34th Solar Physics Division Meeting, June 2003
Session 4 Corona II
Poster, Monday, June 16, 2003, 3:30-5:00pm, Mezzanine

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[4.19] A New Way to Identify Coronal Holes.

O. Malanushenko (NSO), H.P. Jones (NASA's GSFC)

The location of a coronal hole (CH) in the upper chromosphere is usually based on equivalent width (EqW) images in the He 1083 nm line. A CH is seen on these images as bright areas, which represents low values of EqW. But sometimes it is difficult to differentiate a CH from the bright centers of chromospheric network, or filament channels, without complementary data and the skill of an experienced of observer.

To remove the above ambiguity we apply a new spectral analysis technique for the He I 1083 nm line to imaging spectroscopy of several CHs obtained with the NASA/NSO spectromagnetograph (Malanushenko and Jones, 2002, BAAS 33, 700). Reduction includes making dark and flat-field corrections; normalization to a non-linear continuum on the basis of a comparison to a spectral standard; a differential method for the de-blending of spectra; and multi-profile fitting to define the He line components.

We fit a Gaussian profile to the main component of the He line and deduce the parameters of central intensity (I) and half width at half maximum (HW). On the HW-images, CHs are distinguished from the surrounding regions as bright areas; similarly, they are also seen as bright on the I-images. Chromospheric network is seen on W-images as opposite in contrast to the I-images, and this distinction is the basis for our CH identification method. We normalize the I- and HW-images by subtracting their respective quiet-sun means and dividing by the corresponding standard deviations. The sum of the normalized I- and HW-images shows increasing contrast of the CH and a depression of contrast in the network and can be used as an independent CH diagnostic.

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.