XO-4

XO-4 is a star located approximately 896 light-years away from Earth in the Lynx constellation. It has a magnitude of about 11 and cannot be seen with the naked eye but is visible through a small telescope.[3] A search for a binary companion star using adaptive optics at MMT Observatory was negative.[6]

Not to be confused with the OLPC XO-4 from the One Laptop per Child (OLPC) initiative.
XO-4
Observation data
Epoch 2000      Equinox 2000
Constellation Lynx[1]
Right ascension  07h 21m 33.1602s[2]
Declination +58° 16′ 05.112″[2]
Apparent magnitude (V) 10.674 ± 0.019[3]
Characteristics
Spectral type F5V[3]
Apparent magnitude (B) 11.240 ± 0.029[3]
Apparent magnitude (V) 10.674 ± 0.019[3]
Apparent magnitude (J) 9.667 ± 0.021[4]
Apparent magnitude (H) 9.476 ± 0.022[4]
Apparent magnitude (K) 9.406 ± 0.023[4]
Astrometry
Proper motion (μ) RA: −16.989±0.056[2] mas/yr
Dec.: 5.310±0.050[2] mas/yr
Parallax (π)3.6392 ± 0.0385[2] mas
Distance896 ± 9 ly
(275 ± 3 pc)
Details
Mass1.32 ± 0.02[3] M☉
Radius1.56 ± 0.05[3] R☉
Temperature6397 ± 70[3] K
Metallicity [Fe/H]-0.04 ± 0.03[3] dex
Age2.1 ± 0.6[3] Gyr
Other designations
Koit, TYC 3793-1994-1, GSC 03793-01994, 2MASS J07213317+5816051[5]
Database references
SIMBADdata

The star XO-4 is named Koit. The name was selected in the NameExoWorlds campaign by Estonia, during the 100th anniversary of the IAU. Koit is Estonian for dawn, and was named for a character in a folk tale written by Friedrich Robert Faehlmann.[7][8][9]

Planetary system

One known exoplanet, XO-4b, which is classified as a hot jupiter, orbits XO-4. This exoplanet was discovered in 2008 by the XO Telescope project using the transit method.[3] It has been named Hämarik, meaning dusk, and referring to a character from the same Faehlmann story featuring Koit.[10]

The XO-4 planetary system[3][11][12]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
XO-4b 1.72 ± 0.20 MJ 0.0552 ± 0.0003 4.1250823 ± 0.0000039 0(assumed) [note 1] — —

Notes
  1. eccentricity approximately equal to zero is expected theoretically and is consistent with the radial velocities and secondary eclipses timing[3][12]

References
  1. Roman, Nancy G. (1987). "Identification of a Constellation From a Position". Publications of the Astronomical Society of the Pacific. 99 (617): 695–699. Bibcode:1987PASP...99..695R. doi:10.1086/132034. Vizier query form
  2. 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.
  3. McCullough, P. R.; et al. (2008). "XO-4b: An Extrasolar Planet Transiting an F5V Star". arXiv:0805.2921. Bibcode:2008arXiv0805.2921M. Cite journal requires |journal= (help)
  4. Cutri; et al. (2003). "2MASS===07213317+5816051". 2MASS All-Sky Catalog of Point Sources. Retrieved 2012-02-25.
  5. "SIMBAD query result: TYC 3793-1994-1 -- Star". Centre de Données astronomiques de Strasbourg. Retrieved 2009-04-26.
  6. Adams, E. R.; et al. (2013). "Adaptive Optics Images. II. 12 Kepler Objects of Interest and 15 Confirmed Transiting Planets". The Astronomical Journal. 146 (1). 9. arXiv:1305.6548. Bibcode:2013AJ....146....9A. doi:10.1088/0004-6256/146/1/9.
  7. "Approved names". NameExoworlds. Retrieved 2020-01-02.
  8. "International Astronomical Union | IAU". www.iau.org. Retrieved 2020-01-02.
  9. "Estonia has been assigned its own star and planet". Estonian World. Retrieved 2020-01-20.
  10. "Estonia has been assigned its own star and planet". Estonian World. Retrieved 2020-01-20.
  11. Narita, Norio; et al. (2010). "The Rossiter-McLaughlin Effect of the Transiting Exoplanet XO-4b". Publications of the Astronomical Society of Japan. 62 (6): L61–L65. arXiv:1008.3803. Bibcode:2010PASJ...62L..61N. doi:10.1093/pasj/62.6.l61.
  12. Todorov, Kamen O.; et al. (2012). "Warm Spitzer Observations of Three Hot Exoplanets: XO-4b, HAT-P-6b, and HAT-P-8b". The Astrophysical Journal. 746 (1). 111. arXiv:1111.5858. Bibcode:2012ApJ...746..111T. doi:10.1088/0004-637X/746/1/111.
  • "XO-4". Exoplanets. Retrieved 2009-04-28.


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