A search for formation-height oscillations in umbrae.

Details A search for formation-height oscillations in umbrae. A search for formation-height oscillations in umbrae.

Jun 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...310..328b&link_type=abstract

Astronomy and Astrophysics, v.310, p.328-330

Astronomy and Astrophysics

Astrophysics

1

Sunspots, Sun: Oscillations

Scientific paper

The formation heights of spectral lines and continua in sunspots can be determined by measuring the apparent distance of the spot relative to the nearby solar limb. In order to confirm the existence of oscillatory variations of such limb distances and to exclude possible influences of differential image motion between the spot and the nearby limb, we have obtained time series observations of the lines Ca^+^ 8542, Mg b, and the non-magnetic line Fe 5576 simultaneously on two telescopes. No indication is found for periodic fluctuations of the spot's apparent limb distance. Only one of the seven time series shows a significant 40 min period of the line core but not of the continuum in the data from both telescopes. This variation of the line formation height, however, may be attributed to parallel guiding corrections of a spatially inhomogenous umbral chromosphere. The other time series show different periods for the two telescopes, which must be caused by unrelated guiding corrections.

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