Intensity Conserving Spline Interpolation (ICSI): A New Tool for Spectroscopic Analysis

Abstract:

Spectroscopy is an extremely powerful tool for diagnosing astrophysical and other plasmas. For example, the shapes of line profiles provide valuable information on the distribution of velocities along an optically thin line-of-sight and across the finite area of a resolution element. A number of recent studies have measured the asymmetries of line profiles in order to detect faint high-speed upflows, perhaps associated with coronal nanoflares or perhaps associated with chromospheric nanoflares and type II spicules. Over most of the Sun, these asymmetries are very subtle, so great care must be taken. A common technique is to perform a spline fit of the points in the profile in order to extract information at a spectral resolution higher than that of the original data. However, a fundamental problem is that the fits do not conserve intensity. We have therefore developed an iterative procedure called Intensity Conserving Spline Interpolation that does preserve the observed intensity within each wavelength bin. It improves the measurement of line asymmetries and can also help with the determination of line blends.