XO-4b

XO-4b is an extrasolar planet approximately 956 light years away in the constellation of Lynx. This planet was found by the transit method by McCullough in May 2008. The planet has mass 1.72 M_J and radius 1.34 R_J. This planet orbits very close to the F-type parent star, as it is typical for transiting planets, classing this planet as Hot Jupiter.

XO-4b
Hämarik

Size comparison of XO-4b with Jupiter.
Discovery
Discovered by	McCullough et al.
Discovery site	Maui, Hawaii
Discovery date	May 19, 2008
Detection method	Transit
Orbital characteristics
Semi-major axis	0.0555 ± 0.00011 AU (8,303,000 ± 16,000 km)
Eccentricity	0.0024
Orbital period (sidereal)	4.12502 ± 2e-5 d 0.011293 y
Inclination	88.7 ± 1.1
Star	XO-4
Physical characteristics
Mean radius	1.34 ± 0.048 RJ
Mass	1.72 ± 0.2 MJ
Mean density	0.948 g/cm3[citation needed]
Surface gravity	24.8 m/s2 (2.53 g0)
Temperature	~1333[clarification needed]

Orbit

It takes only 4.125 days (or 99 hours) to orbit at a distance of 8.3 gigameters (0.0555 AU) away from the star.^[1]

The study in 2012, utilizing a Rossiter–McLaughlin effect, have determined the planetary orbit is strongly misaligned with the equatorial plane of the star, misalignment equal to -46.7±8.1°.^[2]

Naming

The planet XO-4b is named Hämarik. The name was selected in the NameExoWorlds campaign by Estonia, during the 100th anniversary of the IAU. Hämarik is Estonian for dusk, and was named for a character in a folk tale written by Friedrich Robert Faehlmann.^[3][4][5]

See also

• XO Telescope