Edge-on Orbit Research Articles

CCD photometry of variable stars in the Magellanic Clouds - VII. The eclipsing binaries MACHO*05:36:48.7−69:17:00 in the LMC, and MOA J005018.4−723855 and J005623.5−722123 in the SMC

Using improved techniques, we have obtained CCD uV J I C photometry for three eclipsing binary stars in the Magellanic Clouds and made preliminary analyses of the light curves. MACHO*05:36:48.7-69:17:00in the Large Magellanic Cloud (LMC) is a detached, eccentric system. Apsidal motion is detected with a period of 100 ± 5 yr. The radii of the component stars are less than a fifth of their orbital separation and their masses are plausibly ∼14 and ∼20 M ○. . Similar masses may also characterize the components of MOA J005018.4-723855 in the Small Magellanic Cloud (SMC), but here the more massive star is cooler, fills its Roche lobe, and is probably in an early stage of case A mass transfer. MOA J005623.5-722123 in the SMC is detached with a nearly edge-on orbit. The masses are plausibly ∼14 and ∼16 M ○. . Because of polar gravity brightening, the star occulted at the shallower eclipse may actually have the higher mean effective temperature by a marginal amount.

A Substellar Companion to van Maanen 2

The Hipparcos data for the nearest white dwarf van Maanen 2 (=HIP 3829; distance of 4.4 pc) indicate astrometric binarity, in that the proper motion has a large first derivative not accounted for as a perspective acceleration due to changing distance. The presence of a companion was suspected, but never demonstrated, from the pre-Hipparcos astrometric measurements of photographic plates. Inspection of a digital position probability chart based on the Hipparcos Intermediate Astrometry Data reveals a pendulum-like motion of the photocenter mostly in the east-west direction with a period of about 1.5 yr. Having this period as an initial constraint, an orbital fit was obtained with the following parameters: a0 = 27 mas, P = 1.57 yr, i = 89°, ω = 95°, Ω = 92°, and T0 = 1991.26. Assuming a mass of 0.83 M☉ for the primary white dwarf, the mass of the secondary is 0.08 M☉. Covariance analysis shows, however, that the uncertainty of the semimajor axis estimate and, subsequently, of the mass estimate is great for this nearly edge-on orbit. A more robust estimate is obtained for the semiminor axis, providing a lower bound mass of the companion of 0.06 ± 0.02 M☉.

A search for eclipses of HD 114762 by a low-mass companion

HD 114762 has an unseen companion with a dynamical mass that satisfies the constraint mass sin i = 2.5 x 10 to the 31st gm. The companion is a good candidate for a planetary-mass object, but the inclination of its orbit is unknown and its mass is indeterminate. Tests were conducted for the specific case of a nearly edge-on orbit by looking for eclipses of HD 114762 by the companion. Although the a priori probability of an eclipse is low, this is a crucial case because the companion has its minimum mass if the orbit is edge on. No eclipses were found with a depth greater than 0.01 mag and, therefore, the inclination of the orbit of HD 114762 is less than 89 deg.