HAO 2012 Profiles In Science: Dr. Alfred de Wijn

Contact:

Dr. Alfred de Wijn is a Project Scientist I at the High Altitude Observatory of the National Center for Atmospheric Research. He received his PhD in Astrophysics in 2006 from Utrecht University. He began working at HAO in December 2006. His research has always been focussed on observational studies of magnetism and dynamics in the photosphere, chromosphere, and transition region. More recently, he has taken an interest in polarimetry and instrumentation. He is currently the Instrument Scientist for several projects at HAO.

Scientific and Technical Achievements

Instrument Scientist:

COSMO K-Coronagraph
COSMO ChroMag
ATST ViSP
Mesa Spar

As Instrument Scientist for these projects, Alfred provides a leading role in defining the scientific requirements and ensuring the instrument will meet those requirements. The role is diverse and requires a broad spectrum of skills, ranging from computer modeling of instrument performance to hands-on lab work. Several key accomplishments in 2012 include: end-to-end modeling of the K-coronagraph system; build-up and testing of the K-Coronagraph modulators; assembly of the ChroMag 6-stage Lyot filter and modulator; deployment of the Spar to the dome at the Mesa lab.

Publications

(1) de Wijn, Alfred G. 2012: Probable Identification of the On-disk Counterpart of Spicules in Hinode Ca II H Observations. AJL, Volume 757, Issue 1, article id. L17 (2012). (Link).

Abstract: I present a study of high-resolution time series of Ca II H images and Fe I 630.15 nm spectra taken with the Solar Optical Telescope on the Hinode spacecraft. There is excellent correspondence between the Ca II H and the Fe I line core intensity, except tenuous emission around the network field concentrations in the former that is absent in the latter. Analysis of on-disk observations and a comparison with limb observations suggests that this "network haze" corresponds to spicules, and likely to type-II spicules in particular. They are known to appear in emission in on-disk broadband Ca II H diagnostics and the network haze is strongest in those areas where features similar to type-II spicules are produced in simulations.

(2) Casini, R.; de Wijn, A. G.; Judge, P. G. 2012: Analysis of Seeing-induced Polarization Cross-talk and Modulation Scheme Performance. AJL, Volume 757, Issue 1, article id. 45 (2012). (Link).

Abstract: We analyze the generation of polarization cross-talk in Stokes polarimeters by atmospheric seeing, and its effects on the noise statistics of spectropolarimetric measurements for both single-beam and dual-beam instruments. We investigate the time evolution of seeing-induced correlations between different states of one modulation cycle and compare the response to these correlations of two popular polarization modulation schemes in a dual-beam system. Extension of the formalism to encompass an arbitrary number of modulation cycles enables us to compare our results with earlier work. Even though we discuss examples pertinent to solar physics, the general treatment of the subject and its fundamental results might be useful to a wider community.