We discuss recent work from the Palomar Testbed Interferometer (PTI), including science results and system improvements. In the past two years PTI has been used to observe a wide range of scientifically interesting sources, including binaries, Cepheids and Miras. In addition PTI has been used to observe departures from spherical symmetry in several stars. Recent system improvements incude a new low read-noise camera based on a HAWAII infrared array, routine opteration in two baselines, and operation in the J band. Future developments include an upgrade to three-aperture combination and closure phase measurements, and double-Fourier interferometry.
A dedicated program of measuring angular sizes of Mira variables using the Palomar Testbed Interferometer has resulted in more than 13,000 measurements of over 60 stars. With visibility data in five channels across the K band, atmospheric extension and sources of opacity are evident in the dataset. Using multiple-epoch narrow-band data, phase lags between wavelength-dependent angular size cycles indicate spatial extent of molcular atmospheres. A spectral angular diameter classification system is developed, based on the recurring shapes of the spectral traces seen in the dataset, which correlates to spectral type. A period-radius relationship is explored, and a refinement on the estimation of angular sizes is made.
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