The VAMOS Data Analysis Pipeline
Abstract
This poster illustrates the calibration procedure and the spherical harmonics analysis pipeline developed for the helioseismology data acquired with the VAMOS (Velocity And Magnetic Observations of the Sun) instrument. Calibration is performed in essentially three steps. First, a theoretical solar image is constructed containing all the contributions to the Earth-Sun line-of-sight relative velocity for each observing time. Then the observed Doppler images are fitted to the simulated velocity images. To take into account the center-to-limb dependence of the solar line profiles, the solar disk is divided into concentric rings, and in each of these annuli the observed signal is fitted to the simulated velocity with a second order polynomial. Finally, the Doppler images are effectively calibrated to produce residual images in absolute velocity units. The two-dimensional residual images are decomposed into spherical harmonics and the resulting coefficients are Fourier transformed to produce the solar oscillation power spectra. The spherical harmonics analysis routines, as well as the calibration routines for the VAMOS, have been developed in IDL, version 4.0.1. We show the l- ν diagram of the velocity and of the phase difference I-V between intensity and velocity oscillations, obtained by applying our analysis pipeline to 256 solar Doppler and intensity images in the NaI D lines acquired once per minute with the VAMOS in Napoli on February 20, 1997. In particular, the results regarding the phase difference are interesting because they cover a range of degrees in l (50-200) that up to now has been little explored.
- Publication:
-
Structure and Dynamics of the Interior of the Sun and Sun-like Stars
- Pub Date:
- 1998
- Bibcode:
- 1998ESASP.418..275O