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In a previous publication we reported on the binary system 12 Boötis and its evolutionary state. In particular the 12 Boo primary component is in a rapid phase of evolution, hence accurate measurement of its physical parameters makes it an interesting test case for stellar evolution models. Here we report on a significantly improved determination of the physical orbit of the double-lined spectroscopic binary system 12 Boo. We have a 12 Boo interferometry dataset spanning six years with the Palomar Testbed Interferometer, a smaller amount of data from the Navy Prototype Optical Interferometer, and a radial velocity dataset spanning 14 years from the Harvard-Smithsonian Center for Astrophysics. We have updated the 12 Boo physical orbit model with our expanded interferometric and radial velocity datasets. The revised orbit is in good agreement with previous results, and the physical parameters implied by a combined fit to our visibility and radial velocity data result in precise component masses and luminosities. In particular, the orbital parallax of the system is determined to be 27.74 ± 0.15 mas, and masses of the two components are determined to be 1.4160 ± 0.0049 M ⊙ and 1.3740 ± 0.0045 M ⊙ , respectively. These mass determinations are more precise than the previous report by a factor of four to five.As indicated in the previous publication, even though the two components are nearly equal in mass, the system exhibits a significant brightness difference between the components in the near infrared and visible. We attribute this brightness difference to evolutionary differences between the two components in their transition between main sequence and giant evolutionary phases, and based on theoretical models we can estimate a system age of approximately 3.2 Gyr.Comparisons with stellar models suggest that the 12 Boo primary may be just entering the Hertzsprung gap, but that conclusion is highly dependent on details of the models. Such a dynamic evolutionary state makes the 12 Boo system a unique and important test for stellar models.

Although 47 Oph has been shown to be a binary with a period of ∼27 days using both spectroscopic and interferometric techniques, only a preliminary orbit has been obtained in the previous work due to the shortage of high precision measurements. Since 1997, new spectroscopic and interferometric measurements have been obtained with much higher precision by the spectrograph of the 2.16 m telescope at Xinglong station and the Navy Precision Optical Interferometer, respectively. Combining all of the measurements, a three-dimensional orbit is obtained with high precision in this work. Thus, the component masses are calculated to be 1.50 ± 0.06 and 1.34 ± 0.06  M , respectively. The orbital parallax is 32.6 ± 0.6 mas, which is consistent with the Hipparcos parallax. With the known apparent magnitudes and color indices of the components, the derived luminosities are 7.80 ± 0.36 and 3.41 ± 0.25  L. The estimated radii of the components are 2.06 ± 0.07 and 1.36 ± 0.06  R. Finally, the evolutionary status of the components are investigated with the help of a stellar evolution model.

We present a formal comparison of the performance of algorithms used for synthesis imaging with optical/infrared long-baseline interferometers. Five different algorithms are evaluated based on their performance with simulated test data. Each set of test data is formatted in the OI-FITS format. The data are calibrated power spectra and bispectra measured with an array intended to be typical of existing imaging interferometers. The strengths and limitations of each algorithm are discussed.

The highly redshifted quasar S5 0836+710 (z = 2.172) displays an outstanding one sided jet with complex morphology. The continuous jet shows several remarkable lateral displacements (kinks) of its ridgeline on various length scales. Despite the strength of these distortions the jet is not destroyed by them and remains well collimated. We investigated the possibility to explain the displacements by Kelvin-Helmholtz instabilities.

Studies of the winds from single K and early M evolved stars indicate that these flows typically reach a significant fraction of their terminal velocity within the first couple of stellar radii. The most detailed spatially resolved information of the extended atmospheres of these spectral types comes from the Aur eclipsing binaries. However, the wind acceleration inferred for the evolved primaries in these systems appears significantly slower than for stars of similar spectral type. Since there are no successful theories for mass loss from K and early M evolved stars, it is important to place strong empirical constraints on potential models and determine whether this difference in acceleration is real or an artifact of the analyses. We have undertaken a radio continuum monitoring study of Aurigae ( K4 Ib + B5 V) using the Very Large Array to test the wind density model of Baade et al. that is based on Hubble Space Telescope (HST ) Goddard High Resolution Spectrograph ultraviolet spectra. Aur was monitored at centimeter wavelengths over a complete orbital cycle, and flux variations during the orbit are found to be of similar magnitude to variations at similar orbital phases in the adjacent orbit. During eclipse, the flux does not decrease, showing that the radio emission originates from a volume substantially larger than R 3 K $ (150 R ) 3 surrounding the B star. Using the one-dimensional density model of the K4 Ib primary's wind derived from HST spectral line profile modeling and electron temperature estimates from previous optical and new HST studies, we find that the predicted radio fluxes are consistent with those observed. Three-dimensional hydrodynamic simulations indicate that the accretion flow perturbations near the B star do not contribute significantly to the total radio flux from the system, consistent with the radio eclipse observations. Our radio observations confirm the slow wind acceleration for the evolved K4 Ib component. Aur's velocity structure does not appear to be typical of single stars with similar spectral types. This highlights the need for more comprehensive multiwavelength studies for both single stars, which have been sadly neglected, and other Aur systems to determine if its wind properties are typical.

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