arXiv subjects

J. R. Kuhn

Publications and source records attributed to J. R. Kuhn.

24 records · Page 2Linked to original sources

arXiv2006

The new HiVIS spectropolarimeter and spectropolarimetric calibration of the AEOS telescope

We designed, built, and calibrated a new spectropolarimeter for the HiVIS spectrograph (R 12000-49000) on the AEOS telescope. We also did a polarization calibration of the telescope and instrument. We will introduce the design and use of the spectropolarimeter as well as a new data reduction package we have developed, then discuss the polarization calibration of the spectropolarimeter and the AEOS telescope. We used observations of unpolarized standard stars at many pointings to measure the telescope induced polarization and compare it with a Zemax model. The telescope induces polarization of 1-6% with a strong variation with wavelength and pointing, consistent with the altitude and azimuth variation expected. We then used scattered sunlight as a linearly polarized source to measure the telescopes spectropolarimetric response to linearly polarized light. We then made an all-sky map of the telescope's polarization response to calibrate future spectropolarimetry.

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arXiv2005

Are Neutral Sunspot Winds Important for Penumbral Dynamics and the First Ionization Potential Effect?

The low ionization state in parts of a sunspot may play an important role in its evolution and dynamical state. The cool magnetic interior region of the sunspot develops a substantial neutral atomic and molecular hydrogen osmotic pressure which can drive a wind outward from the umbra. Ambipolar diffusion against the magnetically pinned ionized plasma component can also distort the umbral magnetic field into a filamentary penumbral structure. This may be important for explaining the development of the sunspot penumbra and the Evershed flow. This fractionation process may also be important for the ``First Ionization Potential'' (FIP) effect seen in the solar wind. In support of this mechanism we find evidence for such ionization fractionization in UV observations of molecular hydrogen in a sunspot umbra and penumbra.

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arXiv2005

Radial Alignment of Cluster Galaxies

We report the discovery of a statistically significant radial alignment of cluster galaxies in a sample of 85 X-ray selected clusters observed in the Sloan Digital Sky Survey. The tendency for alignment is a robust feature of our sample and does not vary significantly with individual cluster or galaxy properties. We use dynamical arguments to show that a significant fraction of cluster galaxies should be undergoing a parametric tidal resonance that can cause their long axes to orient themselves towards the center of the cluster potential, and therefore tentatively ascribe the observed radial alignment to this dynamical effect.

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arXiv2003

Light-weight Local Group Dwarf Spheroidal Galaxies

A simple and natural explanation for the dynamics and morphology of the Local Group Dwarf Spheroidal galaxies, Draco (Dra) and Ursa Minor (UMi), is that they are weakly unbound stellar systems with no significant dark matter component. A gentle, but persistent, Milky Way (MW) tide has left them in their current kinematic and morphological state. This short paper reviews the parametric tidal interaction model which accounts for their behavior and discusses new statistical evidence from the observed stellar distribution in Dra which implies that its total mass is not dominated by collisionless dark matter (DM).

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arXiv2002

High Dynamic Range and the Search for Planets

General arguments for optimized coronagraphy in the search for planets are presented. First, off-axis telescopes provide the best telescopic platforms for use with coronagraphy, and telescope fabrication technology now allows the fabrication of such telescopes with diameters of up to 6.5 m. We show that in certain circumstances a smaller telescope with an off-axis primary has a signal-to-noise advantage compared with larger Cassegrain telescopes. Second, to fully exploit the advantages of the coronagraph for suppressing stray light, it is necessary to use a high Strehl ratio adaptive optics system. This can be best achieved initially with modest aperture telescopes of 3--4 m in diameter. Third, application of simultaneous differential imaging and simultaneous polarimetric techniques are required to reach the photon-limit of coronagraphic imaging. These three developments, if pursued together, will yield significant improvements in the search for planets.

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arXiv2001

Imaging Polarimetric Observations of a New Circumstellar Disk System

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.

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