We report the discovery of a massive ( M _ { p } { sin } i = 13.02 \pm 0.64 { M _ { J } } ; total mass 13.25 \pm 0.64 { M _ { J } } ) , large ( 1.95 \pm 0.16 { R _ { J } } ) planet in a transiting , eccentric orbit ( e = 0.260 \pm 0.017 ) around a 10 ^ { th } magnitude F5V star in the constellation Camelopardalis .
We designate the planet XO-3b , and the star XO-3 , also known as GSC 03727-01064 .
The orbital period of XO-3b is 3.1915426 \pm 0.00014 days .
XO-3 lacks a trigonometric distance ; we estimate its distance to be 260 \pm 23 pc .
The radius of XO-3 is 2.13 \pm 0.21 { R _ { \odot } } , its mass is 1.41 \pm 0.08 { M _ { \odot } } , its v sin i = 18.54 \pm 0.17 km s ^ { -1 } , and its metallicity is [ Fe/H ] = -0.177 \pm 0.027 .
This system is unusual for a number of reasons .
XO-3b is one of the most massive planets discovered around any star for which the orbital period is less than 10 days .
The mass is near the deuterium burning limit of 13 { M _ { J } } , which is a proposed boundary between planets and brown dwarfs .
Although Burrows et al .
( 2001 ) propose that formation in a disk or formation in the interstellar medium in a manner similar to stars is a more logical way to differentiate planets and brown dwarfs , our current observations are not adequate to address this distinction .
XO-3b is also unusual in that its eccentricity is large given its relatively short orbital period .
Both the planetary radius and the inclination are functions of the spectroscopically determined stellar radius .
Analysis of the transit light curve of XO-3b suggests that the spectroscopically derived parameters may be over estimated .
Though relatively noisy , the light curves favor a smaller radius in order to better match the steepness of the ingress and egress .
The light curve fits imply a planetary radius of 1.25 \pm 0.15 { R _ { J } } , which would correspond to a mass of 12.03 \pm 0.46 { M _ { J } } .
A precise trigonometric parallax measurement or a very accurate light curve is needed to resolve the uncertainty in the planetary mass and radius .