Plasma motion in umbrae and the surrounding photosphere derived from spectroscopic Doppler measurements and tracer measurements of spots
✍ Scribed by Axel Koch
- Publisher
- Springer
- Year
- 1984
- Tongue
- English
- Weight
- 801 KB
- Volume
- 93
- Category
- Article
- ISSN
- 0038-0938
No coin nor oath required. For personal study only.
✦ Synopsis
The rotational velocity of the Sun is determined by sunspot tracings and by spectroscopic measurements of the photospheric plasma using the non-Zeeman-split line Fel 5576 and absolute iodine reference. Stationary line shifts as limb-effect and longperiodical shifts introduced by supergranulation are discussed. The dependence on solar activity as Ca § emissivity and magnetic fields is investigated including line asymmetries. The results are: (a) The non active photospheric regions rotate with 1995 + 30 m s ~. Solar active regions yield a 60 m s ~ higher value. (b) In quiet regions the absolute limb shift varies between 170 m s ~ at the line core and 310 m s -i at l./Ico~t ~ 0.8 (C-shape); thus the limb shift is mainly due to entire line shifts. (c) In solar active regions (close to spots) asymmetries are widely reduced in line cores; this effect cannot be associated with a variation of the limb effect due to a large scatter of Doppler shifts near spots. (d) A reduced limb shift of 50 m s-t is found in network boundaries and is mainly due to a small scale downflow. (e) Observations with a smaller influence of stray light yield symmetric profiles in umbrae. (f) Differences between umbral rotation rates from tracer and spectroscopic measurements do not exceed 20 m s-1, when considering straylight. The rotational velocity from umbrae exceeds that from the photosphere by 30-60 m s -~. Some individual spots yield nearly the same rotation rate as the photosphere.