The Algol Triple System Spatially Resolved at Optical Wavelengths

Abstract

Interacting binaries typically have separations in the milli-arcsecond regime and hence it has been challenging to resolve them at any wavelength. However, recent advances in optical interferometry have improved our ability to discern the components in these systems and have now enabled the direct determination of physical parameters. We used the Navy Prototype Optical Interferometer to produce for the first time images resolving all three components in the well-known 1 Algol triple system. Specifically, we have separated the tertiary component from the binary and simultaneously resolved the eclipsing binary pair, which represents the nearest and brightest eclipsing binary in the sky. We present revised orbital elements for the triple system, and we have rectified the 180-degree ambiguity in the position angle of Algol C. Our directly determined magnitude differences and masses for this triple star system are consistent with earlier light curve modeling results.

Optical Observations with Milliarcsecond Resolution of Stars, Their Environments and Companions

“…4 and 5. These observations have led to an unambiguous determination that the close pair orbit (A-B) is retrograde and nearly orthogonal to the plane of the wide (AB-C) orbit (Zavala et al 2010). The improvements made to the AB-C orbital plane orientation have removed the time-variable systematic offset expected rived by Linnell et al (1998).…”

“…Estimates made in previous studies were performed by modeling photometric light curve and spectroscopic data and spanned more than one magnitude, from 3.92 ± 0.88 (Richards et al 1988) to 2.71 ± 0.15 (Kim 1989). The NOI directly measured V band magnitude difference favored a magnitude less than 3 (Zavala et al 2010).…”

Chemical History of Algol and its Components

“…In spite of a rich observational history, Algol is still lacking definitive understanding although progress has been made in the last decade (see Retter, Richards & Wu 2005). Its brightness is favourable for new observational techniques, recently allowing Zavala et al (2011) to fully spatially resolve its components. However, Algol has persistently lacked extensive high-precision photometric and spectroscopic observations.…”

Ground-Based and Space Observations of Interacting Binaries

“…In addition, speckle interferometry is applicable to the determination of the angular diameters of objects, and the development of long baseline techniques allows the achievement of angular resolutions sufficiently high for the determination of the diameters of the individual components of close binaries (e.g. Zavala et al 2010). The mas, or sub-mas separation can be reached only with VLB radio interferometry, or the recent, most powerful optical, near-IR long-baseline interferometric equipment, e.g.…”