Some Observations Relating to Umbral Dots

Abstract

Observations of Fraunhofer lines of singly-ionized metals in the spectrum of a sunspot are used to derive information about inhomogeneities in umbrae. It is found that the line profiles show Zeeman splittings corresponding to magnetic field strengths of about 3000G. This is a strong indication that the observed profiles originate within the umbra and are not produced by penumbral light scattered into the umbra. This fact, together with the co-existence of strong lines of the MgH molecule and ionized metal lines in the spectra (after these have been corrected for scattered light) would imply that two distinct types of element must be contributing to the umbral spectrum. The hotter elements may exhibit a range of electron temperatures ranging from |$\sim {5200}^{^{\circ} }\text{K}$| (photospheric) to perhaps 5550°K. It seems that microturbulence in these elements reaches 1·4 km s –1 .