Browsing by Subject "binaries : eclipsing"

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The Orbital Period And Time-Variable Asymmetric Accretion Disk In The X-Ray Binary MSs 1603.6+2600 (=UW Coronae Borealis)
(2008-09) Mason, Paul A.; Robinson, Edward L.; Gray, Candace L.; Hynes, Robert I.; Robinson, Edward L.; Gray, Candace L.
We present CCD photometry of the low-mass X-ray binary UW Coronae Borealis (UW CrB). Its light curve shows eclipses at a period near 111 minutes, but the eclipses vary in depth and shape and often disappear. Restricting our analysis to the deeper eclipses, we find the orbital period to be 110: 976722 +/- 0: 000012 minutes, but the times of mideclipse can deviate by more than 0.025 in phase from the best-fit ephemeris. There is an additional large-amplitude variation with a period of 112: 58 +/- 0: 03 minutes reminiscent of the superhumps seen in the light curves of some cataclysmic variables. The variations of the eclipse morphology are not random, repeating at a period near 5.5 days, and the shape of the superhump-like modulation also varies at this period. We interpret the light curve as the eclipse of the accretion disk around the neutron star by the secondary star. The surface brightness of the accretion disk is strongly asymmetric and highly variable, producing the variations of the eclipse morphology and times of mideclipse. A model in which the distribution of surface brightness is elliptical and precesses at the 5.5 day period reproduces the eclipse depths and the times of mideclipse reasonably well. As 112.6 minutes is the beat period between 110.97672 minutes and 5.5 days, the superhump-like variability is closely related to the precessing elliptical disk, but the causal relationship is unclear.
Xo-3b: A Massive Planet In An Eccentric Orbit Transiting An F5V Star
(2008-04) Johns-Krull, Christopher M.; McCullough, Peter R.; Burke, Christopher J.; Valenti, Jeff A.; Janes, K. A.; Heasley, J. N.; Prato, L.; Bissinger, R.; Fleenor, M.; Foote, C. N.; Garcia-Melendo, E.; Gary, B. L.; Howell, P. J.; Mallia, F.; Masi, G.; Vanmunster, T.; Johns-Krull, Christopher M.
We report the discovery of a massive planet (M-p sin i 13.02 +/- 0.64 M-J; total mass = 13.25 +/- 0.64 M-J), large (1.95 +/- 0.16 R-J) planet in a transiting, eccentric orbit (e = 0.260 +/- 0.017) around a 10th magnitude F5 V 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 +/- 0.00014 days. XO-3 lacks a trigonometric parallax; we estimate its distance to be 260 +/- 23 pc. The radius of XO-3 is 2.13 +/- 0.21 R-circle dot, its mass is 1.41 +/- 0.08 M-circle dot, its v sin i = 18.54 +/- 0.17 km s(-1), and its metallicity is Fe/H = -0.177 +/- 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. 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 overestimated. 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 +/- 0.15 R-J, which would correspond to a mass of 12.03 +/- 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.