Arsen R. Hajian

ANGULAR DIAMETERS OF STARS FROM THE MARK III OPTICAL INTERFEROMETER

Observations of 85 stars were obtained at wavelengths between 451 and 800 nm with the Mark III Stellar Interferometer on Mount Wilson, near Pasadena, California. Angular diameters were determined by fitting a uniform-disk model to the visibility amplitude versus projected baseline length. Half the angular diameters determined at 800 nm have formal errors smaller than 1%. Limb-darkened angular diameters, effective temperatures, and surface brightnesses were determined for these stars, and relationships between these parameters are presented. Scatter in these relationships is larger than would be expected from the measurement uncertainties. We argue that this scatter is not due to an underestimate of the angular diameter errors; whether it is due to photometric errors or is intrinsic to the relationship is unresolved. The agreement with other observations of the same stars at the same wavelengths is good; the width of the difference distribution is comparable to that estimated from the error bars, but the wings of the distribution are larger than Gaussian. Comparison with infrared measurements is more problematic; in disagreement with models, cooler stars appear systematically smaller in the near-infrared than expected, warmer stars larger.

FLIERs and Other Microstructures in Planetary Nebulae. IV. Images of Elliptical PNs from the Hubble Space Telescope

?????We report new results from high spatial resolution Wide Field Planetary Camera 2 imaging studies of FLIERs and other microstructures in the planetary nebulae NGC 3242, 6826, 7009, and 7662. Most FLIERs have head-tail morphologies, with the tails pointing outward from the nucleus. Ionization gradients that decrease with distance from the nebular center are ubiquitous. These are consistent with an ionization front in neutral knots of density ?104 cm-3. Can neutral knots account for the properties of FLIERs? We compare two broad classes of possible explanations for FLIERs with the new images: high-speed bullets ramming through the shells of planetary nebulae, and photoevaporated gas swept by winds into head-tail shapes. Both classes of models fail basic consistency tests. Hence an entirely new conceptual paradigm is needed to account for the phenomenology of FLIERs.

Navy Prototype Optical Interferometer Observations of the Double Stars Mizar A and Matar

We present a detailed analysis of two spectroscopic binaries based on new observations obtained with the Navy Prototype Optical Interferometer (NPOI). While the data calibration needs refinement, first results show the impressive potential of NPOI, both in terms of speed and precision, for imaging and modeling the orbits of spectroscopic binaries. We determine the orbital parameters of Mizar A (ζ1 Ursae Majoris) and Matar (η Pegasi), and derive masses and luminosities using published radial velocities and Hipparcos trigonometric parallaxes. The results on Mizar A are compared to earlier work done with the Mark III interferometer, while data from this instrument were combined with NPOI data in the Matar analysis.

Stellar Angular Diameters of Late-Type Giants and Supergiants Measured with the Navy Prototype Optical Interferometer

We have measured the angular diameters of 50 F, G, K, and M giant and supergiant stars using the Navy Prototype Optical Interferometer at wavelengths between 649 and 850 nm and using three baselines with lengths up to 37.5 m. Uniform-disk diameters, obtained from fits to the visibility amplitude, were transformed to limb-darkened diameters through the use of limb-darkening coefficients for plane-parallel stellar atmosphere models. These limb-darkened diameters are compared with those measured with the Mark III optical interferometer and with those computed by the infrared flux method. Sources of random and systematic error in the observations are discussed.

Hubble Space Telescope Measurements of the Expansion of NGC 6543: Parallax Distance and Nebular Evolution*

The optical expansion parallax of NGC 6543 has been detected and measured using two epochs of HST images separated by a time baseline of only three years. We have utilized three separate methods of deriving the angular expansion of bright fiducials, the results of which are in excellent agreement. We combine our angular expansion estimates with spectroscopically obtained expansion velocities to derive a distance to NGC 6543 of 1001

Direct Confirmation of Stellar Limb Darkening with the Navy Prototype Optical Interferometer

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Properties of the Hα-emitting Circumstellar Regions of Be Stars

269 pc. The deduced kinematic age of the inner bright core of the nebula is 1039

Direct Multi-Wavelength Limb-Darkening Measurements of Three Late-Type Giants with the Navy Prototype Optical Interferometer

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Planetary nebulae expansion distances

259 years; however, the kinematic age of the polar caps that surround the core is larger - perhaps the result of deceleration or earlier mass ejection. The morphology and expansion patterns of NGC 6543 provide insight into a complex history of axisymmetric, interacting stellar mass ejections.

Constraining Disk Parameters of Be Stars using Narrowband Hα Interferometry with the Navy Prototype Optical Interferometer

Using three elements of the Navy Prototype Optical Interferometer and observing in 20 spectral channels covering 520-850 nm, we have implemented a phase bootstrapping technique in which short baselines with high visibilities are used to keep the longer baselines with low visibilities in phase. Using this method, we have been able to extend the spatial frequency coverage beyond the first zero of the stellar visibility function for two K giants α Arietis, and α Cassiopeiae. The data are inconsistent with a uniform-disk model and confirm the presence of limb-darkened radial profiles. Adopting a particular limb-darkening law enables us to determine the diameter with small formal errors (one part in 1000). In addition, we have measured closure phases for both stars. The closure phases show a jump of 180° at the first zero in the visibility amplitude, which was expected.