Sunspot umbral oscillations in Mgiik

✍ Scribed by Joseph B. Gurman

• Publisher: Springer
• Year: 1987
• Tongue: English
• Weight: 853 KB
• Volume: 108
• Category: Article
• ISSN: 0038-0938
• DOI: 10.1007/bf00152077

✦ Synopsis

Time series observations of the profile of the Mgn k line 22795.52 have been obtained in five sunspots with the Ultraviolet Spectrometer and Polarimeter (UVSP) on the Solar Maximum Mission. The three sunspots with umbrae larger than the 3" x 3" pixel size show significant oscillations in integrated line intensity and line eentroid, with frequencies in the range 5.29-7.55 mHz (periods of 132-190 s).

The frequencies of significant peaks in average umbral power spectra agree well with the frequencies of the three lowest-frequency transmission peaks predicted by a model of resonant transmission of acoustic waves. If radiative delays are unimportant, and the fine centroid can be interpreted straightforwardly as a Doppler shift, the measured velocity-intensity phase differences indicate the superposition of upward-and downward-propagating waves in the umbral chromosphere; this is further evidence for the resonant transmission model.

A single, quiet Sun time series of k core profiles yields power spectra and a phase difference consistent with the existence of a chromospheric p-mode.

* The SMM data used in this work were available only because of the repair of the SMM spacecraft by the crew of Challenger on mission 41-C. The pilot for that mission and the commander of Challenger's last mission was Francis R. Scobee. This work is dedicated to his memory.