andromedae". AAVSO Website. American Association of Variable Star Observers. Retrieved 25 May 2014.
  10. Panek, R. J. (October 1980). "Periodic spectral variability of the AP star HR 234". Astronomy and Astrophysics. 90 (3): 341–343. Bibcode:1980A&A....90..341P.
  11. Bohlender, D. A. (August 1989). "The magnetic field and rotation period of the AP star HD 4778". Astronomy and Astrophysics. 220: 215–217. Bibcode:1989A&A...220..215B.
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