USING FE-X 6374-ANGSTROM AND FE-XIV 5303-ANGSTROM SPECTRAL-LINE INTENSITIES TO STUDY THE EFFECT OF LINE-OF-SIGHT INTEGRATION ON CORONAL TEMPERATURE INFERENCES

Polar coronal holes are relatively stable structures persisting over m any solar rotations. The appearance of coronal holes in remote observa tions, however, can change on a daily basis due to variations of the d enser and hotter plasma surrounding them. We explore the effect of the se denser and hotter surrounding regions on coronal hole observations, using daily intensity measurements at 1.15 R(S) of the green Fe XIV 5 303 Angstrom and red Fe X 6374 Angstrom spectral lines. The observatio ns, which were carried out at the National Solar Observatory at Sacram ento Peak, New Mexico, cover a time period of about four solar rotatio ns. We show that the ''coronal hole'' temperatures derived using the l ine ratio technique, vary by more than 0.8 x 10(6) K over the time int erval considered here. We also provide a short discussion of the expec ted accuracy of the atomic data for these two iron spectral lines. Usi ng intensity measurements as a function of distance from the Sun, we b riefly discuss how the regions surrounding the coronal holes might inf luence the inference of the temperature gradient in the coronal holes. The line of sight effect on the temperature gradient should be explor ed in more detail in the future using daily observations of the line i ntensities as a function of distance. These observations could be prov ided by ground-based coronagraphs and by instruments on board SOHO.