SWP MXHI Time Dependence

This figure shows the time dependence of SWP NEWSIPS large aperture high dispersion extractions. It shows the mid-wavelength region of all the available well exposed high dispersion spectra (71 in all) of the B0 V star tau Sco obtained over the lifetime of IUE. The spectra are normalized by their mean spectrum. The temporal ordinate is simply the accumulated number of spectra, and is not linear in time. No smoothing has been done, so individual spectra can be distinguished in the temporal direction.

Notice the following:

1. The region of the strong C⁺³ 1550 Å resonance doublet grows stronger over the lifetime of the mission.

2. The regular structure which appears throughout the image. This corresponds to the echelle ripple pattern, with the low flux portion of the pattern becoming darker over the life time of the mission.

3. The extracted fluxes change by more than 20% over the lifetime of the mission.