A long-standing solar problem has been to measure the coronal magnetic field. We believe it determines the coronal structure and dynamics from the upper chromosphere out into the heliospheric environment. It is only recently that Zeeman splitting observations of infrared coronal emission lines have been successfully used to deduce the coronal magnetic flux density. Here we extend this technique and report first results from a novel coronal magnetometer that uses an off-axis reflecting coronagraph and optical fiber-bundle imaging spectropolarimeter. We determine the line-of-sight magnetic flux density and transverse field orientation in a two-dimensional map with a sensitivity of about 1 G with 20Љ spatial resolution after 70 minutes of integration. These full-Stokes spectropolarimetric measurements of the forbidden Fe xiii 1075 nm coronal emission line reveal the line-of-sight coronal magnetic field 100Љ above an active region to have a flux density of about 4 G.

Few circumstellar disks have been directly observed. Here we use sensitive differential polarimetric techniques to overcome atmospheric speckle noise in order to image the circumstellar material around HD 169142. The detected envelope or disk is considerably smaller than expectations based on the measured strength of the far-IR excess from this system

We analyze velocity dispersion profiles for the Draco and Ursa Minor (UMi) dwarf spheroidal (dSph) galaxies based on published and new Keck HIRES spectra for stars in the outer UMi field. Washington+DDO51 filter photometric catalogs provide additional leverage on membership of individual stars, and beyond 0.5 King limiting radii (r lim ) identify bona fide dSph members up to 4.5 times more efficiently than simple color-magnitude diagram selections. Previously reported "cold populations" at r lim are not obvious in the data and appear only with particular binning; more or less constant and platykurtic dispersion profiles are characteristic of these dSphs to large radii. We report discovery of UMi stars to at least 2.7r lim (i.e., 210 ′ or 4 kpc). Even with conservative assumptions, a UMi mass of M > 4.9 × 10 8 M ⊙ is required to bind these stars, implying an unlikely global mass-to-light ratio of M/L > 900 (M/L) ⊙ . We conclude that we have found stars tidally stripped from UMi.

The major obstacle to the direct detection of companions to nearby stars is the overwhelming brightness of the host star. Current instruments employing the combination of adaptive optics (AO) and coronagraphy can typically detect objects within 2 ′′ of the star that are ∼ 10 4−5 times fainter. Correlated speckle noise is one of the biggest obstacles limiting such high-contrast imaging. We have obtained a series of 284 8 s, AO-corrected, coronagraphically occulted H-band images of the star Vega at the 3.63 m AEOS telescope located on Haleakala, Hawaii. This dataset is unique for studying the temporal behavior of speckle noise, and represents the first time such a study on highly corrected coronagraphic AO images has been carried out in a quantitative way. We find the speckle pattern to be highly stable in both position and time in our data. This is due to the fact that the AO system corrects disturbances to the stellar wave front at the level where the instrumental wave front errors dominate. Because of this, we find that our detection limit is not significantly improved simply with increased exposure time alone. However, we are able to improve our dynamic range by 1.5-2 magnitudes through subtraction of static/quasi-static speckles in two rotating frames: the telescope pupil frame and the deformable mirror frame. The highly stable nature of speckles will exist for any program using a combination of coronagraphy and high-order AO, and underscores the importance of calibration of non-common path errors between the wave front sensor and the image plane. Such calibration is critical for high-contrast AO systems and we demonstrate this using empirical data. From our data, we are able to constrain the mass of any purported companion to Vega to be less than ∼ 45M J at 8 AU and less than ∼ 30M J at 16 AU, radii not previously probed at these sensitivities.

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